Add detail::system_error_category_message, use it in error_code::message

This fixes a regression from commit
a9b64a888a.
Calling `operator<<` with `std::string` only works for `std::ostream`.
Use `c_str()` to restore the previous behavior of using `const char*`,
which works for any `basic_ostream` specialization.

.github/workflows/ci.yml

@@ -0,0 +1,355 @@
+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-18.04
+            install: g++-4.8
+          - toolset: gcc-5
+            cxxstd: "03,11,14,1z"
+            os: ubuntu-18.04
+            install: g++-5
+          - toolset: gcc-6
+            cxxstd: "03,11,14,1z"
+            os: ubuntu-18.04
+            install: g++-6
+          - toolset: gcc-7
+            cxxstd: "03,11,14,17"
+            os: ubuntu-18.04
+          - toolset: gcc-8
+            cxxstd: "03,11,14,17,2a"
+            os: ubuntu-18.04
+            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: clang
+            compiler: clang++-3.9
+            cxxstd: "03,11,14"
+            os: ubuntu-18.04
+            install: clang-3.9
+          - toolset: clang
+            compiler: clang++-4.0
+            cxxstd: "03,11,14"
+            os: ubuntu-18.04
+            install: clang-4.0
+          - toolset: clang
+            compiler: clang++-5.0
+            cxxstd: "03,11,14,1z"
+            os: ubuntu-18.04
+            install: clang-5.0
+          - toolset: clang
+            compiler: clang++-6.0
+            cxxstd: "03,11,14,17"
+            os: ubuntu-18.04
+            install: clang-6.0
+          - toolset: clang
+            compiler: clang++-7
+            cxxstd: "03,11,14,17"
+            os: ubuntu-18.04
+            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: "03,11,14,17,2a"
+            os: ubuntu-20.04
+          - toolset: clang
+            cxxstd: "03,11,14,17,2a"
+            os: macos-10.15
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install packages
+        if: matrix.install
+        run: sudo apt 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
+          ./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-14.1
+            cxxstd: "14,17,latest"
+            addrmd: 32,64
+            os: windows-2016
+          - toolset: msvc-14.2
+            cxxstd: "14,17,latest"
+            addrmd: 32,64
+            os: windows-2019
+          - toolset: msvc-14.3
+            cxxstd: "14,17,latest"
+            addrmd: 32,64
+            os: windows-2022
+          - toolset: gcc
+            cxxstd: "03,11,14,17,2a"
+            addrmd: 64
+            os: windows-2019
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+          cmd /c bootstrap
+          b2 -d0 headers
+
+      - name: Run tests
+        shell: cmd
+        run: |
+          cd ../boost-root
+          b2 -j3 libs/%LIBRARY%/test toolset=${{matrix.toolset}} cxxstd=${{matrix.cxxstd}} address-model=${{matrix.addrmd}} variant=debug,release
+
+  posix-cmake-subdir:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-18.04
+          - os: ubuntu-20.04
+          - os: macos-10.15
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install packages
+        if: matrix.install
+        run: sudo apt 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-18.04
+          - os: ubuntu-20.04
+          - os: macos-10.15
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install packages
+        if: matrix.install
+        run: sudo apt 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-18.04
+          - os: ubuntu-20.04
+          - os: macos-10.15
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install packages
+        if: matrix.install
+        run: sudo apt 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

.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

@@ -1,4 +1,4 @@
-# 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
 
@@ -13,7 +13,10 @@ target_include_directories(boost_system INTERFACE include)
 
 target_link_libraries(boost_system
   INTERFACE
+    Boost::assert
     Boost::config
+    Boost::throw_exception
+    Boost::variant2
     Boost::winapi
 )
 

appveyor.yml

@@ -16,20 +16,17 @@ 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
+      CXXSTD: 14,17,latest
       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
+      TOOLSET: clang-win
+      CXXSTD: 14,17,latest
       ADDRMD: 32,64
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
       ADDPATH: C:\cygwin\bin;
@@ -66,4 +63,4 @@ 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
+  - b2 -j3 libs/system/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% variant=debug,release embed-manifest-via=linker

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 +1,64 @@
 ////
-Copyright 2018 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
+https://www.boost.org/LICENSE_1_0.txt
 ////
 
 [#changes]
 # Revision History
 :idprefix:
 
+## 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 2018-2021 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`.

include/boost/system.hpp

@@ -0,0 +1,17 @@
+#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>
+
+#if (__cplusplus >= 201103L) || (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

@@ -13,20 +13,10 @@
 
 // BOOST_SYSTEM_HAS_SYSTEM_ERROR
 
-#if !defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR)
+#if !defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR) && !defined(BOOST_NO_CXX11_HDR_ATOMIC)
 # 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 +38,28 @@
 # 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
+
+#if defined(__clang__) && (__clang_major__ < 7 || (defined(__APPLE__) && __clang_major__ < 11))
+# define BOOST_SYSTEM_CLANG_6
+#endif
+
 #endif // BOOST_SYSTEM_DETAIL_CONFIG_HPP_INCLUDED

include/boost/system/detail/error_category.hpp

@@ -19,6 +19,7 @@
 
 #if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
 # include <system_error>
+# include <atomic>
 #endif
 
 namespace boost
@@ -38,11 +39,7 @@ 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
 
@@ -58,9 +55,8 @@ 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 +76,16 @@ private:
 
     boost::ulong_long_type id_;
 
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    mutable std::atomic< boost::system::detail::std_category* > ps_;
+
+#else
+
+    boost::system::detail::std_category* ps_;
+
+#endif
+
 protected:
 
 #if !defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) && !defined(BOOST_NO_CXX11_NON_PUBLIC_DEFAULTED_FUNCTIONS)
@@ -97,11 +103,11 @@ protected:
 
 #endif
 
-    BOOST_SYSTEM_CONSTEXPR error_category() BOOST_NOEXCEPT: id_( 0 )
+    BOOST_SYSTEM_CONSTEXPR error_category() BOOST_NOEXCEPT: id_( 0 ), ps_()
     {
     }
 
-    explicit BOOST_SYSTEM_CONSTEXPR error_category( boost::ulong_long_type id ) BOOST_NOEXCEPT: id_( id )
+    explicit BOOST_SYSTEM_CONSTEXPR error_category( boost::ulong_long_type id ) BOOST_NOEXCEPT: id_( id ), ps_()
     {
     }
 
@@ -121,24 +127,24 @@ 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;
         }
@@ -148,13 +154,15 @@ 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)
-
+# 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
 };
 
@@ -165,8 +173,9 @@ 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 +13,13 @@
 #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/config.hpp>
 #include <string>
 #include <cstring>
 
 namespace boost
 {
-
 namespace system
 {
 
@@ -37,7 +37,7 @@ 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 +83,84 @@ 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.hpp>
 
-inline boost::system::error_category::operator std::error_category const & () const
+namespace boost
 {
-    return boost::system::detail::to_std_category( *this );
+namespace system
+{
+
+inline 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_GCC) && BOOST_GCC < 50000
+
+    static const boost::system::detail::std_category generic_instance( this, 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(__CYGWIN__) || defined(__MINGW32__) || (defined(_MSC_VER) && _MSC_VER == 1800) || (defined(BOOST_GCC) && BOOST_GCC < 50000)
+
+    // Under Cygwin (and MinGW!), std::system_category() is POSIX
+    // Under VS2013, std::system_category() isn't quite right
+
+    static const boost::system::detail::std_category system_instance( this, 0x1F4D7 );
+    return system_instance;
+
+#else
+
+    return std::system_category();
+
+#endif
+    }
+
+    detail::std_category* p = ps_.load( std::memory_order_acquire );
+
+    if( p != 0 )
+    {
+        return *p;
+    }
+
+    detail::std_category* q = new detail::std_category( this, 0 );
+
+    if( ps_.compare_exchange_strong( p, q, std::memory_order_release, std::memory_order_acquire ) )
+    {
+        return *q;
+    }
+    else
+    {
+        delete q;
+        return *p;
+    }
 }
 
+} // 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 +3,39 @@
 
 //  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>
+#include <boost/assert/source_location.hpp>
 #include <boost/cstdint.hpp>
 #include <boost/config.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 +52,129 @@ namespace system
 //  and error_code containing a pointer to an object of a type derived
 //  from error_category.
 
+std::size_t hash_value( error_code const & ec );
+
 class error_code
 {
 private:
 
-    int val_;
-    bool failed_;
-    const error_category * cat_;
+    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() )
+        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 );
     }
 
+    template<class ErrorCodeEnum> error_code( ErrorCodeEnum e, source_location const * loc,
+        typename detail::enable_if<is_error_code_enum<ErrorCodeEnum>::value>::type* = 0 ) BOOST_NOEXCEPT:
+        d1_(), lc_flags_( 0 )
+    {
+        error_code e2 = make_error_code( e );
+
+        if( e2.lc_flags_ == 0 || e2.lc_flags_ == 1 )
+        {
+            *this = e2;
+        }
+        else
+        {
+            *this = error_code( e2.d1_.val_, *e2.d1_.cat_, loc );
+        }
+    }
+
+#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+    error_code( std::error_code const& ec ) BOOST_NOEXCEPT:
+        lc_flags_( 1 )
+    {
+        ::new( d2_ ) std::error_code( ec );
+    }
+
+#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 );
     }
 
     template<typename ErrorCodeEnum>
@@ -80,50 +185,145 @@ public:
         return *this;
     }
 
+    template<typename ErrorCodeEnum>
+        typename detail::enable_if<is_error_code_enum<ErrorCodeEnum>::value, void>::type
+        assign( ErrorCodeEnum val, source_location const * loc ) BOOST_NOEXCEPT
+    {
+        *this = error_code( val, loc );
+    }
+
     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 +333,353 @@ 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)
+
+        if( lhs.lc_flags_ == 1 && rhs.lc_flags_ == 1 )
+        {
+            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)
+
+        if( lhs.lc_flags_ == 1 && rhs.lc_flags_ == 1 )
+        {
+            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 );
+    }
+
+    inline friend 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 friend bool operator==( const error_condition & condition, const error_code & code ) 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 friend bool operator!=( const error_code & lhs, const error_condition & rhs ) BOOST_NOEXCEPT
+    {
+        return !( lhs == rhs );
+    }
+
+    inline friend bool operator!=( const error_condition & 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(__CYGWIN__) || defined(__MINGW32__) || (defined(_MSC_VER) && _MSC_VER == 1800) || (defined(BOOST_GCC) && BOOST_GCC < 50000)
+
+            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
-{
-    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)
-{
-    os << ec.category().name() << ':' << ec.value();
-    return os;
-}
-
 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 +709,8 @@ 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 +188,107 @@ 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_GCC) && BOOST_GCC < 50000
+
         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 );
     }
 
 #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/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

@@ -1,9 +1,9 @@
-#ifndef BOOST_SYSTEM_DETAIL_TO_STD_CATEGORY_HPP_INCLUDED
-#define BOOST_SYSTEM_DETAIL_TO_STD_CATEGORY_HPP_INCLUDED
+#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 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)
@@ -15,9 +15,6 @@
 #include <boost/system/detail/error_code.hpp>
 #include <boost/system/detail/generic_category.hpp>
 #include <system_error>
-#include <map>
-#include <memory>
-#include <mutex>
 
 //
 
@@ -73,54 +70,6 @@ public:
     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 )
@@ -170,6 +119,7 @@ inline bool std_category::equivalent( const std::error_code & code, int conditio
         boost::system::error_code bc( code.value(), *pc2->pc_ );
         return pc_->equivalent( bc, condition );
     }
+
 #endif
 
     else if( *pc_ == boost::system::generic_category() )
@@ -188,4 +138,4 @@ inline bool std_category::equivalent( const std::error_code & code, int conditio
 
 } // namespace boost
 
-#endif // #ifndef BOOST_SYSTEM_DETAIL_TO_STD_CATEGORY_HPP_INCLUDED
+#endif // #ifndef BOOST_SYSTEM_DETAIL_STD_CATEGORY_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 +58,9 @@ 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_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;
@@ -80,7 +82,8 @@ 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 +97,16 @@ 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_SHARING_VIOLATION_: return permission_denied;
+    case ERROR_NOT_SUPPORTED_: return not_supported; // WinError.h: "The request is not supported."
     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 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/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/result.hpp

@@ -0,0 +1,528 @@
+#ifndef BOOST_SYSTEM_RESULT_HPP_INCLUDED
+#define BOOST_SYSTEM_RESULT_HPP_INCLUDED
+
+// 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/errc.hpp>
+#include <boost/system/system_error.hpp>
+#include <boost/system/detail/error_code.hpp>
+#include <boost/system/detail/error_category_impl.hpp>
+#include <boost/variant2/variant.hpp>
+#include <boost/throw_exception.hpp>
+#include <boost/assert.hpp>
+#include <boost/config.hpp>
+#include <type_traits>
+#include <utility>
+#include <iosfwd>
+
+//
+
+namespace boost
+{
+namespace system
+{
+
+// throw_exception_from_error
+
+BOOST_NORETURN inline void throw_exception_from_error( error_code const & e )
+{
+    boost::throw_exception( system_error( e ) );
+}
+
+// in_place_*
+
+using in_place_value_t = variant2::in_place_index_t<0>;
+constexpr in_place_value_t in_place_value{};
+
+using in_place_error_t = variant2::in_place_index_t<1>;
+constexpr in_place_error_t in_place_error{};
+
+namespace detail
+{
+
+template<class T> using remove_cvref = typename std::remove_cv< typename std::remove_reference<T>::type >::type;
+
+template<class... T> using is_errc_t = std::is_same<mp11::mp_list<remove_cvref<T>...>, mp11::mp_list<errc::errc_t>>;
+
+} // namespace detail
+
+// result
+
+template<class T, class E = error_code> class result
+{
+private:
+
+    variant2::variant<T, E> v_;
+
+public:
+
+    // constructors
+
+    // default
+    template<class En2 = void, class En = typename std::enable_if<
+        std::is_void<En2>::value &&
+        std::is_default_constructible<T>::value
+        >::type>
+    constexpr result()
+        noexcept( std::is_nothrow_default_constructible<T>::value )
+        : v_( in_place_value )
+    {
+    }
+
+    // implicit, value
+    template<class A = T, typename std::enable_if<
+        std::is_convertible<A, T>::value &&
+        !(detail::is_errc_t<A>::value && std::is_arithmetic<T>::value) &&
+        !std::is_constructible<E, A>::value, int>::type = 0>
+    constexpr result( A&& a )
+        noexcept( std::is_nothrow_constructible<T, A>::value )
+        : v_( in_place_value, std::forward<A>(a) )
+    {
+    }
+
+    // implicit, error
+    template<class A = E, class = void, typename std::enable_if<
+        std::is_convertible<A, E>::value &&
+        !std::is_constructible<T, A>::value, int>::type = 0>
+    constexpr result( A&& a )
+        noexcept( std::is_nothrow_constructible<E, A>::value )
+        : v_( in_place_error, std::forward<A>(a) )
+    {
+    }
+
+    // explicit, value
+    template<class... A, class En = typename std::enable_if<
+        std::is_constructible<T, A...>::value &&
+        !(detail::is_errc_t<A...>::value && std::is_arithmetic<T>::value) &&
+        !std::is_constructible<E, A...>::value
+        >::type>
+    explicit constexpr result( A&&... a )
+        noexcept( std::is_nothrow_constructible<T, A...>::value )
+        : v_( in_place_value, std::forward<A>(a)... )
+    {
+    }
+
+    // explicit, error
+    template<class... A, class En2 = void, class En = typename std::enable_if<
+        !std::is_constructible<T, A...>::value &&
+        std::is_constructible<E, A...>::value
+        >::type>
+    explicit constexpr result( A&&... a )
+        noexcept( std::is_nothrow_constructible<E, A...>::value )
+        : v_( in_place_error, std::forward<A>(a)... )
+    {
+    }
+
+    // tagged, value
+    template<class... A, class En = typename std::enable_if<
+        std::is_constructible<T, A...>::value
+        >::type>
+    constexpr result( in_place_value_t, A&&... a )
+        noexcept( std::is_nothrow_constructible<T, A...>::value )
+        : v_( in_place_value, std::forward<A>(a)... )
+    {
+    }
+
+    // tagged, error
+    template<class... A, class En = typename std::enable_if<
+        std::is_constructible<E, A...>::value
+        >::type>
+    constexpr result( in_place_error_t, A&&... a )
+        noexcept( std::is_nothrow_constructible<E, A...>::value )
+        : v_( in_place_error, std::forward<A>(a)... )
+    {
+    }
+
+    // queries
+
+    constexpr bool has_value() const noexcept
+    {
+        return v_.index() == 0;
+    }
+
+    constexpr bool has_error() const noexcept
+    {
+        return v_.index() != 0;
+    }
+
+    constexpr explicit operator bool() const noexcept
+    {
+        return v_.index() == 0;
+    }
+
+    // checked value access
+#if defined( BOOST_NO_CXX11_REF_QUALIFIERS )
+
+    BOOST_CXX14_CONSTEXPR T value() const
+    {
+        if( has_value() )
+        {
+            return variant2::unsafe_get<0>( v_ );
+        }
+        else
+        {
+            throw_exception_from_error( variant2::unsafe_get<1>( v_ ) );
+        }
+    }
+
+#else
+
+    BOOST_CXX14_CONSTEXPR T& value() &
+    {
+        if( has_value() )
+        {
+            return variant2::unsafe_get<0>( v_ );
+        }
+        else
+        {
+            throw_exception_from_error( variant2::unsafe_get<1>( v_ ) );
+        }
+    }
+
+    BOOST_CXX14_CONSTEXPR T const& value() const&
+    {
+        if( has_value() )
+        {
+            return variant2::unsafe_get<0>( v_ );
+        }
+        else
+        {
+            throw_exception_from_error( variant2::unsafe_get<1>( v_ ) );
+        }
+    }
+
+    template<class U = T>
+        BOOST_CXX14_CONSTEXPR
+        typename std::enable_if<std::is_move_constructible<U>::value, T>::type
+        value() &&
+    {
+        return std::move( value() );
+    }
+
+    template<class U = T>
+        BOOST_CXX14_CONSTEXPR
+        typename std::enable_if<!std::is_move_constructible<U>::value, T&&>::type
+        value() &&
+    {
+        return std::move( value() );
+    }
+
+    template<class U = T>
+        BOOST_CXX14_CONSTEXPR
+        typename std::enable_if<std::is_move_constructible<U>::value, T>::type
+        value() const && = delete;
+
+    template<class U = T>
+        BOOST_CXX14_CONSTEXPR
+        typename std::enable_if<!std::is_move_constructible<U>::value, T const&&>::type
+        value() const &&
+    {
+        return std::move( value() );
+    }
+
+#endif
+
+    // unchecked value access
+
+    BOOST_CXX14_CONSTEXPR T* operator->() noexcept
+    {
+        return variant2::get_if<0>( &v_ );
+    }
+
+    BOOST_CXX14_CONSTEXPR T const* operator->() const noexcept
+    {
+        return variant2::get_if<0>( &v_ );
+    }
+
+#if defined( BOOST_NO_CXX11_REF_QUALIFIERS )
+
+    BOOST_CXX14_CONSTEXPR T& operator*() noexcept
+    {
+        T* p = operator->();
+
+        BOOST_ASSERT( p != 0 );
+
+        return *p;
+    }
+
+    BOOST_CXX14_CONSTEXPR T const& operator*() const noexcept
+    {
+        T const* p = operator->();
+
+        BOOST_ASSERT( p != 0 );
+
+        return *p;
+    }
+
+#else
+
+    BOOST_CXX14_CONSTEXPR T& operator*() & noexcept
+    {
+        T* p = operator->();
+
+        BOOST_ASSERT( p != 0 );
+
+        return *p;
+    }
+
+    BOOST_CXX14_CONSTEXPR T const& operator*() const & noexcept
+    {
+        T const* p = operator->();
+
+        BOOST_ASSERT( p != 0 );
+
+        return *p;
+    }
+
+    template<class U = T>
+        BOOST_CXX14_CONSTEXPR
+        typename std::enable_if<std::is_move_constructible<U>::value, T>::type
+        operator*() && noexcept(std::is_nothrow_move_constructible<T>::value)
+    {
+        return std::move(**this);
+    }
+
+    template<class U = T>
+        BOOST_CXX14_CONSTEXPR
+        typename std::enable_if<!std::is_move_constructible<U>::value, T&&>::type
+        operator*() && noexcept
+    {
+        return std::move(**this);
+    }
+
+    template<class U = T>
+        BOOST_CXX14_CONSTEXPR
+        typename std::enable_if<std::is_move_constructible<U>::value, T>::type
+        operator*() const && noexcept = delete;
+
+    template<class U = T>
+        BOOST_CXX14_CONSTEXPR
+        typename std::enable_if<!std::is_move_constructible<U>::value, T const&&>::type
+        operator*() const && noexcept
+    {
+        return std::move(**this);
+    }
+
+#endif
+
+    // error access
+
+    constexpr E error() const
+        noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_copy_constructible<E>::value )
+    {
+        return has_error()? variant2::unsafe_get<1>( v_ ): E();
+    }
+
+    // swap
+
+    BOOST_CXX14_CONSTEXPR void swap( result& r )
+        noexcept( noexcept( v_.swap( r.v_ ) ) )
+    {
+        v_.swap( r.v_ );
+    }
+
+    friend BOOST_CXX14_CONSTEXPR void swap( result & r1, result & r2 )
+        noexcept( noexcept( r1.swap( r2 ) ) )
+    {
+        r1.swap( r2 );
+    }
+
+    // equality
+
+    friend constexpr bool operator==( result const & r1, result const & r2 )
+        noexcept( noexcept( r1.v_ == r2.v_ ) )
+    {
+        return r1.v_ == r2.v_;
+    }
+
+    friend constexpr bool operator!=( result const & r1, result const & r2 )
+        noexcept( noexcept( !( r1 == r2 ) ) )
+    {
+        return !( r1 == r2 );
+    }
+};
+
+template<class Ch, class Tr, class T, class E> std::basic_ostream<Ch, Tr>& operator<<( std::basic_ostream<Ch, Tr>& os, result<T, E> const & r )
+{
+    if( r.has_value() )
+    {
+        os << "value:" << *r;
+    }
+    else
+    {
+        os << "error:" << r.error();
+    }
+
+    return os;
+}
+
+// result<void>
+
+template<class E> class result<void, E>
+{
+private:
+
+    variant2::variant<variant2::monostate, E> v_;
+
+public:
+
+    // constructors
+
+    // default
+    constexpr result() noexcept
+        : v_( in_place_value )
+    {
+    }
+
+    // explicit, error
+    template<class A, class En = typename std::enable_if<
+        std::is_constructible<E, A>::value &&
+        !std::is_convertible<A, E>::value
+        >::type>
+    explicit constexpr result( A&& a )
+        noexcept( std::is_nothrow_constructible<E, A>::value )
+        : v_( in_place_error, std::forward<A>(a) )
+    {
+    }
+
+    // implicit, error
+    template<class A, class En2 = void, class En = typename std::enable_if<
+        std::is_convertible<A, E>::value
+        >::type>
+    constexpr result( A&& a )
+        noexcept( std::is_nothrow_constructible<E, A>::value )
+        : v_( in_place_error, std::forward<A>(a) )
+    {
+    }
+
+    // more than one arg, error
+    template<class... A, class En2 = void, class En3 = void, class En = typename std::enable_if<
+        std::is_constructible<E, A...>::value &&
+        sizeof...(A) >= 2
+        >::type>
+    constexpr result( A&&... a )
+        noexcept( std::is_nothrow_constructible<E, A...>::value )
+        : v_( in_place_error, std::forward<A>(a)... )
+    {
+    }
+
+    // tagged, value
+    constexpr result( in_place_value_t ) noexcept
+        : v_( in_place_value )
+    {
+    }
+
+    // tagged, error
+    template<class... A, class En = typename std::enable_if<
+        std::is_constructible<E, A...>::value
+        >::type>
+    constexpr result( in_place_error_t, A&&... a )
+        noexcept( std::is_nothrow_constructible<E, A...>::value )
+        : v_( in_place_error, std::forward<A>(a)... )
+    {
+    }
+
+    // queries
+
+    constexpr bool has_value() const noexcept
+    {
+        return v_.index() == 0;
+    }
+
+    constexpr bool has_error() const noexcept
+    {
+        return v_.index() != 0;
+    }
+
+    constexpr explicit operator bool() const noexcept
+    {
+        return v_.index() == 0;
+    }
+
+    // checked value access
+
+    BOOST_CXX14_CONSTEXPR void value() const
+    {
+        if( has_value() )
+        {
+        }
+        else
+        {
+            throw_exception_from_error( variant2::unsafe_get<1>( v_ ) );
+        }
+    }
+
+    // unchecked value access
+
+    BOOST_CXX14_CONSTEXPR void* operator->() noexcept
+    {
+        return variant2::get_if<0>( &v_ );
+    }
+
+    BOOST_CXX14_CONSTEXPR void const* operator->() const noexcept
+    {
+        return variant2::get_if<0>( &v_ );
+    }
+
+    BOOST_CXX14_CONSTEXPR void operator*() const noexcept
+    {
+        BOOST_ASSERT( has_value() );
+    }
+
+    // error access
+
+    constexpr E error() const
+        noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_copy_constructible<E>::value )
+    {
+        return has_error()? variant2::unsafe_get<1>( v_ ): E();
+    }
+
+    // swap
+
+    BOOST_CXX14_CONSTEXPR void swap( result& r )
+        noexcept( noexcept( v_.swap( r.v_ ) ) )
+    {
+        v_.swap( r.v_ );
+    }
+
+    friend BOOST_CXX14_CONSTEXPR void swap( result & r1, result & r2 )
+        noexcept( noexcept( r1.swap( r2 ) ) )
+    {
+        r1.swap( r2 );
+    }
+
+    // equality
+
+    friend constexpr bool operator==( result const & r1, result const & r2 )
+        noexcept( noexcept( r1.v_ == r2.v_ ) )
+    {
+        return r1.v_ == r2.v_;
+    }
+
+    friend constexpr bool operator!=( result const & r1, result const & r2 )
+        noexcept( noexcept( !( r1 == r2 ) ) )
+    {
+        return !( r1 == r2 );
+    }
+};
+
+template<class Ch, class Tr, class E> std::basic_ostream<Ch, Tr>& operator<<( std::basic_ostream<Ch, Tr>& os, result<void, E> const & r )
+{
+    if( r.has_value() )
+    {
+        os << "value:void";
+    }
+    else
+    {
+        os << "error:" << r.error();
+    }
+
+    return os;
+}
+
+} // namespace system
+} // namespace boost
+
+#endif // #ifndef BOOST_SYSTEM_RESULT_HPP_INCLUDED

include/boost/system/system_error.hpp

@@ -1,84 +1,76 @@
-//  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_;
+
+private:
+
+    static std::string build_message( char const * prefix, error_code const & ec )
     {
-    public:
-      explicit system_error( error_code ec )
-          : std::runtime_error(""), m_error_code(ec) {}
+        std::string r;
 
-      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
+        if( prefix )
         {
-          m_what = this->std::runtime_error::what();
-          if ( !m_what.empty() ) m_what += ": ";
-          m_what += m_error_code.message();
+            r += prefix;
+            r += ": ";
         }
-#ifndef BOOST_NO_EXCEPTIONS
-        catch (...) { return std::runtime_error::what(); }
-#endif
-      }
-      return m_what.c_str();
+
+        r += ec.what();
+        return r;
     }
 
-  } // namespace system
+    static std::string build_message( char const * prefix, int ev, error_category const & cat )
+    {
+        return build_message( prefix, error_code( ev, cat ) );
+    }
+
+public:
+
+    explicit system_error( error_code const & ec )
+      : std::runtime_error( build_message( 0, ec ) ), code_( ec ) {}
+
+    system_error( error_code const & ec, std::string const & prefix )
+      : std::runtime_error( build_message( prefix.c_str(), ec ) ), code_( ec ) {}
+
+    system_error( error_code const & ec, char const * prefix )
+      : std::runtime_error( build_message( prefix, ec ) ), code_( ec ) {}
+
+    system_error( int ev, error_category const & ecat )
+      : std::runtime_error( build_message( 0, ev, ecat ) ), code_( ev, ecat ) {}
+
+    system_error( int ev, error_category const & ecat, std::string const & prefix )
+      : std::runtime_error( build_message( prefix.c_str(), ev, ecat ) ), code_( ev, ecat ) {}
+
+    system_error( int ev, error_category const & ecat, char const * prefix )
+      : std::runtime_error( build_message( prefix, ev, ecat ) ), code_( ev, ecat ) {}
+
+    error_code code() const BOOST_NOEXCEPT
+    {
+        return code_;
+    }
+};
+
+} // 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

@@ -69,3 +69,66 @@ 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)
+
+# 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)

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 +10,18 @@
 
 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
+  ;
+
 rule system-run ( sources + )
 {
     local result ;
@@ -61,8 +73,8 @@ 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 +97,63 @@ 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 ;
+
+# result
+
+import ../../config/checks/config : requires ;
+
+CPP11 = [ requires cxx11_variadic_templates cxx11_template_aliases cxx11_decltype cxx11_constexpr cxx11_noexcept ] ;
+
+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) ;

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/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_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_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/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_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/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_copy_assign.cpp

@@ -0,0 +1,686 @@
+// 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 );
+    }
+
+    return boost::report_errors();
+}

test/result_copy_construct.cpp

@@ -0,0 +1,181 @@
+// 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 );
+    }
+
+    return boost::report_errors();
+}

test/result_default_construct.cpp

@@ -0,0 +1,41 @@
+// 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
+{
+};
+
+int main()
+{
+    {
+        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<void> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_eq.cpp

@@ -0,0 +1,153 @@
+// 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 );
+    }
+
+    return boost::report_errors();
+}

test/result_errc_construct.cpp

@@ -0,0 +1,23 @@
+// 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>));
+
+    return boost::report_errors();
+}

test/result_error_access.cpp

@@ -0,0 +1,212 @@
+// 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 );
+    }
+
+    return boost::report_errors();
+}

test/result_error_construct.cpp

@@ -0,0 +1,185 @@
+// 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(), std::error_code( EINVAL, generic_category() ) );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<std::error_code> r( in_place_error, ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        result<std::error_code> r( in_place_error, EINVAL, generic_category() );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), std::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>, std::error_code>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<std::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_FALSE((std::is_constructible<result<int, X>, int>));
+        BOOST_TEST_TRAIT_FALSE((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(), std::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(), std::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_move_assign.cpp

@@ -0,0 +1,604 @@
+// 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 );
+    }
+
+    return boost::report_errors();
+}

test/result_move_construct.cpp

@@ -0,0 +1,249 @@
+// 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 );
+    }
+
+    return boost::report_errors();
+}

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();
+}

test/result_swap.cpp

@@ -0,0 +1,263 @@
+// 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 ), r1c( r1 );
+        result<int> r2( 2 ), r2c( r2 );
+
+        r1.swap( r2 );
+
+        BOOST_TEST_EQ( r1, r2c );
+        BOOST_TEST_EQ( r2, r1c );
+
+        swap( r1, r2 );
+
+        BOOST_TEST_EQ( r1, r1c );
+        BOOST_TEST_EQ( r2, r2c );
+    }
+
+    {
+        result<int> r1( 1, generic_category() ), r1c( r1 );
+        result<int> r2( 2, generic_category() ), r2c( r2 );
+
+        r1.swap( r2 );
+
+        BOOST_TEST_EQ( r1, r2c );
+        BOOST_TEST_EQ( r2, r1c );
+
+        swap( r1, r2 );
+
+        BOOST_TEST_EQ( r1, r1c );
+        BOOST_TEST_EQ( r2, r2c );
+    }
+
+    {
+        result<int> r1( 1 ), r1c( r1 );
+        result<int> r2( 2, generic_category() ), r2c( r2 );
+
+        r1.swap( r2 );
+
+        BOOST_TEST_EQ( r1, r2c );
+        BOOST_TEST_EQ( r2, r1c );
+
+        swap( r1, r2 );
+
+        BOOST_TEST_EQ( r1, r1c );
+        BOOST_TEST_EQ( r2, r2c );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<X, Y> r1( in_place_value, 1 ), r1c( in_place_value, 1 );
+        result<X, Y> r2( in_place_value, 2 ), r2c( in_place_value, 2 );
+
+        BOOST_TEST_EQ( X::instances, 4 );
+        BOOST_TEST_EQ( Y::instances, 0 );
+
+        r1.swap( r2 );
+
+        BOOST_TEST_EQ( r1, r2c );
+        BOOST_TEST_EQ( r2, r1c );
+
+        BOOST_TEST_EQ( X::instances, 4 );
+        BOOST_TEST_EQ( Y::instances, 0 );
+
+        swap( r1, r2 );
+
+        BOOST_TEST_EQ( r1, r1c );
+        BOOST_TEST_EQ( r2, r2c );
+
+        BOOST_TEST_EQ( X::instances, 4 );
+        BOOST_TEST_EQ( Y::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<X, Y> r1( in_place_error, 1 ), r1c( in_place_error, 1 );
+        result<X, Y> r2( in_place_error, 2 ), r2c( in_place_error, 2 );
+
+        BOOST_TEST_EQ( X::instances, 0 );
+        BOOST_TEST_EQ( Y::instances, 4 );
+
+        r1.swap( r2 );
+
+        BOOST_TEST_EQ( r1, r2c );
+        BOOST_TEST_EQ( r2, r1c );
+
+        BOOST_TEST_EQ( X::instances, 0 );
+        BOOST_TEST_EQ( Y::instances, 4 );
+
+        swap( r1, r2 );
+
+        BOOST_TEST_EQ( r1, r1c );
+        BOOST_TEST_EQ( r2, r2c );
+
+        BOOST_TEST_EQ( X::instances, 0 );
+        BOOST_TEST_EQ( Y::instances, 4 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<X, Y> r1( in_place_value, 1 ), r1c( in_place_value, 1 );
+        result<X, Y> r2( in_place_error, 2 ), r2c( in_place_error, 2 );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        r1.swap( r2 );
+
+        BOOST_TEST_EQ( r1, r2c );
+        BOOST_TEST_EQ( r2, r1c );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+        BOOST_TEST_EQ( Y::instances, 2 );
+
+        swap( r1, r2 );
+
+        BOOST_TEST_EQ( r1, r1c );
+        BOOST_TEST_EQ( r2, r2c );
+
+        BOOST_TEST_EQ( X::instances, 2 );
+        BOOST_TEST_EQ( Y::instances, 2 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+    BOOST_TEST_EQ( Y::instances, 0 );
+
+    {
+        result<void> r1, r1c( r1 );
+        result<void> r2, r2c( r2 );
+
+        r1.swap( r2 );
+
+        BOOST_TEST_EQ( r1, r2c );
+        BOOST_TEST_EQ( r2, r1c );
+
+        swap( r1, r2 );
+
+        BOOST_TEST_EQ( r1, r1c );
+        BOOST_TEST_EQ( r2, r2c );
+    }
+
+    {
+        result<void> r1( 1, generic_category() ), r1c( r1 );
+        result<void> r2( 2, generic_category() ), r2c( r2 );
+
+        r1.swap( r2 );
+
+        BOOST_TEST_EQ( r1, r2c );
+        BOOST_TEST_EQ( r2, r1c );
+
+        swap( r1, r2 );
+
+        BOOST_TEST_EQ( r1, r1c );
+        BOOST_TEST_EQ( r2, r2c );
+    }
+
+    {
+        result<void> r1, r1c( r1 );
+        result<void> r2( 2, generic_category() ), r2c( r2 );
+
+        r1.swap( r2 );
+
+        BOOST_TEST_EQ( r1, r2c );
+        BOOST_TEST_EQ( r2, r1c );
+
+        swap( r1, r2 );
+
+        BOOST_TEST_EQ( r1, r1c );
+        BOOST_TEST_EQ( r2, r2c );
+    }
+
+    return boost::report_errors();
+}

test/result_value_access.cpp

@@ -0,0 +1,345 @@
+// 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
+{
+    int v_;
+
+    explicit X( int v ): v_( v ) {}
+
+    X( X const& ) = delete;
+    X& operator=( X const& ) = delete;
+};
+
+struct Y
+{
+};
+
+struct E
+{
+};
+
+BOOST_NORETURN void throw_exception_from_error( Y const & )
+{
+    throw E();
+}
+
+int main()
+{
+    {
+        result<int> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST( r );
+        BOOST_TEST_NOT( !r );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+        BOOST_TEST_EQ( *r, 0 );
+
+        BOOST_TEST_EQ( r.operator->(), &*r );
+    }
+
+    {
+        result<int> const r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST( r );
+        BOOST_TEST_NOT( !r );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+        BOOST_TEST_EQ( *r, 0 );
+
+        BOOST_TEST_EQ( r.operator->(), &*r );
+    }
+
+    {
+        BOOST_TEST( result<int>().has_value() );
+        BOOST_TEST( !result<int>().has_error() );
+
+        BOOST_TEST( result<int>() );
+        BOOST_TEST_NOT( !result<int>() );
+
+        BOOST_TEST_EQ( result<int>().value(), 0 );
+        BOOST_TEST_EQ( *result<int>(), 0 );
+
+        BOOST_TEST( result<int>().operator->() != 0 );
+    }
+
+    {
+        result<int> r( 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST( r );
+        BOOST_TEST_NOT( !r );
+
+        BOOST_TEST_EQ( r.value(), 1 );
+        BOOST_TEST_EQ( *r, 1 );
+
+        BOOST_TEST_EQ( r.operator->(), &*r );
+    }
+
+    {
+        result<int> const r( 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST( r );
+        BOOST_TEST_NOT( !r );
+
+        BOOST_TEST_EQ( r.value(), 1 );
+        BOOST_TEST_EQ( *r, 1 );
+
+        BOOST_TEST_EQ( r.operator->(), &*r );
+    }
+
+    {
+        BOOST_TEST( result<int>( 1 ).has_value() );
+        BOOST_TEST( !result<int>( 1 ).has_error() );
+
+        BOOST_TEST( result<int>( 1 ) );
+        BOOST_TEST_NOT( !result<int>( 1 ) );
+
+        BOOST_TEST_EQ( result<int>( 1 ).value(), 1 );
+        BOOST_TEST_EQ( *result<int>( 1 ), 1 );
+
+        BOOST_TEST( result<int>( 1 ).operator->() != 0 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_NOT( r );
+        BOOST_TEST( !r );
+
+        BOOST_TEST_THROWS( r.value(), system_error );
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<int*>(0) );
+    }
+
+    {
+        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_NOT( r );
+        BOOST_TEST( !r );
+
+        BOOST_TEST_THROWS( r.value(), system_error );
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<int*>(0) );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        BOOST_TEST( !result<int>( ec ).has_value() );
+        BOOST_TEST( result<int>( ec ).has_error() );
+
+        BOOST_TEST_NOT( result<int>( ec ) );
+        BOOST_TEST( !result<int>( ec ) );
+
+        BOOST_TEST_THROWS( result<int>( ec ).value(), system_error );
+
+        BOOST_TEST_EQ( result<int>( ec ).operator->(), static_cast<int*>(0) );
+    }
+
+    {
+        result<X> r( 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST( r );
+        BOOST_TEST_NOT( !r );
+
+        BOOST_TEST_EQ( r.value().v_, 1 );
+        BOOST_TEST_EQ( (*r).v_, 1 );
+        BOOST_TEST_EQ( r->v_, 1 );
+
+        BOOST_TEST_EQ( r.operator->(), &*r );
+    }
+
+    {
+        result<X> const r( 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST( r );
+        BOOST_TEST_NOT( !r );
+
+        BOOST_TEST_EQ( r.value().v_, 1 );
+        BOOST_TEST_EQ( (*r).v_, 1 );
+        BOOST_TEST_EQ( r->v_, 1 );
+
+        BOOST_TEST_EQ( r.operator->(), &*r );
+    }
+
+    {
+        BOOST_TEST( result<X>( 1 ).has_value() );
+        BOOST_TEST( !result<X>( 1 ).has_error() );
+
+        BOOST_TEST( result<X>( 1 ) );
+        BOOST_TEST_NOT( !result<X>( 1 ) );
+
+        BOOST_TEST_EQ( result<X>( 1 ).value().v_, 1 );
+        BOOST_TEST_EQ( (*result<X>( 1 )).v_, 1 );
+        BOOST_TEST_EQ( result<X>( 1 )->v_, 1 );
+    }
+
+    {
+        auto ec = Y();
+
+        result<X, Y> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_NOT( r );
+        BOOST_TEST( !r );
+
+        BOOST_TEST_THROWS( r.value(), E );
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<X*>(0) );
+    }
+
+    {
+        auto ec = Y();
+
+        result<X, Y> const r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_NOT( r );
+        BOOST_TEST( !r );
+
+        BOOST_TEST_THROWS( r.value(), E );
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<X*>(0) );
+    }
+
+    {
+        auto ec = Y();
+
+        BOOST_TEST(( !result<X, Y>( ec ).has_value() ));
+        BOOST_TEST(( result<X, Y>( ec ).has_error() ));
+
+        BOOST_TEST_NOT(( result<X, Y>( ec ) ));
+        BOOST_TEST(( !result<X, Y>( ec ) ));
+
+        BOOST_TEST_THROWS( (result<X, Y>( ec ).value()), E );
+
+        BOOST_TEST_EQ( (result<X, Y>( ec ).operator->()), static_cast<X*>(0) );
+    }
+
+    {
+        result<void> r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST( r );
+        BOOST_TEST_NOT( !r );
+
+        BOOST_TEST_NO_THROW( r.value() );
+
+        BOOST_TEST( r.operator->() != 0 );
+    }
+
+    {
+        result<void> const r;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST( r );
+        BOOST_TEST_NOT( !r );
+
+        BOOST_TEST_NO_THROW( r.value() );
+
+        BOOST_TEST( r.operator->() != 0 );
+    }
+
+    {
+        BOOST_TEST( result<void>().has_value() );
+        BOOST_TEST( !result<void>().has_error() );
+
+        BOOST_TEST( result<void>() );
+        BOOST_TEST_NOT( !result<void>() );
+
+        BOOST_TEST_NO_THROW( result<void>().value() );
+
+        BOOST_TEST( result<void>().operator->() != 0 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<void> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_NOT( r );
+        BOOST_TEST( !r );
+
+        BOOST_TEST_THROWS( r.value(), system_error );
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<void*>(0) );
+    }
+
+    {
+        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_NOT( r );
+        BOOST_TEST( !r );
+
+        BOOST_TEST_THROWS( r.value(), system_error );
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<void*>(0) );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        BOOST_TEST( !result<void>( ec ).has_value() );
+        BOOST_TEST( result<void>( ec ).has_error() );
+
+        BOOST_TEST_NOT( result<void>( ec ) );
+        BOOST_TEST( !result<void>( ec ) );
+
+        BOOST_TEST_THROWS( result<void>( ec ).value(), system_error );
+
+        BOOST_TEST_EQ( result<void>( ec ).operator->(), static_cast<void*>(0) );
+    }
+
+    return boost::report_errors();
+}

test/result_value_construct.cpp

@@ -0,0 +1,132 @@
+// 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_;
+
+    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;
+
+int main()
+{
+    {
+        result<int> r( 0 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        result<int> r = 0;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        result<int, int> r( in_place_value, 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( *r, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value().v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1, 2 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value().v_, 1+2 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X> r( 1, 2, 3 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value().v_, 1+2+3 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<X, X> r( in_place_value, 1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r->v_, 1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<int>, int>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<int, result<int>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int, int>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int, float>, int>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<X>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<X>>));
+    }
+
+    {
+        result<void> r( in_place_value );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_value_construct2.cpp

@@ -0,0 +1,152 @@
+// 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>
+#include <string>
+
+using namespace boost::system;
+
+struct X
+{
+    int a;
+};
+
+struct Y
+{
+    int a, b;
+};
+
+struct E
+{
+    std::string v;
+};
+
+result<X> fx0()
+{
+    return {};
+}
+
+result<X> fx1()
+{
+    return {{ 1 }};
+}
+
+result<Y> fy0()
+{
+    return {};
+}
+
+result<Y> fy2()
+{
+    return {{ 1, 2 }};
+}
+
+result<X, E> fxe0()
+{
+    return {};
+}
+
+result<X, E> fxe1()
+{
+    return {{ 1 }};
+}
+
+result<std::vector<int>> fv0()
+{
+    return {};
+}
+
+result<std::vector<int>> fv1()
+{
+    return {{ 1 }};
+}
+
+result<std::vector<int>> fv2()
+{
+    return {{ 1, 2 }};
+}
+
+int main()
+{
+    {
+        result<X> r = fx0();
+
+        BOOST_TEST( r.has_value() );
+
+        BOOST_TEST_EQ( r->a, 0 );
+    }
+
+    {
+        result<X> r = fx1();
+
+        BOOST_TEST( r.has_value() );
+
+        BOOST_TEST_EQ( r->a, 1 );
+    }
+
+    {
+        result<Y> r = fy0();
+
+        BOOST_TEST( r.has_value() );
+
+        BOOST_TEST_EQ( r->a, 0 );
+        BOOST_TEST_EQ( r->b, 0 );
+    }
+
+    {
+        result<Y> r = fy2();
+
+        BOOST_TEST( r.has_value() );
+
+        BOOST_TEST_EQ( r->a, 1 );
+        BOOST_TEST_EQ( r->b, 2 );
+    }
+
+    {
+        result<X, E> r = fxe0();
+
+        BOOST_TEST( r.has_value() );
+
+        BOOST_TEST_EQ( r->a, 0 );
+    }
+
+    {
+        result<X, E> r = fxe1();
+
+        BOOST_TEST( r.has_value() );
+
+        BOOST_TEST_EQ( r->a, 1 );
+    }
+
+    {
+        result<std::vector<int>> r = fv0();
+
+        BOOST_TEST( r.has_value() );
+
+        BOOST_TEST_EQ( r->size(), 0 );
+    }
+
+    {
+        result<std::vector<int>> r = fv1();
+
+        BOOST_TEST( r.has_value() );
+
+        BOOST_TEST_EQ( r->size(), 1 );
+        BOOST_TEST_EQ( r->at(0), 1 );
+    }
+
+    {
+        result<std::vector<int>> r = fv2();
+
+        BOOST_TEST( r.has_value() );
+
+        BOOST_TEST_EQ( r->size(), 2 );
+        BOOST_TEST_EQ( r->at(0), 1 );
+        BOOST_TEST_EQ( r->at(1), 2 );
+    }
+
+    return boost::report_errors();
+}

test/snprintf_test.cpp

@@ -0,0 +1,60 @@
+// Copyright 2021 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/detail/snprintf.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+int main()
+{
+    {
+        char buffer[ 64 ];
+        boost::system::detail::snprintf( buffer, sizeof(buffer), "...%s...%d...", "xy", 151 );
+
+        BOOST_TEST_CSTR_EQ( buffer, "...xy...151..." );
+    }
+
+    {
+        char buffer[ 64 ];
+        boost::system::detail::snprintf( buffer, sizeof(buffer), "...%s...%d...", "xy", 151 );
+
+        BOOST_TEST_CSTR_EQ( buffer, "...xy...151..." );
+    }
+
+    {
+        char buffer[ 15 ];
+        boost::system::detail::snprintf( buffer, sizeof(buffer), "...%s...%d...", "xy", 151 );
+
+        BOOST_TEST_CSTR_EQ( buffer, "...xy...151..." );
+    }
+
+    {
+        char buffer[ 14 ];
+        boost::system::detail::snprintf( buffer, sizeof(buffer), "...%s...%d...", "xy", 151 );
+
+        BOOST_TEST_CSTR_EQ( buffer, "...xy...151.." );
+    }
+
+    {
+        char buffer[ 5 ];
+        boost::system::detail::snprintf( buffer, sizeof(buffer), "...%s...%d...", "xy", 151 );
+
+        BOOST_TEST_CSTR_EQ( buffer, "...x" );
+    }
+
+    {
+        char buffer[ 1 ];
+        boost::system::detail::snprintf( buffer, sizeof(buffer), "...%s...%d...", "xy", 151 );
+
+        BOOST_TEST_CSTR_EQ( buffer, "" );
+    }
+
+    {
+        char buffer[ 1 ] = { 'Q' };
+        boost::system::detail::snprintf( buffer, 0, "...%s...%d...", "xy", 151 );
+
+        BOOST_TEST_EQ( buffer[0], 'Q' );
+    }
+
+    return boost::report_errors();
+}

test/std_interop_test.cpp

@@ -44,7 +44,8 @@ static void test_generic_category()
 
     int ev = ENOENT;
 
-    BOOST_TEST_EQ( bt.message( ev ), st.message( ev ) );
+    // Under MSVC, it's "no such file or directory" instead of "No such file or directory"
+    BOOST_TEST_EQ( bt.message( ev ).substr( 1 ), st.message( ev ).substr( 1 ) );
 
     {
         boost::system::error_code bc( ev, bt );
@@ -82,34 +83,13 @@ static void test_system_category()
 
     BOOST_TEST_CSTR_EQ( bt.name(), st.name() );
 
+    for( int ev = 1; ev < 6; ++ev )
     {
-        int ev = 5;
-        BOOST_TEST_EQ( bt.message( ev ), st.message( ev ) );
+        std::string bm = bt.message( ev );
+        std::string sm = st.message( ev );
 
-        {
-            boost::system::error_code bc( ev, bt );
-
-            BOOST_TEST_EQ( bc.value(), ev );
-            BOOST_TEST_EQ( &bc.category(), &bt );
-
-            std::error_code sc( bc );
-
-            BOOST_TEST_EQ( sc.value(), ev );
-            BOOST_TEST_EQ( &sc.category(), &st );
-        }
-
-        {
-            boost::system::error_condition bn = bt.default_error_condition( ev );
-            BOOST_TEST( bt.equivalent( ev, bn ) );
-
-            std::error_condition sn( bn );
-            BOOST_TEST( st.equivalent( ev, sn ) );
-        }
-    }
-
-    {
-        int ev = 4;
-        BOOST_TEST_EQ( bt.message( ev ), st.message( ev ) );
+        // We strip whitespace and the trailing dot, MSVC not so much
+        BOOST_TEST_EQ( bm, sm.substr( 0, bm.size() ) );
 
         {
             boost::system::error_code bc( ev, bt );

test/std_interop_test10.cpp

@@ -0,0 +1,66 @@
+// Copyright 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/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <cerrno>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+int main()
+{
+    {
+        boost::system::error_code e1;
+        boost::system::error_code e2( 0, boost::system::system_category() );
+
+        BOOST_TEST_EQ( e1, e2 );
+
+        std::error_code e3( e1 );
+        std::error_code e4( e2 );
+
+        BOOST_TEST_EQ( e3, e4 );
+    }
+
+    {
+        boost::system::error_code e1;
+
+        std::error_code e2( e1 );
+        std::error_code e3( e1.value(), e1.category() );
+
+        BOOST_TEST_EQ( e2, e3 );
+    }
+
+    {
+        boost::system::error_condition e1;
+        boost::system::error_condition e2( 0, boost::system::generic_category() );
+
+        BOOST_TEST_EQ( e1, e2 );
+
+        std::error_condition e3( e1 );
+        std::error_condition e4( e2 );
+
+        BOOST_TEST( e3 == e4 );
+    }
+
+    {
+        boost::system::error_condition e1;
+
+        std::error_condition e2( e1 );
+        std::error_condition e3( e1.value(), e1.category() );
+
+        BOOST_TEST( e2 == e3 );
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test11.cpp

@@ -0,0 +1,47 @@
+// Copyright 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/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config.hpp>
+#include <ios>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "Skipping test, BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined" )
+int main() {}
+
+#elif defined(BOOST_LIBSTDCXX_VERSION) && BOOST_LIBSTDCXX_VERSION < 50000
+
+BOOST_PRAGMA_MESSAGE( "Skipping test, BOOST_LIBSTDCXX_VERSION < 50000" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+int main()
+{
+    {
+        boost::system::error_code ec = std::io_errc::stream;
+
+        BOOST_TEST( ec == std::io_errc::stream );
+        BOOST_TEST_NOT( ec != std::io_errc::stream );
+
+        ec.clear();
+
+        BOOST_TEST_NOT( ec == std::io_errc::stream );
+        BOOST_TEST( ec != std::io_errc::stream );
+
+        ec = std::io_errc::stream;
+
+        BOOST_TEST( ec == std::io_errc::stream );
+        BOOST_TEST_NOT( ec != std::io_errc::stream );
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test2.cpp

@@ -0,0 +1,98 @@
+// Copyright 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/system_category.hpp>
+#include <boost/system/generic_category.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <cerrno>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+void f1( std::error_code ec, int value, std::error_category const& category )
+{
+    BOOST_TEST_EQ( ec.value(), value );
+    BOOST_TEST_EQ( &ec.category(), &category );
+}
+
+void f2( std::error_code const& ec, int value, std::error_category const& category )
+{
+    BOOST_TEST_EQ( ec.value(), value );
+    BOOST_TEST_EQ( &ec.category(), &category );
+}
+
+int main()
+{
+    {
+        boost::system::error_code e1;
+        boost::system::error_code e2( e1 );
+
+        f1( e1, e1.value(), e1.category() );
+#if !defined(BOOST_SYSTEM_CLANG_6)
+        f2( e1, e1.value(), e1.category() );
+#endif
+
+        BOOST_TEST_EQ( e1, e2 );
+    }
+
+    {
+        boost::system::error_code e1( 0, boost::system::system_category() );
+        boost::system::error_code e2( e1 );
+
+        f1( e1, e1.value(), e1.category() );
+#if !defined(BOOST_SYSTEM_CLANG_6)
+        f2( e1, e1.value(), e1.category() );
+#endif
+
+        BOOST_TEST_EQ( e1, e2 );
+    }
+
+    {
+        boost::system::error_code e1( 5, boost::system::system_category() );
+        boost::system::error_code e2( e1 );
+
+        f1( e1, e1.value(), e1.category() );
+#if !defined(BOOST_SYSTEM_CLANG_6)
+        f2( e1, e1.value(), e1.category() );
+#endif
+
+        BOOST_TEST_EQ( e1, e2 );
+    }
+
+    {
+        boost::system::error_code e1( 0, boost::system::generic_category() );
+        boost::system::error_code e2( e1 );
+
+        f1( e1, e1.value(), e1.category() );
+#if !defined(BOOST_SYSTEM_CLANG_6)
+        f2( e1, e1.value(), e1.category() );
+#endif
+
+        BOOST_TEST_EQ( e1, e2 );
+    }
+
+    {
+        boost::system::error_code e1( ENOENT, boost::system::generic_category() );
+        boost::system::error_code e2( e1 );
+
+        f1( e1, e1.value(), e1.category() );
+#if !defined(BOOST_SYSTEM_CLANG_6)
+        f2( e1, e1.value(), e1.category() );
+#endif
+
+        BOOST_TEST_EQ( e1, e2 );
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test3.cpp

@@ -0,0 +1,79 @@
+// Copyright 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/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <cerrno>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+int main()
+{
+    {
+        std::error_code e1;
+        boost::system::error_code e2 = e1;
+
+        BOOST_TEST( !e2.failed() );
+        BOOST_TEST_EQ( e1.message(), e2.message() );
+
+        std::error_code e3 = e2;
+        BOOST_TEST_EQ( e1, e3 );
+    }
+
+    {
+        std::error_code e1( 5, std::system_category() );
+        boost::system::error_code e2 = e1;
+
+        BOOST_TEST( e2.failed() );
+        BOOST_TEST_EQ( e1.message(), e2.message() );
+
+        std::error_code e3 = e2;
+        BOOST_TEST_EQ( e1, e3 );
+    }
+
+    {
+        std::error_code e1( 0, std::generic_category() );
+        boost::system::error_code e2 = e1;
+
+        BOOST_TEST( !e2.failed() );
+        BOOST_TEST_EQ( e1.message(), e2.message() );
+
+        std::error_code e3 = e2;
+        BOOST_TEST_EQ( e1, e3 );
+    }
+
+    {
+        std::error_code e1( ENOENT, std::generic_category() );
+        boost::system::error_code e2 = e1;
+
+        BOOST_TEST( e2.failed() );
+        BOOST_TEST_EQ( e1.message(), e2.message() );
+
+        std::error_code e3 = e2;
+        BOOST_TEST_EQ( e1, e3 );
+    }
+
+    {
+        std::error_code e1 = make_error_code( std::errc::no_such_file_or_directory );
+        boost::system::error_code e2 = e1;
+
+        BOOST_TEST( e2.failed() );
+        BOOST_TEST_EQ( e1.message(), e2.message() );
+
+        std::error_code e3 = e2;
+        BOOST_TEST_EQ( e1, e3 );
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test4.cpp

@@ -0,0 +1,89 @@
+// Copyright 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/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <cerrno>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+void f( std::error_code& e1, std::error_code e2 )
+{
+    e1 = e2;
+}
+
+int main()
+{
+    {
+        boost::system::error_code e1;
+        std::error_code e2;
+
+        f( e1, e2 );
+
+        BOOST_TEST_EQ( e1, boost::system::error_code( e2 ) );
+
+        std::error_code e3( e1 );
+        BOOST_TEST_EQ( e3, e2 );
+    }
+
+    {
+        boost::system::error_code e1;
+        std::error_code e2( 0, std::system_category() );
+
+        f( e1, e2 );
+
+        BOOST_TEST_EQ( e1, boost::system::error_code( e2 ) );
+
+        std::error_code e3( e1 );
+        BOOST_TEST_EQ( e3, e2 );
+    }
+
+    {
+        boost::system::error_code e1;
+        std::error_code e2( 5, std::system_category() );
+
+        f( e1, e2 );
+
+        BOOST_TEST_EQ( e1, boost::system::error_code( e2 ) );
+
+        std::error_code e3( e1 );
+        BOOST_TEST_EQ( e3, e2 );
+    }
+
+    {
+        boost::system::error_code e1;
+        std::error_code e2( 0, std::generic_category() );
+
+        f( e1, e2 );
+
+        BOOST_TEST_EQ( e1, boost::system::error_code( e2 ) );
+
+        std::error_code e3( e1 );
+        BOOST_TEST_EQ( e3, e2 );
+    }
+
+    {
+        boost::system::error_code e1;
+        std::error_code e2( ENOENT, std::generic_category() );
+
+        f( e1, e2 );
+
+        BOOST_TEST_EQ( e1, boost::system::error_code( e2 ) );
+
+        std::error_code e3( e1 );
+        BOOST_TEST_EQ( e3, e2 );
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test5.cpp

@@ -0,0 +1,108 @@
+// Copyright 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/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <cerrno>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+int main()
+{
+    {
+        std::error_code e1;
+        std::error_condition en = e1.default_error_condition();
+
+        BOOST_TEST( e1 == en );
+        BOOST_TEST_NOT( e1 != en );
+
+        boost::system::error_code e2( e1 );
+
+        BOOST_TEST_EQ( e2, e1 );
+        BOOST_TEST_NOT( e2 != e1 );
+
+        BOOST_TEST( e2 == en );
+        BOOST_TEST_NOT( e2 != en );
+
+        std::error_code e3( e2 );
+
+        BOOST_TEST( e3 == en );
+        BOOST_TEST_NOT( e3 != en );
+    }
+
+    {
+        std::error_code e1( 5, std::system_category() );
+        std::error_condition en = e1.default_error_condition();
+
+        BOOST_TEST( e1 == en );
+        BOOST_TEST_NOT( e1 != en );
+
+        boost::system::error_code e2( e1 );
+
+        BOOST_TEST_EQ( e2, e1 );
+        BOOST_TEST_NOT( e2 != e1 );
+
+        BOOST_TEST( e2 == en );
+        BOOST_TEST_NOT( e2 != en );
+
+        std::error_code e3( e2 );
+
+        BOOST_TEST( e3 == en );
+        BOOST_TEST_NOT( e3 != en );
+    }
+
+    {
+        std::error_code e1( 0, std::generic_category() );
+        std::error_condition en = e1.default_error_condition();
+
+        BOOST_TEST( e1 == en );
+        BOOST_TEST_NOT( e1 != en );
+
+        boost::system::error_code e2( e1 );
+
+        BOOST_TEST_EQ( e2, e1 );
+        BOOST_TEST_NOT( e2 != e1 );
+
+        BOOST_TEST( e2 == en );
+        BOOST_TEST_NOT( e2 != en );
+
+        std::error_code e3( e2 );
+
+        BOOST_TEST( e3 == en );
+        BOOST_TEST_NOT( e3 != en );
+    }
+
+    {
+        std::error_code e1( 5, std::generic_category() );
+        std::error_condition en = e1.default_error_condition();
+
+        BOOST_TEST( e1 == en );
+        BOOST_TEST_NOT( e1 != en );
+
+        boost::system::error_code e2( e1 );
+
+        BOOST_TEST_EQ( e2, e1 );
+        BOOST_TEST_NOT( e2 != e1 );
+
+        BOOST_TEST( e2 == en );
+        BOOST_TEST_NOT( e2 != en );
+
+        std::error_code e3( e2 );
+
+        BOOST_TEST( e3 == en );
+        BOOST_TEST_NOT( e3 != en );
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test6.cpp

@@ -0,0 +1,140 @@
+// Copyright 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/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <cerrno>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+int main()
+{
+    {
+        boost::system::error_code e1;
+        boost::system::error_condition en = e1.default_error_condition();
+
+        BOOST_TEST_EQ( e1, en );
+        BOOST_TEST_NOT( e1 != en );
+
+        std::error_code e2( e1 );
+
+        BOOST_TEST_EQ( e2, e1 );
+        BOOST_TEST_NOT( e2 != e1 );
+
+#if defined(_LIBCPP_VERSION)
+
+        // Under MS STL and libstdc++, std::error_code() does not compare
+        // equal to std::error_condition(). Go figure.
+
+        BOOST_TEST_EQ( e2, en );
+        BOOST_TEST_NOT( e2 != en );
+
+        boost::system::error_code e3( e2 );
+
+        BOOST_TEST_EQ( e3, en );
+        BOOST_TEST_NOT( e3 != en );
+
+#endif
+    }
+
+    {
+        boost::system::error_code e1( 0, boost::system::system_category() );
+        boost::system::error_condition en = e1.default_error_condition();
+
+        BOOST_TEST_EQ( e1, en );
+        BOOST_TEST_NOT( e1 != en );
+
+        std::error_code e2( e1 );
+
+        BOOST_TEST_EQ( e2, e1 );
+        BOOST_TEST_NOT( e2 != e1 );
+
+#if defined(_LIBCPP_VERSION)
+
+        BOOST_TEST_EQ( e2, en );
+        BOOST_TEST_NOT( e2 != en );
+
+        boost::system::error_code e3( e2 );
+
+        BOOST_TEST_EQ( e3, en );
+        BOOST_TEST_NOT( e3 != en );
+
+#endif
+    }
+
+    {
+        boost::system::error_code e1( 5, boost::system::system_category() );
+        boost::system::error_condition en = e1.default_error_condition();
+
+        BOOST_TEST_EQ( e1, en );
+        BOOST_TEST_NOT( e1 != en );
+
+        std::error_code e2( e1 );
+
+        BOOST_TEST_EQ( e2, e1 );
+        BOOST_TEST_NOT( e2 != e1 );
+
+        BOOST_TEST_EQ( e2, en );
+        BOOST_TEST_NOT( e2 != en );
+
+        boost::system::error_code e3( e2 );
+
+        BOOST_TEST_EQ( e3, en );
+        BOOST_TEST_NOT( e3 != en );
+    }
+
+    {
+        boost::system::error_code e1( 0, boost::system::generic_category() );
+        boost::system::error_condition en = e1.default_error_condition();
+
+        BOOST_TEST_EQ( e1, en );
+        BOOST_TEST_NOT( e1 != en );
+
+        std::error_code e2( e1 );
+
+        BOOST_TEST_EQ( e2, e1 );
+        BOOST_TEST_NOT( e2 != e1 );
+
+        BOOST_TEST_EQ( e2, en );
+        BOOST_TEST_NOT( e2 != en );
+
+        boost::system::error_code e3( e2 );
+
+        BOOST_TEST_EQ( e3, en );
+        BOOST_TEST_NOT( e3 != en );
+    }
+
+    {
+        boost::system::error_code e1( 5, boost::system::generic_category() );
+        boost::system::error_condition en = e1.default_error_condition();
+
+        BOOST_TEST_EQ( e1, en );
+        BOOST_TEST_NOT( e1 != en );
+
+        std::error_code e2( e1 );
+
+        BOOST_TEST_EQ( e2, e1 );
+        BOOST_TEST_NOT( e2 != e1 );
+
+        BOOST_TEST_EQ( e2, en );
+        BOOST_TEST_NOT( e2 != en );
+
+        boost::system::error_code e3( e2 );
+
+        BOOST_TEST_EQ( e3, en );
+        BOOST_TEST_NOT( e3 != en );
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test7.cpp

@@ -0,0 +1,52 @@
+// Copyright 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/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config.hpp>
+#include <cerrno>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+int main()
+{
+    {
+        boost::system::error_code e1 = make_error_code( boost::system::errc::bad_address );
+
+        BOOST_TEST( e1 == boost::system::errc::bad_address );
+        BOOST_TEST_NOT( e1 != boost::system::errc::bad_address );
+
+        BOOST_TEST( e1 == std::errc::bad_address );
+        BOOST_TEST_NOT( e1 != std::errc::bad_address );
+    }
+
+    {
+        boost::system::error_code e1 = make_error_code( std::errc::bad_address );
+
+        BOOST_TEST( e1 == boost::system::errc::bad_address );
+        BOOST_TEST_NOT( e1 != boost::system::errc::bad_address );
+
+#if defined(BOOST_GCC) && BOOST_GCC >= 40800 && BOOST_GCC < 50000
+
+// fails on g++ 4.8.5 and g++ 4.9.4 from ubuntu-toolchain-r-test for unknown reasons
+// works on the system g++ 4.8.4 on Trusty and the system g++ 4.8.5 on CentOS 7
+
+#else
+        BOOST_TEST( e1 == std::errc::bad_address );
+        BOOST_TEST_NOT( e1 != std::errc::bad_address );
+#endif
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test8.cpp

@@ -0,0 +1,82 @@
+// Copyright 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/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config.hpp>
+#include <cerrno>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+enum my_errc
+{
+    my_enoent = ENOENT
+};
+
+#if defined(BOOST_GCC) && BOOST_GCC < 70000
+
+// g++ 6 and earlier do not allow specializations outside the namespace
+
+namespace boost
+{
+namespace system
+{
+
+template<> struct is_error_condition_enum<my_errc>: std::true_type {};
+
+} // namespace system
+} // namespace boost
+
+namespace std
+{
+
+template<> struct is_error_condition_enum<my_errc>: std::true_type {};
+
+} // namespace std
+
+#else
+
+template<> struct boost::system::is_error_condition_enum<my_errc>: std::true_type {};
+template<> struct std::is_error_condition_enum<my_errc>: std::true_type {};
+
+#endif
+
+boost::system::error_condition make_error_condition( my_errc e )
+{
+    return boost::system::error_condition( e, boost::system::generic_category() );
+}
+
+boost::system::error_code make_error_code( my_errc e )
+{
+    return boost::system::error_code( e, boost::system::generic_category() );
+}
+
+int main()
+{
+    {
+        boost::system::error_code e1 = make_error_code( my_enoent );
+
+        BOOST_TEST( e1 == my_enoent );
+        BOOST_TEST_NOT( e1 != my_enoent );
+    }
+
+    {
+        std::error_code e1 = make_error_code( my_enoent );
+
+        BOOST_TEST( e1 == my_enoent );
+        BOOST_TEST_NOT( e1 != my_enoent );
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test9.cpp

@@ -0,0 +1,77 @@
+// Copyright 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/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config.hpp>
+#include <cerrno>
+
+#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+
+BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+enum my_errc
+{
+    my_enoent = ENOENT
+};
+
+#if defined(BOOST_GCC) && BOOST_GCC < 70000
+
+// g++ 6 and earlier do not allow specializations outside the namespace
+
+namespace boost
+{
+namespace system
+{
+
+template<> struct is_error_code_enum<my_errc>: std::true_type {};
+
+} // namespace system
+} // namespace boost
+
+namespace std
+{
+
+template<> struct is_error_code_enum<my_errc>: std::true_type {};
+
+} // namespace std
+
+#else
+
+template<> struct boost::system::is_error_code_enum<my_errc>: std::true_type {};
+template<> struct std::is_error_code_enum<my_errc>: std::true_type {};
+
+#endif
+
+boost::system::error_code make_error_code( my_errc e )
+{
+    return boost::system::error_code( e, boost::system::generic_category() );
+}
+
+int main()
+{
+    {
+        boost::system::error_code e1 = my_enoent;
+
+        BOOST_TEST( e1 == my_enoent );
+        BOOST_TEST_NOT( e1 != my_enoent );
+    }
+
+    {
+        std::error_code e1 = my_enoent;
+
+        BOOST_TEST( e1 == my_enoent );
+        BOOST_TEST_NOT( e1 != my_enoent );
+    }
+
+    return boost::report_errors();
+}
+
+#endif

test/system_category_test.cpp

@@ -59,6 +59,7 @@ std::string sys_strerror( int ev )
     };
 
     local_free lf_ = { lpMsgBuf };
+    (void)lf_;
 
     if( retval == 0 )
     {

test/system_category_test3.cpp

@@ -18,7 +18,9 @@ int main()
 
     // default_error_condition
     BOOST_TEST( cat.default_error_condition( 0 ) == sys::error_condition() );
-    BOOST_TEST( cat.default_error_condition( -1 ) == sys::error_condition( -1, cat ) );
+
+    // No longer holds; returns a generic condition
+    // BOOST_TEST( cat.default_error_condition( -1 ) == sys::error_condition( -1, cat ) );
 
 #if defined(BOOST_WINDOWS_API)
 

test/system_error_test.cpp

@@ -51,6 +51,7 @@ namespace
           << ex.what() << "\"\n";
     }
 # endif
+    (void)str;
   }
 
   const boost::uint_least32_t uvalue = 2u;
@@ -80,27 +81,25 @@ int main( int, char *[] )
   system_error c6_0( 0, system_category(), "c6_0" ); 
   system_error c6_1( 1, system_category(), "c6_1" );
 
-  TEST( c1_0, 0, "The operation completed successfully" );
-  TEST( c1_1, 1, "Incorrect function" );
-  TEST( c1_2u, 2, "The system cannot find the file specified" );
+  TEST( c1_0, 0, "The operation completed successfully [system:0]" );
+  TEST( c1_1, 1, "Incorrect function [system:1]" );
+  TEST( c1_2u, 2, "The system cannot find the file specified [system:2]" );
 
-  TEST( c2_0, 0, "c2_0: The operation completed successfully" );
-  TEST( c2_1, 1, "c2_1: Incorrect function" );
+  TEST( c2_0, 0, "c2_0: The operation completed successfully [system:0]" );
+  TEST( c2_1, 1, "c2_1: Incorrect function [system:1]" );
 
-  TEST( c3_0, 0, "c3_0: The operation completed successfully" );
-  TEST( c3_1, 1, "c3_1: Incorrect function" );
+  TEST( c3_0, 0, "c3_0: The operation completed successfully [system:0]" );
+  TEST( c3_1, 1, "c3_1: Incorrect function [system:1]" );
 
-  TEST( c4_0, 0, "The operation completed successfully" );
-  TEST( c4_1, 1, "Incorrect function" );
-  TEST( c4_2u, 2, "The system cannot find the file specified" );
+  TEST( c4_0, 0, "The operation completed successfully [system:0]" );
+  TEST( c4_1, 1, "Incorrect function [system:1]" );
+  TEST( c4_2u, 2, "The system cannot find the file specified [system:2]" );
 
-  TEST( c5_0, 0, "c5_0: The operation completed successfully" );
-  TEST( c5_1, 1, "c5_1: Incorrect function" );
+  TEST( c5_0, 0, "c5_0: The operation completed successfully [system:0]" );
+  TEST( c5_1, 1, "c5_1: Incorrect function [system:1]" );
 
-  TEST( c6_0, 0, "c6_0: The operation completed successfully" );
-  TEST( c6_1, 1, "c6_1: Incorrect function" );
+  TEST( c6_0, 0, "c6_0: The operation completed successfully [system:0]" );
+  TEST( c6_1, 1, "c6_1: Incorrect function [system:1]" );
 
   return ::boost::report_errors();
 }
-
-

test/system_error_test2.cpp

@@ -0,0 +1,41 @@
+// Copyright 2021 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/system_error.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <cerrno>
+
+namespace sys = boost::system;
+
+int main()
+{
+    {
+        sys::error_code ec( 5, sys::generic_category() );
+        sys::system_error x1( ec );
+        (void)x1;
+    }
+
+    {
+        sys::error_code ec( 5, sys::system_category() );
+        sys::system_error x1( ec );
+        (void)x1;
+    }
+
+    {
+        sys::system_error x1( make_error_code( sys::errc::invalid_argument ) );
+        (void)x1;
+    }
+
+    {
+        sys::system_error x1( 5, sys::generic_category() );
+        (void)x1;
+    }
+
+    {
+        sys::system_error x1( 5, sys::system_category() );
+        (void)x1;
+    }
+
+    return boost::report_errors();
+}

test/system_error_test3.cpp

@@ -0,0 +1,42 @@
+// Copyright 2021 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/system_error.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <cerrno>
+
+namespace sys = boost::system;
+
+int main()
+{
+    {
+        sys::error_code ec( 5, sys::generic_category() );
+        sys::system_error x1( ec );
+
+		BOOST_TEST_EQ( std::string( x1.what() ), ec.what() );
+    }
+
+    {
+        BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
+
+        sys::error_code ec( 5, sys::system_category(), &loc );
+        sys::system_error x1( ec, "prefix" );
+
+        BOOST_TEST_EQ( std::string( x1.what() ), "prefix: " + ec.what() );
+    }
+
+    {
+        sys::system_error x1( 5, sys::generic_category() );
+
+        BOOST_TEST_EQ( std::string( x1.what() ), sys::error_code( 5, sys::generic_category() ).what() );
+    }
+
+    {
+        sys::system_error x1( 5, sys::system_category(), "prefix" );
+
+        BOOST_TEST_EQ( std::string( x1.what() ), "prefix: " + sys::error_code( 5, sys::system_category() ).what() );
+    }
+
+    return boost::report_errors();
+}

test/warnings_test.cpp

@@ -46,7 +46,7 @@ int main()
     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/windows_error_test.cpp

@@ -0,0 +1,31 @@
+// Copyright 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/windows_error.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(BOOST_WINDOWS_API)
+
+BOOST_PRAGMA_MESSAGE( "Skipping test, BOOST_WINDOWS_API is not defined" )
+int main() {}
+
+#else
+
+#include <boost/core/lightweight_test.hpp>
+#include <windows.h>
+
+int main()
+{
+    namespace sys = boost::system;
+
+    sys::error_code ec = sys::windows_error::invalid_function;
+
+    BOOST_TEST_EQ( ec, sys::windows_error::invalid_function );
+    BOOST_TEST_EQ( ec, sys::error_code( ERROR_INVALID_FUNCTION, sys::system_category() ) );
+    BOOST_TEST( ec == make_error_condition( sys::errc::function_not_supported ) );
+
+    return boost::report_errors();
+}
+
+#endif