Update documentation

Closes #108.

.drone.jsonnet

@@ -0,0 +1,352 @@
+# Copyright 2022 Peter Dimov
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+local library = "system";
+
+local triggers =
+{
+    branch: [ "master", "develop", "feature/*" ]
+};
+
+local ubsan = { UBSAN: '1', UBSAN_OPTIONS: 'print_stacktrace=1' };
+local asan = { ASAN: '1' };
+
+local linux_pipeline(name, image, environment, packages = "", sources = [], arch = "amd64") =
+{
+    name: name,
+    kind: "pipeline",
+    type: "docker",
+    trigger: triggers,
+    platform:
+    {
+        os: "linux",
+        arch: arch
+    },
+    steps:
+    [
+        {
+            name: "everything",
+            image: image,
+            environment: environment,
+            commands:
+            [
+                'set -e',
+                'wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -',
+            ] +
+            (if sources != [] then [ ('apt-add-repository "' + source + '"') for source in sources ] else []) +
+            (if packages != "" then [ 'apt-get update', 'apt-get -y install ' + packages ] else []) +
+            [
+                'export LIBRARY=' + library,
+                './.drone/drone.sh',
+            ]
+        }
+    ]
+};
+
+local macos_pipeline(name, environment, xcode_version = "12.2", osx_version = "catalina", arch = "amd64") =
+{
+    name: name,
+    kind: "pipeline",
+    type: "exec",
+    trigger: triggers,
+    platform: {
+        "os": "darwin",
+        "arch": arch
+    },
+    node: {
+        "os": osx_version
+    },
+    steps: [
+        {
+            name: "everything",
+            environment: environment + { "DEVELOPER_DIR": "/Applications/Xcode-" + xcode_version + ".app/Contents/Developer" },
+            commands:
+            [
+                'export LIBRARY=' + library,
+                './.drone/drone.sh',
+            ]
+        }
+    ]
+};
+
+local windows_pipeline(name, image, environment, arch = "amd64") =
+{
+    name: name,
+    kind: "pipeline",
+    type: "docker",
+    trigger: triggers,
+    platform:
+    {
+        os: "windows",
+        arch: arch
+    },
+    "steps":
+    [
+        {
+            name: "everything",
+            image: image,
+            environment: environment,
+            commands:
+            [
+                'cmd /C .drone\\\\drone.bat ' + library,
+            ]
+        }
+    ]
+};
+
+[
+    linux_pipeline(
+        "Linux 14.04 GCC 4.4",
+        "cppalliance/droneubuntu1404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-4.4', CXXSTD: '98,0x' },
+        "g++-4.4",
+        [ "ppa:ubuntu-toolchain-r/test" ],
+    ),
+
+    linux_pipeline(
+        "Linux 14.04 GCC 4.6",
+        "cppalliance/droneubuntu1404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-4.6', CXXSTD: '98,0x' },
+        "g++-4.6",
+        [ "ppa:ubuntu-toolchain-r/test" ],
+    ),
+
+    linux_pipeline(
+        "Linux 14.04 GCC 4.7",
+        "cppalliance/droneubuntu1404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-4.7', CXXSTD: '98,0x' },
+        "g++-4.7",
+        [ "ppa:ubuntu-toolchain-r/test" ],
+    ),
+
+    linux_pipeline(
+        "Linux 14.04 GCC 4.8*",
+        "cppalliance/droneubuntu1404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11' },
+    ),
+
+    linux_pipeline(
+        "Linux 14.04 GCC 4.9",
+        "cppalliance/droneubuntu1404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-4.9', CXXSTD: '03,11' },
+        "g++-4.9",
+        [ "ppa:ubuntu-toolchain-r/test" ],
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 GCC 5*",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14' },
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 GCC 6",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-6', CXXSTD: '03,11,14' },
+        "g++-6",
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 GCC 7* 32/64",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17', ADDRMD: '32,64' },
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 GCC 8",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-8', CXXSTD: '03,11,14,17' },
+        "g++-8",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 GCC 9* 32",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '32' },
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 GCC 9* 64",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '64' },
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 GCC 9* ARM64",
+        "cppalliance/droneubuntu2004:multiarch",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a' },
+        arch="arm64",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 GCC 9* S390x",
+        "cppalliance/droneubuntu2004:multiarch",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a' },
+        arch="s390x",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 GCC 10 32",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-10', CXXSTD: '03,11,14,17,20', ADDRMD: '32' },
+        "g++-10-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 GCC 10 64",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-10', CXXSTD: '03,11,14,17,20', ADDRMD: '64' },
+        "g++-10-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 GCC 11* 32",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '32' },
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 GCC 11* 64",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '64' },
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 GCC 12 32 ASAN",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-12', CXXSTD: '03,11,14,17,20,2b', ADDRMD: '32' } + asan,
+        "g++-12-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 GCC 12 64 ASAN",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-12', CXXSTD: '03,11,14,17,20,2b', ADDRMD: '64' } + asan,
+        "g++-12-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 GCC 13 32",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '03,11,14,17,20,2b', ADDRMD: '32' },
+        "g++-13-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 GCC 13 64",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '03,11,14,17,20,2b', ADDRMD: '64' },
+        "g++-13-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.5",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.5', CXXSTD: '03,11' },
+        "clang-3.5",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.6",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.6', CXXSTD: '03,11,14' },
+        "clang-3.6",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.7",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.7', CXXSTD: '03,11,14' },
+        "clang-3.7",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.8",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.8', CXXSTD: '03,11,14' },
+        "clang-3.8",
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 Clang 13",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-13', CXXSTD: '03,11,14,17,20' },
+        "clang-13",
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 Clang 14 UBSAN",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-14', CXXSTD: '03,11,14,17,20' } + ubsan,
+        "clang-14",
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 Clang 14 ASAN",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-14', CXXSTD: '03,11,14,17,20' } + asan,
+        "clang-14",
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 Clang 15",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-15', CXXSTD: '03,11,14,17,20,2b' },
+        "clang-15",
+        ["deb http://apt.llvm.org/jammy/ llvm-toolchain-jammy-15 main"],
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 Clang 16",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-16', CXXSTD: '11,14,17,20,2b' },
+        "clang-16",
+    ),
+
+    macos_pipeline(
+        "MacOS 10.15 Xcode 12.2 UBSAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,1z' } + ubsan,
+    ),
+
+    macos_pipeline(
+        "MacOS 10.15 Xcode 12.2 ASAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,1z' } + asan,
+    ),
+
+    macos_pipeline(
+        "MacOS 12.4 Xcode 13.4.1 UBSAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        xcode_version = "13.4.1", osx_version = "monterey", arch = "arm64",
+    ),
+
+    macos_pipeline(
+        "MacOS 12.4 Xcode 13.4.1 ASAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,17,20,2b' } + asan,
+        xcode_version = "13.4.1", osx_version = "monterey", arch = "arm64",
+    ),
+
+    windows_pipeline(
+        "Windows VS2015 msvc-14.0",
+        "cppalliance/dronevs2015",
+        { TOOLSET: 'msvc-14.0', CXXSTD: '14,latest' },
+    ),
+
+    windows_pipeline(
+        "Windows VS2017 msvc-14.1",
+        "cppalliance/dronevs2017",
+        { TOOLSET: 'msvc-14.1', CXXSTD: '14,17,latest' },
+    ),
+
+    windows_pipeline(
+        "Windows VS2019 msvc-14.2",
+        "cppalliance/dronevs2019",
+        { TOOLSET: 'msvc-14.2', CXXSTD: '14,17,20,latest' },
+    ),
+
+    windows_pipeline(
+        "Windows VS2022 msvc-14.3",
+        "cppalliance/dronevs2022:1",
+        { TOOLSET: 'msvc-14.3', CXXSTD: '14,17,20,latest' },
+    ),
+]

.drone/drone.bat

@@ -0,0 +1,23 @@
+@REM Copyright 2022 Peter Dimov
+@REM Distributed under the Boost Software License, Version 1.0.
+@REM https://www.boost.org/LICENSE_1_0.txt
+
+@ECHO ON
+
+set LIBRARY=%1
+set DRONE_BUILD_DIR=%CD%
+
+set BOOST_BRANCH=develop
+if "%DRONE_BRANCH%" == "master" set BOOST_BRANCH=master
+cd ..
+git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+cd boost-root
+git submodule update --init tools/boostdep
+xcopy /s /e /q %DRONE_BUILD_DIR% libs\%LIBRARY%\
+python tools/boostdep/depinst/depinst.py %LIBRARY%
+cmd /c bootstrap
+b2 -d0 headers
+
+if not "%CXXSTD%" == "" set CXXSTD=cxxstd=%CXXSTD%
+if not "%ADDRMD%" == "" set ADDRMD=address-model=%ADDRMD%
+b2 -j3 libs/%LIBRARY%/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% variant=debug,release embed-manifest-via=linker

.drone/drone.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# Copyright 2022 Peter Dimov
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+set -ex
+export PATH=~/.local/bin:/usr/local/bin:$PATH
+
+DRONE_BUILD_DIR=$(pwd)
+
+BOOST_BRANCH=develop
+if [ "$DRONE_BRANCH" = "master" ]; then BOOST_BRANCH=master; fi
+
+cd ..
+git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+cd boost-root
+git submodule update --init tools/boostdep
+cp -r $DRONE_BUILD_DIR/* libs/$LIBRARY
+python tools/boostdep/depinst/depinst.py $LIBRARY
+./bootstrap.sh
+./b2 -d0 headers
+
+echo "using $TOOLSET : : $COMPILER ;" > ~/user-config.jam
+./b2 -j3 libs/$LIBRARY/test toolset=$TOOLSET cxxstd=$CXXSTD variant=debug,release ${ADDRMD:+address-model=$ADDRMD} ${UBSAN:+undefined-sanitizer=norecover debug-symbols=on} ${ASAN:+address-sanitizer=norecover debug-symbols=on} ${LINKFLAGS:+linkflags=$LINKFLAGS}

.github/workflows/ci.yml

@@ -0,0 +1,600 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+      - develop
+      - feature/**
+
+env:
+  UBSAN_OPTIONS: print_stacktrace=1
+
+jobs:
+  posix:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - toolset: gcc-4.8
+            cxxstd: "03,11"
+            os: ubuntu-latest
+            container: ubuntu:18.04
+            install: g++-4.8
+          - toolset: gcc-5
+            cxxstd: "03,11,14,1z"
+            os: ubuntu-latest
+            container: ubuntu:18.04
+            install: g++-5
+          - toolset: gcc-6
+            cxxstd: "03,11,14,1z"
+            os: ubuntu-latest
+            container: ubuntu:18.04
+            install: g++-6
+          - toolset: gcc-7
+            cxxstd: "03,11,14,17"
+            os: ubuntu-latest
+            container: ubuntu:18.04
+          - toolset: gcc-8
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
+            install: g++-8
+          - toolset: gcc-9
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
+          - toolset: gcc-10
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
+            install: g++-10
+          - toolset: gcc-11
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
+            install: g++-11
+          - toolset: gcc-12
+            cxxstd: "03,11,14,17,20,2b"
+            os: ubuntu-22.04
+            install: g++-12
+          - toolset: gcc-13
+            cxxstd: "03,11,14,17,20,2b"
+            os: ubuntu-latest
+            container: ubuntu:23.04
+            install: g++-13
+          - toolset: clang
+            compiler: clang++-3.9
+            cxxstd: "03,11,14"
+            os: ubuntu-latest
+            container: ubuntu:18.04
+            install: clang-3.9
+          - toolset: clang
+            compiler: clang++-4.0
+            cxxstd: "03,11,14"
+            os: ubuntu-latest
+            container: ubuntu:18.04
+            install: clang-4.0
+          - toolset: clang
+            compiler: clang++-5.0
+            cxxstd: "03,11,14,1z"
+            os: ubuntu-latest
+            container: ubuntu:18.04
+            install: clang-5.0
+          - toolset: clang
+            compiler: clang++-6.0
+            cxxstd: "03,11,14,17"
+            os: ubuntu-20.04
+            install: clang-6.0
+          - toolset: clang
+            compiler: clang++-7
+            cxxstd: "03,11,14,17"
+            os: ubuntu-20.04
+            install: clang-7
+          - toolset: clang
+            compiler: clang++-8
+            cxxstd: "03,11,14,17"
+            os: ubuntu-20.04
+            install: clang-8
+          - toolset: clang
+            compiler: clang++-9
+            cxxstd: "03,11,14,17"
+            os: ubuntu-20.04
+            install: clang-9
+          - toolset: clang
+            compiler: clang++-10
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
+          - toolset: clang
+            compiler: clang++-11
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-20.04
+          - toolset: clang
+            compiler: clang++-12
+            cxxstd: "03,11,14,17,20"
+            os: ubuntu-20.04
+          - toolset: clang
+            compiler: clang++-13
+            cxxstd: "03,11,14,17,20,2b"
+            container: ubuntu:22.04
+            os: ubuntu-latest
+            install: clang-13
+          - toolset: clang
+            compiler: clang++-14
+            cxxstd: "03,11,14,17,20,2b"
+            container: ubuntu:22.04
+            os: ubuntu-latest
+            install: clang-14
+          - toolset: clang
+            compiler: clang++-15
+            cxxstd: "03,11,14,17,20,2b"
+            container: ubuntu:22.04
+            os: ubuntu-latest
+            install: clang-15
+          - toolset: clang
+            compiler: clang++-16
+            cxxstd: "03,11,14,17,20,2b"
+            os: ubuntu-latest
+            container: ubuntu:23.04
+            install: clang-16
+          - toolset: clang
+            cxxstd: "03,11,14,17,2a"
+            os: macos-11
+          - toolset: clang
+            cxxstd: "03,11,14,17,20,2b"
+            os: macos-12
+          - toolset: clang
+            cxxstd: "03,11,14,17,20,2b"
+            os: macos-13
+
+    runs-on: ${{matrix.os}}
+    container: ${{matrix.container}}
+
+    defaults:
+      run:
+        shell: bash
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup container environment
+        if: matrix.container
+        run: |
+          apt-get update
+          apt-get -y install sudo python3 git g++
+
+      - name: Install packages
+        if: matrix.install
+        run: |
+          sudo apt-get update
+          sudo apt-get -y install ${{matrix.install}}
+
+      - name: Setup Boost
+        run: |
+          echo GITHUB_REPOSITORY: $GITHUB_REPOSITORY
+          LIBRARY=${GITHUB_REPOSITORY#*/}
+          echo LIBRARY: $LIBRARY
+          echo "LIBRARY=$LIBRARY" >> $GITHUB_ENV
+          echo GITHUB_BASE_REF: $GITHUB_BASE_REF
+          echo GITHUB_REF: $GITHUB_REF
+          REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+          REF=${REF#refs/heads/}
+          echo REF: $REF
+          BOOST_BRANCH=develop && [ "$REF" == "master" ] && BOOST_BRANCH=master || true
+          echo BOOST_BRANCH: $BOOST_BRANCH
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          cp -r $GITHUB_WORKSPACE/* libs/$LIBRARY
+          git submodule update --init tools/boostdep
+          python3 tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
+          ./bootstrap.sh
+          ./b2 -d0 headers
+
+      - name: Create user-config.jam
+        if: matrix.compiler
+        run: |
+          echo "using ${{matrix.toolset}} : : ${{matrix.compiler}} ;" > ~/user-config.jam
+
+      - name: Run tests
+        run: |
+          cd ../boost-root
+          ./b2 -j3 libs/$LIBRARY/test toolset=${{matrix.toolset}} cxxstd=${{matrix.cxxstd}} variant=debug,release
+
+  windows:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - toolset: msvc-14.0
+            cxxstd: "14"
+            addrmd: 32,64
+            os: windows-2019
+          - toolset: msvc-14.2
+            cxxstd: "14,17,20,latest"
+            addrmd: 32,64
+            os: windows-2019
+          - toolset: msvc-14.3
+            cxxstd: "14,17,20,latest"
+            addrmd: 32,64
+            os: windows-2022
+          - toolset: clang-win
+            cxxstd: "14,17,20,latest"
+            addrmd: 32,64
+            os: windows-2022
+          - toolset: gcc
+            cxxstd: "03,11,14,17,2a"
+            addrmd: 64
+            os: windows-2019
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+          cmd /c bootstrap
+          b2 -d0 headers
+
+      - name: Run tests
+        shell: cmd
+        run: |
+          cd ../boost-root
+          b2 -j3 libs/%LIBRARY%/test toolset=${{matrix.toolset}} cxxstd=${{matrix.cxxstd}} address-model=${{matrix.addrmd}} variant=debug,release embed-manifest-via=linker
+
+  posix-cmake-subdir:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-20.04
+          - os: ubuntu-22.04
+          - os: macos-11
+          - os: macos-12
+          - os: macos-13
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install packages
+        if: matrix.install
+        run: sudo apt-get -y install ${{matrix.install}}
+
+      - name: Setup Boost
+        run: |
+          echo GITHUB_REPOSITORY: $GITHUB_REPOSITORY
+          LIBRARY=${GITHUB_REPOSITORY#*/}
+          echo LIBRARY: $LIBRARY
+          echo "LIBRARY=$LIBRARY" >> $GITHUB_ENV
+          echo GITHUB_BASE_REF: $GITHUB_BASE_REF
+          echo GITHUB_REF: $GITHUB_REF
+          REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+          REF=${REF#refs/heads/}
+          echo REF: $REF
+          BOOST_BRANCH=develop && [ "$REF" == "master" ] && BOOST_BRANCH=master || true
+          echo BOOST_BRANCH: $BOOST_BRANCH
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          cp -r $GITHUB_WORKSPACE/* libs/$LIBRARY
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
+
+      - name: Use library with add_subdirectory
+        run: |
+          cd ../boost-root/libs/$LIBRARY/test/cmake_subdir_test
+          mkdir __build__ && cd __build__
+          cmake ..
+          cmake --build .
+          ctest --output-on-failure --no-tests=error
+
+  posix-cmake-install:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-20.04
+          - os: ubuntu-22.04
+          - os: macos-11
+          - os: macos-12
+          - os: macos-13
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install packages
+        if: matrix.install
+        run: sudo apt-get -y install ${{matrix.install}}
+
+      - name: Setup Boost
+        run: |
+          echo GITHUB_REPOSITORY: $GITHUB_REPOSITORY
+          LIBRARY=${GITHUB_REPOSITORY#*/}
+          echo LIBRARY: $LIBRARY
+          echo "LIBRARY=$LIBRARY" >> $GITHUB_ENV
+          echo GITHUB_BASE_REF: $GITHUB_BASE_REF
+          echo GITHUB_REF: $GITHUB_REF
+          REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+          REF=${REF#refs/heads/}
+          echo REF: $REF
+          BOOST_BRANCH=develop && [ "$REF" == "master" ] && BOOST_BRANCH=master || true
+          echo BOOST_BRANCH: $BOOST_BRANCH
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          cp -r $GITHUB_WORKSPACE/* libs/$LIBRARY
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
+
+      - name: Configure
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=$LIBRARY -DCMAKE_INSTALL_PREFIX=~/.local ..
+
+      - name: Install
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install
+
+      - name: Use the installed library
+        run: |
+          cd ../boost-root/libs/$LIBRARY/test/cmake_install_test && mkdir __build__ && cd __build__
+          cmake -DCMAKE_INSTALL_PREFIX=~/.local ..
+          cmake --build .
+          ctest --output-on-failure --no-tests=error
+
+  posix-cmake-test:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-20.04
+          - os: ubuntu-22.04
+          - os: macos-11
+          - os: macos-12
+          - os: macos-13
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install packages
+        if: matrix.install
+        run: sudo apt-get -y install ${{matrix.install}}
+
+      - name: Setup Boost
+        run: |
+          echo GITHUB_REPOSITORY: $GITHUB_REPOSITORY
+          LIBRARY=${GITHUB_REPOSITORY#*/}
+          echo LIBRARY: $LIBRARY
+          echo "LIBRARY=$LIBRARY" >> $GITHUB_ENV
+          echo GITHUB_BASE_REF: $GITHUB_BASE_REF
+          echo GITHUB_REF: $GITHUB_REF
+          REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+          REF=${REF#refs/heads/}
+          echo REF: $REF
+          BOOST_BRANCH=develop && [ "$REF" == "master" ] && BOOST_BRANCH=master || true
+          echo BOOST_BRANCH: $BOOST_BRANCH
+          cd ..
+          git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          cp -r $GITHUB_WORKSPACE/* libs/$LIBRARY
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
+
+      - name: Configure
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=$LIBRARY -DBUILD_TESTING=ON ..
+
+      - name: Build tests
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target tests
+
+      - name: Run tests
+        run: |
+          cd ../boost-root/__build__
+          ctest --output-on-failure --no-tests=error
+
+  windows-cmake-subdir:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Use library with add_subdirectory (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_subdir_test
+          mkdir __build__ && cd __build__
+          cmake ..
+          cmake --build . --config Debug
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Use library with add_subdirectory (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_subdir_test/__build__
+          cmake --build . --config Release
+          ctest --output-on-failure --no-tests=error -C Release
+
+  windows-cmake-install:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Configure
+        shell: cmd
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=%LIBRARY% -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+
+      - name: Install (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install --config Debug
+
+      - name: Install (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install --config Release
+
+      - name: Use the installed library (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_install_test && mkdir __build__ && cd __build__
+          cmake -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+          cmake --build . --config Debug
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Use the installed library (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_install_test/__build__
+          cmake --build . --config Release
+          ctest --output-on-failure --no-tests=error -C Release
+
+  windows-cmake-test:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Configure
+        shell: cmd
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=%LIBRARY% -DBUILD_TESTING=ON ..
+
+      - name: Build tests (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target tests --config Debug
+
+      - name: Run tests (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Build tests (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target tests --config Release
+
+      - name: Run tests (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          ctest --output-on-failure --no-tests=error -C Release

.travis.yml

@@ -4,8 +4,6 @@
 
 language: cpp
 
-sudo: false
-
 dist: xenial
 
 branches:
@@ -26,7 +24,26 @@ matrix:
   include:
     - os: linux
       compiler: g++
-      env: TOOLSET=gcc COMPILER=g++ CXXSTD=03,11
+      env: TOOLSET=gcc COMPILER=g++ CXXSTD=03,11,14 ADDRMD=32,64
+      addons:
+        apt:
+          packages:
+            - g++-multilib
+
+    - os: linux
+      arch: arm64
+      compiler: g++
+      env: TOOLSET=gcc COMPILER=g++ CXXSTD=03,11,14 ADDRMD=32,64
+
+    - os: linux
+      arch: ppc64le
+      compiler: g++
+      env: TOOLSET=gcc COMPILER=g++ CXXSTD=03,11,14
+
+    - os: linux
+      arch: s390x
+      compiler: g++
+      env: TOOLSET=gcc COMPILER=g++ CXXSTD=03,11,14 ADDRMD=32,64
 
     - os: linux
       compiler: g++-4.4
@@ -49,108 +66,20 @@ matrix:
             - ubuntu-toolchain-r-test
 
     - os: linux
-      compiler: g++-4.7
-      env: TOOLSET=gcc COMPILER=g++-4.7 CXXSTD=03,11
-      addons:
-        apt:
-          packages:
-            - g++-4.7
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: g++-4.8
-      env: TOOLSET=gcc COMPILER=g++-4.8 CXXSTD=03,11
-      addons:
-        apt:
-          packages:
-            - g++-4.8
-          sources:
-            - ubuntu-toolchain-r-test
-    - os: linux
-      compiler: g++-4.9
-      env: TOOLSET=gcc COMPILER=g++-4.9 CXXSTD=03,11
-      addons:
-        apt:
-          packages:
-            - g++-4.9
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: g++-5
-      env: TOOLSET=gcc COMPILER=g++-5 CXXSTD=03,11,14,1z
-      addons:
-        apt:
-          packages:
-            - g++-5
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: g++-6
-      env: TOOLSET=gcc COMPILER=g++-6 CXXSTD=03,11,14,1z
-      addons:
-        apt:
-          packages:
-            - g++-6
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: g++-7
-      env: TOOLSET=gcc COMPILER=g++-7 CXXSTD=03,11,14,17
-      addons:
-        apt:
-          packages:
-            - g++-7
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: g++-8
-      env: TOOLSET=gcc COMPILER=g++-8 CXXSTD=03,11,14,17,2a
-      addons:
-        apt:
-          packages:
-            - g++-8
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: g++-9
-      env: TOOLSET=gcc COMPILER=g++-9 CXXSTD=03,11,14,17,2a
-      addons:
-        apt:
-          packages:
-            - g++-9
-          sources:
-            - ubuntu-toolchain-r-test
+      dist: trusty
+      compiler: g++
+      env: TOOLSET=gcc COMPILER=g++ CXXSTD=03,11
 
     - os: linux
       dist: bionic
-      compiler: g++-10
-      env: TOOLSET=gcc COMPILER=g++-10 CXXSTD=03,11,14,17,2a
+      compiler: g++-11
+      env: UBSAN=1 TOOLSET=gcc COMPILER=g++-11 CXXSTD=03,11,14,17,20 UBSAN_OPTIONS=print_stacktrace=1 LINKFLAGS=-fuse-ld=gold
       addons:
         apt:
           packages:
-            - g++-10
+            - g++-11
           sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: g++-9
-      env: UBSAN=1 TOOLSET=gcc COMPILER=g++-9 CXXSTD=03,11,14,17,2a UBSAN_OPTIONS=print_stacktrace=1 LINKFLAGS=-fuse-ld=gold
-      addons:
-        apt:
-          packages:
-            - g++-9
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: clang++
-      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11
+            - sourceline: "ppa:ubuntu-toolchain-r/test"
 
     - os: linux
       dist: trusty
@@ -171,189 +100,75 @@ matrix:
             - clang-3.4
 
     - os: linux
-      dist: trusty
-      compiler: clang++-3.5
-      env: TOOLSET=clang COMPILER=clang++-3.5 CXXSTD=03,11,14,1z
+      compiler: clang++-12
+      env: UBSAN=1 TOOLSET=clang COMPILER=clang++-12 CXXSTD=03,11,14,17,20 UBSAN_OPTIONS=print_stacktrace=1
       addons:
         apt:
           packages:
-            - clang-3.5
+            - clang-12
           sources:
             - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: clang++-3.6
-      env: TOOLSET=clang COMPILER=clang++-3.6 CXXSTD=03,11,14,1z
-      addons:
-        apt:
-          packages:
-            - clang-3.6
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: clang++-3.7
-      env: TOOLSET=clang COMPILER=clang++-3.7 CXXSTD=03,11,14,1z
-      addons:
-        apt:
-          packages:
-            - clang-3.7
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: clang++-3.8
-      env: TOOLSET=clang COMPILER=clang++-3.8 CXXSTD=03,11,14,1z
-      addons:
-        apt:
-          packages:
-            - clang-3.8
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: clang++-3.9
-      env: TOOLSET=clang COMPILER=clang++-3.9 CXXSTD=03,11,14,1z
-      addons:
-        apt:
-          packages:
-            - clang-3.9
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: clang++-4.0
-      env: TOOLSET=clang COMPILER=clang++-4.0 CXXSTD=03,11,14,1z
-      addons:
-        apt:
-          packages:
-            - clang-4.0
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: clang++-5.0
-      env: TOOLSET=clang COMPILER=clang++-5.0 CXXSTD=03,11,14,1z
-      addons:
-        apt:
-          packages:
-            - clang-5.0
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: clang++-6.0
-      env: TOOLSET=clang COMPILER=clang++-6.0 CXXSTD=03,11,14,17
-      addons:
-        apt:
-          packages:
-            - clang-6.0
-          sources:
-            - ubuntu-toolchain-r-test
-
-    - os: linux
-      compiler: clang++-7
-      env: TOOLSET=clang COMPILER=clang++-7 CXXSTD=03,11,14,17,2a
-      addons:
-        apt:
-          packages:
-            - clang-7
-          sources:
-            - ubuntu-toolchain-r-test
-            - llvm-toolchain-xenial-7
-
-    - os: linux
-      compiler: clang++-8
-      env: TOOLSET=clang COMPILER=clang++-8 CXXSTD=03,11,14,17,2a
-      addons:
-        apt:
-          packages:
-            - clang-8
-          sources:
-            - ubuntu-toolchain-r-test
-            - llvm-toolchain-xenial-8
-
-    - os: linux
-      compiler: clang++-9
-      env: TOOLSET=clang COMPILER=clang++-9 CXXSTD=03,11,14,17,2a
-      addons:
-        apt:
-          packages:
-            - clang-9
-          sources:
-            - ubuntu-toolchain-r-test
-            - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main'
+            - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-12 main'
               key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
 
     - os: linux
-      dist: xenial
-      compiler: clang++-10
-      env: TOOLSET=clang COMPILER=clang++-10 CXXSTD=03,11,14,17,2a
-      addons:
-        apt:
-          packages:
-            - clang-10
-          sources:
-            - ubuntu-toolchain-r-test
-            - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-10 main'
-              key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
-
-    - os: linux
-      dist: xenial
-      compiler: clang++-10
-      env: UBSAN=1 TOOLSET=clang COMPILER=clang++-10 CXXSTD=03,11,14,17,2a UBSAN_OPTIONS=print_stacktrace=1
-      addons:
-        apt:
-          packages:
-            - clang-10
-          sources:
-            - ubuntu-toolchain-r-test
-            - sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-10 main'
-              key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'
-
-    - os: linux
-      dist: trusty
+      dist: bionic
       compiler: clang++-libc++
-      env: TOOLSET=clang COMPILER=clang++-libc++ CXXSTD=03,11,14,1z
+      env: UBSAN=1 TOOLSET=clang COMPILER=clang++-libc++ CXXSTD=03,11,14,17,2a UBSAN_OPTIONS=print_stacktrace=1
       addons:
         apt:
           packages:
             - libc++-dev
 
-    - os: linux
-      dist: trusty
-      compiler: clang++-libc++
-      env: UBSAN=1 TOOLSET=clang COMPILER=clang++-libc++ CXXSTD=03,11,14,1z UBSAN_OPTIONS=print_stacktrace=1
-      addons:
-        apt:
-          packages:
-            - libc++-dev
-
-    - os: osx
-      compiler: clang++
-      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
-
-    - os: osx
-      compiler: clang++
-      env: UBSAN=1 TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z UBSAN_OPTIONS=print_stacktrace=1
-
     - os: freebsd
       compiler: clang++
       env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,17,2a
 
+    - os: osx
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z ADDRMD=32,64
+      osx_image: xcode7.3
+
+    - os: osx
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z ADDRMD=32,64
+      osx_image: xcode8.3
+
+    - os: osx
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z ADDRMD=32,64
+      osx_image: xcode9.4
+
+    - os: osx
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
+      osx_image: xcode10.1
+
+    - os: osx
+      osx_image: xcode11.3
+      compiler: clang++
+      env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
+
+    - os: osx
+      osx_image: xcode12.2
+      compiler: clang++
+      env: UBSAN=1 TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z UBSAN_OPTIONS=print_stacktrace=1
+
     - os: linux
       env: CMAKE=1
       script:
         - mkdir __build__ && cd __build__
-        - cmake -DBOOST_ENABLE_CMAKE=1 -DBoost_VERBOSE=1 -DBOOST_INCLUDE_LIBRARIES=system -DBUILD_TESTING=ON ..
-        - ctest --output-on-failure -R boost_system
+        - cmake -DBOOST_INCLUDE_LIBRARIES=system -DBUILD_TESTING=ON ..
+        - cmake --build . --target tests
+        - ctest --output-on-failure --no-tests=error
 
     - os: linux
       env: CMAKE=1 BUILD_SHARED_LIBS=ON
       script:
         - mkdir __build__ && cd __build__
-        - cmake -DBOOST_ENABLE_CMAKE=1 -DBoost_VERBOSE=1 -DBUILD_SHARED_LIBS=ON -DBOOST_INCLUDE_LIBRARIES=system -DBUILD_TESTING=ON ..
-        - ctest --output-on-failure -R boost_system
+        - cmake -DBUILD_SHARED_LIBS=ON -DBOOST_INCLUDE_LIBRARIES=system -DBUILD_TESTING=ON ..
+        - cmake --build . --target tests
+        - ctest --output-on-failure --no-tests=error
 
     - os: linux
       env: CMAKE_SUBDIR_TEST=1
@@ -375,7 +190,7 @@ matrix:
       script:
         - pip install --user cmake
         - mkdir __build__ && cd __build__
-        - cmake -DBOOST_ENABLE_CMAKE=1 -DBoost_VERBOSE=1 -DBOOST_INCLUDE_LIBRARIES="system;core" -DBUILD_TESTING=OFF -DCMAKE_INSTALL_PREFIX=~/.local ..
+        - cmake -DBOOST_INCLUDE_LIBRARIES=system -DCMAKE_INSTALL_PREFIX=~/.local ..
         - cmake --build . --target install
         - cd ../libs/system/test/cmake_install_test && mkdir __build__ && cd __build__
         - cmake -DCMAKE_INSTALL_PREFIX=~/.local ..
@@ -396,7 +211,7 @@ install:
 script:
   - |-
     echo "using $TOOLSET : : $COMPILER ;" > ~/user-config.jam
-  - ./b2 -j3 libs/system/test toolset=$TOOLSET cxxstd=$CXXSTD variant=debug,release ${UBSAN:+cxxflags=-fsanitize=undefined cxxflags=-fno-sanitize-recover=undefined linkflags=-fsanitize=undefined define=UBSAN=1 debug-symbols=on} ${LINKFLAGS:+linkflags=$LINKFLAGS}
+  - ./b2 -j3 libs/system/test toolset=$TOOLSET cxxstd=$CXXSTD variant=debug,release ${ADDRMD:+address-model=$ADDRMD} ${UBSAN:+cxxflags=-fsanitize=undefined cxxflags=-fno-sanitize-recover=undefined linkflags=-fsanitize=undefined define=UBSAN=1 debug-symbols=on} ${LINKFLAGS:+linkflags=$LINKFLAGS}
 
 notifications:
   email:

CMakeLists.txt

@@ -1,8 +1,8 @@
-# Copyright 2018-2020 Peter Dimov
+# Copyright 2018-2021 Peter Dimov
 # Distributed under the Boost Software License, Version 1.0.
 # See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt
 
-cmake_minimum_required(VERSION 3.5...3.16)
+cmake_minimum_required(VERSION 3.5...3.20)
 
 project(boost_system VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
 
@@ -13,10 +13,22 @@ target_include_directories(boost_system INTERFACE include)
 
 target_link_libraries(boost_system
   INTERFACE
+    Boost::assert
     Boost::config
+    Boost::throw_exception
+    Boost::variant2
     Boost::winapi
 )
 
+if(CMAKE_VERSION VERSION_GREATER 3.18 AND CMAKE_GENERATOR MATCHES "Visual Studio")
+
+  file(GLOB_RECURSE boost_system_IDEFILES CONFIGURE_DEPENDS include/*.hpp)
+  source_group(TREE ${PROJECT_SOURCE_DIR}/include FILES ${boost_system_IDEFILES} PREFIX "Header Files")
+  list(APPEND boost_system_IDEFILES extra/boost_system.natvis)
+  target_sources(boost_system PRIVATE ${boost_system_IDEFILES})
+
+endif()
+
 if(BUILD_TESTING)
 
   add_subdirectory(test)

README.md

@@ -0,0 +1,25 @@
+# Boost.System
+
+The Boost.System library, part of [Boost C++ Libraries](https://boost.org),
+implements an extensible framework for error reporting in the form of an
+`error_code` class and supporting facilities.
+
+It has been proposed for the C++11 standard, has been accepted, and
+is now available as part of the standard library in the `<system_error>`
+header. However, the Boost implementation has continued to evolve and
+gain enhancements and additional functionality, such as support for
+attaching [source locations](https://www.boost.org/doc/libs/release/libs/assert/doc/html/assert.html#source_location_support)
+to `error_code`, and a `result<T>` class that can carry either a value
+or an error code.
+
+See [the documentation of System](http://boost.org/libs/system) for more
+information.
+
+Since `<system_error>` is a relatively undocumented portion of the C++
+standard library, the documentation of Boost.System may be useful to you
+even if you use the standard components.
+
+## License
+
+Distributed under the
+[Boost Software License, Version 1.0](http://boost.org/LICENSE_1_0.txt).

appveyor.yml

@@ -16,20 +16,13 @@ environment:
   matrix:
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
       TOOLSET: msvc-9.0,msvc-10.0,msvc-11.0
+      ADDRMD: 32
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
       TOOLSET: msvc-12.0,msvc-14.0
       ADDRMD: 32,64
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
       TOOLSET: msvc-14.1
-      CXXSTD: 14,17
-      ADDRMD: 32,64
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
-      TOOLSET: clang-win
-      CXXSTD: 14,17
-      ADDRMD: 64
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
-      TOOLSET: msvc-14.2
-      CXXSTD: 14,17
+      CXXSTD: 14,17,latest
       ADDRMD: 32,64
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
       ADDPATH: C:\cygwin\bin;
@@ -47,6 +40,12 @@ environment:
       ADDPATH: C:\mingw-w64\x86_64-6.3.0-posix-seh-rt_v5-rev1\mingw64\bin;
       TOOLSET: gcc
       CXXSTD: 03,11,14,1z
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+      CMAKE: 1
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      CMAKE_SUBDIR: 1
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      CMAKE_INSTALL: 1
 
 install:
   - set BOOST_BRANCH=develop
@@ -66,4 +65,27 @@ test_script:
   - PATH=%ADDPATH%%PATH%
   - if not "%CXXSTD%" == "" set CXXSTD=cxxstd=%CXXSTD%
   - if not "%ADDRMD%" == "" set ADDRMD=address-model=%ADDRMD%
-  - b2 -j3 libs/system/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% variant=debug,release
+  - if "%CMAKE%%CMAKE_SUBDIR%%CMAKE_INSTALL%" == ""  b2 -j3 libs/system/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% variant=debug,release embed-manifest-via=linker
+
+  - if not "%CMAKE%" == ""  mkdir __build__ && cd __build__
+  - if not "%CMAKE%" == ""  cmake -DBUILD_TESTING=ON -DBOOST_INCLUDE_LIBRARIES=system -DBoost_VERBOSE=ON ..
+  - if not "%CMAKE%" == ""  cmake --build . --target tests -j 3 --config Debug & ctest --output-on-failure --no-tests=error -j 3 -C Debug
+  - if not "%CMAKE%" == ""  cmake --build . --target tests -j 3 --config Release & ctest --output-on-failure --no-tests=error -j 3 -C Release
+  - if not "%CMAKE%" == ""  cmake --build . --target tests -j 3 --config MinSizeRel & ctest --output-on-failure --no-tests=error -j 3 -C MinSizeRel
+  - if not "%CMAKE%" == ""  cmake --build . --target tests -j 3 --config RelWithDebInfo & ctest --output-on-failure --no-tests=error -j 3 -C RelWithDebInfo
+
+  - if not "%CMAKE_SUBDIR%" == ""  cd libs/system/test/cmake_subdir_test && mkdir __build__ && cd __build__
+  - if not "%CMAKE_SUBDIR%" == ""  cmake ..
+  - if not "%CMAKE_SUBDIR%" == ""  cmake --build . --config Debug && cmake --build . --target check --config Debug
+  - if not "%CMAKE_SUBDIR%" == ""  cmake --build . --config Release && cmake --build . --target check --config Release
+  - if not "%CMAKE_SUBDIR%" == ""  cmake --build . --config MinSizeRel && cmake --build . --target check --config MinSizeRel
+  - if not "%CMAKE_SUBDIR%" == ""  cmake --build . --config RelWithDebInfo && cmake --build . --target check --config RelWithDebInfo
+
+  - if not "%CMAKE_INSTALL%" == ""  mkdir __build__ && cd __build__
+  - if not "%CMAKE_INSTALL%" == ""  cmake -DBOOST_INCLUDE_LIBRARIES=system -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+  - if not "%CMAKE_INSTALL%" == ""  cmake --build . --target install --config Debug
+  - if not "%CMAKE_INSTALL%" == ""  cmake --build . --target install --config Release
+  - if not "%CMAKE_INSTALL%" == ""  cd ../libs/system/test/cmake_install_test && mkdir __build__ && cd __build__
+  - if not "%CMAKE_INSTALL%" == ""  cmake -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+  - if not "%CMAKE_INSTALL%" == ""  cmake --build . --config Debug && cmake --build . --target check --config Debug
+  - if not "%CMAKE_INSTALL%" == ""  cmake --build . --config Release && cmake --build . --target check --config Release

build/Jamfile.v2

@@ -5,7 +5,7 @@
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or www.boost.org/LICENSE_1_0.txt)
 
-# See library home page at http://www.boost.org/libs/system
+# See library home page at https://www.boost.org/libs/system
 
 project boost/system
     : source-location ../src

doc/system.adoc

@@ -4,19 +4,22 @@ Copyright 2018 Peter Dimov
 Distributed under the Boost Software License, Version 1.0.
 
 See accompanying file LICENSE_1_0.txt or copy at
-http://www.boost.org/LICENSE_1_0.txt
+https://www.boost.org/LICENSE_1_0.txt
 ////
 
 # Boost.System: Extensible Error Reporting
 Beman Dawes, Christopher Kohlhoff, Peter Dimov
 :toc: left
-:toclevels: 3
+:toclevels: 4
 :idprefix:
 :docinfo: private-footer
+:source-highlighter: rouge
+:source-language: c++
 
 :leveloffset: +1
 
 include::system/introduction.adoc[]
+include::system/usage.adoc[]
 include::system/changes.adoc[]
 include::system/rationale.adoc[]
 include::system/reference.adoc[]

doc/system/changes.adoc

@@ -1,16 +1,98 @@
 ////
-Copyright 2018 Peter Dimov
-
+Copyright 2018-2022 Peter Dimov
 Distributed under the Boost Software License, Version 1.0.
-
-See accompanying file LICENSE_1_0.txt or copy at
-http://www.boost.org/LICENSE_1_0.txt
+https://www.boost.org/LICENSE_1_0.txt
 ////
 
 [#changes]
 # Revision History
 :idprefix:
 
+## Changes in Boost 1.84
+
+* Added support for `result<U&, E>`.
+* Added `operator|` for `result`.
+* Added `operator&` for `result`.
+* Added `operator&=` for `result`.
+
+## Changes in Boost 1.81
+
+* The macro `BOOST_SYSTEM_DISABLE_THREADS` can now be defined to disable
+  the use of `<mutex>` (e.g. on single-threaded libstdc++).
+* Added `value_type`, `error_type`, `in_place_value`, `in_place_error`
+  to `result<>`.
+* Added `emplace` to `result<>`.
+
+## Changes in Boost 1.80
+
+* When an `error_code` is converted to `std::error_code` and then back
+  to `error_code`, the original is now restored, if possible.
+* Reworked the conversion from `error_category` to `std::error_category`
+  to avoid the one-time allocation that shows up on leak checkers.
+* Added a constructor that allows replacing the source location of an
+  `error_code`, and a corresponding `assign`.
+* Added a converting constructor to `result`.
+
+## Changes in Boost 1.79
+
+* Added a `boost::source_location` parameter to `throw_exception_from_error`.
+* Added `throw_exception_from_error` overloads for `errc::errc_t`,
+  `std::error_code`, `std::errc`, `std::exception_ptr`.
+* `result<T>::value` now automatically supplies `BOOST_CURRENT_LOCATION` to
+  `throw_exception_from_error` via a default argument.
+* Added an `errc::make_error_code` overload taking a source location.
+
+## Changes in Boost 1.78
+
+* Added support for source locations to `error_code`.
+* Added `error_code::to_string`, `error_condition::to_string`, `error_code::what`.
+* `system_error::what()` now contains the source location, if present.
+* Added `result<T, E = error_code>`, a class holding either a value or an
+  error, defined in `<boost/system/result.hpp>`.
+
+## Changes in Boost 1.77
+
+* The conversion operator from `error_category` to `std::error_category`
+  has been improved and no longer requires `<map>` or `<mutex>`.
+* The comparison operators of `error_category` are now inline friends
+  instead of member functions (a side effect of the previous change.)
+* `error_condition` now defers calling `generic_category()` to avoid
+  instantiating the object until it's actually needed.
+* `error_condition::failed` and `error_condition::message` have been
+  undeprecated, and `operator bool()` now once again returns `failed()`.
+* The system category now doesn't call `generic_category()`, to avoid
+  instantiating the object.
+* The return value of `default_error_condition` changes in some cases into
+  an `error_condition` from the generic category, instead of from the system
+  category. This happens on POSIX when the input `error_code` is from
+  the system category and does not correspond to any `errc_t` value.
+* The interoperability of `error_code` and `std::error_code` has been
+  improved substantially. It is now possible to construct
+  `boost::system::error_code` from `std::error_code`, and it's possible
+  to pass `boost::system::error_code` to functions taking `std::error_code&`.
+* A stream insertion operator for `error_condition` has been added.
+
+## Changes in Boost 1.76
+
+* `windows_error.hpp` is no longer deprecated.
+
+## Changes in Boost 1.75
+
+* The platform-specific headers `windows_error.hpp`, `linux_error.hpp`,
+  and `cygwin_error.hpp` emit deprecation messages and are slated for
+  removal.
+* The old names for `generic_category()` and `system_category()` emit
+  deprecation messages and are slated for removal.
+* `error_condition::failed` is deprecated and is slated for removal.
+  `operator bool()` for `error_condition` has been reverted to its old
+  meaning of `value() != 0`. This is done for compatibility with
+  `std::error_condition` as the next release is expected to improve
+  interoperability with `<system_error>` even further. _Note that this
+  does not affect_ `error_code::failed`, which is still alive and well.
+* The overload of `error_condition::message` that takes a buffer is
+  deprecated and is slated for removal, for the same reasons. _Note that
+  this does not affect_ `error_code::message`.
+
 ## Changes in Boost 1.74
 
 * `operator bool()` now returns `failed()` instead of `value() != 0`.

doc/system/copyright.adoc

@@ -1,5 +1,5 @@
 ////
-Copyright 2018 Peter Dimov
+Copyright 2018-2021 Peter Dimov
 
 Distributed under the Boost Software License, Version 1.0.
 
@@ -14,6 +14,6 @@ http://www.boost.org/LICENSE_1_0.txt
 This documentation is
 
 * Copyright 2003-2017 Beman Dawes
-* Copyright 2018 Peter Dimov
+* Copyright 2018-2022 Peter Dimov
 
 and is distributed under the http://www.boost.org/LICENSE_1_0.txt[Boost Software License, Version 1.0].

doc/system/introduction.adoc

@@ -1,6 +1,6 @@
 ////
 Copyright 2003-2017 Beman Dawes
-Copyright 2018 Peter Dimov
+Copyright 2018, 2021 Peter Dimov
 
 Distributed under the Boost Software License, Version 1.0.
 
@@ -12,39 +12,67 @@ http://www.boost.org/LICENSE_1_0.txt
 # Introduction
 :idprefix: intro_
 
-Error conditions originating from the operating system or other low-level
-application program interfaces (API's) are typically reported via an integer
-representing an error code. When these low-level API calls are wrapped in
-portable code, such as in a portable library, some users want to deal with the
-error codes in portable ways. Other users need to get at the system specific
-error codes, so they can deal with system specific needs. The Boost System
-library provides simple, light-weight `error_code` objects that encapsulate
-system-specific error code values, yet also provide access to more abstract
-and portable error conditions via `error_condition` objects.
+Errors originating from the operating system or other low-level application
+program interfaces (APIs) are typically reported via an integer representing
+an error code, either by returning the code directly from the function (e.g.
+`pthread_mutex_init`) or by using a side channel such as the `errno`
+pseudo-variable under POSIX or `GetLastError()` under Windows.
 
-Because `error_code` objects can represent errors from sources other than the
-operating system, including user-defined sources, each `error_code` and
-`error_condition` has an associated `error_category`.
+However, these integer error values can only be interpreted when their source
+is known. The value 5 under Windows means `ERROR_ACCESS_DENIED` when returned
+by `GetLastError()`, but `EIO` when retrieved from `errno`. And conversely,
+the same error condition "access denied" is represented by the value 5 when
+returned by `GetLastError()` and 13 (`EACCES`) when retrieved from `errno`.
 
-An exception class, `system_error`, is provided. Derived from
-`std::runtime_error`, it captures the underlying `error_code` for the problem
-causing the exception so that this important information is not lost.
+This means that in order for code to be able to handle errors from both
+sources (to retrieve a text message describing the error, or to check whether
+the error means "access denied"), it needs to know where the integer error
+value originated. For this to be possible, the integer error value needs to
+be accompanied by a piece of information identifying the source.
 
-While exceptions are the preferred {cpp} default error code reporting
-mechanism, users of libraries dependent on low-level API's often need overloads
-reporting error conditions via error code arguments and/or return values rather
-than via throwing exceptions. Otherwise, when errors are not exceptional
-occurrences and must be dealt with as they arise, programs become littered with
-try/catch blocks, unreadable, and inefficient. The Boost System library
-supports both error reporting by exception and by error code.
+Boost.System provides a framework in which this is possible. Errors are
+represented by a class `error_code` which contains both the error value and
+a pointer to their source (called "category"), represented as a class derived
+from `error_category`.
 
-In addition to portable errors codes and conditions supported by the
-`error_code.hpp` header, system-specific headers support the Cygwin, Linux,
-and Windows platforms. These headers are effectively no-ops if included for
-platforms other than their intended target.
+The category provides member functions such as `message`, which returns a text
+message for a specific error value, and `equivalent`, which can be used to test
+whether a specific error value correspond to an error condition such as "access
+denied". `error_code` uses these category-provided functions in the
+implementation of its `message` and `operator==` member functions.
 
-Boost.System is part of the {cpp}11 Standard Library.
-A number of changes, particularly to names, were made by the C++ committee
-during standardization. The Boost implementation has been tracking those changes.
-See <<#ref_deprecated_names,Deprecated Names>> for synonyms provided to prevent
-breakage of existing user code.
+Boost.System contains two predefined category classes, the generic category
+(a reference to which is returned by `generic_category()`) and the system
+category (`system_category()`). The generic category represents the error
+values of the portable subset of `errno` values defined by the POSIX standard,
+whereas the system category is OS dependent. Under POSIX, the system category
+represents the `errno` values returned by the OS APIs (a superset of those in
+the generic category), whereas under Windows, the system category represents
+the error values returned by `GetLastError()`.
+
+The framework is extensible. Users can define their own categories by
+deriving a class from `error_category` and implementing a function that
+returns a reference to an instance of it. This capability is useful both for
+describing library-defined error values, and for adapting existing C API
+libraries that return integer error values.
+
+For those who prefer error reporting via exceptions, Boost.System provides
+a standard exception class `system_error` that stores an `error_code`.
+
+Boost.System was standardized in {cpp}11 as `<system_error>`. For a while,
+the two were equivalent, but Boost.System has evolved since then and now
+contains a number of extensions over its standard sibling:
+
+* A non-allocating overload of `message`;
+* Support for nonzero error codes meaning success, via the `failed` member
+  functions;
+* Support for 64 bit category identifiers, as a solution to the problem
+  that sometimes it's not possible to ensure that only one instance of a
+  category exists in the program;
+* Support for attaching source locations (file/line/function) to error codes;
+* A class `result<T>` that can be used to return either a value or an error
+  code from a function;
+* Various other minor improvements.
+
+`boost::system::error_code` can be converted to, and constructed from,
+`std::error_code`.

extra/boost_system.natvis

@@ -0,0 +1,53 @@
+<?xml version="1.0" encoding="utf-8"?>
+<AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
+
+    <Type Name="boost::system::error_category">
+        <DisplayString Condition="id_ == 0xb2ab117a257edfd0">[generic]</DisplayString>
+        <DisplayString Condition="id_ == 0xb2ab117a257edfd1">[system]</DisplayString>
+        <DisplayString Condition="id_ == 0xb2ab117a257edfd2">[interop]</DisplayString>
+        <DisplayString Condition="id_ != 0">[{id_,x}]</DisplayString>
+        <DisplayString>@{((uintptr_t)this),x}</DisplayString>
+    </Type>
+
+    <Type Name="boost::system::error_code">
+        <DisplayString Condition="lc_flags_ == 0">{d1_.val_} [system] ✓</DisplayString>
+
+        <DisplayString Condition="lc_flags_ == 1 &amp;&amp; ((std::error_code*)d2_)->_Mycat->_Addr==1">{((std::error_code*)d2_)->_Myval} [std:future]</DisplayString>
+        <DisplayString Condition="lc_flags_ == 1 &amp;&amp; ((std::error_code*)d2_)->_Mycat->_Addr==3">{((std::error_code*)d2_)->_Myval} [std:generic]</DisplayString>
+        <DisplayString Condition="lc_flags_ == 1 &amp;&amp; ((std::error_code*)d2_)->_Mycat->_Addr==5">{((std::error_code*)d2_)->_Myval} [std:iostream]</DisplayString>
+        <DisplayString Condition="lc_flags_ == 1 &amp;&amp; ((std::error_code*)d2_)->_Mycat->_Addr==7">{((std::error_code*)d2_)->_Myval} [std:system]</DisplayString>
+        <DisplayString Condition="lc_flags_ == 1">{((std::error_code*)d2_)->_Myval} std@{((uintptr_t)((std::error_code*)d2_)->_Mycat),x}</DisplayString>
+
+        <DisplayString Condition="d1_.cat_->id_ == 0xb2ab117a257edfd0 &amp;&amp;
+            (lc_flags_ == 2 || (lc_flags_ &gt; 3 &amp;&amp; ( lc_flags_ % 2 == 0 )))">{d1_.val_} [generic] ✓</DisplayString>
+        <DisplayString Condition="d1_.cat_->id_ == 0xb2ab117a257edfd1 &amp;&amp;
+            (lc_flags_ == 2 || (lc_flags_ &gt; 3 &amp;&amp; ( lc_flags_ % 2 == 0 )))">{d1_.val_} [system] ✓</DisplayString>
+        <DisplayString Condition="d1_.cat_->id_ == 0xb2ab117a257edfd2 &amp;&amp;
+            (lc_flags_ == 2 || (lc_flags_ &gt; 3 &amp;&amp; ( lc_flags_ % 2 == 0 )))">{d1_.val_} [interop] ✓</DisplayString>
+        <DisplayString Condition="d1_.cat_->id_ != 0 &amp;&amp;
+            (lc_flags_ == 2 || (lc_flags_ &gt; 3 &amp;&amp; ( lc_flags_ % 2 == 0 )))">{d1_.val_} [{d1_.cat_->id_,x}] ✓</DisplayString>
+        <DisplayString Condition=
+            "lc_flags_ == 2 || (lc_flags_ &gt; 3 &amp;&amp; ( lc_flags_ % 2 == 0 ))">{d1_.val_} @{((uintptr_t)d1_.cat_),x} ✓</DisplayString>
+
+        <DisplayString Condition="d1_.cat_->id_ == 0xb2ab117a257edfd0 &amp;&amp;
+            (lc_flags_ &gt;= 3 &amp;&amp; ( lc_flags_ % 2 == 1 ))">{d1_.val_} [generic]</DisplayString>
+        <DisplayString Condition="d1_.cat_->id_ == 0xb2ab117a257edfd1 &amp;&amp;
+            (lc_flags_ &gt;= 3 &amp;&amp; ( lc_flags_ % 2 == 1 ))">{d1_.val_} [system]</DisplayString>
+        <DisplayString Condition="d1_.cat_->id_ == 0xb2ab117a257edfd2 &amp;&amp;
+            (lc_flags_ &gt;= 3 &amp;&amp; ( lc_flags_ % 2 == 1 ))">{d1_.val_} [interop]</DisplayString>
+        <DisplayString Condition="d1_.cat_->id_ != 0 &amp;&amp;
+            (lc_flags_ &gt;= 3 &amp;&amp; ( lc_flags_ % 2 == 1 ))">{d1_.val_} [{d1_.cat_->id_,x}]</DisplayString>
+        <DisplayString Condition=
+            "lc_flags_ &gt;= 3 &amp;&amp; ( lc_flags_ % 2 == 1 )">{d1_.val_} @{((uintptr_t)d1_.cat_),x}</DisplayString>
+
+        <Expand>
+            <Item Name="std::error_code" Condition="lc_flags_ == 1">(std::error_code*)d2_</Item>
+            <Item Name="[location]" Condition="lc_flags_ &gt; 3">*((boost::source_location*)(lc_flags_ &amp; ~1))</Item>
+        </Expand>
+    </Type>
+
+    <Type Name="boost::system::result&lt;*,*&gt;">
+        <DisplayString>{v_}</DisplayString>
+    </Type>
+
+</AutoVisualizer>

include/boost/system.hpp

@@ -0,0 +1,18 @@
+#ifndef BOOST_SYSTEM_HPP_INCLUDED
+#define BOOST_SYSTEM_HPP_INCLUDED
+
+// Copyright 2021 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt)
+//
+// See library home page at http://www.boost.org/libs/system
+
+#include <boost/system/error_code.hpp>
+#include <boost/system/system_error.hpp>
+#include <boost/config.hpp>
+
+#if (__cplusplus >= 201103L) && !(defined(BOOST_GCC) && BOOST_GCC < 40800) || (defined(_MSC_VER) && _MSC_VER >= 1900)
+# include <boost/system/result.hpp>
+#endif
+
+#endif // #ifndef BOOST_SYSTEM_HPP_INCLUDED

include/boost/system/cygwin_error.hpp

@@ -10,6 +10,13 @@
 #ifndef BOOST_SYSTEM_CYGWIN_ERROR_HPP
 #define BOOST_SYSTEM_CYGWIN_ERROR_HPP
 
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(BOOST_ALLOW_DEPRECATED_HEADERS)
+  BOOST_PRAGMA_MESSAGE("This header is deprecated and is slated for removal."
+  " If you want it retained, please open an issue in github.com/boostorg/system.")
+#endif
+
 //  This header is effectively empty for compiles on operating systems where
 //  it is not applicable.
 

include/boost/system/detail/append_int.hpp

@@ -0,0 +1,32 @@
+#ifndef BOOST_SYSTEM_DETAIL_APPEND_INT_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_APPEND_INT_HPP_INCLUDED
+
+// Copyright 2021 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/system/detail/snprintf.hpp>
+#include <string>
+
+//
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+inline void append_int( std::string& s, int v )
+{
+    char buffer[ 32 ];
+    detail::snprintf( buffer, sizeof( buffer ), ":%d", v );
+
+    s += buffer;
+}
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_APPEND_INT_HPP_INCLUDED

include/boost/system/detail/config.hpp

@@ -1,32 +1,29 @@
 #ifndef BOOST_SYSTEM_DETAIL_CONFIG_HPP_INCLUDED
 #define BOOST_SYSTEM_DETAIL_CONFIG_HPP_INCLUDED
 
-// Copyright 2018 Peter Dimov
+// Copyright 2018-2022 Peter Dimov
 //
 // Distributed under the Boost Software License, Version 1.0. (See accompanying
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 // See http://www.boost.org/libs/system for documentation.
 
+#include <boost/system/detail/requires_cxx11.hpp>
 #include <boost/config.hpp>
 #include <boost/config/workaround.hpp>
 
 // BOOST_SYSTEM_HAS_SYSTEM_ERROR
+//
+// The macro BOOST_SYSTEM_DISABLE_THREADS can be defined on configurations
+// that provide <system_error> and <atomic>, but not <mutex>, such as the
+// single-threaded libstdc++.
+//
+// https://github.com/boostorg/system/issues/92
 
-#if !defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR)
+#if !defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR) && !defined(BOOST_NO_CXX11_HDR_ATOMIC) && ( !defined(BOOST_NO_CXX11_HDR_MUTEX) || defined(BOOST_SYSTEM_DISABLE_THREADS) )
 # define BOOST_SYSTEM_HAS_SYSTEM_ERROR
 #endif
 
-#if BOOST_WORKAROUND(BOOST_GCC, < 40600)
-// g++ 4.4's <map> is not good enough
-# undef BOOST_SYSTEM_HAS_SYSTEM_ERROR
-#endif
-
-#if defined(BOOST_NO_CXX11_HDR_MUTEX)
-// Required for thread-safe map manipulation
-# undef BOOST_SYSTEM_HAS_SYSTEM_ERROR
-#endif
-
 // BOOST_SYSTEM_NOEXCEPT
 // Retained for backward compatibility
 
@@ -48,4 +45,46 @@
 # define BOOST_SYSTEM_CONSTEXPR
 #endif
 
+// BOOST_SYSTEM_DEPRECATED
+
+#if defined(__clang__)
+# define BOOST_SYSTEM_DEPRECATED(msg) __attribute__((deprecated(msg)))
+#elif defined(__GNUC__)
+# if __GNUC__ * 100 + __GNUC_MINOR__ >= 405
+#  define BOOST_SYSTEM_DEPRECATED(msg) __attribute__((deprecated(msg)))
+# else
+#  define BOOST_SYSTEM_DEPRECATED(msg) __attribute__((deprecated))
+# endif
+#elif defined(_MSC_VER)
+#  define BOOST_SYSTEM_DEPRECATED(msg) __declspec(deprecated(msg))
+#elif defined(__sun)
+#  define BOOST_SYSTEM_DEPRECATED(msg) __attribute__((deprecated(msg)))
+#else
+# define BOOST_SYSTEM_DEPRECATED(msg)
+#endif
+
+// BOOST_SYSTEM_CLANG_6
+
+// Android NDK r18b has Clang 7.0.2 that still needs the workaround
+// https://github.com/boostorg/system/issues/100
+#if defined(__clang__) && (__clang_major__ < 7 || (defined(__APPLE__) && __clang_major__ < 11) || (defined(__ANDROID__) && __clang_major__ == 7))
+# define BOOST_SYSTEM_CLANG_6
+#endif
+
+//
+
+#if defined(BOOST_LIBSTDCXX_VERSION) && BOOST_LIBSTDCXX_VERSION < 50000
+# define BOOST_SYSTEM_AVOID_STD_GENERIC_CATEGORY
+#endif
+
+#if defined(__CYGWIN__) || defined(__MINGW32__) || (defined(_MSC_VER) && _MSC_VER == 1800) || (defined(BOOST_LIBSTDCXX_VERSION) && BOOST_LIBSTDCXX_VERSION < 90000)
+
+// Under Cygwin (and MinGW!), std::system_category() is POSIX
+// Under VS2013, std::system_category() isn't quite right
+// Under libstdc++ before 7.4, before 8.3, before 9.1, default_error_condition
+// for the system category returns a condition from the system category
+
+# define BOOST_SYSTEM_AVOID_STD_SYSTEM_CATEGORY
+#endif
+
 #endif // BOOST_SYSTEM_DETAIL_CONFIG_HPP_INCLUDED

include/boost/system/detail/error_category.hpp

@@ -13,12 +13,14 @@
 #include <boost/system/detail/config.hpp>
 #include <boost/cstdint.hpp>
 #include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
 #include <string>
 #include <functional>
 #include <cstddef>
 
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 # include <system_error>
+# include <atomic>
 #endif
 
 namespace boost
@@ -38,11 +40,7 @@ namespace detail
 
 BOOST_SYSTEM_CONSTEXPR bool failed_impl( int ev, error_category const & cat );
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
-std::error_category const & to_std_category( error_category const & cat );
-
-#endif
+class std_category;
 
 } // namespace detail
 
@@ -51,6 +49,11 @@ std::error_category const & to_std_category( error_category const & cat );
 #pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
 #endif
 
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1900
+#pragma warning(push)
+#pragma warning(disable: 4351) //  new behavior: elements of array will be default initialized
+#endif
+
 class BOOST_SYMBOL_VISIBLE error_category
 {
 private:
@@ -58,9 +61,8 @@ private:
     friend std::size_t hash_value( error_code const & ec );
     friend BOOST_SYSTEM_CONSTEXPR bool detail::failed_impl( int ev, error_category const & cat );
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-    friend std::error_category const & detail::to_std_category( error_category const & cat );
-#endif
+    friend class error_code;
+    friend class error_condition;
 
 #if !defined(BOOST_NO_CXX11_DELETED_FUNCTIONS)
 public:
@@ -80,6 +82,24 @@ private:
 
     boost::ulong_long_type id_;
 
+    static std::size_t const stdcat_size_ = 4 * sizeof( void const* );
+
+    union
+    {
+        mutable unsigned char stdcat_[ stdcat_size_ ];
+        void const* stdcat_align_;
+    };
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    mutable std::atomic< unsigned > sc_init_;
+
+#else
+
+    unsigned sc_init_;
+
+#endif
+
 protected:
 
 #if !defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) && !defined(BOOST_NO_CXX11_NON_PUBLIC_DEFAULTED_FUNCTIONS)
@@ -97,11 +117,18 @@ protected:
 
 #endif
 
-    BOOST_SYSTEM_CONSTEXPR error_category() BOOST_NOEXCEPT: id_( 0 )
+#if !BOOST_WORKAROUND(BOOST_GCC, < 40800)
+    BOOST_CONSTEXPR
+#endif
+    error_category() BOOST_NOEXCEPT: id_( 0 ), stdcat_(), sc_init_()
     {
     }
 
-    explicit BOOST_SYSTEM_CONSTEXPR error_category( boost::ulong_long_type id ) BOOST_NOEXCEPT: id_( id )
+    explicit
+#if !BOOST_WORKAROUND(BOOST_GCC, < 40800)
+    BOOST_CONSTEXPR
+#endif
+    error_category( boost::ulong_long_type id ) BOOST_NOEXCEPT: id_( id ), stdcat_(), sc_init_()
     {
     }
 
@@ -121,24 +148,24 @@ public:
         return ev != 0;
     }
 
-    BOOST_SYSTEM_CONSTEXPR bool operator==( const error_category & rhs ) const BOOST_NOEXCEPT
+    friend BOOST_SYSTEM_CONSTEXPR bool operator==( error_category const & lhs, error_category const & rhs ) BOOST_NOEXCEPT
     {
-        return rhs.id_ == 0? this == &rhs: id_ == rhs.id_;
+        return rhs.id_ == 0? &lhs == &rhs: lhs.id_ == rhs.id_;
     }
 
-    BOOST_SYSTEM_CONSTEXPR bool operator!=( const error_category & rhs ) const BOOST_NOEXCEPT
+    friend BOOST_SYSTEM_CONSTEXPR bool operator!=( error_category const & lhs, error_category const & rhs ) BOOST_NOEXCEPT
     {
-        return !( *this == rhs );
+        return !( lhs == rhs );
     }
 
-    BOOST_SYSTEM_CONSTEXPR bool operator<( const error_category & rhs ) const BOOST_NOEXCEPT
+    friend BOOST_SYSTEM_CONSTEXPR bool operator<( error_category const & lhs, error_category const & rhs ) BOOST_NOEXCEPT
     {
-        if( id_ < rhs.id_ )
+        if( lhs.id_ < rhs.id_ )
         {
             return true;
         }
 
-        if( id_ > rhs.id_ )
+        if( lhs.id_ > rhs.id_ )
         {
             return false;
         }
@@ -148,16 +175,26 @@ public:
             return false; // equal
         }
 
-        return std::less<error_category const *>()( this, &rhs );
+        return std::less<error_category const *>()( &lhs, &rhs );
     }
 
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 
+    void init_stdcat() const;
+
+# if defined(__SUNPRO_CC) // trailing __global is not supported
     operator std::error_category const & () const;
+# else
+    operator std::error_category const & () const BOOST_SYMBOL_VISIBLE;
+# endif
 
 #endif
 };
 
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1900
+#pragma warning(pop)
+#endif
+
 #if ( defined( BOOST_GCC ) && BOOST_GCC >= 40600 ) || defined( BOOST_CLANG )
 #pragma GCC diagnostic pop
 #endif
@@ -165,8 +202,9 @@ public:
 namespace detail
 {
 
-static const boost::ulong_long_type generic_category_id = ( boost::ulong_long_type( 0xB2AB117A ) << 32 ) + 0x257EDF0D;
-static const boost::ulong_long_type system_category_id = ( boost::ulong_long_type( 0x8FAFD21E ) << 32 ) + 0x25C5E09B;
+static const boost::ulong_long_type generic_category_id = ( boost::ulong_long_type( 0xB2AB117A ) << 32 ) + 0x257EDFD0;
+static const boost::ulong_long_type system_category_id = generic_category_id + 1;
+static const boost::ulong_long_type interop_category_id = generic_category_id + 2;
 
 BOOST_SYSTEM_CONSTEXPR inline bool failed_impl( int ev, error_category const & cat )
 {

include/boost/system/detail/error_category_impl.hpp

@@ -13,13 +13,14 @@
 #include <boost/system/detail/error_category.hpp>
 #include <boost/system/detail/error_condition.hpp>
 #include <boost/system/detail/error_code.hpp>
+#include <boost/system/detail/snprintf.hpp>
+#include <boost/system/detail/config.hpp>
 #include <boost/config.hpp>
 #include <string>
 #include <cstring>
 
 namespace boost
 {
-
 namespace system
 {
 
@@ -37,7 +38,7 @@ inline bool error_category::equivalent( int code, const error_condition & condit
 
 inline bool error_category::equivalent( const error_code & code, int condition ) const BOOST_NOEXCEPT
 {
-    return *this == code.category() && code.value() == condition;
+    return code.equals( condition, *this );
 }
 
 inline char const * error_category::message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT
@@ -83,26 +84,107 @@ inline char const * error_category::message( int ev, char * buffer, std::size_t
 #if !defined(BOOST_NO_EXCEPTIONS)
     catch( ... )
     {
-        return "Message text unavailable";
+        detail::snprintf( buffer, len, "No message text available for error %d", ev );
+        return buffer;
     }
 #endif
 }
 
 } // namespace system
-
 } // namespace boost
 
 // interoperability with std::error_code, std::error_condition
 
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 
-#include <boost/system/detail/to_std_category.hpp>
+#include <boost/system/detail/std_category_impl.hpp>
+#include <boost/system/detail/mutex.hpp>
+#include <new>
 
-inline boost::system::error_category::operator std::error_category const & () const
+namespace boost
 {
-    return boost::system::detail::to_std_category( *this );
+namespace system
+{
+
+inline void error_category::init_stdcat() const
+{
+    static_assert( sizeof( stdcat_ ) >= sizeof( boost::system::detail::std_category ), "sizeof(stdcat_) is not enough for std_category" );
+
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1900
+    // no alignof
+#else
+
+    static_assert( alignof( decltype(stdcat_align_) ) >= alignof( boost::system::detail::std_category ), "alignof(stdcat_) is not enough for std_category" );
+
+#endif
+
+    // detail::mutex has a constexpr default constructor,
+    // and therefore guarantees static initialization, on
+    // everything except VS 2013 (msvc-12.0)
+
+    static system::detail::mutex mx_;
+
+    system::detail::lock_guard<system::detail::mutex> lk( mx_ );
+
+    if( sc_init_.load( std::memory_order_acquire ) == 0 )
+    {
+        ::new( static_cast<void*>( stdcat_ ) ) boost::system::detail::std_category( this, system::detail::id_wrapper<0>() );
+        sc_init_.store( 1, std::memory_order_release );
+    }
 }
 
+#if defined( BOOST_GCC ) && BOOST_GCC >= 40800 && BOOST_GCC < 70000
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstrict-aliasing"
+#endif
+
+inline BOOST_NOINLINE error_category::operator std::error_category const & () const
+{
+    if( id_ == detail::generic_category_id )
+    {
+// This condition must be the same as the one in error_condition.hpp
+#if defined(BOOST_SYSTEM_AVOID_STD_GENERIC_CATEGORY)
+
+        static const boost::system::detail::std_category generic_instance( this, system::detail::id_wrapper<0x1F4D3>() );
+        return generic_instance;
+
+#else
+
+        return std::generic_category();
+
+#endif
+    }
+
+    if( id_ == detail::system_category_id )
+    {
+// This condition must be the same as the one in error_code.hpp
+#if defined(BOOST_SYSTEM_AVOID_STD_SYSTEM_CATEGORY)
+
+        static const boost::system::detail::std_category system_instance( this, system::detail::id_wrapper<0x1F4D7>() );
+        return system_instance;
+
+#else
+
+        return std::system_category();
+
+#endif
+    }
+
+    if( sc_init_.load( std::memory_order_acquire ) == 0 )
+    {
+        init_stdcat();
+    }
+
+    return *static_cast<boost::system::detail::std_category const*>( static_cast<void const*>( stdcat_ ) );
+}
+
+#if defined( BOOST_GCC ) && BOOST_GCC >= 40800 && BOOST_GCC < 70000
+#pragma GCC diagnostic pop
+#endif
+
+} // namespace system
+} // namespace boost
+
 #endif // #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 
 #endif // #ifndef BOOST_SYSTEM_DETAIL_ERROR_CATEGORY_IMPL_HPP_INCLUDED

include/boost/system/detail/error_code.hpp

@@ -3,22 +3,45 @@
 
 //  Copyright Beman Dawes 2006, 2007
 //  Copyright Christoper Kohlhoff 2007
-//  Copyright Peter Dimov 2017, 2018
+//  Copyright Peter Dimov 2017-2021
 //
 //  Distributed under the Boost Software License, Version 1.0. (See accompanying
 //  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 //  See library home page at http://www.boost.org/libs/system
 
+#include <boost/system/is_error_code_enum.hpp>
 #include <boost/system/detail/error_category.hpp>
 #include <boost/system/detail/error_condition.hpp>
 #include <boost/system/detail/system_category.hpp>
+#include <boost/system/detail/system_category_impl.hpp>
+#include <boost/system/detail/interop_category.hpp>
 #include <boost/system/detail/enable_if.hpp>
-#include <boost/system/is_error_code_enum.hpp>
+#include <boost/system/detail/is_same.hpp>
+#include <boost/system/detail/append_int.hpp>
+#include <boost/system/detail/snprintf.hpp>
 #include <boost/system/detail/config.hpp>
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+# include <boost/system/detail/std_category.hpp>
+#endif
+
+#include <boost/assert/source_location.hpp>
 #include <boost/cstdint.hpp>
 #include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
 #include <ostream>
+#include <new>
+#include <cstdio>
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+# include <system_error>
+#endif
+
+#if defined(BOOST_GCC) && BOOST_GCC >= 40600 && BOOST_GCC < 70000
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wstrict-aliasing"
+#endif
 
 namespace boost
 {
@@ -35,41 +58,146 @@ namespace system
 //  and error_code containing a pointer to an object of a type derived
 //  from error_category.
 
+bool operator==( const error_code & code, const error_condition & condition ) BOOST_NOEXCEPT;
+std::size_t hash_value( error_code const & ec );
+
 class error_code
 {
 private:
 
-    int val_;
-    bool failed_;
-    const error_category * cat_;
+    friend bool operator==( const error_code & code, const error_condition & condition ) BOOST_NOEXCEPT;
+    friend std::size_t hash_value( error_code const & ec );
+
+private:
+
+    struct data
+    {
+        int val_;
+        const error_category * cat_;
+    };
+
+    union
+    {
+        data d1_;
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+        unsigned char d2_[ sizeof(std::error_code) ];
+#endif
+    };
+
+    // 0: default constructed, d1_ value initialized
+    // 1: holds std::error_code in d2_
+    // 2: holds error code in d1_, failed == false
+    // 3: holds error code in d1_, failed == true
+    // >3: pointer to source_location, failed_ in lsb
+    boost::uintptr_t lc_flags_;
+
+private:
+
+    char const* category_name() const BOOST_NOEXCEPT
+    {
+        // return category().name();
+
+        if( lc_flags_ == 0 )
+        {
+            // must match detail::system_error_category::name()
+            return "system";
+        }
+        else if( lc_flags_ == 1 )
+        {
+            // must match detail::interop_error_category::name()
+            return "std:unknown";
+        }
+        else
+        {
+            return d1_.cat_->name();
+        }
+    }
 
 public:
 
     // constructors:
 
-    BOOST_SYSTEM_CONSTEXPR error_code() BOOST_NOEXCEPT:
-        val_( 0 ), failed_( false ), cat_( &system_category() )
+#if !BOOST_WORKAROUND(BOOST_GCC, < 40800)
+    BOOST_CONSTEXPR
+#endif
+    error_code() BOOST_NOEXCEPT:
+        d1_(), lc_flags_( 0 )
     {
     }
 
     BOOST_SYSTEM_CONSTEXPR error_code( int val, const error_category & cat ) BOOST_NOEXCEPT:
-        val_( val ), failed_( detail::failed_impl( val, cat ) ), cat_( &cat )
+        d1_(), lc_flags_( 2 + detail::failed_impl( val, cat ) )
     {
+        d1_.val_ = val;
+        d1_.cat_ = &cat;
+    }
+
+    error_code( int val, const error_category & cat, source_location const * loc ) BOOST_NOEXCEPT:
+        d1_(), lc_flags_( ( loc? reinterpret_cast<boost::uintptr_t>( loc ): 2 ) | +detail::failed_impl( val, cat ) )
+    {
+        d1_.val_ = val;
+        d1_.cat_ = &cat;
     }
 
     template<class ErrorCodeEnum> BOOST_SYSTEM_CONSTEXPR error_code( ErrorCodeEnum e,
-        typename detail::enable_if<is_error_code_enum<ErrorCodeEnum>::value>::type* = 0 ) BOOST_NOEXCEPT
+        typename detail::enable_if<
+            is_error_code_enum<ErrorCodeEnum>::value
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+            || std::is_error_code_enum<ErrorCodeEnum>::value
+#endif
+        >::type* = 0 ) BOOST_NOEXCEPT: d1_(), lc_flags_( 0 )
     {
         *this = make_error_code( e );
     }
 
+    error_code( error_code const& ec, source_location const * loc ) BOOST_NOEXCEPT:
+        d1_(), lc_flags_( 0 )
+    {
+        *this = ec;
+
+        if( ec.lc_flags_ != 0 && ec.lc_flags_ != 1 )
+        {
+            lc_flags_ = ( loc? reinterpret_cast<boost::uintptr_t>( loc ): 2 ) | ( ec.lc_flags_ & 1 );
+        }
+    }
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    error_code( std::error_code const& ec ) BOOST_NOEXCEPT:
+        d1_(), lc_flags_( 0 )
+    {
+#ifndef BOOST_NO_RTTI
+
+        if( detail::std_category const* pc2 = dynamic_cast< detail::std_category const* >( &ec.category() ) )
+        {
+            *this = boost::system::error_code( ec.value(), pc2->original_category() );
+        }
+        else
+
+#endif
+        {
+            ::new( d2_ ) std::error_code( ec );
+            lc_flags_ = 1;
+        }
+    }
+
+#endif
+
     // modifiers:
 
     BOOST_SYSTEM_CONSTEXPR void assign( int val, const error_category & cat ) BOOST_NOEXCEPT
     {
-        val_ = val;
-        failed_ = detail::failed_impl( val, cat );
-        cat_ = &cat;
+        *this = error_code( val, cat );
+    }
+
+    void assign( int val, const error_category & cat, source_location const * loc ) BOOST_NOEXCEPT
+    {
+        *this = error_code( val, cat, loc );
+    }
+
+    void assign( error_code const& ec, source_location const * loc ) BOOST_NOEXCEPT
+    {
+        *this = error_code( ec, loc );
     }
 
     template<typename ErrorCodeEnum>
@@ -82,48 +210,136 @@ public:
 
     BOOST_SYSTEM_CONSTEXPR void clear() BOOST_NOEXCEPT
     {
-        val_ = 0;
-        failed_ = false;
-        cat_ = &system_category();
+        *this = error_code();
     }
 
     // observers:
 
     BOOST_SYSTEM_CONSTEXPR int value() const BOOST_NOEXCEPT
     {
-        return val_;
+        if( lc_flags_ != 1 )
+        {
+            return d1_.val_;
+        }
+        else
+        {
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+            std::error_code const& ec = *reinterpret_cast<std::error_code const*>( d2_ );
+
+            unsigned cv = static_cast<unsigned>( ec.value() );
+            unsigned ch = static_cast<unsigned>( reinterpret_cast<boost::uintptr_t>( &ec.category() ) % 2097143 ); // 2^21-9, prime
+
+            return static_cast<int>( cv + 1000 * ch );
+#else
+
+            return -1;
+#endif
+        }
     }
 
     BOOST_SYSTEM_CONSTEXPR const error_category & category() const BOOST_NOEXCEPT
     {
-        return *cat_;
+        if( lc_flags_ == 0 )
+        {
+            return system_category();
+        }
+        else if( lc_flags_ == 1 )
+        {
+            return detail::interop_category();
+        }
+        else
+        {
+            return *d1_.cat_;
+        }
     }
 
+    // deprecated?
     error_condition default_error_condition() const BOOST_NOEXCEPT
     {
-        return cat_->default_error_condition( value() );
+        return category().default_error_condition( value() );
     }
 
     std::string message() const
     {
-        return cat_->message( value() );
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+        if( lc_flags_ == 1 )
+        {
+            std::error_code const& ec = *reinterpret_cast<std::error_code const*>( d2_ );
+            return ec.message();
+        }
+
+#endif
+
+        if( lc_flags_ == 0 )
+        {
+            return detail::system_error_category_message( value() );
+        }
+        else
+        {
+            return category().message( value() );
+        }
     }
 
     char const * message( char * buffer, std::size_t len ) const BOOST_NOEXCEPT
     {
-        return cat_->message( value(), buffer, len );
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+        if( lc_flags_ == 1 )
+        {
+            std::error_code const& ec = *reinterpret_cast<std::error_code const*>( d2_ );
+
+#if !defined(BOOST_NO_EXCEPTIONS)
+            try
+#endif
+            {
+                detail::snprintf( buffer, len, "%s", ec.message().c_str() );
+                return buffer;
+            }
+#if !defined(BOOST_NO_EXCEPTIONS)
+            catch( ... )
+            {
+                detail::snprintf( buffer, len, "No message text available for error std:%s:%d", ec.category().name(), ec.value() );
+                return buffer;
+            }
+#endif
+        }
+#endif
+
+        if( lc_flags_ == 0 )
+        {
+            return detail::system_error_category_message( value(), buffer, len );
+        }
+        else
+        {
+            return category().message( value(), buffer, len );
+        }
     }
 
     BOOST_SYSTEM_CONSTEXPR bool failed() const BOOST_NOEXCEPT
     {
-        return failed_;
+        if( lc_flags_ & 1 )
+        {
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+            if( lc_flags_ == 1 )
+            {
+                std::error_code const& ec = *reinterpret_cast<std::error_code const*>( d2_ );
+                return ec.value() != 0;
+            }
+#endif
+            return true;
+        }
+        else
+        {
+            return false;
+        }
     }
 
 #if !defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS)
 
     BOOST_SYSTEM_CONSTEXPR explicit operator bool() const BOOST_NOEXCEPT  // true if error
     {
-        return failed_;
+        return failed();
     }
 
 #else
@@ -133,56 +349,353 @@ public:
 
     BOOST_SYSTEM_CONSTEXPR operator unspecified_bool_type() const  BOOST_NOEXCEPT // true if error
     {
-        return failed_? unspecified_bool_true: 0;
+        return failed()? unspecified_bool_true: 0;
     }
 
     BOOST_SYSTEM_CONSTEXPR bool operator!() const BOOST_NOEXCEPT // true if no error
     {
-        return !failed_;
+        return !failed();
     }
 
 #endif
 
+    bool has_location() const BOOST_NOEXCEPT
+    {
+        return lc_flags_ >= 4;
+    }
+
+    source_location const & location() const BOOST_NOEXCEPT
+    {
+        BOOST_STATIC_CONSTEXPR source_location loc;
+        return lc_flags_ >= 4? *reinterpret_cast<source_location const*>( lc_flags_ &~ static_cast<boost::uintptr_t>( 1 ) ): loc;
+    }
+
     // relationals:
 
+private:
+
+    // private equality for use in error_category::equivalent
+
+    friend class error_category;
+
+    BOOST_SYSTEM_CONSTEXPR bool equals( int val, error_category const& cat ) const BOOST_NOEXCEPT
+    {
+        if( lc_flags_ == 0 )
+        {
+            return val == 0 && cat.id_ == detail::system_category_id;
+        }
+        else if( lc_flags_ == 1 )
+        {
+            return cat.id_ == detail::interop_category_id && val == value();
+        }
+        else
+        {
+            return val == d1_.val_ && cat == *d1_.cat_;
+        }
+    }
+
+public:
+
     //  the more symmetrical non-member syntax allows enum
     //  conversions work for both rhs and lhs.
 
     BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( const error_code & lhs, const error_code & rhs ) BOOST_NOEXCEPT
     {
-        return lhs.val_ == rhs.val_ && *lhs.cat_ == *rhs.cat_;
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+        bool s1 = lhs.lc_flags_ == 1;
+        bool s2 = rhs.lc_flags_ == 1;
+
+        if( s1 != s2 ) return false;
+
+        if( s1 && s2 )
+        {
+            std::error_code const& e1 = *reinterpret_cast<std::error_code const*>( lhs.d2_ );
+            std::error_code const& e2 = *reinterpret_cast<std::error_code const*>( rhs.d2_ );
+
+            return e1 == e2;
+        }
+        else
+#endif
+        {
+            return lhs.value() == rhs.value() && lhs.category() == rhs.category();
+        }
     }
 
     BOOST_SYSTEM_CONSTEXPR inline friend bool operator<( const error_code & lhs, const error_code & rhs ) BOOST_NOEXCEPT
     {
-        return *lhs.cat_ < *rhs.cat_ || ( *lhs.cat_ == *rhs.cat_ && lhs.val_ < rhs.val_ );
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+        bool s1 = lhs.lc_flags_ == 1;
+        bool s2 = rhs.lc_flags_ == 1;
+
+        if( s1 < s2 ) return true;
+        if( s2 < s1 ) return false;
+
+        if( s1 && s2 )
+        {
+            std::error_code const& e1 = *reinterpret_cast<std::error_code const*>( lhs.d2_ );
+            std::error_code const& e2 = *reinterpret_cast<std::error_code const*>( rhs.d2_ );
+
+            return e1 < e2;
+        }
+        else
+#endif
+        {
+            return lhs.category() < rhs.category() || (lhs.category() == rhs.category() && lhs.value() < rhs.value());
+        }
+    }
+
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( const error_code & lhs, const error_code & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
     }
 
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 
-    operator std::error_code () const
+    inline friend bool operator==( std::error_code const & lhs, error_code const & rhs ) BOOST_NOEXCEPT
     {
-        return std::error_code( value(), category() );
+        return lhs == static_cast< std::error_code >( rhs );
+    }
+
+    inline friend bool operator==( error_code const & lhs, std::error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return static_cast< std::error_code >( lhs ) == rhs;
+    }
+
+    inline friend bool operator!=( std::error_code const & lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    inline friend bool operator!=( error_code const & lhs, std::error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    //
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    inline friend bool operator==( error_code const & lhs, E rhs ) BOOST_NOEXCEPT
+    {
+        return lhs == make_error_condition( rhs );
+    }
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    inline friend bool operator==( E lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return make_error_condition( lhs ) == rhs;
+    }
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    inline friend bool operator!=( error_code const & lhs, E rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    inline friend bool operator!=( E lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    //
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( error_code const & lhs, E rhs ) BOOST_NOEXCEPT
+    {
+        return lhs == make_error_code( rhs );
+    }
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( E lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return make_error_code( lhs ) == rhs;
+    }
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( error_code const & lhs, E rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( E lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+#if defined(BOOST_SYSTEM_CLANG_6)
+
+    inline friend bool operator==( error_code const & lhs, std::error_condition const & rhs ) BOOST_NOEXCEPT
+    {
+        return static_cast< std::error_code >( lhs ) == rhs;
+    }
+
+    inline friend bool operator==( std::error_condition const & lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return lhs == static_cast< std::error_code >( rhs );
+    }
+
+    inline friend bool operator!=( error_code const & lhs, std::error_condition const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    inline friend bool operator!=( std::error_condition const & lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
     }
 
 #endif
+
+    // conversions
+
+    operator std::error_code () const
+    {
+        if( lc_flags_ == 1 )
+        {
+            return *reinterpret_cast<std::error_code const*>( d2_ );
+        }
+        else if( lc_flags_ == 0 )
+        {
+// This condition must be the same as the one in error_category_impl.hpp
+#if defined(BOOST_SYSTEM_AVOID_STD_SYSTEM_CATEGORY)
+
+            return std::error_code( 0, boost::system::system_category() );
+
+#else
+
+            return std::error_code();
+
+#endif
+        }
+        else
+        {
+            return std::error_code( d1_.val_, *d1_.cat_ );
+        }
+    }
+
+    operator std::error_code ()
+    {
+        return const_cast<error_code const&>( *this );
+    }
+
+    template<class T,
+      class E = typename detail::enable_if<detail::is_same<T, std::error_code>::value>::type>
+      operator T& ()
+    {
+        if( lc_flags_ != 1 )
+        {
+            std::error_code e2( *this );
+            ::new( d2_ ) std::error_code( e2 );
+            lc_flags_ = 1;
+        }
+
+        return *reinterpret_cast<std::error_code*>( d2_ );
+    }
+
+#if defined(BOOST_SYSTEM_CLANG_6)
+
+    template<class T,
+      class E = typename std::enable_if<std::is_same<T, std::error_code>::value>::type>
+      operator T const& () = delete;
+
+#endif
+
+#endif
+
+    std::string to_string() const
+    {
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+        if( lc_flags_ == 1 )
+        {
+            std::error_code const& e2 = *reinterpret_cast<std::error_code const*>( d2_ );
+
+            std::string r( "std:" );
+            r += e2.category().name();
+            detail::append_int( r, e2.value() );
+
+            return r;
+        }
+        else
+#endif
+        {
+            std::string r = category_name();
+            detail::append_int( r, value() );
+            return r;
+        }
+    }
+
+    template<class Ch, class Tr>
+        inline friend std::basic_ostream<Ch, Tr>&
+        operator<< (std::basic_ostream<Ch, Tr>& os, error_code const & ec)
+    {
+        return os << ec.to_string().c_str();
+    }
+
+    std::string what() const
+    {
+        std::string r = message();
+
+        r += " [";
+        r += to_string();
+
+        if( has_location() )
+        {
+            r += " at ";
+            r += location().to_string();
+        }
+
+        r += "]";
+        return r;
+    }
 };
 
-BOOST_SYSTEM_CONSTEXPR inline bool operator!=( const error_code & lhs, const error_code & rhs ) BOOST_NOEXCEPT
+inline bool operator==( const error_code & code, const error_condition & condition ) BOOST_NOEXCEPT
+{
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    if( code.lc_flags_ == 1 )
+    {
+        return static_cast<std::error_code>( code ) == static_cast<std::error_condition>( condition );
+    }
+    else
+
+#endif
+    {
+        return code.category().equivalent( code.value(), condition ) || condition.category().equivalent( code, condition.value() );
+    }
+}
+
+inline bool operator==( const error_condition & condition, const error_code & code ) BOOST_NOEXCEPT
+{
+    return code == condition;
+}
+
+inline bool operator!=( const error_code & lhs, const error_condition & rhs ) BOOST_NOEXCEPT
 {
     return !( lhs == rhs );
 }
 
-template<class Ch, class Tr>
-    inline std::basic_ostream<Ch, Tr>&
-    operator<< (std::basic_ostream<Ch, Tr>& os, error_code const & ec)
+inline bool operator!=( const error_condition & lhs, const error_code & rhs ) BOOST_NOEXCEPT
 {
-    os << ec.category().name() << ':' << ec.value();
-    return os;
+    return !( lhs == rhs );
 }
 
 inline std::size_t hash_value( error_code const & ec )
 {
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    if( ec.lc_flags_ == 1 )
+    {
+        std::error_code const& e2 = *reinterpret_cast<std::error_code const*>( ec.d2_ );
+        return std::hash<std::error_code>()( e2 );
+    }
+
+#endif
+
     error_category const & cat = ec.category();
 
     boost::ulong_long_type id_ = cat.id_;
@@ -212,4 +725,8 @@ inline std::size_t hash_value( error_code const & ec )
 
 } // namespace boost
 
+#if defined(BOOST_GCC) && BOOST_GCC >= 40600 && BOOST_GCC < 70000
+# pragma GCC diagnostic pop
+#endif
+
 #endif // #ifndef BOOST_SYSTEM_DETAIL_ERROR_CODE_HPP_INCLUDED

include/boost/system/detail/error_condition.hpp

@@ -3,7 +3,7 @@
 
 //  Copyright Beman Dawes 2006, 2007
 //  Copyright Christoper Kohlhoff 2007
-//  Copyright Peter Dimov 2017, 2018
+//  Copyright Peter Dimov 2017-2021
 //
 //  Distributed under the Boost Software License, Version 1.0. (See accompanying
 //  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
@@ -13,6 +13,9 @@
 #include <boost/system/detail/error_category.hpp>
 #include <boost/system/detail/generic_category.hpp>
 #include <boost/system/detail/enable_if.hpp>
+#include <boost/system/detail/is_same.hpp>
+#include <boost/system/detail/errc.hpp>
+#include <boost/system/detail/append_int.hpp>
 #include <boost/system/is_error_condition_enum.hpp>
 #include <boost/system/detail/config.hpp>
 #include <boost/config.hpp>
@@ -27,40 +30,69 @@ namespace system
 
 // error_conditions are portable, error_codes are system or library specific
 
+namespace detail
+{
+
+struct generic_value_tag
+{
+    int value;
+    BOOST_SYSTEM_CONSTEXPR explicit generic_value_tag( int v ): value( v ) {}
+};
+
+} // namespace detail
+
 class error_condition
 {
 private:
 
     int val_;
-    bool failed_;
     error_category const * cat_;
 
+private:
+
+    boost::ulong_long_type cat_id() const BOOST_NOEXCEPT
+    {
+        return cat_? cat_->id_: detail::generic_category_id;
+    }
+
 public:
 
     // constructors:
 
     BOOST_SYSTEM_CONSTEXPR error_condition() BOOST_NOEXCEPT:
-        val_( 0 ), failed_( false ), cat_( &generic_category() )
+        val_( 0 ), cat_( 0 )
     {
     }
 
     BOOST_SYSTEM_CONSTEXPR error_condition( int val, const error_category & cat ) BOOST_NOEXCEPT:
-        val_( val ), failed_( detail::failed_impl( val, cat ) ), cat_( &cat )
+        val_( val ), cat_( &cat )
+    {
+    }
+
+    BOOST_SYSTEM_CONSTEXPR explicit error_condition( boost::system::detail::generic_value_tag vt ) BOOST_NOEXCEPT:
+        val_( vt.value ), cat_( 0 )
     {
     }
 
     template<class ErrorConditionEnum> BOOST_SYSTEM_CONSTEXPR error_condition( ErrorConditionEnum e,
-        typename detail::enable_if<is_error_condition_enum<ErrorConditionEnum>::value>::type* = 0) BOOST_NOEXCEPT
+      typename detail::enable_if<
+        is_error_condition_enum<ErrorConditionEnum>::value && !boost::system::detail::is_same<ErrorConditionEnum, errc::errc_t>::value
+      >::type* = 0) BOOST_NOEXCEPT
     {
         *this = make_error_condition( e );
     }
 
+    template<class ErrorConditionEnum> BOOST_SYSTEM_CONSTEXPR error_condition( ErrorConditionEnum e,
+      typename detail::enable_if<boost::system::detail::is_same<ErrorConditionEnum, errc::errc_t>::value>::type* = 0) BOOST_NOEXCEPT:
+        val_( e ), cat_( 0 )
+    {
+    }
+
     // modifiers:
 
     BOOST_SYSTEM_CONSTEXPR void assign( int val, const error_category & cat ) BOOST_NOEXCEPT
     {
         val_ = val;
-        failed_ = detail::failed_impl( val, cat );
         cat_ = &cat;
     }
 
@@ -68,15 +100,14 @@ public:
         BOOST_SYSTEM_CONSTEXPR typename detail::enable_if<is_error_condition_enum<ErrorConditionEnum>::value, error_condition>::type &
         operator=( ErrorConditionEnum val ) BOOST_NOEXCEPT
     {
-        *this = make_error_condition( val );
+        *this = error_condition( val );
         return *this;
     }
 
     BOOST_SYSTEM_CONSTEXPR void clear() BOOST_NOEXCEPT
     {
         val_ = 0;
-        failed_ = false;
-        cat_ = &generic_category();
+        cat_ = 0;
     }
 
     // observers:
@@ -88,29 +119,50 @@ public:
 
     BOOST_SYSTEM_CONSTEXPR const error_category & category() const BOOST_NOEXCEPT
     {
-        return *cat_;
+        return cat_? *cat_: generic_category();
     }
 
     std::string message() const
     {
-        return cat_->message( value() );
+        if( cat_ )
+        {
+            return cat_->message( value() );
+        }
+        else
+        {
+            return detail::generic_error_category_message( value() );
+        }
     }
 
     char const * message( char * buffer, std::size_t len ) const BOOST_NOEXCEPT
     {
-        return cat_->message( value(), buffer, len );
+        if( cat_ )
+        {
+            return cat_->message( value(), buffer, len );
+        }
+        else
+        {
+            return detail::generic_error_category_message( value(), buffer, len );
+        }
     }
 
     BOOST_SYSTEM_CONSTEXPR bool failed() const BOOST_NOEXCEPT
     {
-        return failed_;
+        if( cat_ )
+        {
+            return detail::failed_impl( val_, *cat_ );
+        }
+        else
+        {
+            return val_ != 0;
+        }
     }
 
 #if !defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS)
 
     BOOST_SYSTEM_CONSTEXPR explicit operator bool() const BOOST_NOEXCEPT  // true if error
     {
-        return failed_;
+        return failed();
     }
 
 #else
@@ -120,12 +172,12 @@ public:
 
     BOOST_SYSTEM_CONSTEXPR operator unspecified_bool_type() const BOOST_NOEXCEPT  // true if error
     {
-        return failed_? unspecified_bool_true: 0;
+        return failed()? unspecified_bool_true: 0;
     }
 
     BOOST_SYSTEM_CONSTEXPR bool operator!() const BOOST_NOEXCEPT  // true if no error
     {
-        return !failed_;
+        return !failed();
     }
 
 #endif
@@ -136,28 +188,159 @@ public:
 
     BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( const error_condition & lhs, const error_condition & rhs ) BOOST_NOEXCEPT
     {
-        return lhs.val_ == rhs.val_ && *lhs.cat_ == *rhs.cat_;
+        if( lhs.val_ != rhs.val_ )
+        {
+            return false;
+        }
+        else if( lhs.cat_ == 0 )
+        {
+            return rhs.cat_id() == detail::generic_category_id;
+        }
+        else if( rhs.cat_ == 0 )
+        {
+            return lhs.cat_id() == detail::generic_category_id;
+        }
+        else
+        {
+            return *lhs.cat_ == *rhs.cat_;
+        }
     }
 
     BOOST_SYSTEM_CONSTEXPR inline friend bool operator<( const error_condition & lhs, const error_condition & rhs ) BOOST_NOEXCEPT
     {
-        return *lhs.cat_ < *rhs.cat_ || ( *lhs.cat_ == *rhs.cat_ && lhs.val_ < rhs.val_ );
+        error_category const& lcat = lhs.category();
+        error_category const& rcat = rhs.category();
+        return lcat < rcat || ( lcat == rcat && lhs.val_ < rhs.val_ );
+    }
+
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( const error_condition & lhs, const error_condition & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
     }
 
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 
     operator std::error_condition () const
     {
+// This condition must be the same as the one in error_category_impl.hpp
+#if defined(BOOST_SYSTEM_AVOID_STD_GENERIC_CATEGORY)
+
         return std::error_condition( value(), category() );
+
+#else
+
+        if( cat_ )
+        {
+            return std::error_condition( val_, *cat_ );
+        }
+        else
+        {
+            return std::error_condition( val_, std::generic_category() );
+        }
+
+#endif
+    }
+
+    inline friend bool operator==( std::error_code const & lhs, error_condition const & rhs ) BOOST_NOEXCEPT
+    {
+        return lhs == static_cast< std::error_condition >( rhs );
+    }
+
+    inline friend bool operator==( error_condition const & lhs, std::error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return static_cast< std::error_condition >( lhs ) == rhs;
+    }
+
+    inline friend bool operator!=( std::error_code const & lhs, error_condition const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    inline friend bool operator!=( error_condition const & lhs, std::error_code const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    //
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( error_condition const & lhs, E rhs ) BOOST_NOEXCEPT
+    {
+        return lhs == make_error_condition( rhs );
+    }
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( E lhs, error_condition const & rhs ) BOOST_NOEXCEPT
+    {
+        return make_error_condition( lhs ) == rhs;
+    }
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( error_condition const & lhs, E rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( E lhs, error_condition const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    //
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    inline friend bool operator==( error_condition const & lhs, E rhs ) BOOST_NOEXCEPT
+    {
+        return lhs == make_error_code( rhs );
+    }
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    inline friend bool operator==( E lhs, error_condition const & rhs ) BOOST_NOEXCEPT
+    {
+        return make_error_code( lhs ) == rhs;
+    }
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    inline friend bool operator!=( error_condition const & lhs, E rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    inline friend bool operator!=( E lhs, error_condition const & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
     }
 
 #endif
-};
 
-BOOST_SYSTEM_CONSTEXPR inline bool operator!=( const error_condition & lhs, const error_condition & rhs ) BOOST_NOEXCEPT
-{
-    return !( lhs == rhs );
-}
+    std::string to_string() const
+    {
+        std::string r( "cond:" );
+
+        if( cat_ )
+        {
+            r += cat_->name();
+        }
+        else
+        {
+            r += "generic";
+        }
+
+        detail::append_int( r, value() );
+
+        return r;
+    }
+
+    template<class Ch, class Tr>
+        inline friend std::basic_ostream<Ch, Tr>&
+        operator<< (std::basic_ostream<Ch, Tr>& os, error_condition const & en)
+    {
+        os << en.to_string();
+        return os;
+    }
+};
 
 } // namespace system
 

include/boost/system/detail/generic_category.hpp

@@ -109,10 +109,10 @@ inline error_category const & generic_category() BOOST_NOEXCEPT
 
 #ifdef BOOST_SYSTEM_ENABLE_DEPRECATED
 
-inline const error_category & get_generic_category() { return generic_category(); }
-inline const error_category & get_posix_category() { return generic_category(); }
-static const error_category & posix_category BOOST_ATTRIBUTE_UNUSED = generic_category();
-static const error_category & errno_ecat BOOST_ATTRIBUTE_UNUSED = generic_category();
+BOOST_SYSTEM_DEPRECATED("please use generic_category()") inline const error_category & get_generic_category() { return generic_category(); }
+BOOST_SYSTEM_DEPRECATED("please use generic_category()") inline const error_category & get_posix_category() { return generic_category(); }
+BOOST_SYSTEM_DEPRECATED("please use generic_category()") static const error_category & posix_category BOOST_ATTRIBUTE_UNUSED = generic_category();
+BOOST_SYSTEM_DEPRECATED("please use generic_category()") static const error_category & errno_ecat BOOST_ATTRIBUTE_UNUSED = generic_category();
 
 #endif
 

include/boost/system/detail/interop_category.hpp

@@ -0,0 +1,107 @@
+#ifndef BOOST_SYSTEM_DETAIL_INTEROP_CATEGORY_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_INTEROP_CATEGORY_HPP_INCLUDED
+
+//  Copyright Beman Dawes 2006, 2007
+//  Copyright Christoper Kohlhoff 2007
+//  Copyright Peter Dimov 2017, 2018, 2021
+//
+//  Distributed under the Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+//  See library home page at http://www.boost.org/libs/system
+
+#include <boost/system/detail/error_category.hpp>
+#include <boost/system/detail/snprintf.hpp>
+#include <boost/system/detail/config.hpp>
+#include <boost/config.hpp>
+
+namespace boost
+{
+
+namespace system
+{
+
+namespace detail
+{
+
+// interop_error_category, used for std::error_code
+
+#if ( defined( BOOST_GCC ) && BOOST_GCC >= 40600 ) || defined( BOOST_CLANG )
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
+#endif
+
+class BOOST_SYMBOL_VISIBLE interop_error_category: public error_category
+{
+public:
+
+    BOOST_SYSTEM_CONSTEXPR interop_error_category() BOOST_NOEXCEPT:
+        error_category( detail::interop_category_id )
+    {
+    }
+
+    const char * name() const BOOST_NOEXCEPT BOOST_OVERRIDE
+    {
+        return "std:unknown";
+    }
+
+    std::string message( int ev ) const BOOST_OVERRIDE;
+    char const * message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
+};
+
+#if ( defined( BOOST_GCC ) && BOOST_GCC >= 40600 ) || defined( BOOST_CLANG )
+#pragma GCC diagnostic pop
+#endif
+
+inline char const * interop_error_category::message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT
+{
+    detail::snprintf( buffer, len, "Unknown interop error %d", ev );
+    return buffer;
+}
+
+inline std::string interop_error_category::message( int ev ) const
+{
+    char buffer[ 48 ];
+    return message( ev, buffer, sizeof( buffer ) );
+}
+
+// interop_category()
+
+#if defined(BOOST_SYSTEM_HAS_CONSTEXPR)
+
+template<class T> struct BOOST_SYMBOL_VISIBLE interop_cat_holder
+{
+    static constexpr interop_error_category instance{};
+};
+
+// Before C++17 it was mandatory to redeclare all static constexpr
+#if defined(BOOST_NO_CXX17_INLINE_VARIABLES)
+template<class T> constexpr interop_error_category interop_cat_holder<T>::instance;
+#endif
+
+constexpr error_category const & interop_category() BOOST_NOEXCEPT
+{
+    return interop_cat_holder<void>::instance;
+}
+
+#else // #if defined(BOOST_SYSTEM_HAS_CONSTEXPR)
+
+#if !defined(__SUNPRO_CC) // trailing __global is not supported
+inline error_category const & interop_category() BOOST_NOEXCEPT BOOST_SYMBOL_VISIBLE;
+#endif
+
+inline error_category const & interop_category() BOOST_NOEXCEPT
+{
+    static const detail::interop_error_category instance;
+    return instance;
+}
+
+#endif // #if defined(BOOST_SYSTEM_HAS_CONSTEXPR)
+
+} // namespace detail
+
+} // namespace system
+
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_INTEROP_CATEGORY_HPP_INCLUDED

include/boost/system/detail/is_generic_value.hpp

@@ -1,125 +0,0 @@
-#ifndef BOOST_SYSTEM_DETAIL_IS_GENERIC_VALUE_HPP_INCLUDED
-#define BOOST_SYSTEM_DETAIL_IS_GENERIC_VALUE_HPP_INCLUDED
-
-// Copyright 2018 Peter Dimov
-//
-// Distributed under the Boost Software License, Version 1.0. (See accompanying
-// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-//
-// See library home page at http://www.boost.org/libs/system
-
-#include <boost/system/detail/errc.hpp>
-
-namespace boost
-{
-
-namespace system
-{
-
-namespace detail
-{
-
-inline bool is_generic_value( int ev ) BOOST_NOEXCEPT
-{
-    using namespace errc;
-
-    static int const gen[] =
-    {
-        success,
-        address_family_not_supported,
-        address_in_use,
-        address_not_available,
-        already_connected,
-        argument_list_too_long,
-        argument_out_of_domain,
-        bad_address,
-        bad_file_descriptor,
-        bad_message,
-        broken_pipe,
-        connection_aborted,
-        connection_already_in_progress,
-        connection_refused,
-        connection_reset,
-        cross_device_link,
-        destination_address_required,
-        device_or_resource_busy,
-        directory_not_empty,
-        executable_format_error,
-        file_exists,
-        file_too_large,
-        filename_too_long,
-        function_not_supported,
-        host_unreachable,
-        identifier_removed,
-        illegal_byte_sequence,
-        inappropriate_io_control_operation,
-        interrupted,
-        invalid_argument,
-        invalid_seek,
-        io_error,
-        is_a_directory,
-        message_size,
-        network_down,
-        network_reset,
-        network_unreachable,
-        no_buffer_space,
-        no_child_process,
-        no_link,
-        no_lock_available,
-        no_message_available,
-        no_message,
-        no_protocol_option,
-        no_space_on_device,
-        no_stream_resources,
-        no_such_device_or_address,
-        no_such_device,
-        no_such_file_or_directory,
-        no_such_process,
-        not_a_directory,
-        not_a_socket,
-        not_a_stream,
-        not_connected,
-        not_enough_memory,
-        not_supported,
-        operation_canceled,
-        operation_in_progress,
-        operation_not_permitted,
-        operation_not_supported,
-        operation_would_block,
-        owner_dead,
-        permission_denied,
-        protocol_error,
-        protocol_not_supported,
-        read_only_file_system,
-        resource_deadlock_would_occur,
-        resource_unavailable_try_again,
-        result_out_of_range,
-        state_not_recoverable,
-        stream_timeout,
-        text_file_busy,
-        timed_out,
-        too_many_files_open_in_system,
-        too_many_files_open,
-        too_many_links,
-        too_many_symbolic_link_levels,
-        value_too_large,
-        wrong_protocol_type
-    };
-
-    int const n = sizeof( gen ) / sizeof( gen[0] );
-
-    for( int i = 0; i < n; ++i )
-    {
-        if( ev == gen[ i ] ) return true;
-    }
-
-    return false;
-}
-
-} // namespace detail
-
-} // namespace system
-
-} // namespace boost
-
-#endif // #ifndef BOOST_SYSTEM_DETAIL_IS_GENERIC_VALUE_HPP_INCLUDED

include/boost/system/detail/is_same.hpp

@@ -0,0 +1,33 @@
+#ifndef BOOST_SYSTEM_DETAIL_IS_SAME_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_IS_SAME_HPP_INCLUDED
+
+// Copyright 2021 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0
+// http://www.boost.org/LICENSE_1_0.txt
+
+namespace boost
+{
+
+namespace system
+{
+
+namespace detail
+{
+
+template<class T1, class T2> struct is_same
+{
+    enum _vt { value = 0 };
+};
+
+template<class T> struct is_same<T, T>
+{
+    enum _vt { value = 1 };
+};
+
+} // namespace detail
+
+} // namespace system
+
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_IS_SAME_HPP_INCLUDED

include/boost/system/detail/mutex.hpp

@@ -0,0 +1,128 @@
+#ifndef BOOST_SYSTEM_DETAIL_MUTEX_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_MUTEX_HPP_INCLUDED
+
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/config.hpp>
+
+#if defined(BOOST_SYSTEM_DISABLE_THREADS)
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+struct mutex
+{
+    void lock()
+    {
+    }
+
+    void unlock()
+    {
+    }
+};
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#else // defined(BOOST_SYSTEM_DISABLE_THREADS)
+
+#if defined(BOOST_MSSTL_VERSION) && BOOST_MSSTL_VERSION >= 140
+
+// Under the MS STL, std::mutex::mutex() is not constexpr, as is
+// required by the standard, which leads to initialization order
+// issues. However, shared_mutex is based on SRWLock and its
+// default constructor is constexpr, so we use that instead.
+
+#include <boost/winapi/config.hpp>
+
+// SRWLOCK is not available when targeting Windows XP
+#if BOOST_USE_WINAPI_VERSION >= BOOST_WINAPI_VERSION_WIN6
+
+#include <shared_mutex>
+
+#if BOOST_MSSTL_VERSION >= 142 || _HAS_SHARED_MUTEX
+# define BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX
+#endif
+
+#endif // BOOST_MSSTL_VERSION >= 142 || _HAS_SHARED_MUTEX
+
+#endif // BOOST_USE_WINAPI_VERSION >= BOOST_WINAPI_VERSION_WIN6
+
+#if defined(BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX)
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+typedef std::shared_mutex mutex;
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#else // defined(BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX)
+
+#include <mutex>
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+using std::mutex;
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#endif // defined(BOOST_SYSTEM_HAS_MSSTL_SHARED_MUTEX)
+#endif // defined(BOOST_SYSTEM_DISABLE_THREADS)
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+template<class Mtx> class lock_guard
+{
+private:
+
+    Mtx& mtx_;
+
+private:
+
+    lock_guard( lock_guard const& );
+    lock_guard& operator=( lock_guard const& );
+
+public:
+
+    explicit lock_guard( Mtx& mtx ): mtx_( mtx )
+    {
+        mtx_.lock();
+    }
+
+    ~lock_guard()
+    {
+        mtx_.unlock();
+    }
+};
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_MUTEX_HPP_INCLUDED

include/boost/system/detail/requires_cxx11.hpp

@@ -0,0 +1,21 @@
+#ifndef BOOST_SYSTEM_DETAIL_REQUIRES_CXX11_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_REQUIRES_CXX11_HPP_INCLUDED
+
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX11_CONSTEXPR) || \
+    defined(BOOST_NO_CXX11_NOEXCEPT) || \
+    defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS) || \
+    defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) || \
+    defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE("C++03 support was deprecated in Boost.System 1.82 and will be removed in Boost.System 1.85.")
+
+#endif
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_REQUIRES_CXX11_HPP_INCLUDED

include/boost/system/detail/snprintf.hpp

@@ -0,0 +1,73 @@
+#ifndef BOOST_SYSTEM_DETAIL_SNPRINTF_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_SNPRINTF_HPP_INCLUDED
+
+// Copyright 2018, 2020, 2021 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// See library home page at http://www.boost.org/libs/system
+
+#include <boost/config.hpp>
+#include <cstdio>
+#include <cstdarg>
+
+//
+
+namespace boost
+{
+
+namespace system
+{
+
+namespace detail
+{
+
+#if ( defined(_MSC_VER) && _MSC_VER < 1900 ) || ( defined(__MINGW32__) && !defined(__MINGW64_VERSION_MAJOR) )
+
+inline void snprintf( char * buffer, std::size_t len, char const * format, ... )
+{
+# if defined( BOOST_MSVC )
+#  pragma warning( push )
+#  pragma warning( disable: 4996 )
+# endif
+
+    if( len == 0 ) return;
+
+    va_list args;
+    va_start( args, format );
+
+    _vsnprintf( buffer, len - 1, format, args );
+    buffer[ len - 1 ] = 0;
+
+    va_end( args );
+
+# if defined( BOOST_MSVC )
+#  pragma warning( pop )
+# endif
+}
+
+#else
+
+#if defined(__GNUC__) && __GNUC__ >= 3
+__attribute__((__format__ (__printf__, 3, 4)))
+#endif
+inline void snprintf( char * buffer, std::size_t len, char const * format, ... )
+{
+    va_list args;
+    va_start( args, format );
+
+    std::vsnprintf( buffer, len, format, args );
+
+    va_end( args );
+}
+
+#endif
+
+} // namespace detail
+
+} // namespace system
+
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_SNPRINTF_HPP_INCLUDED

include/boost/system/detail/std_category.hpp

@@ -0,0 +1,88 @@
+#ifndef BOOST_SYSTEM_DETAIL_STD_CATEGORY_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_STD_CATEGORY_HPP_INCLUDED
+
+// Support for interoperability between Boost.System and <system_error>
+//
+// Copyright 2018, 2021 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// See library home page at http://www.boost.org/libs/system
+
+#include <boost/system/detail/error_category.hpp>
+#include <boost/config.hpp>
+#include <system_error>
+
+//
+
+namespace boost
+{
+
+namespace system
+{
+
+namespace detail
+{
+
+template<unsigned Id> struct id_wrapper {};
+
+class BOOST_SYMBOL_VISIBLE std_category: public std::error_category
+{
+private:
+
+    boost::system::error_category const * pc_;
+
+public:
+
+    boost::system::error_category const & original_category() const BOOST_NOEXCEPT
+    {
+        return *pc_;
+    }
+
+public:
+
+    template<unsigned Id>
+    explicit std_category( boost::system::error_category const * pc, id_wrapper<Id> ): pc_( pc )
+    {
+#if defined(_MSC_VER) && defined(_CPPLIB_VER) && _MSC_VER >= 1900 && _MSC_VER < 2000
+
+        // We used to assign to the protected _Addr member of std::error_category
+        // here when Id != 0, but this should never happen now because this code
+        // path is no longer used
+
+#if !defined(BOOST_NO_CXX11_STATIC_ASSERT)
+
+        static_assert( Id == 0, "This constructor should only be called with Id == 0 under MS STL 14.0+" );
+
+#endif
+
+#endif
+    }
+
+    const char * name() const BOOST_NOEXCEPT BOOST_OVERRIDE
+    {
+        return pc_->name();
+    }
+
+    std::string message( int ev ) const BOOST_OVERRIDE
+    {
+        return pc_->message( ev );
+    }
+
+    std::error_condition default_error_condition( int ev ) const BOOST_NOEXCEPT BOOST_OVERRIDE
+    {
+        return pc_->default_error_condition( ev );
+    }
+
+    inline bool equivalent( int code, const std::error_condition & condition ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
+    inline bool equivalent( const std::error_code & code, int condition ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
+};
+
+} // namespace detail
+
+} // namespace system
+
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_STD_CATEGORY_HPP_INCLUDED

include/boost/system/detail/std_category_impl.hpp

@@ -0,0 +1,97 @@
+#ifndef BOOST_SYSTEM_DETAIL_STD_CATEGORY_IMPL_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_STD_CATEGORY_IMPL_HPP_INCLUDED
+
+// Support for interoperability between Boost.System and <system_error>
+//
+// Copyright 2018, 2021 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// See library home page at http://www.boost.org/libs/system
+
+#include <boost/system/detail/std_category.hpp>
+#include <boost/system/detail/error_condition.hpp>
+#include <boost/system/detail/error_code.hpp>
+#include <boost/system/detail/generic_category.hpp>
+
+//
+
+namespace boost
+{
+
+namespace system
+{
+
+namespace detail
+{
+
+inline bool std_category::equivalent( int code, const std::error_condition & condition ) const BOOST_NOEXCEPT
+{
+    if( condition.category() == *this )
+    {
+        boost::system::error_condition bn( condition.value(), *pc_ );
+        return pc_->equivalent( code, bn );
+    }
+    else if( condition.category() == std::generic_category() || condition.category() == boost::system::generic_category() )
+    {
+        boost::system::error_condition bn( condition.value(), boost::system::generic_category() );
+        return pc_->equivalent( code, bn );
+    }
+
+#ifndef BOOST_NO_RTTI
+
+    else if( std_category const* pc2 = dynamic_cast< std_category const* >( &condition.category() ) )
+    {
+        boost::system::error_condition bn( condition.value(), *pc2->pc_ );
+        return pc_->equivalent( code, bn );
+    }
+
+#endif
+
+    else
+    {
+        return default_error_condition( code ) == condition;
+    }
+}
+
+inline bool std_category::equivalent( const std::error_code & code, int condition ) const BOOST_NOEXCEPT
+{
+    if( code.category() == *this )
+    {
+        boost::system::error_code bc( code.value(), *pc_ );
+        return pc_->equivalent( bc, condition );
+    }
+    else if( code.category() == std::generic_category() || code.category() == boost::system::generic_category() )
+    {
+        boost::system::error_code bc( code.value(), boost::system::generic_category() );
+        return pc_->equivalent( bc, condition );
+    }
+
+#ifndef BOOST_NO_RTTI
+
+    else if( std_category const* pc2 = dynamic_cast< std_category const* >( &code.category() ) )
+    {
+        boost::system::error_code bc( code.value(), *pc2->pc_ );
+        return pc_->equivalent( bc, condition );
+    }
+
+#endif
+
+    else if( *pc_ == boost::system::generic_category() )
+    {
+        return std::generic_category().equivalent( code, condition );
+    }
+    else
+    {
+        return false;
+    }
+}
+
+} // namespace detail
+
+} // namespace system
+
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_STD_CATEGORY_IMPL_HPP_INCLUDED

include/boost/system/detail/system_category.hpp

@@ -98,8 +98,8 @@ inline error_category const & system_category() BOOST_NOEXCEPT
 
 #ifdef BOOST_SYSTEM_ENABLE_DEPRECATED
 
-inline const error_category & get_system_category() { return system_category(); }
-static const error_category & native_ecat BOOST_ATTRIBUTE_UNUSED = system_category();
+BOOST_SYSTEM_DEPRECATED("please use system_category()") inline const error_category & get_system_category() { return system_category(); }
+BOOST_SYSTEM_DEPRECATED("please use system_category()") static const error_category & native_ecat BOOST_ATTRIBUTE_UNUSED = system_category();
 
 #endif
 

include/boost/system/detail/system_category_condition_win32.hpp

@@ -58,7 +58,10 @@ inline int system_category_condition_win32( int ev ) BOOST_NOEXCEPT
 
     case ERROR_ACCESS_DENIED_: return permission_denied;
     case ERROR_ALREADY_EXISTS_: return file_exists;
+    case ERROR_BAD_NETPATH_: return no_such_file_or_directory;
+    case ERROR_BAD_NET_NAME_: return no_such_file_or_directory;
     case ERROR_BAD_UNIT_: return no_such_device;
+    case ERROR_BROKEN_PIPE_: return broken_pipe;
     case ERROR_BUFFER_OVERFLOW_: return filename_too_long;
     case ERROR_BUSY_: return device_or_resource_busy;
     case ERROR_BUSY_DRIVE_: return device_or_resource_busy;
@@ -73,6 +76,7 @@ inline int system_category_condition_win32( int ev ) BOOST_NOEXCEPT
     case ERROR_DIR_NOT_EMPTY_: return directory_not_empty;
     case ERROR_DIRECTORY_: return invalid_argument; // WinError.h: "The directory name is invalid"
     case ERROR_DISK_FULL_: return no_space_on_device;
+    case ERROR_FILENAME_EXCED_RANGE_: return filename_too_long;
     case ERROR_FILE_EXISTS_: return file_exists;
     case ERROR_FILE_NOT_FOUND_: return no_such_file_or_directory;
     case ERROR_HANDLE_DISK_FULL_: return no_space_on_device;
@@ -80,7 +84,8 @@ inline int system_category_condition_win32( int ev ) BOOST_NOEXCEPT
     case ERROR_INVALID_DRIVE_: return no_such_device;
     case ERROR_INVALID_FUNCTION_: return function_not_supported;
     case ERROR_INVALID_HANDLE_: return invalid_argument;
-    case ERROR_INVALID_NAME_: return invalid_argument;
+    case ERROR_INVALID_NAME_: return no_such_file_or_directory;
+    case ERROR_INVALID_PARAMETER_: return invalid_argument;
     case ERROR_LOCK_VIOLATION_: return no_lock_available;
     case ERROR_LOCKED_: return no_lock_available;
     case ERROR_NEGATIVE_SEEK_: return invalid_argument;
@@ -94,14 +99,20 @@ inline int system_category_condition_win32( int ev ) BOOST_NOEXCEPT
     case ERROR_OUTOFMEMORY_: return not_enough_memory;
     case ERROR_PATH_NOT_FOUND_: return no_such_file_or_directory;
     case ERROR_READ_FAULT_: return io_error;
+    case ERROR_REPARSE_TAG_INVALID_: return invalid_argument;
     case ERROR_RETRY_: return resource_unavailable_try_again;
     case ERROR_SEEK_: return io_error;
+    case ERROR_SEM_TIMEOUT_: return timed_out;
     case ERROR_SHARING_VIOLATION_: return permission_denied;
+    case ERROR_NOT_SUPPORTED_: return not_supported; // WinError.h: "The request is not supported."
+    case ERROR_TIMEOUT_: return timed_out;
     case ERROR_TOO_MANY_OPEN_FILES_: return too_many_files_open;
     case ERROR_WRITE_FAULT_: return io_error;
     case ERROR_WRITE_PROTECT_: return permission_denied;
 
-	case WSAEACCES_: return permission_denied;
+    case 258: return timed_out; // WAIT_TIMEOUT
+
+    case WSAEACCES_: return permission_denied;
     case WSAEADDRINUSE_: return address_in_use;
     case WSAEADDRNOTAVAIL_: return address_not_available;
     case WSAEAFNOSUPPORT_: return address_family_not_supported;

include/boost/system/detail/system_category_impl.hpp

@@ -11,10 +11,9 @@
 //  See library home page at http://www.boost.org/libs/system
 
 #include <boost/system/detail/system_category.hpp>
+#include <boost/system/detail/system_category_message.hpp>
 #include <boost/system/detail/error_condition.hpp>
-#include <boost/system/detail/generic_category.hpp>
 #include <boost/system/api_config.hpp>
-#include <boost/config.hpp>
 
 #if !defined(BOOST_POSIX_API) && !defined(BOOST_WINDOWS_API)
 #  error BOOST_POSIX_API or BOOST_WINDOWS_API must be defined
@@ -24,7 +23,6 @@
 
 #if defined(BOOST_WINDOWS_API)
 
-#include <boost/system/detail/system_category_message_win32.hpp>
 #include <boost/system/detail/system_category_condition_win32.hpp>
 
 inline boost::system::error_condition boost::system::detail::system_error_category::default_error_condition( int ev ) const BOOST_NOEXCEPT
@@ -37,47 +35,27 @@ inline boost::system::error_condition boost::system::detail::system_error_catego
     }
     else
     {
-        return error_condition( e2, generic_category() );
+        return error_condition( boost::system::detail::generic_value_tag( e2 ) );
     }
 }
 
-inline std::string boost::system::detail::system_error_category::message( int ev ) const
-{
-    return system_category_message_win32( ev );
-}
-
-inline char const * boost::system::detail::system_error_category::message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT
-{
-    return system_category_message_win32( ev, buffer, len );
-}
-
 #else // #if defined(BOOST_WINDOWS_API)
 
-#include <boost/system/detail/generic_category_message.hpp>
-#include <boost/system/detail/is_generic_value.hpp>
-
 inline boost::system::error_condition boost::system::detail::system_error_category::default_error_condition( int ev ) const BOOST_NOEXCEPT
 {
-    if( is_generic_value( ev ) )
-    {
-        return error_condition( ev, generic_category() );
-    }
-    else
-    {
-        return error_condition( ev, *this );
-    }
-}
-
-inline std::string boost::system::detail::system_error_category::message( int ev ) const
-{
-    return generic_error_category_message( ev );
-}
-
-inline char const * boost::system::detail::system_error_category::message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT
-{
-    return generic_error_category_message( ev, buffer, len );
+    return error_condition( boost::system::detail::generic_value_tag( ev ) );
 }
 
 #endif // #if defined(BOOST_WINDOWS_API)
 
+inline std::string boost::system::detail::system_error_category::message( int ev ) const
+{
+    return system_error_category_message( ev );
+}
+
+inline char const * boost::system::detail::system_error_category::message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT
+{
+    return system_error_category_message( ev, buffer, len );
+}
+
 #endif // #ifndef BOOST_SYSTEM_DETAIL_SYSTEM_CATEGORY_IMPL_HPP_INCLUDED

include/boost/system/detail/system_category_message.hpp

@@ -0,0 +1,71 @@
+#ifndef BOOST_SYSTEM_DETAIL_SYSTEM_CATEGORY_MESSAGE_HPP_INCLUDED
+#define BOOST_SYSTEM_DETAIL_SYSTEM_CATEGORY_MESSAGE_HPP_INCLUDED
+
+// Implementation of system_error_category_message
+//
+// Copyright 2018, 2022 Peter Dimov
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// See library home page at http://www.boost.org/libs/system
+
+#include <boost/system/api_config.hpp>
+
+#if !defined(BOOST_POSIX_API) && !defined(BOOST_WINDOWS_API)
+#  error BOOST_POSIX_API or BOOST_WINDOWS_API must be defined
+#endif
+
+#if defined(BOOST_WINDOWS_API)
+
+#include <boost/system/detail/system_category_message_win32.hpp>
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+inline std::string system_error_category_message( int ev )
+{
+    return system_category_message_win32( ev );
+}
+
+inline char const * system_error_category_message( int ev, char * buffer, std::size_t len ) BOOST_NOEXCEPT
+{
+    return system_category_message_win32( ev, buffer, len );
+}
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#else // #if defined(BOOST_WINDOWS_API)
+
+#include <boost/system/detail/generic_category_message.hpp>
+
+namespace boost
+{
+namespace system
+{
+namespace detail
+{
+
+inline std::string system_error_category_message( int ev )
+{
+    return generic_error_category_message( ev );
+}
+
+inline char const * system_error_category_message( int ev, char * buffer, std::size_t len ) BOOST_NOEXCEPT
+{
+    return generic_error_category_message( ev, buffer, len );
+}
+
+} // namespace detail
+} // namespace system
+} // namespace boost
+
+#endif // #if defined(BOOST_WINDOWS_API)
+
+#endif // #ifndef BOOST_SYSTEM_DETAIL_SYSTEM_CATEGORY_MESSAGE_HPP_INCLUDED

include/boost/system/detail/system_category_message_win32.hpp

@@ -10,6 +10,7 @@
 //
 // See library home page at http://www.boost.org/libs/system
 
+#include <boost/system/detail/snprintf.hpp>
 #include <boost/winapi/error_handling.hpp>
 #include <boost/winapi/character_code_conversion.hpp>
 #include <boost/winapi/local_memory.hpp>
@@ -27,35 +28,12 @@ namespace system
 namespace detail
 {
 
-#if ( defined(_MSC_VER) && _MSC_VER < 1900 ) || ( defined(__MINGW32__) && !defined(__MINGW64_VERSION_MAJOR) )
-
 inline char const * unknown_message_win32( int ev, char * buffer, std::size_t len )
 {
-# if defined( BOOST_MSVC )
-#  pragma warning( push )
-#  pragma warning( disable: 4996 )
-# endif
-
-    _snprintf( buffer, len - 1, "Unknown error (%d)", ev );
-
-    buffer[ len - 1 ] = 0;
-    return buffer;
-
-# if defined( BOOST_MSVC )
-#  pragma warning( pop )
-# endif
-}
-
-#else
-
-inline char const * unknown_message_win32( int ev, char * buffer, std::size_t len )
-{
-    std::snprintf( buffer, len, "Unknown error (%d)", ev );
+    detail::snprintf( buffer, len, "Unknown error (%d)", ev );
     return buffer;
 }
 
-#endif
-
 inline boost::winapi::UINT_ message_cp_win32()
 {
 #if defined(BOOST_SYSTEM_USE_UTF8)

include/boost/system/detail/to_std_category.hpp

@@ -1,191 +0,0 @@
-#ifndef BOOST_SYSTEM_DETAIL_TO_STD_CATEGORY_HPP_INCLUDED
-#define BOOST_SYSTEM_DETAIL_TO_STD_CATEGORY_HPP_INCLUDED
-
-// Support for interoperability between Boost.System and <system_error>
-//
-// Copyright 2018 Peter Dimov
-//
-// Distributed under the Boost Software License, Version 1.0. (See accompanying
-// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-//
-// See library home page at http://www.boost.org/libs/system
-
-#include <boost/system/detail/error_category.hpp>
-#include <boost/system/detail/error_condition.hpp>
-#include <boost/system/detail/error_code.hpp>
-#include <boost/system/detail/generic_category.hpp>
-#include <system_error>
-#include <map>
-#include <memory>
-#include <mutex>
-
-//
-
-namespace boost
-{
-
-namespace system
-{
-
-namespace detail
-{
-
-class BOOST_SYMBOL_VISIBLE std_category: public std::error_category
-{
-private:
-
-    boost::system::error_category const * pc_;
-
-public:
-
-    explicit std_category( boost::system::error_category const * pc, unsigned id ): pc_( pc )
-    {
-        if( id != 0 )
-        {
-#if defined(_MSC_VER) && defined(_CPPLIB_VER) && _MSC_VER >= 1900 && _MSC_VER < 2000
-
-            // Poking into the protected _Addr member of std::error_category
-            // is not a particularly good programming practice, but what can
-            // you do
-
-            _Addr = id;
-
-#endif
-        }
-    }
-
-    const char * name() const BOOST_NOEXCEPT BOOST_OVERRIDE
-    {
-        return pc_->name();
-    }
-
-    std::string message( int ev ) const BOOST_OVERRIDE
-    {
-        return pc_->message( ev );
-    }
-
-    std::error_condition default_error_condition( int ev ) const BOOST_NOEXCEPT BOOST_OVERRIDE
-    {
-        return pc_->default_error_condition( ev );
-    }
-
-    bool equivalent( int code, const std::error_condition & condition ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
-    bool equivalent( const std::error_code & code, int condition ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
-};
-
-#if !defined(__SUNPRO_CC) // trailing __global is not supported
-inline std::error_category const & to_std_category( boost::system::error_category const & cat ) BOOST_SYMBOL_VISIBLE;
-#endif
-
-struct cat_ptr_less
-{
-    bool operator()( boost::system::error_category const * p1, boost::system::error_category const * p2 ) const BOOST_NOEXCEPT
-    {
-        return *p1 < *p2;
-    }
-};
-
-inline std::error_category const & to_std_category( boost::system::error_category const & cat )
-{
-    if( cat.id_ == boost::system::detail::system_category_id )
-    {
-        static const std_category system_instance( &cat, 0x1F4D7 );
-        return system_instance;
-    }
-    else if( cat.id_ == boost::system::detail::generic_category_id )
-    {
-        static const std_category generic_instance( &cat, 0x1F4D3 );
-        return generic_instance;
-    }
-    else
-    {
-        typedef std::map< boost::system::error_category const *, std::unique_ptr<std_category>, cat_ptr_less > map_type;
-
-        static map_type map_;
-        static std::mutex map_mx_;
-
-        std::lock_guard<std::mutex> guard( map_mx_ );
-
-        map_type::iterator i = map_.find( &cat );
-
-        if( i == map_.end() )
-        {
-            std::unique_ptr<std_category> p( new std_category( &cat, 0 ) );
-
-            std::pair<map_type::iterator, bool> r = map_.insert( map_type::value_type( &cat, std::move( p ) ) );
-
-            i = r.first;
-        }
-
-        return *i->second;
-    }
-}
-
-inline bool std_category::equivalent( int code, const std::error_condition & condition ) const BOOST_NOEXCEPT
-{
-    if( condition.category() == *this )
-    {
-        boost::system::error_condition bn( condition.value(), *pc_ );
-        return pc_->equivalent( code, bn );
-    }
-    else if( condition.category() == std::generic_category() || condition.category() == boost::system::generic_category() )
-    {
-        boost::system::error_condition bn( condition.value(), boost::system::generic_category() );
-        return pc_->equivalent( code, bn );
-    }
-
-#ifndef BOOST_NO_RTTI
-
-    else if( std_category const* pc2 = dynamic_cast< std_category const* >( &condition.category() ) )
-    {
-        boost::system::error_condition bn( condition.value(), *pc2->pc_ );
-        return pc_->equivalent( code, bn );
-    }
-
-#endif
-
-    else
-    {
-        return default_error_condition( code ) == condition;
-    }
-}
-
-inline bool std_category::equivalent( const std::error_code & code, int condition ) const BOOST_NOEXCEPT
-{
-    if( code.category() == *this )
-    {
-        boost::system::error_code bc( code.value(), *pc_ );
-        return pc_->equivalent( bc, condition );
-    }
-    else if( code.category() == std::generic_category() || code.category() == boost::system::generic_category() )
-    {
-        boost::system::error_code bc( code.value(), boost::system::generic_category() );
-        return pc_->equivalent( bc, condition );
-    }
-
-#ifndef BOOST_NO_RTTI
-
-    else if( std_category const* pc2 = dynamic_cast< std_category const* >( &code.category() ) )
-    {
-        boost::system::error_code bc( code.value(), *pc2->pc_ );
-        return pc_->equivalent( bc, condition );
-    }
-#endif
-
-    else if( *pc_ == boost::system::generic_category() )
-    {
-        return std::generic_category().equivalent( code, condition );
-    }
-    else
-    {
-        return false;
-    }
-}
-
-} // namespace detail
-
-} // namespace system
-
-} // namespace boost
-
-#endif // #ifndef BOOST_SYSTEM_DETAIL_TO_STD_CATEGORY_HPP_INCLUDED

include/boost/system/errc.hpp

@@ -16,6 +16,7 @@
 #include <boost/system/detail/generic_category.hpp>
 #include <boost/system/detail/error_category_impl.hpp>
 #include <boost/system/detail/config.hpp>
+#include <boost/assert/source_location.hpp>
 #include <boost/config.hpp>
 
 namespace boost
@@ -35,6 +36,12 @@ BOOST_SYSTEM_CONSTEXPR inline error_code make_error_code( errc_t e ) BOOST_NOEXC
     return error_code( e, generic_category() );
 }
 
+// explicit conversion:
+inline error_code make_error_code( errc_t e, boost::source_location const * loc ) BOOST_NOEXCEPT
+{
+    return error_code( e, generic_category(), loc );
+}
+
 // implicit conversion:
 BOOST_SYSTEM_CONSTEXPR inline error_condition make_error_condition( errc_t e ) BOOST_NOEXCEPT
 {

include/boost/system/error_code.hpp

@@ -17,38 +17,5 @@
 #include <boost/system/generic_category.hpp>
 #include <boost/system/system_category.hpp>
 #include <boost/system/detail/throws.hpp>
-#include <boost/config.hpp>
-
-namespace boost
-{
-
-namespace system
-{
-
-// non-member functions of error_code and error_condition
-
-inline bool operator==( const error_code & code, const error_condition & condition ) BOOST_NOEXCEPT
-{
-    return code.category().equivalent( code.value(), condition ) || condition.category().equivalent( code, condition.value() );
-}
-
-inline bool operator!=( const error_code & lhs, const error_condition & rhs ) BOOST_NOEXCEPT
-{
-    return !( lhs == rhs );
-}
-
-inline bool operator==( const error_condition & condition, const error_code & code ) BOOST_NOEXCEPT
-{
-    return code.category().equivalent( code.value(), condition ) || condition.category().equivalent( code, condition.value() );
-}
-
-inline bool operator!=( const error_condition & lhs, const error_code & rhs ) BOOST_NOEXCEPT
-{
-    return !( lhs == rhs );
-}
-
-} // namespace system
-
-} // namespace boost
 
 #endif // BOOST_SYSTEM_ERROR_CODE_HPP_INCLUDED

include/boost/system/system_error.hpp

@@ -1,84 +1,55 @@
-//  Boost system_error.hpp  --------------------------------------------------//
-
-//  Copyright Beman Dawes 2006
-
-//  Distributed under the Boost Software License, Version 1.0. (See accompanying
-//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-
 #ifndef BOOST_SYSTEM_SYSTEM_ERROR_HPP
 #define BOOST_SYSTEM_SYSTEM_ERROR_HPP
 
-#include <boost/system/error_code.hpp>
+// Copyright Beman Dawes 2006
+// Copyright Peter Dimov 2021
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/errc.hpp>
+#include <boost/system/detail/error_code.hpp>
 #include <string>
 #include <stdexcept>
 #include <cassert>
 
 namespace boost
 {
-  namespace system
-  {
-    //  class system_error  ------------------------------------------------------------//
+namespace system
+{
 
-    class BOOST_SYMBOL_VISIBLE system_error : public std::runtime_error
-    // BOOST_SYMBOL_VISIBLE is needed by GCC to ensure system_error thrown from a shared
-    // library can be caught. See svn.boost.org/trac/boost/ticket/3697
+class BOOST_SYMBOL_VISIBLE system_error: public std::runtime_error
+{
+private:
+
+    error_code code_;
+
+public:
+
+    explicit system_error( error_code const & ec ):
+        std::runtime_error( ec.what() ), code_( ec ) {}
+
+    system_error( error_code const & ec, std::string const & prefix ):
+        std::runtime_error( prefix + ": " + ec.what() ), code_( ec ) {}
+
+    system_error( error_code const & ec, char const * prefix ):
+        std::runtime_error( std::string( prefix ) + ": " + ec.what() ), code_( ec ) {}
+
+    system_error( int ev, error_category const & ecat ):
+        std::runtime_error( error_code( ev, ecat ).what() ), code_( ev, ecat ) {}
+
+    system_error( int ev, error_category const & ecat, std::string const & prefix ):
+        std::runtime_error( prefix + ": " + error_code( ev, ecat ).what() ), code_( ev, ecat ) {}
+
+    system_error( int ev, error_category const & ecat, char const * prefix ):
+        std::runtime_error( std::string( prefix ) + ": " + error_code( ev, ecat ).what() ), code_( ev, ecat ) {}
+
+    error_code code() const BOOST_NOEXCEPT
     {
-    public:
-      explicit system_error( error_code ec )
-          : std::runtime_error(""), m_error_code(ec) {}
-
-      system_error( error_code ec, const std::string & what_arg )
-          : std::runtime_error(what_arg), m_error_code(ec) {}
-
-      system_error( error_code ec, const char* what_arg )
-          : std::runtime_error(what_arg), m_error_code(ec) {}
-
-      system_error( int ev, const error_category & ecat )
-          : std::runtime_error(""), m_error_code(ev,ecat) {}
-
-      system_error( int ev, const error_category & ecat,
-        const std::string & what_arg )
-          : std::runtime_error(what_arg), m_error_code(ev,ecat) {}
-
-      system_error( int ev, const error_category & ecat,
-        const char * what_arg )
-          : std::runtime_error(what_arg), m_error_code(ev,ecat) {}
-
-      virtual ~system_error() BOOST_NOEXCEPT_OR_NOTHROW {}
-
-      error_code code() const BOOST_NOEXCEPT { return m_error_code; }
-      const char * what() const BOOST_NOEXCEPT_OR_NOTHROW BOOST_OVERRIDE;
-
-    private:
-      error_code           m_error_code;
-      mutable std::string  m_what;
-    };
-
-    //  implementation  ------------------------------------------------------//
-
-    inline const char * system_error::what() const BOOST_NOEXCEPT_OR_NOTHROW
-    // see http://www.boost.org/more/error_handling.html for lazy build rationale
-    {
-      if ( m_what.empty() )
-      {
-#ifndef BOOST_NO_EXCEPTIONS
-        try
-#endif
-        {
-          m_what = this->std::runtime_error::what();
-          if ( !m_what.empty() ) m_what += ": ";
-          m_what += m_error_code.message();
-        }
-#ifndef BOOST_NO_EXCEPTIONS
-        catch (...) { return std::runtime_error::what(); }
-#endif
-      }
-      return m_what.c_str();
+        return code_;
     }
+};
 
-  } // namespace system
+} // namespace system
 } // namespace boost
 
 #endif // BOOST_SYSTEM_SYSTEM_ERROR_HPP
-
-

include/boost/system/windows_error.hpp

@@ -18,16 +18,6 @@
 #ifdef BOOST_WINDOWS_API
 
 #include <boost/system/error_code.hpp>
-
-//// Neither MinGW or Cygwin versions of winerror.h work if used alone, so on
-//// either of those platforms include the full windows.h
-//
-//#if defined(__MINGW32__) || defined(__CYGWIN__)
-//#include <windows.h>
-//#else
-//#include <winerror.h>
-//#endif
-
 #include <boost/winapi/error_codes.hpp>
 
 namespace boost
@@ -82,7 +72,8 @@ namespace boost
         wrong_disk = boost::winapi::ERROR_WRONG_DISK_,
         sharing_buffer_exceeded = boost::winapi::ERROR_SHARING_BUFFER_EXCEEDED_,
         handle_eof = boost::winapi::ERROR_HANDLE_EOF_,
-        handle_disk_full= boost::winapi::ERROR_HANDLE_DISK_FULL_,
+        handle_disk_full = boost::winapi::ERROR_HANDLE_DISK_FULL_,
+        not_supported = boost::winapi::ERROR_NOT_SUPPORTED_,
         rem_not_list = boost::winapi::ERROR_REM_NOT_LIST_,
         dup_name = boost::winapi::ERROR_DUP_NAME_,
         bad_net_path = boost::winapi::ERROR_BAD_NETPATH_,
@@ -94,7 +85,7 @@ namespace boost
         broken_pipe = boost::winapi::ERROR_BROKEN_PIPE_,
         open_failed = boost::winapi::ERROR_OPEN_FAILED_,
         buffer_overflow = boost::winapi::ERROR_BUFFER_OVERFLOW_,
-        disk_full= boost::winapi::ERROR_DISK_FULL_,
+        disk_full = boost::winapi::ERROR_DISK_FULL_,
         // ...
         lock_failed = boost::winapi::ERROR_LOCK_FAILED_,
         busy = boost::winapi::ERROR_BUSY_,

index.html

@@ -8,8 +8,8 @@ Automatic redirection failed, please go to
 </body>
 </html>
 <!--
-	<EFBFBD> Copyright Beman Dawes, 2001
+	© Copyright Beman Dawes, 2001
 	Distributed under the Boost Software License, Version 1.0.
 	See accompanying file LICENSE_1_0.txt or copy at
-	http://www.boost.org/LICENSE_1_0.txt
+	https://www.boost.org/LICENSE_1_0.txt
 -->

meta/libraries.json

@@ -4,8 +4,14 @@
     "authors": [
         "Beman Dawes"
     ],
-    "description": "Operating system support, including the diagnostics support that will be part of the C++0x standard library.",
+    "maintainers": [
+        "Peter Dimov <pdimov -at- gmail.com>"
+    ],
+    "description": "Extensible error reporting.",
     "category": [
-        "System"
-    ]
+        "System",
+        "Error-handling",
+        "Programming"
+    ],
+    "cxxstd": "03"
 }

test/CMakeLists.txt

@@ -15,6 +15,7 @@ macro(system_run s1)
   boost_test(SOURCES ${s1} ${ARGN})
   boost_test(SOURCES ${s1} ${ARGN} COMPILE_DEFINITIONS BOOST_NO_ANSI_APIS NAME ${n1}_no_ansi)
   boost_test(SOURCES ${s1} ${ARGN} COMPILE_DEFINITIONS BOOST_SYSTEM_USE_UTF8 NAME ${n1}_utf8)
+  boost_test(SOURCES ${s1} ${ARGN} COMPILE_DEFINITIONS BOOST_SYSTEM_DISABLE_THREADS NAME ${n1}_nthr)
 
 endmacro()
 
@@ -69,3 +70,109 @@ lib(boost_system_std_single_instance_lib2 STD_SINGLE_INSTANCE_DYN_LINK std_singl
 
 system_run(std_single_instance_test.cpp std_single_instance_1.cpp std_single_instance_2.cpp)
 boost_test(SOURCES std_single_instance_test.cpp NAME std_single_instance_test_lib LINK_LIBRARIES boost_system_std_single_instance_lib1 boost_system_std_single_instance_lib2)
+
+boost_test(TYPE run SOURCES is_error_code_enum_test.cpp)
+boost_test(TYPE run SOURCES is_error_condition_enum_test.cpp)
+boost_test(TYPE run SOURCES errc_test.cpp)
+boost_test(TYPE run SOURCES errc_test2.cpp)
+boost_test(TYPE run SOURCES error_category_test2.cpp)
+boost_test(TYPE run SOURCES error_condition_test.cpp)
+boost_test(TYPE run SOURCES error_condition_test2.cpp)
+boost_test(TYPE run SOURCES generic_category_test2.cpp)
+boost_test(TYPE run SOURCES generic_category_test3.cpp)
+boost_test(TYPE run SOURCES system_category_test2.cpp)
+boost_test(TYPE run SOURCES system_category_test3.cpp)
+
+boost_test(TYPE run SOURCES windows_error_test.cpp)
+boost_test(TYPE run SOURCES cygwin_error_test.cpp)
+boost_test(TYPE run SOURCES linux_error_test.cpp)
+
+boost_test(TYPE link SOURCES errc_test3.cpp)
+
+boost_test(TYPE run SOURCES snprintf_test.cpp)
+
+boost_test(TYPE run SOURCES std_interop_test2.cpp)
+boost_test(TYPE run SOURCES std_interop_test3.cpp)
+boost_test(TYPE run SOURCES std_interop_test4.cpp)
+boost_test(TYPE run SOURCES std_interop_test5.cpp)
+boost_test(TYPE run SOURCES std_interop_test6.cpp)
+boost_test(TYPE run SOURCES std_interop_test7.cpp)
+boost_test(TYPE run SOURCES std_interop_test8.cpp)
+boost_test(TYPE run SOURCES std_interop_test9.cpp)
+
+boost_test(TYPE run SOURCES ec_location_test.cpp)
+
+boost_test(TYPE run SOURCES error_condition_test3.cpp)
+boost_test(TYPE run SOURCES error_code_test2.cpp)
+boost_test(TYPE run SOURCES system_error_test2.cpp)
+boost_test(TYPE run SOURCES std_interop_test10.cpp)
+
+boost_test(TYPE run SOURCES ec_location_test2.cpp)
+boost_test(TYPE run SOURCES ec_what_test.cpp)
+boost_test(TYPE run SOURCES system_error_test3.cpp)
+
+boost_test(TYPE run SOURCES std_interop_test11.cpp)
+
+boost_test(TYPE run SOURCES ec_wstream_test.cpp)
+
+boost_test(TYPE run SOURCES std_interop_test12.cpp)
+
+boost_test(TYPE run SOURCES errc_test4.cpp)
+
+boost_test(TYPE run SOURCES std_interop_test13.cpp)
+boost_test(TYPE run SOURCES std_interop_test14.cpp)
+
+boost_test(TYPE run SOURCES ec_location_test3.cpp)
+boost_test(TYPE run SOURCES ec_location_test4.cpp)
+
+boost_test(TYPE compile SOURCES constexpr_test2.cpp)
+
+boost_test(TYPE run SOURCES error_code_test3.cpp)
+boost_test(TYPE run SOURCES std_interop_test15.cpp)
+
+boost_test(TYPE run SOURCES win32_generic_test.cpp)
+
+boost_test(TYPE run SOURCES ec_hash_value_test.cpp)
+
+boost_test(TYPE run SOURCES std_interop_test16.cpp)
+
+# result
+
+set(BOOST_TEST_COMPILE_FEATURES cxx_std_11)
+
+boost_test(TYPE run SOURCES result_default_construct.cpp)
+boost_test(TYPE run SOURCES result_value_construct.cpp)
+boost_test(TYPE run SOURCES result_error_construct.cpp)
+boost_test(TYPE run SOURCES result_copy_construct.cpp)
+boost_test(TYPE run SOURCES result_move_construct.cpp)
+boost_test(TYPE run SOURCES result_copy_assign.cpp)
+boost_test(TYPE run SOURCES result_move_assign.cpp)
+boost_test(TYPE run SOURCES result_value_access.cpp)
+boost_test(TYPE run SOURCES result_error_access.cpp)
+boost_test(TYPE run SOURCES result_swap.cpp)
+boost_test(TYPE run SOURCES result_eq.cpp)
+boost_test(TYPE run SOURCES result_range_for.cpp)
+boost_test(TYPE run SOURCES result_value_construct2.cpp)
+boost_test(TYPE run SOURCES result_error_construct2.cpp)
+boost_test(TYPE run SOURCES result_errc_construct.cpp)
+boost_test(TYPE run SOURCES result_convert_construct.cpp)
+boost_test(TYPE run SOURCES result_typedefs.cpp)
+boost_test(TYPE run SOURCES result_value_construct3.cpp)
+boost_test(TYPE run SOURCES result_error_construct3.cpp)
+boost_test(TYPE run SOURCES result_emplace.cpp)
+boost_test(TYPE run SOURCES result_error_construct4.cpp)
+boost_test(TYPE run SOURCES result_value_construct4.cpp)
+boost_test(TYPE run SOURCES result_value_construct5.cpp)
+boost_test(TYPE run SOURCES result_error_move.cpp)
+boost_test(TYPE run SOURCES result_value_construct6.cpp)
+boost_test(TYPE run SOURCES result_value_construct7.cpp)
+boost_test(TYPE run SOURCES result_error_construct5.cpp)
+boost_test(TYPE run SOURCES result_or_value.cpp)
+boost_test(TYPE compile-fail SOURCES result_or_value_fail.cpp)
+boost_test(TYPE compile-fail SOURCES result_or_value_fail2.cpp)
+boost_test(TYPE run SOURCES result_or_fn0v.cpp)
+boost_test(TYPE run SOURCES result_or_fn0r.cpp)
+boost_test(TYPE run SOURCES result_and_fn1v.cpp)
+boost_test(TYPE run SOURCES result_and_fn1r.cpp)
+boost_test(TYPE run SOURCES result_and_eq_fn1v.cpp)
+boost_test(TYPE run SOURCES result_and_eq_fn1r.cpp)

test/Jamfile.v2

@@ -1,7 +1,7 @@
 # Boost System Library test Jamfile
 
 # Copyright Beman Dawes 2003, 2006
-# Copyright 2017-2019 Peter Dimov
+# Copyright 2017-2021 Peter Dimov
 
 # Distributed under the Boost Software License, Version 1.0.
 # See accompanying file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt
@@ -10,6 +10,20 @@
 
 import testing ;
 
+project
+  : default-build
+
+    <warnings>extra
+
+  : requirements
+
+    <toolset>msvc:<warnings-as-errors>on
+    <toolset>gcc:<warnings-as-errors>on
+    <toolset>clang:<warnings-as-errors>on
+
+    <toolset>gcc-4.4:<cxxflags>-Wno-sign-compare
+  ;
+
 rule system-run ( sources + )
 {
     local result ;
@@ -19,6 +33,7 @@ rule system-run ( sources + )
     result += [ run $(sources) : : : <library>/boost/system//boost_system <link>shared : $(sources[1]:B)_shared ] ;
     result += [ run $(sources) : : : <define>BOOST_NO_ANSI_APIS : $(sources[1]:B)_no_ansi ] ;
     result += [ run $(sources) : : : <define>BOOST_SYSTEM_USE_UTF8 : $(sources[1]:B)_utf8 ] ;
+    result += [ run $(sources) : : : <define>BOOST_SYSTEM_DISABLE_THREADS : $(sources[1]:B)_nthr ] ;
 
     return $(result) ;
 }
@@ -47,7 +62,11 @@ run single_instance_test.cpp single_instance_lib1 single_instance_lib2 : : : <li
 run single_instance_test.cpp single_instance_lib1 single_instance_lib2 : : : <link>shared : single_instance_lib_shared ;
 
 system-run before_main_test.cpp ;
-run-fail throws_assign_fail.cpp ;
+
+run-fail throws_assign_fail.cpp : : :
+    # GCC 12 catches this at compile time with a warning
+    <toolset>gcc,<variant>release:<build>no ;
+
 system-run constexpr_test.cpp ;
 system-run win32_hresult_test.cpp ;
 
@@ -61,8 +80,8 @@ system-run failed_constexpr_test.cpp ;
 # Quick (CI) test
 run quick.cpp ;
 
-compile warnings_test.cpp
-  : <warnings>pedantic
+run warnings_test.cpp
+  : : : <warnings>pedantic
     <toolset>msvc:<warnings-as-errors>on
     <toolset>gcc:<warnings-as-errors>on
     <toolset>clang:<warnings-as-errors>on ;
@@ -85,3 +104,105 @@ run generic_category_test2.cpp ;
 run generic_category_test3.cpp ;
 run system_category_test2.cpp ;
 run system_category_test3.cpp ;
+
+run windows_error_test.cpp ;
+run cygwin_error_test.cpp ;
+run linux_error_test.cpp ;
+
+link errc_test3.cpp ;
+
+run snprintf_test.cpp ;
+
+run std_interop_test2.cpp ;
+run std_interop_test3.cpp ;
+run std_interop_test4.cpp ;
+run std_interop_test5.cpp
+  : : :
+  # crash on xenial, but the real g++ 4.8 on both centos 7 and trusty works
+  <toolset>gcc-4.8:<build>no
+  <toolset>gcc-4.9:<build>no
+  ;
+
+run std_interop_test6.cpp ;
+run std_interop_test7.cpp ;
+run std_interop_test8.cpp ;
+run std_interop_test9.cpp ;
+
+run ec_location_test.cpp ;
+
+run error_condition_test3.cpp ;
+run error_code_test2.cpp ;
+run system_error_test2.cpp ;
+run std_interop_test10.cpp ;
+
+run ec_location_test2.cpp ;
+run ec_what_test.cpp ;
+run system_error_test3.cpp ;
+
+run std_interop_test11.cpp ;
+
+run ec_wstream_test.cpp ;
+
+run std_interop_test12.cpp ;
+
+run errc_test4.cpp ;
+
+run std_interop_test13.cpp ;
+run std_interop_test14.cpp ;
+
+run ec_location_test3.cpp ;
+run ec_location_test4.cpp ;
+
+compile constexpr_test2.cpp ;
+
+run error_code_test3.cpp ;
+run std_interop_test15.cpp ;
+
+run win32_generic_test.cpp ;
+
+run ec_hash_value_test.cpp ;
+
+run std_interop_test16.cpp ;
+
+# result
+
+import ../../config/checks/config : requires ;
+
+CPP11 = [ requires cxx11_variadic_templates cxx11_template_aliases cxx11_decltype cxx11_constexpr cxx11_noexcept ] <toolset>gcc-4.7:<build>no ;
+
+run result_default_construct.cpp : : : $(CPP11) ;
+run result_value_construct.cpp : : : $(CPP11) ;
+run result_error_construct.cpp : : : $(CPP11) ;
+run result_copy_construct.cpp : : : $(CPP11) ;
+run result_move_construct.cpp : : : $(CPP11) ;
+run result_copy_assign.cpp : : : $(CPP11) ;
+run result_move_assign.cpp : : : $(CPP11) ;
+run result_value_access.cpp : : : $(CPP11) ;
+run result_error_access.cpp : : : $(CPP11) ;
+run result_swap.cpp : : : $(CPP11) <toolset>gcc-10:<cxxflags>"-Wno-maybe-uninitialized" ;
+run result_eq.cpp : : : $(CPP11) ;
+run result_range_for.cpp : : : $(CPP11) ;
+run result_value_construct2.cpp : : : $(CPP11) ;
+run result_error_construct2.cpp : : : $(CPP11) ;
+run result_errc_construct.cpp : : : $(CPP11) ;
+run result_convert_construct.cpp : : : $(CPP11) ;
+run result_typedefs.cpp : : : $(CPP11) ;
+run result_value_construct3.cpp : : : $(CPP11) ;
+run result_error_construct3.cpp : : : $(CPP11) ;
+run result_emplace.cpp : : : $(CPP11) ;
+run result_error_construct4.cpp : : : $(CPP11) ;
+run result_value_construct4.cpp : : : $(CPP11) ;
+run result_value_construct5.cpp : : : $(CPP11) ;
+run result_error_move.cpp : : : $(CPP11) ;
+run result_value_construct6.cpp : : : $(CPP11) ;
+run result_value_construct7.cpp : : : $(CPP11) ;
+run result_error_construct5.cpp : : : $(CPP11) ;
+run result_or_value.cpp : : : $(CPP11) ;
+compile-fail result_or_value_fail.cpp : $(CPP11) ;
+compile-fail result_or_value_fail2.cpp : $(CPP11) ;
+run result_or_fn0v.cpp : : : $(CPP11) ;
+run result_or_fn0r.cpp : : : $(CPP11) ;
+run result_and_fn1v.cpp : : : $(CPP11) ;
+run result_and_fn1r.cpp : : : $(CPP11) ;
+run result_and_eq_fn1v.cpp : : : $(CPP11) ;
+run result_and_eq_fn1r.cpp : : : $(CPP11) ;

test/after_main_test.cpp

@@ -5,8 +5,13 @@
 #include <boost/system/error_code.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <boost/core/quick_exit.hpp>
+#include <boost/config.hpp>
 #include <cerrno>
 
+#if defined(BOOST_MSVC)
+# pragma warning(disable: 4722) // Z::~Z never returns
+#endif
+
 using namespace boost::system;
 
 struct Z
@@ -27,4 +32,6 @@ static error_code e2( ENOENT, generic_category() );
 
 int main()
 {
+    (void)e1;
+    (void)e2;
 }

test/cmake_install_test/CMakeLists.txt

@@ -7,12 +7,11 @@ cmake_minimum_required(VERSION 3.5...3.16)
 project(cmake_install_test LANGUAGES CXX)
 
 find_package(boost_system REQUIRED)
-find_package(boost_core REQUIRED)
 
-add_executable(quick ../quick.cpp)
-target_link_libraries(quick Boost::system Boost::core)
+add_executable(main main.cpp)
+target_link_libraries(main Boost::system)
 
 enable_testing()
-add_test(quick quick)
+add_test(main main)
 
 add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)

test/cmake_install_test/main.cpp

@@ -0,0 +1,44 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+// See library home page at http://www.boost.org/libs/system
+
+#include <boost/system.hpp>
+#include <cassert>
+#include <cerrno>
+
+#define BOOST_TEST(expr) assert(expr)
+#define BOOST_TEST_EQ(x1, x2) assert((x1)==(x2))
+
+int main()
+{
+    boost::system::error_category const & bt = boost::system::generic_category();
+
+    int ev = ENOENT;
+
+    boost::system::error_code bc( ev, bt );
+
+    BOOST_TEST_EQ( bc.value(), ev );
+    BOOST_TEST_EQ( &bc.category(), &bt );
+
+    boost::system::error_condition bn = bt.default_error_condition( ev );
+
+    BOOST_TEST_EQ( bn.value(), ev );
+    BOOST_TEST_EQ( &bn.category(), &bt );
+
+    BOOST_TEST( bt.equivalent( ev, bn ) );
+
+    BOOST_TEST( bc == bn );
+
+    boost::system::error_code bc2 = make_error_code( boost::system::errc::no_such_file_or_directory );
+
+    BOOST_TEST_EQ( bc2, bc );
+    BOOST_TEST_EQ( bc2.value(), ev );
+    BOOST_TEST_EQ( &bc.category(), &bt );
+
+    boost::system::system_error x( bc, "prefix" );
+
+    BOOST_TEST_EQ( x.code(), bc );
+    BOOST_TEST_EQ( std::string( x.what() ), "prefix: " + bc.what() );
+}

test/cmake_subdir_test/CMakeLists.txt

@@ -1,8 +1,8 @@
-# Copyright 2018, 2019 Peter Dimov
+# Copyright 2018-2021 Peter Dimov
 # Distributed under the Boost Software License, Version 1.0.
 # See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt
 
-cmake_minimum_required(VERSION 3.5...3.16)
+cmake_minimum_required(VERSION 3.5...3.20)
 
 project(cmake_subdir_test LANGUAGES CXX)
 
@@ -10,7 +10,11 @@ add_subdirectory(../.. boostorg/system)
 add_subdirectory(../../../assert boostorg/assert)
 add_subdirectory(../../../config boostorg/config)
 add_subdirectory(../../../core boostorg/core)
+add_subdirectory(../../../mp11 boostorg/mp11)
 add_subdirectory(../../../predef boostorg/predef)
+add_subdirectory(../../../static_assert boostorg/static_assert)
+add_subdirectory(../../../throw_exception boostorg/throw_exception)
+add_subdirectory(../../../variant2 boostorg/variant2)
 add_subdirectory(../../../winapi boostorg/winapi)
 
 add_executable(quick ../quick.cpp)
@@ -19,4 +23,4 @@ target_link_libraries(quick Boost::system Boost::core)
 enable_testing()
 add_test(quick quick)
 
-add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)
+add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure --no-tests=error -C $<CONFIG>)

test/constexpr_test2.cpp

@@ -0,0 +1,35 @@
+// Copyright 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_code.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_GCC) && BOOST_GCC >= 40700 && BOOST_GCC < 40800
+
+BOOST_PRAGMA_MESSAGE("Skipping test, BOOST_GCC is 407xx")
+
+#else
+
+struct X
+{
+    boost::system::error_code ec;
+};
+
+X const& f()
+{
+#if defined(BOOST_CLANG_VERSION) && BOOST_CLANG_VERSION < 30900
+
+    BOOST_STATIC_CONSTEXPR X x = {};
+    return x;
+
+#else
+
+    BOOST_STATIC_CONSTEXPR X x;
+    return x;
+
+#endif
+}
+
+#endif

test/cygwin_error_test.cpp

@@ -0,0 +1,29 @@
+// Copyright 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/cygwin_error.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__CYGWIN__)
+
+BOOST_PRAGMA_MESSAGE( "Skipping test, __CYGWIN__ is not defined" )
+int main() {}
+
+#else
+
+#include <boost/core/lightweight_test.hpp>
+
+int main()
+{
+    namespace sys = boost::system;
+
+    sys::error_code ec = sys::cygwin_error::no_package;
+
+    BOOST_TEST_EQ( ec, sys::cygwin_error::no_package );
+    BOOST_TEST_EQ( ec, sys::error_code( ENOPKG, sys::system_category() ) );
+
+    return boost::report_errors();
+}
+
+#endif

test/ec_hash_value_test.cpp

@@ -0,0 +1,132 @@
+// Copyright 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_code.hpp>
+#include <boost/system/generic_category.hpp>
+#include <boost/system/system_category.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <cerrno>
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+#include <system_error>
+#endif
+
+namespace sys = boost::system;
+
+int main()
+{
+    // normal against normal (equal, system)
+    {
+        sys::error_code e2( 0, sys::system_category() );
+        sys::error_code e3( e2.value(), e2.category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal against normal (equal, generic)
+    {
+        sys::error_code e2( EINVAL, sys::generic_category() );
+        sys::error_code e3( e2.value(), e2.category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal against normal (inequal, value, generic)
+    {
+        sys::error_code e2( 0, sys::generic_category() );
+        sys::error_code e3( EINVAL, sys::generic_category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal against normal (inequal, value, system)
+    {
+        sys::error_code e2( 1, sys::system_category() );
+        sys::error_code e3( 2, sys::system_category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal against normal (inequal, category)
+    {
+        sys::error_code e2( 0, sys::system_category() );
+        sys::error_code e3( 0, sys::generic_category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // empty against normal
+    {
+        sys::error_code e2;
+        sys::error_code e3( e2.value(), e2.category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    // std:: wrapping against normal
+    {
+        std::error_code e1( EINVAL, std::generic_category() );
+
+        sys::error_code e2( e1 );
+        sys::error_code e3( e2.value(), e2.category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // empty against wrapping std:: empty
+    {
+        std::error_code e1;
+
+        sys::error_code e2( e1 );
+        sys::error_code e3;
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // empty against roundtrip via std
+    {
+        sys::error_code e2;
+
+        std::error_code e1( e2 );
+        sys::error_code e3( e1 );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal/generic against roundtrip via std
+    {
+        sys::error_code e2( EINVAL, boost::system::generic_category() );
+
+        std::error_code e1( e2 );
+        sys::error_code e3( e1 );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal/system against roundtrip via std
+    {
+        sys::error_code e2( 0, boost::system::system_category() );
+
+        std::error_code e1( e2 );
+        sys::error_code e3( e1 );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+#endif
+
+    return boost::report_errors();
+}

test/ec_location_test.cpp

@@ -0,0 +1,116 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <cerrno>
+
+int main()
+{
+    int const val = ENOENT;
+    boost::system::error_category const & cat = boost::system::generic_category();
+
+    {
+        boost::system::error_code ec( val, cat );
+
+        BOOST_TEST_EQ( ec.value(), val );
+        BOOST_TEST_EQ( &ec.category(), &cat );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+    {
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        boost::system::error_code ec( val, cat, &loc );
+
+        BOOST_TEST_EQ( ec.value(), val );
+        BOOST_TEST_EQ( &ec.category(), &cat );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 27 );
+    }
+
+    {
+        boost::system::error_code ec;
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &boost::system::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec = boost::system::error_code( val, cat, &loc );
+
+        BOOST_TEST_EQ( ec.value(), val );
+        BOOST_TEST_EQ( &ec.category(), &cat );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 51 );
+    }
+
+    {
+        boost::system::error_code ec;
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &boost::system::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec.assign( val, cat, &loc );
+
+        BOOST_TEST_EQ( ec.value(), val );
+        BOOST_TEST_EQ( &ec.category(), &cat );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 75 );
+    }
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    {
+        std::error_code e2( val, std::generic_category() );
+
+        boost::system::error_code ec( e2 );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec.assign( val, cat, &loc );
+
+        BOOST_TEST_EQ( ec.value(), val );
+        BOOST_TEST_EQ( &ec.category(), &cat );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 100 );
+    }
+
+#endif
+
+    return boost::report_errors();
+}

test/ec_location_test2.cpp

@@ -0,0 +1,287 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <cerrno>
+
+namespace sys = boost::system;
+
+enum E
+{
+    none = 0,
+    einval = EINVAL
+};
+
+namespace boost
+{
+namespace system
+{
+
+template<> struct is_error_code_enum< ::E >
+{
+    static const bool value = true;
+};
+
+} // namespace system
+} // namespace boost
+
+sys::error_code make_error_code( E e )
+{
+    return e == 0? sys::error_code(): sys::error_code( e, sys::generic_category() );
+}
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+enum E2
+{
+    e2inval = EINVAL
+};
+
+namespace boost
+{
+namespace system
+{
+
+template<> struct is_error_code_enum< ::E2 >
+{
+    static const bool value = true;
+};
+
+} // namespace system
+} // namespace boost
+
+std::error_code make_error_code( E2 e )
+{
+    return std::error_code( e, std::generic_category() );
+}
+
+#endif
+
+int main()
+{
+    {
+        sys::error_code ec( einval );
+
+        BOOST_TEST_EQ( ec.value(), EINVAL );
+        BOOST_TEST_EQ( &ec.category(), &sys::generic_category() );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+    {
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        sys::error_code ec( einval, &loc );
+
+        BOOST_TEST_EQ( ec.value(), EINVAL );
+        BOOST_TEST_EQ( &ec.category(), &sys::generic_category() );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 77 );
+    }
+
+    {
+        sys::error_code ec( none );
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+    {
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        sys::error_code ec( none, &loc );
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+    {
+        sys::error_code ec;
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec = sys::error_code( einval, &loc );
+
+        BOOST_TEST_EQ( ec.value(), EINVAL );
+        BOOST_TEST_EQ( &ec.category(), &sys::generic_category() );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 127 );
+    }
+
+    {
+        sys::error_code ec;
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec = sys::error_code( none, &loc );
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+    {
+        sys::error_code ec;
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec.assign( einval, &loc );
+
+        BOOST_TEST_EQ( ec.value(), EINVAL );
+        BOOST_TEST_EQ( &ec.category(), &sys::generic_category() );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 175 );
+    }
+
+    {
+        sys::error_code ec;
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec.assign( none, &loc );
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    {
+        sys::error_code ec( e2inval );
+
+        BOOST_TEST_EQ( ec, std::error_code( EINVAL, std::generic_category() ) );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+    {
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        sys::error_code ec( e2inval, &loc );
+
+        BOOST_TEST_EQ( ec, std::error_code( EINVAL, std::generic_category() ) );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+    {
+        sys::error_code ec;
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec = sys::error_code( e2inval, &loc );
+
+        BOOST_TEST_EQ( ec, std::error_code( EINVAL, std::generic_category() ) );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+    {
+        sys::error_code ec;
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST_EQ( &ec.category(), &sys::system_category() );
+
+        BOOST_TEST( !ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec.assign( e2inval, &loc );
+
+        BOOST_TEST_EQ( ec, std::error_code( EINVAL, std::generic_category() ) );
+
+        BOOST_TEST( ec.failed() );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location().line(), 0 );
+    }
+
+#endif
+
+    return boost::report_errors();
+}

test/ec_location_test3.cpp

@@ -0,0 +1,90 @@
+// Copyright 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <cerrno>
+
+int main()
+{
+    int const val = ENOENT;
+    boost::system::error_category const & cat = boost::system::generic_category();
+
+    {
+        boost::system::error_code ec;
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        boost::system::error_code ec2( ec, &loc );
+
+        BOOST_TEST_EQ( ec2, ec );
+
+        BOOST_TEST( !ec2.has_location() );
+        BOOST_TEST_EQ( ec2.location(), boost::source_location() );
+
+        boost::system::error_code ec3( ec2, 0 );
+
+        BOOST_TEST_EQ( ec3, ec2 );
+
+        BOOST_TEST( !ec3.has_location() );
+        BOOST_TEST_EQ( ec3.location(), boost::source_location() );
+    }
+
+    {
+        boost::system::error_code ec( val, cat );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        boost::system::error_code ec2( ec, &loc );
+
+        BOOST_TEST_EQ( ec2, ec );
+
+        BOOST_TEST( ec2.has_location() );
+        BOOST_TEST_EQ( ec2.location(), loc );
+
+        boost::system::error_code ec3( ec2, 0 );
+
+        BOOST_TEST_EQ( ec3, ec2 );
+
+        BOOST_TEST( !ec3.has_location() );
+        BOOST_TEST_EQ( ec3.location(), boost::source_location() );
+    }
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    {
+        std::error_code e2( val, std::generic_category() );
+
+        boost::system::error_code ec( e2 );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        boost::system::error_code ec2( ec, &loc );
+
+        BOOST_TEST_EQ( ec2, ec );
+
+        BOOST_TEST( !ec2.has_location() );
+        BOOST_TEST_EQ( ec2.location(), boost::source_location() );
+
+        boost::system::error_code ec3( ec2, 0 );
+
+        BOOST_TEST_EQ( ec3, ec2 );
+
+        BOOST_TEST( !ec3.has_location() );
+        BOOST_TEST_EQ( ec3.location(), boost::source_location() );
+    }
+
+#endif
+
+    return boost::report_errors();
+}

test/ec_location_test4.cpp

@@ -0,0 +1,93 @@
+// Copyright 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <cerrno>
+
+int main()
+{
+    int const val = ENOENT;
+    boost::system::error_category const & cat = boost::system::generic_category();
+
+    {
+        boost::system::error_code ec;
+        boost::system::error_code ec2( ec );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec.assign( ec, &loc );
+
+        BOOST_TEST_EQ( ec, ec2 );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+
+        ec.assign( ec, 0 );
+
+        BOOST_TEST_EQ( ec, ec2 );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+    }
+
+    {
+        boost::system::error_code ec( val, cat );
+        boost::system::error_code ec2( ec );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec.assign( ec, &loc );
+
+        BOOST_TEST_EQ( ec, ec2 );
+
+        BOOST_TEST( ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), loc );
+
+        ec.assign( ec, 0 );
+
+        BOOST_TEST_EQ( ec, ec2 );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+    }
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    {
+        std::error_code e2( val, std::generic_category() );
+
+        boost::system::error_code ec( e2 );
+        boost::system::error_code ec2( ec );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        ec.assign( ec, &loc );
+
+        BOOST_TEST_EQ( ec, ec2 );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+
+        ec.assign( ec, 0 );
+
+        BOOST_TEST_EQ( ec, ec2 );
+
+        BOOST_TEST( !ec.has_location() );
+        BOOST_TEST_EQ( ec.location(), boost::source_location() );
+    }
+
+#endif
+
+    return boost::report_errors();
+}

test/ec_what_test.cpp

@@ -0,0 +1,91 @@
+// Copyright 2020, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_code.hpp>
+#include <boost/system/generic_category.hpp>
+#include <boost/system/system_category.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+namespace sys = boost::system;
+
+int main()
+{
+    {
+        sys::error_code ec;
+
+        BOOST_TEST_EQ( ec.value(), 0 );
+        BOOST_TEST( ec.category() == sys::system_category() );
+
+        BOOST_TEST_EQ( ec.what(), ec.message() + " [system:0]" );
+    }
+
+    {
+        sys::error_code ec( 5, sys::generic_category() );
+
+        BOOST_TEST_EQ( ec.value(), 5 );
+        BOOST_TEST( ec.category() == sys::generic_category() );
+
+        BOOST_TEST_EQ( ec.what(), ec.message() + " [generic:5]" );
+    }
+
+    {
+        sys::error_code ec( 5, sys::system_category() );
+
+        BOOST_TEST_EQ( ec.value(), 5 );
+        BOOST_TEST( ec.category() == sys::system_category() );
+
+        BOOST_TEST_EQ( ec.what(), ec.message() + " [system:5]" );
+    }
+
+    {
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        sys::error_code ec( 5, sys::generic_category(), &loc );
+
+        BOOST_TEST_EQ( ec.value(), 5 );
+        BOOST_TEST( ec.category() == sys::generic_category() );
+        BOOST_TEST_EQ( &ec.location(), &loc );
+
+        BOOST_TEST_EQ( ec.what(), ec.message() + " [generic:5 at " + loc.to_string() + "]" );
+    }
+
+    {
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        sys::error_code ec( 5, sys::system_category(), &loc );
+
+        BOOST_TEST_EQ( ec.value(), 5 );
+        BOOST_TEST( ec.category() == sys::system_category() );
+        BOOST_TEST_EQ( &ec.location(), &loc );
+
+        BOOST_TEST_EQ( ec.what(), ec.message() + " [system:5 at " + loc.to_string() + "]" );
+    }
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    {
+        std::error_code ec;
+        sys::error_code ec2( ec );
+
+        BOOST_TEST_EQ( ec2.what(), ec2.message() + " [std:system:0]" );
+    }
+
+    {
+        std::error_code ec( 5, std::generic_category() );
+        sys::error_code ec2( ec );
+
+        BOOST_TEST_EQ( ec2.what(), ec2.message() + " [std:generic:5]" );
+    }
+
+    {
+        std::error_code ec( 5, std::system_category() );
+        sys::error_code ec2( ec );
+
+        BOOST_TEST_EQ( ec2.what(), ec2.message() + " [std:system:5]" );
+    }
+
+#endif
+
+    return boost::report_errors();
+}

test/ec_wstream_test.cpp

@@ -0,0 +1,21 @@
+// Copyright 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_code.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <sstream>
+
+namespace sys = boost::system;
+
+int main()
+{
+    {
+        std::wostringstream os;
+        os << sys::error_code();
+
+        BOOST_TEST( os.str() == L"system:0" );
+    }
+
+    return boost::report_errors();
+}

test/errc_test3.cpp

@@ -0,0 +1,34 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/errc.hpp>
+
+int main()
+{
+    make_error_code( boost::system::errc::success ).value();
+    make_error_code( boost::system::errc::success ).category();
+    make_error_code( boost::system::errc::success ).default_error_condition();
+    make_error_code( boost::system::errc::success ).message();
+    make_error_code( boost::system::errc::success ).failed();
+    make_error_code( boost::system::errc::success ).clear();
+
+    make_error_condition( boost::system::errc::success ).value();
+    make_error_condition( boost::system::errc::success ).category();
+    make_error_condition( boost::system::errc::success ).message();
+    make_error_condition( boost::system::errc::success ).failed();
+    make_error_condition( boost::system::errc::success ).clear();
+
+    make_error_code( boost::system::errc::no_such_file_or_directory ).value();
+    make_error_code( boost::system::errc::no_such_file_or_directory ).category();
+    make_error_code( boost::system::errc::no_such_file_or_directory ).default_error_condition();
+    make_error_code( boost::system::errc::no_such_file_or_directory ).message();
+    make_error_code( boost::system::errc::no_such_file_or_directory ).failed();
+    make_error_code( boost::system::errc::no_such_file_or_directory ).clear();
+
+    make_error_condition( boost::system::errc::no_such_file_or_directory ).value();
+    make_error_condition( boost::system::errc::no_such_file_or_directory ).category();
+    make_error_condition( boost::system::errc::no_such_file_or_directory ).message();
+    make_error_condition( boost::system::errc::no_such_file_or_directory ).failed();
+    make_error_condition( boost::system::errc::no_such_file_or_directory ).clear();
+}

test/errc_test4.cpp

@@ -0,0 +1,17 @@
+// Copyright 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/errc.hpp>
+#include <boost/assert/source_location.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+int main()
+{
+    BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+    BOOST_TEST( make_error_code( boost::system::errc::no_such_file_or_directory, &loc ).has_location() );
+    BOOST_TEST_EQ( make_error_code( boost::system::errc::no_such_file_or_directory, &loc ).location().to_string(), loc.to_string() );
+
+    return boost::report_errors();
+}

test/error_category_test.cpp

@@ -8,11 +8,9 @@
 
 // See library home page at http://www.boost.org/libs/system
 
-// Avoid spurious VC++ warnings
-# define _CRT_SECURE_NO_WARNINGS
-
 #include <boost/system/error_code.hpp>
 #include <boost/core/lightweight_test.hpp>
+#include <boost/core/snprintf.hpp>
 #include <cstdio>
 
 //
@@ -31,7 +29,7 @@ public:
     virtual std::string message( int ev ) const
     {
         char buffer[ 256 ];
-        std::sprintf( buffer, "user message %d", ev );
+        boost::core::snprintf( buffer, sizeof( buffer ), "user message %d", ev );
 
         return buffer;
     }

test/error_category_test2.cpp

@@ -8,11 +8,9 @@
 
 // See library home page at http://www.boost.org/libs/system
 
-// Avoid spurious VC++ warnings
-#define _CRT_SECURE_NO_WARNINGS
-
 #include <boost/system/error_category.hpp>
 #include <boost/core/lightweight_test.hpp>
+#include <boost/core/snprintf.hpp>
 #include <cstdio>
 
 //
@@ -31,7 +29,7 @@ public:
     virtual std::string message( int ev ) const
     {
         char buffer[ 256 ];
-        std::sprintf( buffer, "user message %d", ev );
+        boost::core::snprintf( buffer, sizeof( buffer ), "user message %d", ev );
 
         return buffer;
     }

test/error_code_test.cpp

@@ -11,11 +11,8 @@
 
 #include <boost/config/warning_disable.hpp>
 
-#include <boost/detail/lightweight_test.hpp>
 #include <boost/system/error_code.hpp>
-#include <boost/system/cygwin_error.hpp>
-#include <boost/system/linux_error.hpp>
-#include <boost/system/windows_error.hpp>
+#include <boost/core/lightweight_test.hpp>
 #include <iostream>
 #include <sstream>
 #include <string>
@@ -111,6 +108,7 @@ int main( int, char ** )
 
   std::cout << "Conversion use cases...\n";
   error_condition x1( errc::file_exists );
+  (void)x1;
   //error_code x2( errc::file_exists ); // should fail to compile
   make_error_code(errc::file_exists);
   make_error_condition(errc::file_exists);
@@ -294,29 +292,7 @@ int main( int, char ** )
   BOOST_TEST( ec.default_error_condition().value() == errc::permission_denied );
   BOOST_TEST( ec.default_error_condition().category() == generic_category() );
 
-# ifdef __CYGWIN__
-
-  std::cout << "Cygwin tests...\n";
-  ec = cygwin_error::no_package;
-  BOOST_TEST( ec == cygwin_error::no_package );
-  BOOST_TEST( ec == error_code( ENOPKG, system_category() ) );
-  BOOST_TEST( ec == error_code( cygwin_error::no_package, system_category() ) );
-  BOOST_TEST( ec.default_error_condition().category() == system_category() );
-
-# elif defined(linux) || defined(__linux) || defined(__linux__)
-
-  std::cout << "Linux tests...\n";
-  ec = linux_error::dot_dot_error;
-  BOOST_TEST( ec == linux_error::dot_dot_error );
-  BOOST_TEST( ec == error_code( EDOTDOT, system_category() ) );
-  BOOST_TEST( ec == error_code( linux_error::dot_dot_error, system_category() ) );
-  BOOST_TEST( ec.default_error_condition().category() == system_category() );
-
-# endif
-
 #endif
   
   return ::boost::report_errors();
 }
-
-

test/error_code_test2.cpp

@@ -0,0 +1,94 @@
+// Copyright 2020, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_code.hpp>
+#include <boost/system/generic_category.hpp>
+#include <boost/system/system_category.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+namespace sys = boost::system;
+
+int main()
+{
+    char buffer[ 1024 ];
+
+    sys::error_code ec;
+
+    BOOST_TEST_EQ( ec.value(), 0 );
+    BOOST_TEST( ec.category() == sys::system_category() );
+    BOOST_TEST_EQ( ec.message(), ec.category().message( ec.value() ) );
+    BOOST_TEST_CSTR_EQ( ec.message( buffer, sizeof( buffer ) ), ec.category().message( ec.value(), buffer, sizeof( buffer ) ) );
+    BOOST_TEST( !ec.failed() );
+    BOOST_TEST( !ec );
+
+    BOOST_TEST_EQ( ec.to_string(), std::string( "system:0" ) );
+
+    {
+        sys::error_code ec2( ec );
+
+        BOOST_TEST_EQ( ec2.value(), 0 );
+        BOOST_TEST( ec2.category() == sys::system_category() );
+        BOOST_TEST_EQ( ec2.message(), ec2.category().message( ec2.value() ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.category().message( ec2.value(), buffer, sizeof( buffer ) ) );
+        BOOST_TEST( !ec2.failed() );
+        BOOST_TEST( !ec2 );
+
+        BOOST_TEST_EQ( ec, ec2 );
+        BOOST_TEST_NOT( ec != ec2 );
+
+        BOOST_TEST_EQ( ec2.to_string(), std::string( "system:0" ) );
+    }
+
+    {
+        sys::error_code ec2( ec.value(), ec.category() );
+
+        BOOST_TEST_EQ( ec2.value(), 0 );
+        BOOST_TEST( ec2.category() == sys::system_category() );
+        BOOST_TEST_EQ( ec2.message(), ec2.category().message( ec2.value() ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.category().message( ec2.value(), buffer, sizeof( buffer ) ) );
+        BOOST_TEST( !ec2.failed() );
+        BOOST_TEST( !ec2 );
+
+        BOOST_TEST_EQ( ec, ec2 );
+        BOOST_TEST_NOT( ec != ec2 );
+
+        BOOST_TEST_EQ( ec2.to_string(), std::string( "system:0" ) );
+    }
+
+    {
+        sys::error_code ec2( 5, sys::generic_category() );
+
+        BOOST_TEST_EQ( ec2.value(), 5 );
+        BOOST_TEST( ec2.category() == sys::generic_category() );
+        BOOST_TEST_EQ( ec2.message(), ec2.category().message( ec2.value() ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.category().message( ec2.value(), buffer, sizeof( buffer ) ) );
+        BOOST_TEST( ec2.failed() );
+        BOOST_TEST( ec2 );
+        BOOST_TEST_NOT( !ec2 );
+
+        BOOST_TEST_NE( ec, ec2 );
+        BOOST_TEST_NOT( ec == ec2 );
+
+        BOOST_TEST_EQ( ec2.to_string(), std::string( "generic:5" ) );
+    }
+
+    {
+        sys::error_code ec2( 5, sys::system_category() );
+
+        BOOST_TEST_EQ( ec2.value(), 5 );
+        BOOST_TEST( ec2.category() == sys::system_category() );
+        BOOST_TEST_EQ( ec2.message(), ec2.category().message( ec2.value() ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.category().message( ec2.value(), buffer, sizeof( buffer ) ) );
+        BOOST_TEST( ec2.failed() );
+        BOOST_TEST( ec2 );
+        BOOST_TEST_NOT( !ec2 );
+
+        BOOST_TEST_NE( ec, ec2 );
+        BOOST_TEST_NOT( ec == ec2 );
+
+        BOOST_TEST_EQ( ec2.to_string(), std::string( "system:5" ) );
+    }
+
+    return boost::report_errors();
+}

test/error_code_test3.cpp

@@ -0,0 +1,69 @@
+// Copyright 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_code.hpp>
+#include <boost/system/error_condition.hpp>
+#include <boost/system/generic_category.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+namespace sys = boost::system;
+
+enum my_errc
+{
+    enomem_c = ENOMEM
+};
+
+enum my_errn
+{
+    enomem_n = ENOMEM
+};
+
+namespace boost {
+namespace system {
+
+template<> struct is_error_code_enum<my_errc>
+{
+    static const bool value = true;
+};
+
+template<> struct is_error_condition_enum<my_errn>
+{
+    static const bool value = true;
+};
+
+} // namespace system
+} // namespace boost
+
+sys::error_code make_error_code( my_errc e )
+{
+    return sys::error_code( e, sys::generic_category() );
+}
+
+sys::error_condition make_error_condition( my_errn e )
+{
+    return sys::error_condition( e, sys::generic_category() );
+}
+
+int main()
+{
+    sys::error_code ec = make_error_code( sys::errc::not_enough_memory );
+    sys::error_condition en( sys::errc::not_enough_memory );
+
+    BOOST_TEST_EQ( ec, en );
+    BOOST_TEST_EQ( en, ec );
+
+    BOOST_TEST_EQ( ec, enomem_c );
+    BOOST_TEST_EQ( enomem_c, ec );
+
+    BOOST_TEST_EQ( ec, enomem_n );
+    BOOST_TEST_EQ( enomem_n, ec );
+
+    BOOST_TEST_EQ( en, enomem_c );
+    BOOST_TEST_EQ( enomem_c, en );
+
+    BOOST_TEST_EQ( en, enomem_n );
+    BOOST_TEST_EQ( enomem_n, en );
+
+    return boost::report_errors();
+}

test/error_condition_test3.cpp

@@ -0,0 +1,94 @@
+// Copyright 2020, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_condition.hpp>
+#include <boost/system/generic_category.hpp>
+#include <boost/system/system_category.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+namespace sys = boost::system;
+
+int main()
+{
+    char buffer[ 1024 ];
+
+    sys::error_condition en;
+
+    BOOST_TEST_EQ( en.value(), 0 );
+    BOOST_TEST( en.category() == sys::generic_category() );
+    BOOST_TEST_EQ( en.message(), en.category().message( en.value() ) );
+    BOOST_TEST_CSTR_EQ( en.message( buffer, sizeof( buffer ) ), en.category().message( en.value(), buffer, sizeof( buffer ) ) );
+    BOOST_TEST( !en.failed() );
+    BOOST_TEST( !en );
+
+    BOOST_TEST_EQ( en.to_string(), std::string( "cond:generic:0" ) );
+
+    {
+        sys::error_condition en2( en );
+
+        BOOST_TEST_EQ( en2.value(), 0 );
+        BOOST_TEST( en2.category() == sys::generic_category() );
+        BOOST_TEST_EQ( en2.message(), en2.category().message( en2.value() ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.category().message( en2.value(), buffer, sizeof( buffer ) ) );
+        BOOST_TEST( !en2.failed() );
+        BOOST_TEST( !en2 );
+
+        BOOST_TEST_EQ( en, en2 );
+        BOOST_TEST_NOT( en != en2 );
+
+        BOOST_TEST_EQ( en2.to_string(), std::string( "cond:generic:0" ) );
+    }
+
+    {
+        sys::error_condition en2( en.value(), en.category() );
+
+        BOOST_TEST_EQ( en2.value(), 0 );
+        BOOST_TEST( en2.category() == sys::generic_category() );
+        BOOST_TEST_EQ( en2.message(), en2.category().message( en2.value() ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.category().message( en2.value(), buffer, sizeof( buffer ) ) );
+        BOOST_TEST( !en2.failed() );
+        BOOST_TEST( !en2 );
+
+        BOOST_TEST_EQ( en, en2 );
+        BOOST_TEST_NOT( en != en2 );
+
+        BOOST_TEST_EQ( en2.to_string(), std::string( "cond:generic:0" ) );
+    }
+
+    {
+        sys::error_condition en2( 5, sys::generic_category() );
+
+        BOOST_TEST_EQ( en2.value(), 5 );
+        BOOST_TEST( en2.category() == sys::generic_category() );
+        BOOST_TEST_EQ( en2.message(), en2.category().message( en2.value() ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.category().message( en2.value(), buffer, sizeof( buffer ) ) );
+        BOOST_TEST( en2.failed() );
+        BOOST_TEST( en2 );
+        BOOST_TEST_NOT( !en2 );
+
+        BOOST_TEST_NE( en, en2 );
+        BOOST_TEST_NOT( en == en2 );
+
+        BOOST_TEST_EQ( en2.to_string(), std::string( "cond:generic:5" ) );
+    }
+
+    {
+        sys::error_condition en2( 5, sys::system_category() );
+
+        BOOST_TEST_EQ( en2.value(), 5 );
+        BOOST_TEST( en2.category() == sys::system_category() );
+        BOOST_TEST_EQ( en2.message(), en2.category().message( en2.value() ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.category().message( en2.value(), buffer, sizeof( buffer ) ) );
+        BOOST_TEST( en2.failed() );
+        BOOST_TEST( en2 );
+        BOOST_TEST_NOT( !en2 );
+
+        BOOST_TEST_NE( en, en2 );
+        BOOST_TEST_NOT( en == en2 );
+
+        BOOST_TEST_EQ( en2.to_string(), std::string( "cond:system:5" ) );
+    }
+
+    return boost::report_errors();
+}

test/failed_constexpr_test.cpp

@@ -33,6 +33,12 @@ BOOST_STATIC_ASSERT( !ec3.failed() );
 BOOST_STATIC_ASSERT( ec3? false: true );
 BOOST_STATIC_ASSERT( !ec3 );
 
+#if defined(__GNUC__) && __GNUC__ == 7 && __cplusplus == 201703L
+
+// 'cat_' is not a constant expression
+
+#else
+
 constexpr error_condition en1( 1, system_category() );
 
 BOOST_STATIC_ASSERT( en1.failed() );
@@ -51,6 +57,8 @@ BOOST_STATIC_ASSERT( !en3.failed() );
 BOOST_STATIC_ASSERT( en3? false: true );
 BOOST_STATIC_ASSERT( !en3 );
 
+#endif
+
 int main()
 {
 }

test/failed_test.cpp

@@ -2,11 +2,9 @@
 // Copyright 2018 Peter Dimov.
 // Distributed under the Boost Software License, Version 1.0.
 
-// Avoid spurious VC++ warnings
-#define _CRT_SECURE_NO_WARNINGS
-
 #include <boost/system/error_code.hpp>
 #include <boost/core/lightweight_test.hpp>
+#include <boost/core/snprintf.hpp>
 #include <cstdio>
 
 using namespace boost::system;
@@ -28,7 +26,7 @@ struct http_category_impl: public error_category
     {
         char buffer[ 32 ];
 
-        std::sprintf( buffer, "HTTP/1.0 %d", ev );
+        boost::core::snprintf( buffer, sizeof( buffer ), "HTTP/1.0 %d", ev );
         return buffer;
     }
 

test/header_only_test.cpp

@@ -16,8 +16,10 @@
 #include <boost/detail/lightweight_test.hpp>
 #include <boost/system/error_code.hpp>
 
-int main( int, char*[] )
+int main()
 {
-  boost::system::error_code ec( 0, boost::system::system_category() );
-  return ::boost::report_errors();
+    boost::system::error_code ec( 0, boost::system::system_category() );
+    (void)ec;
+
+    return ::boost::report_errors();
 }

test/linux_error_test.cpp

@@ -0,0 +1,29 @@
+// Copyright 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/linux_error.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__linux__)
+
+BOOST_PRAGMA_MESSAGE( "Skipping test, __linux__ is not defined" )
+int main() {}
+
+#else
+
+#include <boost/core/lightweight_test.hpp>
+
+int main()
+{
+    namespace sys = boost::system;
+
+    sys::error_code ec = sys::linux_error::dot_dot_error;
+
+    BOOST_TEST_EQ( ec, sys::linux_error::dot_dot_error );
+    BOOST_TEST_EQ( ec, sys::error_code( EDOTDOT, sys::system_category() ) );
+
+    return boost::report_errors();
+}
+
+#endif

test/quick.cpp

@@ -1,15 +1,10 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2021 Peter Dimov.
 // Distributed under the Boost Software License, Version 1.0.
-//
-// See accompanying file LICENSE_1_0.txt or copy at
-// http://www.boost.org/LICENSE_1_0.txt
+// https://www.boost.org/LICENSE_1_0.txt
 
 // See library home page at http://www.boost.org/libs/system
 
-#include <boost/system/system_error.hpp>
-#include <boost/system/error_code.hpp>
+#include <boost/system.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <cerrno>
 
@@ -33,10 +28,16 @@ int main()
 
     BOOST_TEST( bc == bn );
 
+    boost::system::error_code bc2 = make_error_code( boost::system::errc::no_such_file_or_directory );
+
+    BOOST_TEST_EQ( bc2, bc );
+    BOOST_TEST_EQ( bc2.value(), ev );
+    BOOST_TEST_EQ( &bc.category(), &bt );
+
     boost::system::system_error x( bc, "prefix" );
 
     BOOST_TEST_EQ( x.code(), bc );
-    BOOST_TEST_EQ( std::string( x.what() ), "prefix: " + bc.message() );
+    BOOST_TEST_EQ( std::string( x.what() ), "prefix: " + bc.what() );
 
     return boost::report_errors();
 }

test/result_and_eq_fn1r.cpp

@@ -0,0 +1,126 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& r )
+    {
+        if( &r != this )
+        {
+            v_ = r.v_;
+            r.v_ = 0;
+        }
+
+        return *this;
+    }
+};
+
+struct E
+{
+};
+
+struct E2
+{
+    E2() {}
+    E2( E ) {}
+};
+
+result<int, E> fi( int x )
+{
+    return 2 * x + 1;
+}
+
+result<int, E2> fi2( int )
+{
+    return E2();
+}
+
+result<X, E> fy( Y y )
+{
+    return X{ 2 * y.v_ + 1 };
+}
+
+result<Y, E2> fy2( Y )
+{
+    return E2();
+}
+
+result<int&, E> fri( int& )
+{
+    static int x = 2;
+    return x;
+}
+
+result<int&, E2> fri2( int& )
+{
+    return E2();
+}
+
+int main()
+{
+    {
+        result<int, E2> r( 1 );
+
+        r &= fi;
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 3 );
+
+        r &= fi2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fi;
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        result<Y, E2> r( in_place_value, 1 );
+
+        r &= fy;
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 3 );
+
+        r &= fy2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fy;
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        int x1 = 1;
+        result<int&, E2> r( x1 );
+
+        r &= fri;
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &*fri( x1 ) );
+
+        r &= fri2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fri;
+        BOOST_TEST( r.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_and_eq_fn1v.cpp

@@ -0,0 +1,114 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& r )
+    {
+        if( &r != this )
+        {
+            v_ = r.v_;
+            r.v_ = 0;
+        }
+
+        return *this;
+    }
+};
+
+struct E
+{
+};
+
+int f( int x )
+{
+    return x * 2 + 1;
+}
+
+X g( Y y )
+{
+    return X{ y.v_ * 2 + 1 };
+}
+
+int& h( int& )
+{
+    static int x = 2;
+    return x;
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        r &= f;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 3 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        r &= f;
+
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        result<Y> r( in_place_value, 1 );
+
+        r &= g;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 3 );
+    }
+
+    {
+        result<Y, E> r( in_place_error );
+
+        r &= g;
+
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        int x1 = 1;
+        result<int&> r( x1 );
+
+        r &= h;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &h( x1 ) );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        r &= h;
+
+        BOOST_TEST( r.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_and_fn1r.cpp

@@ -0,0 +1,347 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& ) = delete;
+};
+
+struct E
+{
+};
+
+struct E2
+{
+    E2() {}
+    E2( E ) {}
+};
+
+result<int, E2> fi( int x )
+{
+    return 2 * x + 1;
+}
+
+result<int, E2> fi2( int )
+{
+    return E2();
+}
+
+result<void, E2> fi3( int )
+{
+    return {};
+}
+
+result<X, E2> fy( Y y )
+{
+    return X{ 2 * y.v_ + 1 };
+}
+
+result<X, E2> fy2( Y )
+{
+    return E2();
+}
+
+result<void, E2> fy3( Y )
+{
+    return {};
+}
+
+result<int, E2> fri( int& x )
+{
+    return x * 2 + 1;
+}
+
+result<int&, E2> fri2( int& )
+{
+    return E2();
+}
+
+result<void, E2> fri3( int& )
+{
+    return {};
+}
+
+int main()
+{
+    {
+        result<int, E> r( 1 );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        result<int, E> const r( 1 );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( 1 ) & fi;
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( 1 ) & fi2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<int, E>( 1 ) & fi3;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( in_place_error ) & fi;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( in_place_error ) & fi2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<int, E>( in_place_error ) & fi3;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_value, 1 ) & fy;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2->v_, 3 );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_value, 1 ) & fy2;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<Y, E>( in_place_value, 1 ) & fy3;
+
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_error ) & fy;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_error ) & fy2;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<Y, E>( in_place_error ) & fy3;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        int x1 = 1;
+        result<int&, E> r( x1 );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        int x1 = 1;
+        result<int&, E> const r( x1 );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        int x1 = 1;
+
+        result<int, E2> r2 = result<int&, E>( x1 ) & fri;
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&, E2> r2 = result<int&, E>( x1 ) & fri2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        int x1 = 1;
+
+        result<void, E2> r2 = result<int&, E>( x1 ) & fri3;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int&, E> const r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<int&, E>( in_place_error ) & fri;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int&, E2> r2 = result<int&, E>( in_place_error ) & fri2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<int&, E>( in_place_error ) & fri3;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_and_fn1v.cpp

@@ -0,0 +1,158 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& ) = delete;
+};
+
+struct E
+{
+};
+
+int f( int x )
+{
+    return x * 2 + 1;
+}
+
+X g( Y y )
+{
+    return X{ y.v_ * 2 + 1 };
+}
+
+int& h( int& )
+{
+    static int x = 2;
+    return x;
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+        result<int> r2 = r & f;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int> const r( 1 );
+        result<int> r2 = r & f;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int> r2 = result<int>( 1 ) & f;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+        result<int, E> r2 = r & f;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+        result<int, E> r2 = r & f;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E> r2 = result<int, E>( in_place_error ) & f;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<X> r2 = result<Y>( in_place_value, 1 ) & g;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2->v_, 3 );
+    }
+
+    {
+        result<X, E> r2 = result<Y, E>( in_place_error ) & g;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r( x1 );
+
+        result<int&> r2 = r & h;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &h( x1 ) );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r( x1 );
+
+        result<int&> r2 = r & h;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &h( x1 ) );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r2 = result<int&>( x1 ) & h;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &h( x1 ) );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        result<int&, E> r2 = r & h;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int&, E> const r( in_place_error );
+
+        result<int&, E> r2 = r & h;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int&, E> r2 = result<int&, E>( in_place_error ) & h;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_convert_construct.cpp

@@ -0,0 +1,306 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    X(): v_() { ++instances; }
+
+    X( int v ): v_( v ) { ++instances; }
+
+    X( X const& r ): v_( r.v_ ) { ++instances; }
+
+    X& operator=( X const& ) = delete;
+
+    ~X() { --instances; }
+};
+
+bool operator==( X const & x1, X const & x2 )
+{
+    return x1.v_ == x2.v_;
+}
+
+std::ostream& operator<<( std::ostream& os, X const & x )
+{
+    os << "X:" << x.v_;
+    return os;
+}
+
+int X::instances = 0;
+
+int main()
+{
+    {
+        result<int> r( 5 );
+        result<long> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 5 );
+    }
+
+    {
+        result<int> const r( 6 );
+        result<long> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 6 );
+    }
+
+    {
+        result<long> r2 = result<int>( 7 );
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 7 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<int> r( 5 );
+        result<X> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 5 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<int> const r( 6 );
+        result<X> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 6 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r2 = result<int>( 7 );
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 7 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<long> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<long> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<long> r2 = result<int>( ec );
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<char const*, int> r( "test" );
+        result<std::string, X> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, std::string( "test" ) );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<char const*, int> const r( "test" );
+        result<std::string, X> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, std::string( "test" ) );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<std::string, X> r2 = result<char const*, int>( "test" );
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, std::string( "test" ) );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<char const*, int> r( 5 );
+        result<std::string, X> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(5) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<char const*, int> const r( 6 );
+        result<std::string, X> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(6) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    {
+        result<std::string, X> r2 = result<char const*, int>( 7 );
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(7) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
+    {
+        result<void, int> r;
+        result<void, X> r2 = r;
+
+        BOOST_TEST( r2 );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, int> const r;
+        result<void, X> r2 = r;
+
+        BOOST_TEST( r2 );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, X> r2 = result<void, int>();
+
+        BOOST_TEST( r2 );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, int> r( 5 );
+        result<void, X> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(5) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, int> const r( 6 );
+        result<void, X> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(6) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    {
+        result<void, X> r2 = result<void, int>( 7 );
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(7) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
+    {
+        int x = 5;
+
+        result<int&> r( x );
+        result<int const&> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 5 );
+    }
+
+    {
+        int x = 6;
+
+        result<int&> const r( x );
+        result<int const&> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 6 );
+    }
+
+    {
+        int x = 7;
+
+        result<int const&> r2 = result<int&>( x );
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 7 );
+    }
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<long>, result<int>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<result<int>, result<long>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int>, result<void*>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<void*>, result<int>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int>, result<void>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<void>, result<int>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<void>, result<int>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<int>, result<void>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int, void*>, result<int, int>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<int, int>, result<int, void*>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<void, void*>, result<void, int>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<void, int>, result<void, void*>>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<int const&>, result<int&>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<result<int&>, result<int const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&>, result<int>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<int>, result<int const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&>, result<long&>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<long&>, result<int const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&>, result<long const&>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<long const&>, result<int const&>>));
+    }
+
+    return boost::report_errors();
+}

test/result_copy_assign.cpp

@@ -0,0 +1,832 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <iosfwd>
+#include <cerrno>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    explicit X( int v = 0 ): v_( v ) { ++instances; }
+
+    X( X const& r ): v_( r.v_ ) { ++instances; }
+
+    X& operator=( X const& ) = default;
+
+    ~X() { --instances; }
+};
+
+bool operator==( X const & x1, X const & x2 )
+{
+    return x1.v_ == x2.v_;
+}
+
+std::ostream& operator<<( std::ostream& os, X const & x )
+{
+    os << "X:" << x.v_;
+    return os;
+}
+
+int X::instances = 0;
+
+struct Y
+{
+    static int instances;
+
+    int v_;
+
+    explicit Y( int v = 0 ): v_( v ) { ++instances; }
+
+    Y( Y const& r ) noexcept: v_( r.v_ ) { ++instances; }
+
+    Y& operator=( Y const& ) = default;
+
+    ~Y() { --instances; }
+};
+
+bool operator==( Y const & y1, Y const & y2 )
+{
+    return y1.v_ == y2.v_;
+}
+
+std::ostream& operator<<( std::ostream& os, Y const & y )
+{
+    os << "Y:" << y.v_;
+    return os;
+}
+
+int Y::instances = 0;
+
+int main()
+{
+    // default-initialized lhs
+
+    {
+        result<int> r;
+        result<int> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> r;
+        result<int> r2( 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> r;
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> const r;
+        result<int> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> const r;
+        result<int> r2( 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> const r;
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r;
+        result<X> r2;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r;
+        result<X> r2( 1 );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r;
+        result<X> r2( ENOENT, generic_category() );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> const r;
+        result<X> r2;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> const r;
+        result<X> r2( 1 );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> const r;
+        result<X> r2( ENOENT, generic_category() );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    // value lhs
+
+    {
+        result<int> r( 0 );
+        result<int> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> r( 0 );
+        result<int> r2( 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> r( 0 );
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> const r( 0 );
+        result<int> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> const r( 0 );
+        result<int> r2( 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> const r( 0 );
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1 );
+        result<X> r2;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1 );
+        result<X> r2( 2 );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1 );
+        result<X> r2( ENOENT, generic_category() );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> const r( 1 );
+        result<X> r2;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> const r( 1 );
+        result<X> r2( 2 );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> const r( 1 );
+        result<X> r2( ENOENT, generic_category() );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    // error lhs
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<int> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<int> r2( 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> const r( ec );
+        result<int> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> const r( ec );
+        result<int> r2( 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> const r( ec );
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> r( ec );
+        result<X> r2;
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> r( ec );
+        result<X> r2( 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> r( ec );
+        result<X> r2( ENOENT, generic_category() );
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> const r( ec );
+        result<X> r2;
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> const r( ec );
+        result<X> r2( 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> const r( ec );
+        result<X> r2( ENOENT, generic_category() );
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<std::string, Y> r( 1 );
+        result<std::string, Y> r2( 2 );
+
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<std::string, Y> r( 1 );
+        result<std::string, Y> r2( "str" );
+
+        BOOST_TEST_EQ( Y::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<std::string, Y> const r( 1 );
+        result<std::string, Y> r2( 2 );
+
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<std::string, Y> const r( 1 );
+        result<std::string, Y> r2( "str" );
+
+        BOOST_TEST_EQ( Y::instances, 1 );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    // void
+
+    {
+        result<void> r;
+        result<void> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<void> r;
+        result<void> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<void> const r;
+        result<void> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<void> const r;
+        result<void> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r( ec );
+        result<void> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r( ec );
+        result<void> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> const r( ec );
+        result<void> r2;
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> const r( ec );
+        result<void> r2( ENOENT, generic_category() );
+
+        r2 = r;
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    // reference
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r1( x1 );
+        result<int&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int const x1 = 1;
+        int const x2 = 2;
+
+        result<int const&> r1( x1 );
+        result<int const&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> const r1( x1 );
+        result<int&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int const x1 = 1;
+        int const x2 = 2;
+
+        result<int const &> const r1( x1 );
+        result<int const &> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r1( x1 );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x2 = 2;
+
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        int x2 = 2;
+
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> const r1( ec );
+        result<int&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> const r1( ec );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    return boost::report_errors();
+}

test/result_copy_construct.cpp

@@ -0,0 +1,299 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    X(): v_() { ++instances; }
+
+    explicit X( int v ): v_( v ) { ++instances; }
+
+    X( int v1, int v2 ): v_( v1+v2 ) { ++instances; }
+    X( int v1, int v2, int v3 ): v_( v1+v2+v3 ) { ++instances; }
+
+    X( X const& r ): v_( r.v_ ) { ++instances; }
+
+    X& operator=( X const& ) = delete;
+
+    ~X() { --instances; }
+};
+
+bool operator==( X const & x1, X const & x2 )
+{
+    return x1.v_ == x2.v_;
+}
+
+std::ostream& operator<<( std::ostream& os, X const & x )
+{
+    os << "X:" << x.v_;
+    return os;
+}
+
+int X::instances = 0;
+
+int main()
+{
+    {
+        result<int> r;
+        result<int> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> const r;
+        result<int> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r;
+        result<X> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+        BOOST_TEST_EQ( X::instances, 2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<int> r( 1 );
+        result<int> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> const r( 1 );
+        result<int> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1 );
+        result<X> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+        BOOST_TEST_EQ( X::instances, 2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> const r( 1 );
+        result<X> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+        BOOST_TEST_EQ( X::instances, 2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<int> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> const r( ec );
+        result<int> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<std::string, X> r( 1 );
+        result<std::string, X> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+        BOOST_TEST_EQ( X::instances, 2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<std::string, X> const r( 1 );
+        result<std::string, X> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+        BOOST_TEST_EQ( X::instances, 2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
+    {
+        result<void> r;
+        result<void> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<void> const r;
+        result<void> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r( ec );
+        result<void> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> const r( ec );
+        result<void> r2( r );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    //
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r1( x1 );
+        result<int&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int const x1 = 1;
+
+        result<int const&> r1( x1 );
+        result<int const&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int const x1 = 1;
+
+        result<int const&> const r1( x1 );
+        result<int const&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X x1( 1 );
+
+        result<X&> r1( x1 );
+        result<X&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X x1( 1 );
+
+        result<X&> const r1( x1 );
+        result<X&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X const x1( 1 );
+
+        result<X const&> r1( x1 );
+        result<X const&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X const x1( 1 );
+
+        result<X const&> const r1( x1 );
+        result<X const&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> const r1( ec );
+        result<int&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    //
+
+    return boost::report_errors();
+}

test/result_default_construct.cpp

@@ -0,0 +1,107 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+};
+
+struct Y
+{
+    Y( int );
+};
+
+int main()
+{
+    {
+        result<int> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        result<int> r{};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        result<int> r = {};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        result<X> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        result<X> r{};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        result<X> r = {};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        result<void> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        result<void> r{};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        result<void> r = {};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<int>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<int, int>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<X>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<X, int>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<void>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<void, int>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_default_constructible<result<Y>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_default_constructible<result<Y, int>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_default_constructible<result<int&>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_default_constructible<result<int&, int>>));
+    }
+
+    return boost::report_errors();
+}

test/result_emplace.cpp

@@ -0,0 +1,218 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <cerrno>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    explicit X( int v ): v_( v ) { ++instances; }
+
+    X( int v1, int v2 ): v_( v1+v2 ) { ++instances; }
+    X( int v1, int v2, int v3 ): v_( v1+v2+v3 ) { ++instances; }
+
+    X( X const& ) = delete;
+    X& operator=( X const& ) = delete;
+
+    ~X() { --instances; }
+};
+
+int X::instances = 0;
+
+struct Y
+{
+    static int instances;
+
+    Y() noexcept { ++instances; }
+
+    Y( Y const& ) noexcept { ++instances; }
+
+    Y& operator=( Y const& ) = default;
+
+    ~Y() { --instances; }
+};
+
+int Y::instances = 0;
+
+int main()
+{
+    {
+        result<int> r;
+
+        BOOST_TEST( r.has_value() );
+
+        r.emplace( 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value(), 1 );
+    }
+
+    {
+        result<int> r( ENOENT, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+
+        r.emplace( 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value(), 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 0 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value().v_, 0 );
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r.emplace( 1 );
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value().v_, 1 );
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r.emplace( 1, 2 );
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value().v_, 1+2 );
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r.emplace( 1, 2, 3 );
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value().v_, 1+2+3 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( ENOENT, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        r.emplace( 1, 2 );
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value().v_, 1+2 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<int, Y> r( Y{} );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST_EQ( Y::instances, 1 );
+
+        r.emplace( 1 );
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( *r, 1 );
+        BOOST_TEST_EQ( Y::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<X, Y> r( in_place_error );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST_EQ( X::instances, 0 );
+        BOOST_TEST_EQ( Y::instances, 1 );
+
+        r.emplace( 1, 2, 3 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r->v_, 1+2+3 );
+        BOOST_TEST_EQ( X::instances, 1 );
+        BOOST_TEST_EQ( Y::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<void> r;
+
+        BOOST_TEST( r.has_value() );
+
+        r.emplace();
+        BOOST_TEST( r.has_value() );
+    }
+
+    {
+        result<void> r( ENOENT, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+
+        r.emplace();
+        BOOST_TEST( r.has_value() );
+    }
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<void, Y> r( in_place_error );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST_EQ( Y::instances, 1 );
+
+        r.emplace();
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( Y::instances, 0 );
+    }
+
+    {
+        int x1 = 1;
+        result<int&> r( x1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value(), 1 );
+
+        int x2 = 2;
+        r.emplace( x2 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value(), 2 );
+    }
+
+    {
+        result<int&> r( ENOENT, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+
+        int x2 = 2;
+        r.emplace( x2 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( r.value(), 2 );
+    }
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<int&, Y> r( in_place_error );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST_EQ( Y::instances, 1 );
+
+        int x2 = 2;
+        r.emplace( x2 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( *r, 2 );
+        BOOST_TEST_EQ( Y::instances, 0 );
+    }
+
+    return boost::report_errors();
+}

test/result_eq.cpp

@@ -0,0 +1,231 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <iosfwd>
+#include <cerrno>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    explicit X( int v ): v_( v ) { ++instances; }
+
+    X( X const& r ) = delete;
+    X( X&& r ): v_( r.v_ ) { r.v_ = 0; ++instances; }
+
+    X& operator=( X const& ) = delete;
+
+    X& operator=( X&& r )
+    {
+        v_ = r.v_;
+        r.v_ = 0;
+
+        return *this;
+    }
+
+    ~X() { --instances; }
+};
+
+bool operator==( X const & x1, X const & x2 )
+{
+    return x1.v_ == x2.v_;
+}
+
+std::ostream& operator<<( std::ostream& os, X const & x )
+{
+    os << "X:" << x.v_;
+    return os;
+}
+
+int X::instances = 0;
+
+struct Y
+{
+    static int instances;
+
+    int v_;
+
+    explicit Y( int v = 0 ): v_( v ) { ++instances; }
+
+    Y( Y const& r ) noexcept: v_( r.v_ ) { ++instances; }
+    Y( Y&& r ) noexcept: v_( r.v_ ) { r.v_ = 0; ++instances; }
+
+    Y& operator=( Y const& ) = default;
+
+    Y& operator=( Y&& r )
+    {
+        v_ = r.v_;
+        r.v_ = 0;
+
+        return *this;
+    }
+
+    ~Y() { --instances; }
+};
+
+bool operator==( Y const & y1, Y const & y2 )
+{
+    return y1.v_ == y2.v_;
+}
+
+std::ostream& operator<<( std::ostream& os, Y const & y )
+{
+    os << "Y:" << y.v_;
+    return os;
+}
+
+int Y::instances = 0;
+
+int main()
+{
+    {
+        result<int> r1( 1 );
+        result<int> r2( 2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        result<int> r1( 1, generic_category() );
+        result<int> r2( 2, generic_category() );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        result<int> r1( 1 );
+        result<int> r2( 2, generic_category() );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        result<X, Y> r1( in_place_value, 1 );
+        result<X, Y> r2( in_place_value, 2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        result<X, Y> r1( in_place_error, 1 );
+        result<X, Y> r2( in_place_error, 2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        result<X, Y> r1( in_place_value, 1 );
+        result<X, Y> r2( in_place_error, 2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        result<void> r1;
+        result<void> r2;
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        result<void> r1( 1, generic_category() );
+        result<void> r2( 2, generic_category() );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r1( x1 );
+        result<int&> r2( x2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( x2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        result<int&> r1( 1, generic_category() );
+        result<int&> r2( 2, generic_category() );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( 2, generic_category() );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        X x1( 1 );
+        X x2( 2 );
+
+        result<X&, Y> r1( x1 );
+        result<X&, Y> r2( x2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        X x1( 1 );
+        X x2( 1 );
+
+        result<X&, Y> r1( x1 );
+        result<X&, Y> r2( x2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        result<X&, Y> r1( in_place_error, 1 );
+        result<X&, Y> r2( in_place_error, 2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        X x1( 1 );
+
+        result<X&, Y> r1( x1 );
+        result<X&, Y> r2( in_place_error, 2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    return boost::report_errors();
+}

test/result_errc_construct.cpp

@@ -0,0 +1,32 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+
+using namespace boost::system;
+
+int main()
+{
+    BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<int>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int>, errc::errc_t>));
+
+    BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<double>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<double>, errc::errc_t>));
+
+    BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<bool>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, errc::errc_t>));
+
+    BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<int const&>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&>, errc::errc_t>));
+
+    BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<double const&>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<double const&>, errc::errc_t>));
+
+    BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<bool const&>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const&>, errc::errc_t>));
+
+    return boost::report_errors();
+}

test/result_error_access.cpp

@@ -0,0 +1,280 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <string>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+
+    explicit X( int v = 0 ): v_( v ) {}
+
+    X( X const& ) = default;
+    X& operator=( X const& ) = delete;
+};
+
+int main()
+{
+    {
+        result<int> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        result<int> const r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        BOOST_TEST( result<int>().has_value() );
+        BOOST_TEST( !result<int>().has_error() );
+
+        BOOST_TEST_EQ( result<int>().error(), error_code() );
+    }
+
+    {
+        result<int> r( 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        BOOST_TEST( result<int>( 1 ).has_value() );
+        BOOST_TEST( !result<int>( 1 ).has_error() );
+
+        BOOST_TEST_EQ( result<int>( 1 ).error(), error_code() );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> const r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        BOOST_TEST( !result<int>( ec ).has_value() );
+        BOOST_TEST( result<int>( ec ).has_error() );
+
+        BOOST_TEST_EQ( result<int>( ec ).error(), ec );
+    }
+
+    {
+        result<std::string, X> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1 );
+    }
+
+    {
+        result<std::string, X> const r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1 );
+    }
+
+    {
+        BOOST_TEST(( !result<std::string, X>( 1 ).has_value() ));
+        BOOST_TEST(( result<std::string, X>( 1 ).has_error() ));
+
+        BOOST_TEST_EQ( (result<std::string, X>( 1 ).error().v_), 1 );
+    }
+
+    {
+        result<std::string, X> r( "s" );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 0 );
+    }
+
+    {
+        result<std::string, X> const r( "s" );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 0 );
+    }
+
+    {
+        BOOST_TEST(( result<std::string, X>( "s" ).has_value() ));
+        BOOST_TEST(( !result<std::string, X>( "s" ).has_error() ));
+
+        BOOST_TEST_EQ( (result<std::string, X>( "s" ).error().v_), 0 );
+    }
+
+    //
+
+    {
+        result<void> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        result<void> const r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        BOOST_TEST( result<void>().has_value() );
+        BOOST_TEST( !result<void>().has_error() );
+
+        BOOST_TEST_EQ( result<void>().error(), error_code() );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> const r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        BOOST_TEST( !result<void>( ec ).has_value() );
+        BOOST_TEST( result<void>( ec ).has_error() );
+
+        BOOST_TEST_EQ( result<void>( ec ).error(), ec );
+    }
+
+    //
+
+    {
+        int x1 = 1;
+
+        result<int&> r( x1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r( x1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        int x1 = 1;
+
+        BOOST_TEST( result<int&>( x1 ).has_value() );
+        BOOST_TEST( !result<int&>( x1 ).has_error() );
+
+        BOOST_TEST_EQ( result<int&>( x1 ).error(), error_code() );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> const r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        BOOST_TEST( !result<int&>( ec ).has_value() );
+        BOOST_TEST( result<int&>( ec ).has_error() );
+
+        BOOST_TEST_EQ( result<int&>( ec ).error(), ec );
+    }
+
+    //
+
+    return boost::report_errors();
+}

test/result_error_construct.cpp

@@ -0,0 +1,191 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <string>
+#include <cerrno>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    X(): v_() { ++instances; }
+
+    explicit X( int v ): v_( v ) { ++instances; }
+
+    X( int v1, int v2 ): v_( v1+v2 ) { ++instances; }
+    X( int v1, int v2, int v3 ): v_( v1+v2+v3 ) { ++instances; }
+
+    X( X const& r ): v_( r.v_ ) { ++instances; }
+
+    X& operator=( X const& ) = delete;
+
+    ~X() { --instances; }
+};
+
+int X::instances = 0;
+
+int main()
+{
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r = ec;
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        result<int> r( EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<error_code> r( in_place_error, ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        result<error_code> r( in_place_error, EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<std::string, X> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<int, X> r( 1, 2 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1+2 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<int, X> r( 1, 2, 3 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1+2+3 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X, X> r( in_place_error, 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<int>, error_code>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<error_code, result<int>>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<std::string, X>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<std::string, X>>));
+
+        // We'd like this to be false due to the ambiguity caused by X having
+        // an explicit constructor taking an int, which should be viable in this
+        // context, but the implicit constructor is enabled, and there's no way to
+        // disallow it
+        //
+        // BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int, X>, int>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<int, result<int, X>>));
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r = ec;
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        result<void> r( EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    return boost::report_errors();
+}

test/result_error_construct2.cpp

@@ -0,0 +1,57 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <string>
+
+using namespace boost::system;
+
+struct X
+{
+    int a, b;
+};
+
+result<X> fx1()
+{
+    return {{ EINVAL, generic_category() }};
+}
+
+struct Y
+{
+    std::string v;
+};
+
+struct E
+{
+    int v;
+};
+
+result<Y, E> fy1()
+{
+    return {{ 42 }};
+}
+
+int main()
+{
+    {
+        result<X> r = fx1();
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    {
+        result<Y, E> r = fy1();
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v, 42 );
+    }
+
+    return boost::report_errors();
+}

test/result_error_construct3.cpp

@@ -0,0 +1,183 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <string>
+#include <cerrno>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    X(): v_() { ++instances; }
+
+    explicit X( int v ): v_( v ) { ++instances; }
+
+    X( int v1, int v2 ): v_( v1+v2 ) { ++instances; }
+    X( int v1, int v2, int v3 ): v_( v1+v2+v3 ) { ++instances; }
+
+    X( X const& r ): v_( r.v_ ) { ++instances; }
+
+    X& operator=( X const& ) = delete;
+
+    ~X() { --instances; }
+};
+
+int X::instances = 0;
+
+int main()
+{
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        using R = result<int>;
+        R r( R::in_place_error, ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        using R = result<int>;
+        R r( R::in_place_error, EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        using R = result<error_code>;
+        R r( R::in_place_error, ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        using R = result<error_code>;
+        R r( R::in_place_error, EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        using R = result<std::string, X>;
+        R r( R::in_place_error, 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        using R = result<int, X>;
+        R r( R::in_place_error, 1, 2 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1+2 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        using R = result<int, X>;
+        R r( R::in_place_error, 1, 2, 3 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1+2+3 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        using R = result<X, X>;
+        R r( R::in_place_error, 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        using R = result<void>;
+        R r( R::in_place_error, ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        using R = result<void>;
+        R r( R::in_place_error, EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        using R = result<int&>;
+        R r( R::in_place_error, ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        using R = result<int&>;
+        R r( R::in_place_error, EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    return boost::report_errors();
+}

test/result_error_construct4.cpp

@@ -0,0 +1,49 @@
+// Copyright 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+// Eigen::Matrix4d has an explicit templated constructor
+// https://github.com/boostorg/system/issues/103
+// https://github.com/boostorg/json/issues/843
+
+struct X
+{
+    X() {}
+    template<class T> explicit X( T const& ) {}
+};
+
+int main()
+{
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> r = ec;
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    {
+        auto ec = make_error_code( std::errc::invalid_argument );
+
+        result<X> r = ec;
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+#endif
+
+    return boost::report_errors();
+}

test/result_error_construct5.cpp

@@ -0,0 +1,160 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <string>
+#include <cerrno>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    X(): v_() { ++instances; }
+
+    explicit X( int v ): v_( v ) { ++instances; }
+
+    X( int v1, int v2 ): v_( v1+v2 ) { ++instances; }
+    X( int v1, int v2, int v3 ): v_( v1+v2+v3 ) { ++instances; }
+
+    X( X const& r ): v_( r.v_ ) { ++instances; }
+
+    X& operator=( X const& ) = delete;
+
+    ~X() { --instances; }
+};
+
+int X::instances = 0;
+
+int main()
+{
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r = ec;
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        result<int&> r( EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<error_code&> r( in_place_error, ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        result<error_code&> r( in_place_error, EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code( EINVAL, generic_category() ) );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<std::string&, X> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<int&, X> r( 1, 2 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1+2 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<int&, X> r( 1, 2, 3 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1+2+3 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X&, X> r( in_place_error, 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<int&>, error_code>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<error_code, result<int&>>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<std::string&, X>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<std::string&, X>>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<int&, X>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<int&, X>>));
+
+        // There's an ambiguity here between int& and X, but since is_convertible
+        // is true, is_constructible can't be false.
+
+        // BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int&, X>, int&>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<int&, result<int&, X>>));
+    }
+
+    return boost::report_errors();
+}

test/result_error_move.cpp

@@ -0,0 +1,133 @@
+// Copyright 2023 Klemens Morgenstern
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <string>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+
+    explicit X( int v = 0 ): v_( v ) {}
+
+    X( X const& ) = delete;
+    X& operator=( X const& ) = delete;
+
+    X( X && ) = default;
+    X& operator=( X && ) = default;
+};
+
+int main()
+{
+    {
+        result<std::string, X> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 1 );
+    }
+
+    {
+        BOOST_TEST(( !result<std::string, X>( 1 ).has_value() ));
+        BOOST_TEST(( result<std::string, X>( 1 ).has_error() ));
+
+        BOOST_TEST_EQ( (result<std::string, X>( 1 ).error().v_), 1 );
+    }
+
+    {
+        result<std::string, X> r( "s" );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 0 );
+    }
+
+    {
+        BOOST_TEST(( result<std::string, X>( "s" ).has_value() ));
+        BOOST_TEST(( !result<std::string, X>( "s" ).has_error() ));
+
+        BOOST_TEST_EQ( (result<std::string, X>( "s" ).error().v_), 0 );
+    }
+
+    //
+
+    {
+        result<void, X> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 1 );
+    }
+
+    {
+        BOOST_TEST(( !result<void, X>( 1 ).has_value() ));
+        BOOST_TEST(( result<void, X>( 1 ).has_error() ));
+
+        BOOST_TEST_EQ( (result<void, X>( 1 ).error().v_), 1 );
+    }
+
+    {
+        result<void, X> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 0 );
+    }
+
+    {
+        BOOST_TEST(( result<void, X>().has_value() ));
+        BOOST_TEST(( !result<void, X>().has_error() ));
+
+        BOOST_TEST_EQ( (result<void, X>().error().v_), 0 );
+    }
+
+    //
+
+    {
+        result<double&, X> r( 1 );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 1 );
+    }
+
+    {
+        BOOST_TEST(( !result<double&, X>( 1 ).has_value() ));
+        BOOST_TEST(( result<double&, X>( 1 ).has_error() ));
+
+        BOOST_TEST_EQ( (result<double&, X>( 1 ).error().v_), 1 );
+    }
+
+    {
+        double x = 1.0;
+
+        result<double&, X> r( x );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( std::move( r ).error().v_, 0 );
+    }
+
+    {
+        double x = 1.0;
+
+        BOOST_TEST(( result<double&, X>( x ).has_value() ));
+        BOOST_TEST(( !result<double&, X>( x ).has_error() ));
+
+        BOOST_TEST_EQ( (result<double&, X>( x ).error().v_), 0 );
+    }
+
+    //
+
+    return boost::report_errors();
+}

test/result_move_assign.cpp

@@ -0,0 +1,711 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <iosfwd>
+#include <cerrno>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    explicit X( int v = 0 ): v_( v ) { ++instances; }
+
+    X( X const& r ) = delete;
+    X( X&& r ): v_( r.v_ ) { r.v_ = 0; ++instances; }
+
+    X& operator=( X const& ) = delete;
+
+    X& operator=( X&& r )
+    {
+        v_ = r.v_;
+        r.v_ = 0;
+
+        return *this;
+    }
+
+    ~X() { --instances; }
+};
+
+bool operator==( X const & x1, X const & x2 )
+{
+    return x1.v_ == x2.v_;
+}
+
+std::ostream& operator<<( std::ostream& os, X const & x )
+{
+    os << "X:" << x.v_;
+    return os;
+}
+
+int X::instances = 0;
+
+struct Y
+{
+    static int instances;
+
+    int v_;
+
+    explicit Y( int v = 0 ): v_( v ) { ++instances; }
+
+    Y( Y const& r ) noexcept: v_( r.v_ ) { ++instances; }
+    Y( Y&& r ) noexcept: v_( r.v_ ) { r.v_ = 0; ++instances; }
+
+    Y& operator=( Y const& ) = default;
+
+    Y& operator=( Y&& r )
+    {
+        v_ = r.v_;
+        r.v_ = 0;
+
+        return *this;
+    }
+
+    ~Y() { --instances; }
+};
+
+bool operator==( Y const & y1, Y const & y2 )
+{
+    return y1.v_ == y2.v_;
+}
+
+std::ostream& operator<<( std::ostream& os, Y const & y )
+{
+    os << "Y:" << y.v_;
+    return os;
+}
+
+int Y::instances = 0;
+
+int main()
+{
+    // default-initialized lhs
+
+    {
+        result<int> r;
+        result<int> r2;
+
+        r2 = std::move( r );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 0 );
+    }
+
+    {
+        result<int> r2;
+
+        r2 = result<int>();
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 0 );
+    }
+
+    {
+        result<int> r;
+        result<int> r2( 1 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 0 );
+    }
+
+    {
+        result<int> r2( 1 );
+
+        r2 = result<int>();
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 0 );
+    }
+
+    {
+        result<int> r;
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = std::move( r );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 0 );
+    }
+
+    {
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = result<int>();
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r;
+        result<X> r2;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), X() );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r;
+        result<X> r2( 1 );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), X() );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r;
+        result<X> r2( ENOENT, generic_category() );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), X() );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    // value lhs
+
+    {
+        result<int> r( 1 );
+        result<int> r2;
+
+        r2 = std::move( r );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> r( 1 );
+        result<int> r2( 2 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    {
+        result<int> r( 1 );
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = std::move( r );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+
+        BOOST_TEST_EQ( r, r2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1 );
+        result<X> r2;
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+
+        BOOST_TEST_EQ( r.value().v_, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1 );
+        result<X> r2( 2 );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+
+        BOOST_TEST_EQ( r.value().v_, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1 );
+        result<X> r2( ENOENT, generic_category() );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+
+        BOOST_TEST_EQ( r.value().v_, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    // error lhs
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<int> r2;
+
+        r2 = std::move( r );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r2;
+
+        r2 = result<int>( ec );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<int> r2( 1 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r2( 1 );
+
+        r2 = result<int>( ec );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = std::move( r );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r2( ENOENT, generic_category() );
+
+        r2 = result<int>( ec );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> r( ec );
+        result<X> r2;
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> r( ec );
+        result<X> r2( 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> r( ec );
+        result<X> r2( ENOENT, generic_category() );
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( X::instances, 0 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<std::string, Y> r( 1 );
+        result<std::string, Y> r2( 2 );
+
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error().v_, 1 );
+
+        BOOST_TEST_EQ( r.error().v_, 0 );
+    }
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<std::string, Y> r( 1 );
+        result<std::string, Y> r2( "str" );
+
+        BOOST_TEST_EQ( Y::instances, 1 );
+
+        r2 = std::move( r );
+
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error().v_, 1 );
+
+        BOOST_TEST_EQ( r.error().v_, 0 );
+    }
+
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    //
+
+    {
+        result<void> r;
+        result<void> r2;
+
+        r2 = std::move( r );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+    }
+
+    {
+        result<void> r2;
+
+        r2 = result<void>();
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+    }
+
+    {
+        result<void> r;
+        result<void> r2( ENOENT, generic_category() );
+
+        r2 = std::move( r );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+    }
+
+    {
+        result<void> r2( ENOENT, generic_category() );
+
+        r2 = result<void>();
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r( ec );
+        result<void> r2;
+
+        r2 = std::move( r );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r2;
+
+        r2 = result<void>( ec );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r( ec );
+        result<void> r2( ENOENT, generic_category() );
+
+        r2 = std::move( r );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r2( ENOENT, generic_category() );
+
+        r2 = result<void>( ec );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    //
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r1( x1 );
+        result<int&> r2( x2 );
+
+        r2 = std::move( r1 );
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = std::move( r1 );
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( x1 );
+
+        r2 = std::move( r1 );
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        int x1 = 1;
+
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r2( x1 );
+
+        r2 = result<int&>( ec );
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = std::move( r1 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = result<int&>( ec );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    //
+
+    return boost::report_errors();
+}

test/result_move_construct.cpp

@@ -0,0 +1,395 @@
+// Copyright 2017, 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    static int instances;
+
+    int v_;
+
+    X(): v_() { ++instances; }
+
+    explicit X( int v ): v_( v ) { ++instances; }
+
+    X( int v1, int v2 ): v_( v1+v2 ) { ++instances; }
+    X( int v1, int v2, int v3 ): v_( v1+v2+v3 ) { ++instances; }
+
+    X( X const& r ): v_( r.v_ ) { ++instances; }
+    X( X&& r ): v_( r.v_ ) { r.v_ = 0; ++instances; }
+
+    X& operator=( X const& ) = delete;
+
+    ~X() { --instances; }
+};
+
+bool operator==( X const & x1, X const & x2 )
+{
+    return x1.v_ == x2.v_;
+}
+
+std::ostream& operator<<( std::ostream& os, X const & x )
+{
+    os << "X:" << x.v_;
+    return os;
+}
+
+int X::instances = 0;
+
+int main()
+{
+    {
+        result<int> r;
+        result<int> r2( std::move( r ) );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 0 );
+    }
+
+    {
+        result<int> r2( result<int>{} );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r;
+        result<X> r2( std::move( r ) );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), X() );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r2( result<X>{} );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), X() );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<int> r( 1 );
+        result<int> r2( std::move( r ) );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+    }
+
+    {
+        result<int> r2( result<int>( 1 ) );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1 );
+        result<X> r2( std::move( r ) );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value().v_, 0 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r2( result<X>( 1 ) );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+        result<int> r2( std::move( r ) );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r2( result<int>{ ec } );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<std::string, X> r( 1 );
+        result<std::string, X> r2( std::move( r ) );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error().v_, 0 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<std::string, X> r2( result<std::string, X>( 1 ) );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
+    {
+        result<void> r;
+        result<void> r2( std::move( r ) );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+    }
+
+    {
+        result<void> r2( result<void>{} );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r( ec );
+        result<void> r2( std::move( r ) );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r2( result<void>{ ec } );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    //
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( std::move( r1 ) );
+
+        BOOST_TEST( r1.has_value() );
+        BOOST_TEST( !r1.has_error() );
+
+        BOOST_TEST_EQ( r1.value(), 1 );
+        BOOST_TEST_EQ( &*r1, &x1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int const x1 = 1;
+
+        result<int const&> r1( x1 );
+        result<int const&> r2( std::move( r1 ) );
+
+        BOOST_TEST( r1.has_value() );
+        BOOST_TEST( !r1.has_error() );
+
+        BOOST_TEST_EQ( r1.value(), 1 );
+        BOOST_TEST_EQ( &*r1, &x1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r2(( result<int&>( x1 ) ));
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int const x1 = 1;
+
+        result<int const&> r2(( result<int const&>( x1 ) ));
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        X x1( 1 );
+
+        result<X&> r1( x1 );
+        result<X&> r2( std::move( r1 ) );
+
+        BOOST_TEST( r1.has_value() );
+        BOOST_TEST( !r1.has_error() );
+
+        BOOST_TEST_EQ( r1.value().v_, 1 );
+        BOOST_TEST_EQ( &*r1, &x1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X x1( 1 );
+
+        result<X&> r2(( result<X&>( x1 ) ));
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X const x1( 1 );
+
+        result<X const&> r1( x1 );
+        result<X const&> r2( std::move( r1 ) );
+
+        BOOST_TEST( r1.has_value() );
+        BOOST_TEST( !r1.has_error() );
+
+        BOOST_TEST_EQ( r1.value().v_, 1 );
+        BOOST_TEST_EQ( &*r1, &x1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X const x1( 1 );
+
+        result<X const&> r2(( result<X const&>( x1 ) ));
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
+    return boost::report_errors();
+}

test/result_or_fn0r.cpp

@@ -0,0 +1,359 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& ) = delete;
+};
+
+struct E
+{
+};
+
+result<int, E> fi()
+{
+    return 2;
+}
+
+result<int, E> fi2()
+{
+    return E();
+}
+
+result<Y, E> fy()
+{
+    return Y{ 2 };
+}
+
+result<Y, E> fy2()
+{
+    return E();
+}
+
+result<int&, E> fri()
+{
+    static int x = 2;
+    return x;
+}
+
+result<int&, E> fri2()
+{
+    return E();
+}
+
+result<void, E> fv()
+{
+    return {};
+}
+
+result<void, E> fv2()
+{
+    return E();
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        int x = r | fi | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        int x = r | fi | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        int x = result<int>( 1 ) | fi | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> r( 1 );
+
+        int x = r | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        int x = r | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        int x = result<int>( 1 ) | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> r( in_place_error );
+
+        int x = r | fi | 3;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        result<int> const r( in_place_error );
+
+        int x = r | fi | 3;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        int x = result<int>( in_place_error ) | fi | 3;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        result<int> r( in_place_error );
+
+        int x = r | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 3 );
+    }
+
+    {
+        result<int> const r( in_place_error );
+
+        int x = r | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 3 );
+    }
+
+    {
+        int x = result<int>( in_place_error ) | fi2 | 3;
+
+        BOOST_TEST_EQ( x, 3 );
+    }
+
+    {
+        Y y = result<X>( X{1} ) | fy | X{3};
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<X>( X{1} ) | fy2 | X{3};
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<X, E>( in_place_error ) | fy | X{3};
+
+        BOOST_TEST_EQ( y.v_, 2 );
+    }
+
+    {
+        Y y = result<X, E>( in_place_error ) | fy2 | Y{3};
+
+        BOOST_TEST_EQ( y.v_, 3 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        result<int&> r( x1 );
+
+        int& x = r | fri | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        result<int&> const r( x1 );
+
+        int& x = r | fri | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        int& x = result<int&>( x1 ) | fri | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        result<int&> r( x1 );
+
+        int& x = r | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        result<int&> const r( x1 );
+
+        int& x = r | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x3 = 3;
+
+        int& x = result<int&>( x1 ) | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x3 = 3;
+
+        result<int&, E> r( in_place_error );
+
+        int& x = r | fri | x3;
+
+        BOOST_TEST_EQ( &x, &*fri() );
+    }
+
+    {
+        int x3 = 3;
+
+        result<int&, E> const r( in_place_error );
+
+        int& x = r | fri | x3;
+
+        BOOST_TEST_EQ( &x, &*fri() );
+    }
+
+    {
+        int x3 = 3;
+
+        int& x = result<int&, E>( in_place_error ) | fri | x3;
+
+        BOOST_TEST_EQ( &x, &*fri() );
+    }
+
+    {
+        int x3 = 3;
+
+        result<int&, E> r( in_place_error );
+
+        int& x = r | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x3 );
+    }
+
+    {
+        int x3 = 3;
+
+        result<int&, E> const r( in_place_error );
+
+        int& x = r | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x3 );
+    }
+
+    {
+        int x3 = 3;
+
+        int& x = result<int&, E>( in_place_error ) | fri2 | x3;
+
+        BOOST_TEST_EQ( &x, &x3 );
+    }
+
+    {
+        result<void> r;
+        result<void, E> r2 = r | fv;
+
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void> r;
+        result<void, E> r2 = r | fv2;
+
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void> r( in_place_error );
+        result<void, E> r2 = r | fv;
+
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void> r( in_place_error );
+        result<void, E> r2 = r | fv2;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E> r2 = result<void>() | fv;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void, E> r2 = result<void>() | fv2;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void, E> r2 = result<void>( in_place_error ) | fv;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void, E> r2 = result<void>( in_place_error ) | fv2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_or_fn0v.cpp

@@ -0,0 +1,162 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& ) = delete;
+};
+
+struct E
+{
+};
+
+int f()
+{
+    return 2;
+}
+
+X g()
+{
+    return { 2 };
+}
+
+int& h()
+{
+    static int x = 2;
+    return x;
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        int x = r | f;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        int x = r | f;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        int x = result<int>( 1 ) | f;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        int x = r | f;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+
+        int x = r | f;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        int x = result<int, E>( in_place_error ) | f;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        Y y = result<Y>( in_place_value, 1 ) | g;
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<Y, E>( in_place_error ) | g;
+
+        BOOST_TEST_EQ( y.v_, 2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r( x1 );
+
+        int& x = r | h;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r( x1 );
+
+        int& x = r | h;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+
+        int& x = result<int&>( x1 ) | h;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        int& x = r | h;
+
+        BOOST_TEST_EQ( &x, &h() );
+    }
+
+    {
+        result<int&, E> const r( in_place_error );
+
+        int& x = r | h;
+
+        BOOST_TEST_EQ( &x, &h() );
+    }
+
+    {
+        int& x = result<int&, E>( in_place_error ) | h;
+
+        BOOST_TEST_EQ( &x, &h() );
+    }
+
+    return boost::report_errors();
+}

test/result_or_value.cpp

@@ -0,0 +1,167 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& ) = delete;
+};
+
+struct E
+{
+};
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        int x = r | 2;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        int x = r | 2;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        int x = result<int>( 1 ) | 2;
+
+        BOOST_TEST_EQ( x, 1 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        int x = r | 2;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+
+        int x = r | 2;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        int x = result<int, E>( in_place_error ) | 2;
+
+        BOOST_TEST_EQ( x, 2 );
+    }
+
+    {
+        Y y = result<Y>( in_place_value, 1 ) | Y{2};
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<Y, E>( in_place_error ) | Y{2};
+
+        BOOST_TEST_EQ( y.v_, 2 );
+    }
+
+    {
+        Y y = result<Y>( in_place_value, 1 ) | X{2};
+
+        BOOST_TEST_EQ( y.v_, 1 );
+    }
+
+    {
+        Y y = result<Y, E>( in_place_error ) | X{2};
+
+        BOOST_TEST_EQ( y.v_, 2 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r( x1 );
+
+        int& x = r | x2;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> const r( x1 );
+
+        int& x = r | x2;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        int& x = result<int&>( x1 ) | x2;
+
+        BOOST_TEST_EQ( &x, &x1 );
+    }
+
+    {
+        int x2 = 2;
+
+        result<int&, E> r( in_place_error );
+
+        int& x = r | x2;
+
+        BOOST_TEST_EQ( &x, &x2 );
+    }
+
+    {
+        int x2 = 2;
+
+        result<int&, E> const r( in_place_error );
+
+        int& x = r | x2;
+
+        BOOST_TEST_EQ( &x, &x2 );
+    }
+
+    {
+        int x2 = 2;
+
+        int& x = result<int&, E>( in_place_error ) | x2;
+
+        BOOST_TEST_EQ( &x, &x2 );
+    }
+
+    return boost::report_errors();
+}

test/result_or_value_fail.cpp

@@ -0,0 +1,14 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+
+using namespace boost::system;
+
+int main()
+{
+    int x = 1;
+    result<int const&> r( x );
+    r | 2;
+}

test/result_or_value_fail2.cpp

@@ -0,0 +1,13 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+
+using namespace boost::system;
+
+int main()
+{
+    int x = 1;
+    result<int const&>( x ) | 2;
+}

test/result_range_for.cpp

@@ -0,0 +1,30 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <vector>
+
+using namespace boost::system;
+
+result<std::vector<int>> f()
+{
+    return std::vector<int>{ 1, 2, 3 };
+}
+
+int main()
+{
+    {
+        int s = 0;
+
+        for( int x: f().value() )
+        {
+            s += x;
+        }
+
+        BOOST_TEST_EQ( s, 6 );
+    }
+
+    return boost::report_errors();
+}