Update .drone.jsonnet

Fixes -Wnonnull warnings when calling message with a nullptr buffer

.drone.jsonnet

@@ -32,6 +32,8 @@ local linux_pipeline(name, image, environment, packages = "", sources = [], arch
             commands:
             [
                 'set -e',
+                'uname -a',
+                'echo $DRONE_STAGE_MACHINE',
                 'wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -',
             ] +
             (if sources != [] then [ ('apt-add-repository "' + source + '"') for source in sources ] else []) +
@@ -97,140 +99,249 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
 
 [
     linux_pipeline(
-        "Linux 14.04 GCC 4.4",
-        "cppalliance/droneubuntu1404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-4.4', CXXSTD: '98,0x' },
-        "g++-4.4",
-        [ "ppa:ubuntu-toolchain-r/test" ],
+        "Linux 16.04 GCC 4.8",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-4.8', CXXSTD: '11' },
+        "g++-4.8",
     ),
 
     linux_pipeline(
-        "Linux 14.04 GCC 4.6",
-        "cppalliance/droneubuntu1404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-4.6', CXXSTD: '98,0x' },
-        "g++-4.6",
-        [ "ppa:ubuntu-toolchain-r/test" ],
-    ),
-
-    linux_pipeline(
-        "Linux 14.04 GCC 4.7",
-        "cppalliance/droneubuntu1404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-4.7', CXXSTD: '98,0x' },
-        "g++-4.7",
-        [ "ppa:ubuntu-toolchain-r/test" ],
-    ),
-
-    linux_pipeline(
-        "Linux 14.04 GCC 4.8*",
-        "cppalliance/droneubuntu1404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11' },
-    ),
-
-    linux_pipeline(
-        "Linux 14.04 GCC 4.9",
-        "cppalliance/droneubuntu1404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-4.9', CXXSTD: '03,11' },
+        "Linux 16.04 GCC 4.9",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-4.9', CXXSTD: '11' },
         "g++-4.9",
-        [ "ppa:ubuntu-toolchain-r/test" ],
     ),
 
     linux_pipeline(
         "Linux 16.04 GCC 5*",
         "cppalliance/droneubuntu1604:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14' },
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '11,14' },
     ),
 
     linux_pipeline(
         "Linux 18.04 GCC 6",
         "cppalliance/droneubuntu1804:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-6', CXXSTD: '03,11,14' },
+        { TOOLSET: 'gcc', COMPILER: 'g++-6', CXXSTD: '11,14' },
         "g++-6",
     ),
 
     linux_pipeline(
         "Linux 18.04 GCC 7* 32/64",
         "cppalliance/droneubuntu1804:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17', ADDRMD: '32,64' },
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '11,14,17', ADDRMD: '32,64' },
     ),
 
     linux_pipeline(
         "Linux 18.04 GCC 8",
         "cppalliance/droneubuntu1804:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-8', CXXSTD: '03,11,14,17' },
+        { TOOLSET: 'gcc', COMPILER: 'g++-8', CXXSTD: '11,14,17' },
         "g++-8",
     ),
 
     linux_pipeline(
         "Linux 20.04 GCC 9* 32",
         "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '32' },
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '11,14,17,2a', ADDRMD: '32' },
     ),
 
     linux_pipeline(
         "Linux 20.04 GCC 9* 64",
         "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '64' },
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '11,14,17,2a', ADDRMD: '64' },
     ),
 
     linux_pipeline(
-        "Linux 20.04 GCC 9 ARM64 32/64",
+        "Linux 20.04 GCC 9* ARM64",
         "cppalliance/droneubuntu2004:multiarch",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '32,64' },
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '11,14,17,2a' },
         arch="arm64",
     ),
 
     linux_pipeline(
-        "Linux 20.04 GCC 10 32 ASAN",
+        "Linux 20.04 GCC 9* S390x",
+        "cppalliance/droneubuntu2004:multiarch",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '11,14,17,2a' },
+        arch="s390x",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 GCC 10 32",
         "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-10', CXXSTD: '03,11,14,17,20', ADDRMD: '32' } + asan,
+        { TOOLSET: 'gcc', COMPILER: 'g++-10', CXXSTD: '11,14,17,20', ADDRMD: '32' },
         "g++-10-multilib",
     ),
 
     linux_pipeline(
-        "Linux 20.04 GCC 10 64 ASAN",
+        "Linux 20.04 GCC 10 64",
         "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-10', CXXSTD: '03,11,14,17,20', ADDRMD: '64' } + asan,
+        { TOOLSET: 'gcc', COMPILER: 'g++-10', CXXSTD: '11,14,17,20', ADDRMD: '64' },
         "g++-10-multilib",
     ),
 
     linux_pipeline(
-        "Linux 20.04 Clang 13",
-        "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-13', CXXSTD: '03,11,14,17,20' },
+        "Linux 22.04 GCC 11* 32",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '11,14,17,2a', ADDRMD: '32' },
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 GCC 11* 64",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '11,14,17,2a', ADDRMD: '64' },
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 GCC 12 32",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-12', CXXSTD: '11,14,17,20,2b', ADDRMD: '32' },
+        "g++-12-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 GCC 12 64",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-12', CXXSTD: '11,14,17,20,2b', ADDRMD: '64' },
+        "g++-12-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 GCC 13 32 UBSAN",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '11,14,17,20,2b', ADDRMD: '32' } + ubsan,
+        "g++-13-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 GCC 13 64 UBSAN",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '11,14,17,20,2b', ADDRMD: '64' } + ubsan,
+        "g++-13-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 GCC 13 32 ASAN",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '11,14,17,20,2b', ADDRMD: '32' } + asan,
+        "g++-13-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 GCC 14 UBSAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        "g++-14-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 GCC 14 ASAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b' } + asan,
+        "g++-14-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.5",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.5', CXXSTD: '11' },
+        "clang-3.5",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.6",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.6', CXXSTD: '11,14' },
+        "clang-3.6",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.7",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.7', CXXSTD: '11,14' },
+        "clang-3.7",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.8",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.8', CXXSTD: '11,14' },
+        "clang-3.8",
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 Clang 13",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-13', CXXSTD: '11,14,17,20' },
         "clang-13",
-        ["deb http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main"],
     ),
 
     linux_pipeline(
-        "Linux 20.04 Clang 14 UBSAN",
-        "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-14', CXXSTD: '03,11,14,17,20' } + ubsan,
+        "Linux 22.04 Clang 14",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-14', CXXSTD: '11,14,17,20' },
         "clang-14",
-        ["deb http://apt.llvm.org/focal/ llvm-toolchain-focal-14 main"],
     ),
 
     linux_pipeline(
-        "Linux 20.04 Clang 14 ASAN",
-        "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-14', CXXSTD: '03,11,14,17,20' } + asan,
-        "clang-14",
-        ["deb http://apt.llvm.org/focal/ llvm-toolchain-focal-14 main"],
+        "Linux 22.04 Clang 15",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-15', CXXSTD: '11,14,17,20,2b' },
+        "clang-15",
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 Clang 16",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-16', CXXSTD: '11,14,17,20,2b' },
+        "clang-16",
+    ),
+
+    linux_pipeline(
+        "Linux 23.10 Clang 17",
+        "cppalliance/droneubuntu2310:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' },
+        "clang-17",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 Clang 18 UBSAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        "clang-18",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 Clang 18 ASAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' } + asan,
+        "clang-18",
     ),
 
     macos_pipeline(
         "MacOS 10.15 Xcode 12.2 UBSAN",
-        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,1z' } + ubsan,
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,1z' } + ubsan,
     ),
 
     macos_pipeline(
         "MacOS 10.15 Xcode 12.2 ASAN",
-        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,1z' } + asan,
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,1z' } + asan,
+    ),
+
+    macos_pipeline(
+        "MacOS 12.4 Xcode 13.4.1 UBSAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        xcode_version = "13.4.1", osx_version = "monterey", arch = "arm64",
+    ),
+
+    macos_pipeline(
+        "MacOS 12.4 Xcode 13.4.1 ASAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,17,20,2b' } + asan,
+        xcode_version = "13.4.1", osx_version = "monterey", arch = "arm64",
     ),
 
     windows_pipeline(
         "Windows VS2015 msvc-14.0",
         "cppalliance/dronevs2015",
-        { TOOLSET: 'msvc-14.0', CXXSTD: '14,latest' },
+        { TOOLSET: 'msvc-14.0', CXXSTD: '14,latest', B2_DONT_EMBED_MANIFEST: '1' },
     ),
 
     windows_pipeline(

.drone/drone.sh

@@ -5,6 +5,7 @@
 # https://www.boost.org/LICENSE_1_0.txt
 
 set -ex
+export PATH=~/.local/bin:/usr/local/bin:$PATH
 
 DRONE_BUILD_DIR=$(pwd)
 

.github/workflows/ci.yml

@@ -18,108 +18,173 @@ jobs:
       matrix:
         include:
           - toolset: gcc-4.8
-            cxxstd: "03,11"
-            os: ubuntu-18.04
+            cxxstd: "11"
+            os: ubuntu-latest
+            container: ubuntu:18.04
             install: g++-4.8
           - toolset: gcc-5
-            cxxstd: "03,11,14,1z"
-            os: ubuntu-18.04
+            cxxstd: "11,14,1z"
+            os: ubuntu-latest
+            container: ubuntu:18.04
             install: g++-5
           - toolset: gcc-6
-            cxxstd: "03,11,14,1z"
-            os: ubuntu-18.04
+            cxxstd: "11,14,1z"
+            os: ubuntu-latest
+            container: ubuntu:18.04
             install: g++-6
           - toolset: gcc-7
-            cxxstd: "03,11,14,17"
-            os: ubuntu-18.04
+            cxxstd: "11,14,17"
+            os: ubuntu-latest
+            container: ubuntu:18.04
           - toolset: gcc-8
-            cxxstd: "03,11,14,17,2a"
-            os: ubuntu-18.04
+            cxxstd: "11,14,17,2a"
+            os: ubuntu-20.04
             install: g++-8
           - toolset: gcc-9
-            cxxstd: "03,11,14,17,2a"
+            cxxstd: "11,14,17,2a"
             os: ubuntu-20.04
           - toolset: gcc-10
-            cxxstd: "03,11,14,17,2a"
+            cxxstd: "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
+            cxxstd: "11,14,17,2a"
+            os: ubuntu-22.04
           - toolset: gcc-12
-            cxxstd: "03,11,14,17,20"
+            cxxstd: "11,14,17,20,2b"
             os: ubuntu-22.04
             install: g++-12
+          - toolset: gcc-13
+            cxxstd: "11,14,17,20,2b"
+            os: ubuntu-latest
+            container: ubuntu:23.04
+            install: g++-13
+          - toolset: gcc-14
+            cxxstd: "11,14,17,20,2b"
+            os: ubuntu-latest
+            container: ubuntu:24.04
+            install: g++-14
           - toolset: clang
             compiler: clang++-3.9
-            cxxstd: "03,11,14"
-            os: ubuntu-18.04
+            cxxstd: "11,14"
+            os: ubuntu-latest
+            container: ubuntu:18.04
             install: clang-3.9
           - toolset: clang
             compiler: clang++-4.0
-            cxxstd: "03,11,14"
-            os: ubuntu-18.04
+            cxxstd: "11,14"
+            os: ubuntu-latest
+            container: ubuntu:18.04
             install: clang-4.0
           - toolset: clang
             compiler: clang++-5.0
-            cxxstd: "03,11,14,1z"
-            os: ubuntu-18.04
+            cxxstd: "11,14,1z"
+            os: ubuntu-latest
+            container: ubuntu:18.04
             install: clang-5.0
           - toolset: clang
             compiler: clang++-6.0
-            cxxstd: "03,11,14,17"
-            os: ubuntu-18.04
+            cxxstd: "11,14,17"
+            os: ubuntu-20.04
             install: clang-6.0
           - toolset: clang
             compiler: clang++-7
-            cxxstd: "03,11,14,17"
-            os: ubuntu-18.04
+            cxxstd: "11,14,17"
+            os: ubuntu-20.04
             install: clang-7
           - toolset: clang
             compiler: clang++-8
-            cxxstd: "03,11,14,17"
+            cxxstd: "11,14,17"
             os: ubuntu-20.04
             install: clang-8
           - toolset: clang
             compiler: clang++-9
-            cxxstd: "03,11,14,17"
+            cxxstd: "11,14,17"
             os: ubuntu-20.04
             install: clang-9
           - toolset: clang
             compiler: clang++-10
-            cxxstd: "03,11,14,17,2a"
+            cxxstd: "11,14,17,2a"
             os: ubuntu-20.04
           - toolset: clang
             compiler: clang++-11
-            cxxstd: "03,11,14,17,2a"
+            cxxstd: "11,14,17,2a"
             os: ubuntu-20.04
           - toolset: clang
             compiler: clang++-12
-            cxxstd: "03,11,14,17,20"
+            cxxstd: "11,14,17,20"
             os: ubuntu-20.04
           - toolset: clang
             compiler: clang++-13
-            cxxstd: "03,11,14,17,20"
-            os: ubuntu-22.04
+            cxxstd: "11,14,17,20,2b"
+            container: ubuntu:22.04
+            os: ubuntu-latest
             install: clang-13
           - toolset: clang
             compiler: clang++-14
-            cxxstd: "03,11,14,17,20"
-            os: ubuntu-22.04
+            cxxstd: "11,14,17,20,2b"
+            container: ubuntu:22.04
+            os: ubuntu-latest
             install: clang-14
           - toolset: clang
-            cxxstd: "03,11,14,17,2a"
-            os: macos-10.15
+            compiler: clang++-15
+            cxxstd: "11,14,17,20,2b"
+            container: ubuntu:22.04
+            os: ubuntu-latest
+            install: clang-15
+          - toolset: clang
+            compiler: clang++-16
+            cxxstd: "11,14,17,20,2b"
+            container: ubuntu:23.04
+            os: ubuntu-latest
+            install: clang-16
+          - toolset: clang
+            compiler: clang++-17
+            cxxstd: "11,14,17,20,2b"
+            container: ubuntu:23.10
+            os: ubuntu-latest
+            install: clang-17
+          - toolset: clang
+            compiler: clang++-18
+            cxxstd: "11,14,17,20,2b"
+            container: ubuntu:24.04
+            os: ubuntu-latest
+            install: clang-18
+          - toolset: clang
+            cxxstd: "11,14,17,20,2b"
+            os: macos-12
+          - toolset: clang
+            cxxstd: "11,14,17,20,2b"
+            os: macos-13
+          - toolset: clang
+            cxxstd: "11,14,17,20,2b"
+            os: macos-14
 
     runs-on: ${{matrix.os}}
+    container: ${{matrix.container}}
+
+    defaults:
+      run:
+        shell: bash
 
     steps:
-      - uses: actions/checkout@v2
+      - name: Enable Node 16
+        run: |
+          echo "ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true" >> $GITHUB_ENV
+
+      - uses: actions/checkout@v3
+
+      - name: Setup container environment
+        if: matrix.container
+        run: |
+          apt-get update
+          apt-get -y install sudo python3 git g++
 
       - name: Install packages
         if: matrix.install
-        run: sudo apt install ${{matrix.install}}
+        run: |
+          sudo apt-get update
+          sudo apt-get -y install ${{matrix.install}}
 
       - name: Setup Boost
         run: |
@@ -139,7 +204,7 @@ jobs:
           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
+          python3 tools/boostdep/depinst/depinst.py --git_args "--jobs 3" $LIBRARY
           ./bootstrap.sh
           ./b2 -d0 headers
 
@@ -171,18 +236,18 @@ jobs:
             addrmd: 32,64
             os: windows-2022
           - toolset: clang-win
-            cxxstd: "14,17,latest"
+            cxxstd: "14,17,20,latest"
             addrmd: 32,64
             os: windows-2022
           - toolset: gcc
-            cxxstd: "03,11,14,17,2a"
+            cxxstd: "11,14,17,2a"
             addrmd: 64
             os: windows-2019
 
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Setup Boost
         shell: cmd
@@ -217,19 +282,20 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-18.04
           - os: ubuntu-20.04
           - os: ubuntu-22.04
-          - os: macos-10.15
+          - os: macos-12
+          - os: macos-13
+          - os: macos-14
 
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Install packages
         if: matrix.install
-        run: sudo apt install ${{matrix.install}}
+        run: sudo apt-get -y install ${{matrix.install}}
 
       - name: Setup Boost
         run: |
@@ -264,19 +330,20 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-18.04
           - os: ubuntu-20.04
           - os: ubuntu-22.04
-          - os: macos-10.15
+          - os: macos-12
+          - os: macos-13
+          - os: macos-14
 
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Install packages
         if: matrix.install
-        run: sudo apt install ${{matrix.install}}
+        run: sudo apt-get -y install ${{matrix.install}}
 
       - name: Setup Boost
         run: |
@@ -321,19 +388,20 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-18.04
           - os: ubuntu-20.04
           - os: ubuntu-22.04
-          - os: macos-10.15
+          - os: macos-12
+          - os: macos-13
+          - os: macos-14
 
     runs-on: ${{matrix.os}}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Install packages
         if: matrix.install
-        run: sudo apt install ${{matrix.install}}
+        run: sudo apt-get -y install ${{matrix.install}}
 
       - name: Setup Boost
         run: |
@@ -370,3 +438,183 @@ jobs:
         run: |
           cd ../boost-root/__build__
           ctest --output-on-failure --no-tests=error
+
+  windows-cmake-subdir:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Use library with add_subdirectory (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_subdir_test
+          mkdir __build__ && cd __build__
+          cmake ..
+          cmake --build . --config Debug
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Use library with add_subdirectory (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_subdir_test/__build__
+          cmake --build . --config Release
+          ctest --output-on-failure --no-tests=error -C Release
+
+  windows-cmake-install:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Configure
+        shell: cmd
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=%LIBRARY% -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+
+      - name: Install (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install --config Debug
+
+      - name: Install (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install --config Release
+
+      - name: Use the installed library (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_install_test && mkdir __build__ && cd __build__
+          cmake -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+          cmake --build . --config Debug
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Use the installed library (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_install_test/__build__
+          cmake --build . --config Release
+          ctest --output-on-failure --no-tests=error -C Release
+
+  windows-cmake-test:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Configure
+        shell: cmd
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=%LIBRARY% -DBUILD_TESTING=ON ..
+
+      - name: Build tests (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target tests --config Debug
+
+      - name: Run tests (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Build tests (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target tests --config Release
+
+      - name: Run tests (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          ctest --output-on-failure --no-tests=error -C Release

CMakeLists.txt

@@ -1,8 +1,8 @@
 # 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
 
-cmake_minimum_required(VERSION 3.5...3.16)
+cmake_minimum_required(VERSION 3.8...3.20)
 
 project(boost_system VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
 
@@ -20,7 +20,18 @@ target_link_libraries(boost_system
     Boost::winapi
 )
 
-if(BUILD_TESTING)
+target_compile_features(boost_system INTERFACE cxx_std_11)
+
+if(CMAKE_VERSION VERSION_GREATER 3.18 AND CMAKE_GENERATOR MATCHES "Visual Studio")
+
+  file(GLOB_RECURSE boost_system_IDEFILES CONFIGURE_DEPENDS include/*.hpp)
+  source_group(TREE ${PROJECT_SOURCE_DIR}/include FILES ${boost_system_IDEFILES} PREFIX "Header Files")
+  list(APPEND boost_system_IDEFILES extra/boost_system.natvis)
+  target_sources(boost_system PRIVATE ${boost_system_IDEFILES})
+
+endif()
+
+if(BUILD_TESTING AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/CMakeLists.txt")
 
   add_subdirectory(test)
 

appveyor.yml

@@ -14,32 +14,27 @@ branches:
 
 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,latest
-      ADDRMD: 32,64
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
-      ADDPATH: C:\cygwin\bin;
-      TOOLSET: gcc
-      CXXSTD: 03,11,14,1z
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+      ADDRMD: 32
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      TOOLSET: msvc-14.1
+      CXXSTD: 14,17,latest
+      ADDRMD: 64
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
       ADDPATH: C:\cygwin64\bin;
       TOOLSET: gcc
-      CXXSTD: 03,11,14,1z
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
-      ADDPATH: C:\mingw\bin;
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      ADDPATH: C:\mingw-w64\i686-8.1.0-posix-dwarf-rt_v6-rev0\mingw32\bin;
       TOOLSET: gcc
-      CXXSTD: 03,11,14,1z
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
-      ADDPATH: C:\mingw-w64\x86_64-6.3.0-posix-seh-rt_v5-rev1\mingw64\bin;
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      ADDPATH: C:\mingw-w64\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\bin;
       TOOLSET: gcc
-      CXXSTD: 03,11,14,1z
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+      CMAKE_SUBDIR: 1
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+      CMAKE_INSTALL: 1
 
 install:
   - set BOOST_BRANCH=develop
@@ -59,4 +54,27 @@ test_script:
   - PATH=%ADDPATH%%PATH%
   - if not "%CXXSTD%" == "" set CXXSTD=cxxstd=%CXXSTD%
   - if not "%ADDRMD%" == "" set ADDRMD=address-model=%ADDRMD%
-  - b2 -j3 libs/system/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% variant=debug,release embed-manifest-via=linker
+  - if "%CMAKE%%CMAKE_SUBDIR%%CMAKE_INSTALL%" == ""  b2 -j3 libs/system/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% variant=debug,release embed-manifest-via=linker
+
+  - if not "%CMAKE%" == ""  mkdir __build__ && cd __build__
+  - if not "%CMAKE%" == ""  cmake -DBUILD_TESTING=ON -DBOOST_INCLUDE_LIBRARIES=system -DBoost_VERBOSE=ON ..
+  - if not "%CMAKE%" == ""  cmake --build . --target tests -j 3 --config Debug & ctest --output-on-failure --no-tests=error -j 3 -C Debug
+  - if not "%CMAKE%" == ""  cmake --build . --target tests -j 3 --config Release & ctest --output-on-failure --no-tests=error -j 3 -C Release
+  - if not "%CMAKE%" == ""  cmake --build . --target tests -j 3 --config MinSizeRel & ctest --output-on-failure --no-tests=error -j 3 -C MinSizeRel
+  - if not "%CMAKE%" == ""  cmake --build . --target tests -j 3 --config RelWithDebInfo & ctest --output-on-failure --no-tests=error -j 3 -C RelWithDebInfo
+
+  - if not "%CMAKE_SUBDIR%" == ""  cd libs/system/test/cmake_subdir_test && mkdir __build__ && cd __build__
+  - if not "%CMAKE_SUBDIR%" == ""  cmake ..
+  - if not "%CMAKE_SUBDIR%" == ""  cmake --build . --config Debug && cmake --build . --target check --config Debug
+  - if not "%CMAKE_SUBDIR%" == ""  cmake --build . --config Release && cmake --build . --target check --config Release
+  - if not "%CMAKE_SUBDIR%" == ""  cmake --build . --config MinSizeRel && cmake --build . --target check --config MinSizeRel
+  - if not "%CMAKE_SUBDIR%" == ""  cmake --build . --config RelWithDebInfo && cmake --build . --target check --config RelWithDebInfo
+
+  - if not "%CMAKE_INSTALL%" == ""  mkdir __build__ && cd __build__
+  - if not "%CMAKE_INSTALL%" == ""  cmake -DBOOST_INCLUDE_LIBRARIES=system -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+  - if not "%CMAKE_INSTALL%" == ""  cmake --build . --target install --config Debug
+  - if not "%CMAKE_INSTALL%" == ""  cmake --build . --target install --config Release
+  - if not "%CMAKE_INSTALL%" == ""  cd ../libs/system/test/cmake_install_test && mkdir __build__ && cd __build__
+  - if not "%CMAKE_INSTALL%" == ""  cmake -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+  - if not "%CMAKE_INSTALL%" == ""  cmake --build . --config Debug && cmake --build . --target check --config Debug
+  - if not "%CMAKE_INSTALL%" == ""  cmake --build . --config Release && cmake --build . --target check --config Release

doc/system/changes.adoc

@@ -8,6 +8,34 @@ https://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix:
 
+## Changes in Boost 1.86
+
+* Support `result<T> & fv`, where `fv` returns `void`.
+* Support `result<void> &= fv;`, where `fv` returns `void`.
+
+## Changes in Boost 1.85
+
+* {cpp}03 is no longer supported; a {cpp}11 compiler is required. (This includes GCC 4.8 or later, and MSVC 14.0 (VS 2015) or later.)
+* The deprecated header `boost/system/cygwin_error.hpp` has been removed.
+* The original and obsolete (32 bit) MinGW is no longer supported. MinGW-w64 (both 64 and 32 bit) is still supported.
+* `operator&` now works for `result<void>` (by way of taking a nullary function.)
+* Added `operator|=` for `result`.
+
+## Changes in Boost 1.84
+
+* Added support for `result<U&, E>`.
+* Added `operator|` for `result`.
+* Added `operator&` for `result`.
+* Added `operator&=` for `result`.
+
+## Changes in Boost 1.81
+
+* The macro `BOOST_SYSTEM_DISABLE_THREADS` can now be defined to disable
+  the use of `<mutex>` (e.g. on single-threaded libstdc++).
+* Added `value_type`, `error_type`, `in_place_value`, `in_place_error`
+  to `result<>`.
+* Added `emplace` to `result<>`.
+
 ## Changes in Boost 1.80
 
 * When an `error_code` is converted to `std::error_code` and then back

doc/system/reference.adoc

@@ -12,13 +12,6 @@ http://www.boost.org/LICENSE_1_0.txt
 # Reference
 :idprefix: ref_
 
-## Use of {cpp}11 and {cpp}14 Features
-
-The library is documented to use several {cpp}11 and {cpp}14 features,
-including `noexcept`, explicit conversion operators and `constexpr`. The
-actual implementation uses {cpp}11 and {cpp}14 features only when they are
-available, and otherwise falls back on {cpp}03 features.
-
 ## Macros
 
 When `BOOST_SYSTEM_ENABLE_DEPRECATED` is defined, the library provides
@@ -29,6 +22,11 @@ When `BOOST_SYSTEM_USE_UTF8` is defined, on Windows the library returns
 UTF-8 messages using code page `CP_UTF8` instead of the default `CP_ACP`.
 This macro has no effect on POSIX.
 
+When `BOOST_SYSTEM_DISABLE_THREADS` is defined, the library assumes that
+the current platform doesn't support multiple threads and disables the use
+of the standard header `<mutex>`, eliminating the mutex locks. The single
+threaded `libstdc++` is one such platform.
+
 ## Deprecated Names
 
 In the process of adding Boost.System to the {cpp}11 standard library, the
@@ -1512,6 +1510,38 @@ constexpr in_place_error_t in_place_error{};
 
 template<class T, class E = error_code> class result;
 template<class E> class result<void, E>;
+template<class U, class E> class result<U&, E>;
+
+// operator|
+
+template<class T, class E, class U> T operator|( result<T, E> const& r, U&& u );
+template<class T, class E, class U> T operator|( result<T, E>&& r, U&& u );
+
+template<class T, class E, class F> T operator|( result<T, E> const& r, F&& f );
+template<class T, class E, class F> T operator|( result<T, E>&& r, F&& f );
+
+template<class T, class E, class F, class R = ...> R operator|( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class R = ...> R operator|( result<T, E>&& r, F&& f );
+template<class E, class F, class R = ...> R operator|( result<void, E> const& r, F&& f );
+template<class E, class F, class R = ...> R operator|( result<void, E>&& r, F&& f );
+
+// operator&
+
+template<class T, class E, class F, class U = ...>
+  result<U, E> operator&( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class U = ...>
+  result<U, E> operator&( result<T, E>&& r, F&& f );
+
+template<class T, class E, class F, class R = ...> R operator&( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class R = ...> R operator&( result<T, E>&& r, F&& f );
+
+// operator&=
+
+template<class T, class E, class F, class U = ...>
+  result<T, E>& operator&=( result<T, E>& r, F&& f );
+
+template<class T, class E, class F, class R = ...>
+  result<T, E>& operator&=( result<T, E>& r, F&& f );
 
 } // namespace system
 } // namespace boost
@@ -1595,6 +1625,12 @@ template<class T, class E = error_code> class result
 {
 public:
 
+    using value_type = T;
+    using error_type = E;
+
+    static constexpr in_place_value_t in_place_value{};
+    static constexpr in_place_error_t in_place_error{};
+
     // constructors
 
     constexpr result();
@@ -1646,7 +1682,13 @@ public:
 
     // error access
 
-    constexpr E error() const;
+    constexpr E error() const &;
+    constexpr E error() &&;
+
+    // emplace
+
+    template<class... A>
+      constexpr T& emplace( A&&... a );
 
     // swap
 
@@ -1696,7 +1738,7 @@ Effects: ::
     ensures that `*this` holds the error `E( std::forward<A>(a)... )`.
   - Otherwise, this constructor does not participate in overload resolution.
 Remarks: ::
-  This constructor is only enabled when `sizeof...(T) > 0`.
+  This constructor is only enabled when `sizeof...(A) > 0`.
 
 ```
 template<class... A>
@@ -1730,7 +1772,7 @@ template<class T2, class E2>
 * {blank}
 +
 Ensures: ::
-  If `r2.has_value()` is `true`, `*this` holds the value `T( *r2 )`, otherwise `*this` holds the value `E( r2.error() )`.
+  If `r2.has_value()` is `true`, `*this` holds the value `T( *r2 )`, otherwise `*this` holds the error `E( r2.error() )`.
 Remarks: ::
   This constructor is only enabled when `std::is_convertible<T2, T>::value && std::is_convertible<E2, E>::value` is `true`.
 
@@ -1742,7 +1784,7 @@ template<class T2, class E2>
 * {blank}
 +
 Ensures: ::
-  If `r2.has_value()` is `true`, `*this` holds the value `T( std::move( *r2 ) )`, otherwise `*this` holds the value `E( r2.error() )`.
+  If `r2.has_value()` is `true`, `*this` holds the value `T( std::move( *r2 ) )`, otherwise `*this` holds the error `E( r2.error() )`.
 Remarks: ::
   This constructor is only enabled when `std::is_convertible<T2, T>::value && std::is_convertible<E2, E>::value` is `true`.
 
@@ -1835,7 +1877,8 @@ Returns: ::
 #### Error Access
 
 ```
-constexpr E error() const;
+constexpr E error() const &;
+constexpr E error() &&;
 ```
 [none]
 * {blank}
@@ -1843,6 +1886,20 @@ constexpr E error() const;
 Effects: ::
   If `*this` holds an error, returns it. Otherwise, returns `E()`.
 
+#### emplace
+
+```
+template<class... A>
+  constexpr T& emplace( A&&... a );
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds the value `T( std::forward<A>(a)... )`.
+Returns: ::
+  A reference to the contained value.
+
 #### swap
 
 ```
@@ -1911,6 +1968,12 @@ template<class E> class result<void, E>
 {
 public:
 
+    using value_type = void;
+    using error_type = E;
+
+    static constexpr in_place_value_t in_place_value{};
+    static constexpr in_place_error_t in_place_error{};
+
     // constructors
 
     constexpr result() noexcept;
@@ -1923,6 +1986,9 @@ public:
     template<class... A>
       constexpr result( in_place_error_t, A&&... a );
 
+    template<class E2>
+      constexpr result( result<void, E2> const& r2 );
+
     // queries
 
     constexpr bool has_value() const noexcept;
@@ -1943,7 +2009,12 @@ public:
 
     // error access
 
-    constexpr E error() const;
+    constexpr E error() const &;
+    constexpr E error() &&;
+
+    // emplace
+
+    constexpr void emplace();
 
     // swap
 
@@ -1989,7 +2060,7 @@ Effects: ::
     ensures that `*this` holds the error `E( std::forward<A>(a)... )`.
   - Otherwise, this constructor does not participate in overload resolution.
 Remarks: ::
-  This constructor is only enabled when `sizeof...(T) > 0`.
+  This constructor is only enabled when `sizeof...(A) > 0`.
 
 ```
 template<class... A>
@@ -2013,6 +2084,18 @@ Ensures: ::
 Remarks: ::
   This constructor is only enabled when `std::is_constructible<E, A...>::value` is `true`.
 
+```
+template<class E2>
+  constexpr result( result<void, E2> const& r2 );
+```
+[none]
+* {blank}
++
+Ensures: ::
+  If `r2.has_value()` is `true`, `*this` holds an unspecified value, otherwise `*this` holds the error `E( r2.error() )`.
+Remarks: ::
+  This constructor is only enabled when `std::is_convertible<E2, E>::value` is `true`.
+
 #### Queries
 
 ```
@@ -2080,7 +2163,8 @@ Effects: ::
 #### Error Access
 
 ```
-constexpr E error() const;
+constexpr E error() const &;
+constexpr E error() &&;
 ```
 [none]
 * {blank}
@@ -2088,6 +2172,17 @@ constexpr E error() const;
 Effects: ::
   If `*this` holds an error, returns it. Otherwise, returns `E()`.
 
+#### emplace
+
+```
+constexpr void emplace();
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds an unspecified value.
+
 #### swap
 
 ```
@@ -2146,6 +2241,637 @@ Effects: ::
 Returns: ::
   `os`.
 
+### result<U&, E>
+
+```
+namespace boost {
+namespace system {
+
+template<class U, class E> class result<U&, E>
+{
+public:
+
+    using value_type = U&;
+    using error_type = E;
+
+    static constexpr in_place_value_t in_place_value{};
+    static constexpr in_place_error_t in_place_error{};
+
+    // constructors
+
+    template<class A>
+      constexpr result( A&& a ) noexcept;
+
+    template<class... A>
+      constexpr result( A&&... a );
+
+    template<class A>
+      constexpr result( in_place_value_t, A&& a ) noexcept;
+
+    template<class... A>
+      constexpr result( in_place_error_t, A&&... a );
+
+    template<class U2, class E2>
+      constexpr result( result<U2&, E2> const& r2 );
+
+    // queries
+
+    constexpr bool has_value() const noexcept;
+    constexpr bool has_error() const noexcept;
+    constexpr explicit operator bool() const noexcept;
+
+    // checked value access
+
+    constexpr U& value( boost::source_location const & loc =
+      BOOST_CURRENT_LOCATION ) const;
+
+    // unchecked value access
+
+    constexpr U* operator->() const noexcept;
+    constexpr U& operator*() const noexcept;
+
+    // error access
+
+    constexpr E error() const &;
+    constexpr E error() &&;
+
+    // emplace
+
+    template<class A>
+      constexpr U& emplace( A&& a ) noexcept;
+
+    // swap
+
+    constexpr void swap( result& r );
+    friend constexpr void swap( result & r1, result & r2 );
+
+    // equality
+
+    friend constexpr bool operator==( result const & r1, result const & r2 );
+    friend constexpr bool operator!=( result const & r1, result const & r2 );
+};
+
+} // namespace system
+} // namespace boost
+```
+
+#### Constructors
+
+```
+template<class A>
+  constexpr result( A&& a ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds the reference `static_cast<U&>( std::forward<A>(a) )`.
+Remarks: ::
+  This constructor is only enabled when `A` is `B&` and `std::is_convertible<B*, U*>::value` is `true`.
+
+```
+template<class... A>
+  constexpr result( A&&... a );
+```
+[none]
+* {blank}
++
+Effects: ::
+  - If `std::is_constructible<E, A...>::value && !std::is_constructible<U&, A...>::value`,
+    ensures that `*this` holds the error `E( std::forward<A>(a)... )`.
+  - Otherwise, this constructor does not participate in overload resolution.
+Remarks: ::
+  This constructor is only enabled when `sizeof...(A) > 0`.
+
+```
+template<class A>
+  constexpr result( in_place_value_t, A&& a ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds the reference `static_cast<U&>( std::forward<A>(a) )`.
+Remarks: ::
+  This constructor is only enabled when `A` is `B&` and `std::is_convertible<B*, U*>::value` is `true`.
+
+```
+template<class... A>
+  constexpr result( in_place_error_t, A&&... a );
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds the error `E( std::forward<A>(a)... )`.
+Remarks: ::
+  This constructor is only enabled when `std::is_constructible<E, A...>::value` is `true`.
+
+```
+template<class U2, class E2>
+  constexpr result( result<U2&, E2> const& r2 );
+```
+[none]
+* {blank}
++
+Ensures: ::
+  If `r2.has_value()` is `true`, `*this` holds the reference `static_cast<U&>( *r2 )`, otherwise `*this` holds the error `E( r2.error() )`.
+Remarks: ::
+  This constructor is only enabled when `std::is_convertible<U2*, U*>::value && std::is_convertible<E2, E>::value` is `true`.
+
+#### Queries
+
+```
+constexpr bool has_value() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+  `true` when `*this` holds a value, `false` otherwise.
+
+```
+constexpr bool has_error() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+  `!has_value()`.
+
+```
+constexpr explicit operator bool() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+  `has_value()`.
+
+#### Checked Value Access
+
+```
+constexpr U& value(
+  boost::source_location const & loc = BOOST_CURRENT_LOCATION ) const;
+```
+[none]
+* {blank}
++
+Effects: ::
+  If `*this` holds a reference, returns it. Otherwise,
+  calls `throw_exception_from_error`, passing it a reference to
+  the held error, and `loc`.
+
+#### Unchecked Value Access
+
+```
+constexpr U* operator->() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: ::
+  If `*this` holds a reference, a pointer to its referent. Otherwise, `nullptr`.
+
+```
+constexpr U& operator*() const noexcept;
+```
+[none]
+* {blank}
++
+Requires: :: `*this` holds a reference.
+Returns: ::
+  `*operator\->()`.
+
+#### Error Access
+
+```
+constexpr E error() const &;
+constexpr E error() &&;
+```
+[none]
+* {blank}
++
+Effects: ::
+  If `*this` holds an error, returns it. Otherwise, returns `E()`.
+
+#### emplace
+
+```
+template<class A>
+  constexpr U& emplace( A&& a ) noexcept;
+```
+[none]
+* {blank}
++
+Ensures: ::
+  `*this` holds the reference `static_cast<U&>( std::forward<A>(a)... )`.
+Returns: ::
+  The contained reference.
+Remarks: ::
+  This function is only enabled when `A` is `B&` and `std::is_convertible<B*, U*>::value` is `true`.
+
+#### swap
+
+```
+constexpr void swap( result& r );
+```
+[none]
+* {blank}
++
+Effects: ::
+  Exchanges the contents of `*this` and `r`.
+
+```
+friend constexpr void swap( result & r1, result & r2 );
+```
+[none]
+* {blank}
++
+Effects: ::
+  Exchanges the contents of `r1` and `r2`.
+
+#### Equality
+
+```
+friend constexpr bool operator==( result const & r1, result const & r2 );
+```
+[none]
+* {blank}
++
+Effects: ::
+  - If `r1` holds a reference `t1` and `r2` holds a reference `t2`, returns `t1 == t2`.
+  - If `r1` holds an error `e1` and `r2` holds an error `e2`, returns `e1 == e2`.
+  - Otherwise, returns `false`.
+
+```
+friend constexpr bool operator!=( result const & r1, result const & r2 );
+```
+[none]
+* {blank}
++
+Returns: ::
+  `!( r1 == r2 )`.
+
+### Chaining
+
+#### operator|
+
+```
+template<class T, class E, class U> T operator|( result<T, E> const& r, U&& u );
+template<class T, class E, class U> T operator|( result<T, E>&& r, U&& u );
+```
+[none]
+* {blank}
++
+Returns the value in `r`, or if `r` contains an error, a default value `u`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `*r`.
+  - Otherwise, returns `u`.
+Remarks: ::
+  Only enabled when `U` is convertible to `T`.
+Example: ::
++
+```
+result<int> get_server_port(); // can fail
+
+int get_port()
+{
+    return get_server_port() | 443;
+}
+```
+
+```
+template<class T, class E, class F> T operator|( result<T, E> const& r, F&& f );
+template<class T, class E, class F> T operator|( result<T, E>&& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the value in `r`, or if `r` contains an error, a default value obtained
+by invoking the function `f`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `*r`.
+  - Otherwise, returns `f()`.
+Remarks: ::
+  Only enabled when `f()` is convertible to `T`.
+Example: ::
++
+```
+result<int> get_server_port(); // can fail
+int get_default_port();
+
+int get_port()
+{
+    return get_server_port() | get_default_port;
+}
+```
++
+Note that the right hand side is `get_default_port` and not `get_default_port()`.
+This is important; spelled this way, the function `get_default_port` is called
+only when `get_server_port_impl()` fails. If it were
++
+```
+    return get_server_port() | get_default_port();
+```
++
+the function would have been called unconditionally.
++
+Another, equivalent, way is to use a lambda
++
+```
+    return get_server_port() | []{ return get_default_port(); };
+```
++
+which isn't necessary here, but would be needed for more complex expressions.
+
+```
+template<class T, class E, class F, class R = ...> R operator|( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class R = ...> R operator|( result<T, E>&& r, F&& f );
+template<class E, class F, class R = ...> R operator|( result<void, E> const& r, F&& f );
+template<class E, class F, class R = ...> R operator|( result<void, E>&& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the value in `r`, or if `r` contains an error, another `result` obtained
+by invoking the function `f`.
++
+Let `R` be the type of `f()`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `*r`.
+  - Otherwise, returns `f()`.
+Remarks: ::
+  Only enabled when `R` is an instance of `result` and `T` is convertible to `R::value_type`.
+Example: ::
++
+```
+result<int> get_server_port(); // can fail
+result<int> get_default_port(); // can fail
+
+int get_port()
+{
+    return get_server_port() | get_default_port | 443;
+}
+```
+
+#### operator|=
+
+```
+template<class T, class E, class U> result<T, E>& operator|=( result<T, E>& r, U&& u );
+```
+[none]
+* {blank}
++
+If `r` contains an error, assigns a value to it, constructed from `u`.
++
+Effects: ::
+  If `r.has_value()` is `false`, assigns `u` to `r`.
+Returns: ::
+  `r`.
+Remarks: ::
+  Only enabled when `U` is convertible to `T`.
+
+```
+template<class T, class E, class F> result<T, E>& operator|=( result<T, E>& r, F&& f );
+```
+[none]
+* {blank}
++
+If `r` contains an error, assigns `f()` to it.
++
+Effects: ::
+  If `r.has_value()` is `false`, assigns `f()` to `r`.
+Returns: ::
+  `r`.
+Remarks: ::
+  Only enabled when the type of `f()` is either
+  - convertible to `T` or
+  - an instance of `result` convertible to `result<T, E>`.
+Example: ::
++
+```
+result<response> query_impl( std::string_view server, request const& req );
+
+result<response> query( std::vector<std::string_view> const& servers, request const& req )
+{
+    result<response> r = make_error_code( errc::invalid_argument );
+
+    for( auto const& server: servers )
+    {
+        r |= std::bind( query_impl, server, std::ref( req ) );
+    }
+
+    return r;
+}
+```
+
+
+#### operator&
+
+```
+template<class T, class E, class F, class U = ...>
+  result<U, E> operator&( result<T, E> const& r, F&& f );
+
+template<class T, class E, class F, class U = ...>
+  result<U, E> operator&( result<T, E>&& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the error in `r`, or if `r` contains a value, transforms the value by calling `f` on it.
++
+Let `U` be the type of `f(*r)`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `f(*r)`.
+  - Otherwise, returns `r.error()`.
+Remarks: ::
+  Only enabled when `U` is not an instance of `result`.
+Example: ::
++
+```
+struct currency_type
+{
+    char code_[ 4 ] = {};
+};
+
+result<double> get_exchange_rate( currency_type from, currency_type to );
+
+result<double> convert( double amount, currency_type from, currency_type to )
+{
+    return get_exchange_rate( from, to ) & [&](double rate){ return rate * amount; };
+}
+```
+
+```
+template<class E, class F, class U = ...>
+  result<U, E> operator&( result<void, E> const& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the error in `r`, or if `r` contains a value, replaces it with the result of calling `f`.
++
+Let `U` be the type of `f()`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `f()`.
+  - Otherwise, returns `r.error()`.
+Remarks: ::
+  Only enabled when `U` is not an instance of `result`.
+
+
+```
+template<class T, class E, class F, class R = ...> R operator&( result<T, E> const& r, F&& f );
+template<class T, class E, class F, class R = ...> R operator&( result<T, E>&& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the error in `r`, or if `r` contains a value, another `result` obtained
+by invoking the function `f` on the value in `r`.
++
+Let `R` be the type of `f(*r)`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `f(*r)`.
+  - Otherwise, returns `r.error()`.
+Remarks: ::
+  Only enabled when `R` is an instance of `result` and `E` is convertible to `R::error_type`.
+Example: ::
++
+```
+struct JsonValue
+{
+    result<JsonValue const&> at( std::size_t i ) const noexcept;
+    result<JsonValue const&> at( std::string_view key ) const noexcept;
+    template<class T> result<T> to_number() const noexcept;
+};
+
+namespace helpers
+{
+
+inline auto at( std::size_t i ) {
+    return [=](JsonValue const& jv){ return jv.at( i ); }; }
+
+inline auto at( std::string_view key ) {
+    return [=](JsonValue const& jv){ return jv.at( key ); }; }
+
+template<class T> inline auto to_number() {
+    return [](JsonValue const& jv){ return jv.to_number<T>(); }; }
+
+} // namespace helpers
+
+int get_port( JsonValue const& config, int def )
+{
+    using namespace helpers;
+    return config.at( "servers" ) & at( 0 ) & at( "port" ) & to_number<int>() | def;
+}
+```
+
+```
+template<class E, class F, class R = ...> R operator&( result<void, E> const& r, F&& f );
+```
+[none]
+* {blank}
++
+Returns the error in `r`, or if `r` contains a value, another `result` obtained
+by invoking the function `f`.
++
+Let `R` be the type of `f()`.
++
+Effects: ::
+  - If `r.has_value()` is `true`, returns `f()`.
+  - Otherwise, returns `r.error()`.
+Remarks: ::
+  Only enabled when `R` is an instance of `result` and `E` is convertible to `R::error_type`.
+
+
+#### operator&=
+
+```
+template<class T, class E, class F, class U = ...>
+  result<T, E>& operator&=( result<T, E>& r, F&& f );
+```
+[none]
+* {blank}
++
+If `r` contains a value, replaces it with the result of invoking the function `f` on the value in `r`.
++
+Let `U` be the type of `f(*r)`.
++
+Effects: :: If `r.has_value()` is `true`, assigns `f(*std::move(r))` to `r`.
+Returns: :: `r`.
+Remarks: ::
+  Only enabled when `U` is not an instance of `result` and is convertible to `T`.
+
+```
+template<class T, class E, class F, class R = ...>
+  result<T, E>& operator&=( result<T, E>& r, F&& f );
+```
+[none]
+* {blank}
++
+If `r` contains a value, replaces `r` with the result of invoking the function `f` on the value in `r`.
++
+Let `R` be the type of `f(*r)`.
++
+Effects: :: If `r.has_value()` is `true`, assigns `f(*std::move(r))` to `r`.
+Returns: :: `r`.
+Remarks: ::
+  Only enabled when `R` is an instance of `result` and is convertible to `result<T, E>`.
+Example: ::
++
+```
+struct JsonValue
+{
+    result<JsonValue const&> at( std::string_view key ) const noexcept;
+};
+
+namespace helpers
+{
+
+inline auto at( std::string_view key ) {
+    return [=](JsonValue const& jv){ return jv.at( key ); }; }
+
+} // namespace helpers
+
+result<JsonValue const&> at_path( JsonValue const& jv,
+    std::initializer_list<std::string_view> path )
+{
+    result<JsonValue const&> r( jv );
+
+    using namespace helpers;
+
+    for( auto key: path )
+    {
+        r &= at( key );
+    }
+
+    return r;
+}
+```
+
+```
+template<class E, class F, class R = ...>
+  result<void, E>& operator&=( result<void, E>& r, F&& f );
+```
+[none]
+* {blank}
++
+If `r` contains a value, replaces `r` with the result of invoking the function `f`.
++
+Let `R` be the type of `f()`.
++
+Effects: :: If `r.has_value()` is `true`, assigns `f()` to `r`.
+Returns: :: `r`.
+Remarks: ::
+  Only enabled when `R` is an instance of `result<void, E2>` and `E2` is convertible to `E`.
+
 ## <boost/system.hpp>
 
 This convenience header includes all the headers previously described.

extra/boost_system.natvis

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

include/boost/system.hpp

@@ -9,10 +9,6 @@
 
 #include <boost/system/error_code.hpp>
 #include <boost/system/system_error.hpp>
-#include <boost/config.hpp>
-
-#if (__cplusplus >= 201103L) && !(defined(BOOST_GCC) && BOOST_GCC < 40800) || (defined(_MSC_VER) && _MSC_VER >= 1900)
-# include <boost/system/result.hpp>
-#endif
+#include <boost/system/result.hpp>
 
 #endif // #ifndef BOOST_SYSTEM_HPP_INCLUDED

include/boost/system/cygwin_error.hpp

@@ -1,63 +0,0 @@
-//  boost/system/cygwin_error.hpp  -------------------------------------------//
-
-//  Copyright Beman Dawes 2007
-
-//  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
-
-#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.
-
-# ifdef __CYGWIN__
-
-#include <boost/system/error_code.hpp>
-
-namespace boost
-{
-  namespace system
-  {
-    //  To construct an error_code after a API error:
-    //
-    //      error_code( errno, system_category() )
-
-    //  User code should use the portable "posix" enums for POSIX errors; this
-    //  allows such code to be portable to non-POSIX systems. For the non-POSIX
-    //  errno values that POSIX-based systems typically provide in addition to 
-    //  POSIX values, use the system specific enums below.
-
-   namespace cygwin_error
-    {
-      enum cygwin_errno
-      {
-        no_net = ENONET,
-        no_package = ENOPKG,
-        no_share = ENOSHARE
-      };
-    }  // namespace cygwin_error
-
-    template<> struct is_error_code_enum<cygwin_error::cygwin_errno>
-      { static const bool value = true; };
-
-    namespace cygwin_error
-    {
-      inline error_code make_error_code( cygwin_errno e )
-        { return error_code( e, system_category() ); }
-    }
-  }
-}
-
-#endif  // __CYGWIN__
-
-#endif  // BOOST_SYSTEM_CYGWIN_ERROR_HPP

include/boost/system/detail/config.hpp

@@ -11,16 +11,16 @@
 #include <boost/config.hpp>
 #include <boost/config/workaround.hpp>
 
-// BOOST_SYSTEM_HAS_SYSTEM_ERROR
-
-#if !defined(BOOST_NO_CXX11_HDR_SYSTEM_ERROR) && !defined(BOOST_NO_CXX11_HDR_ATOMIC) && !defined(BOOST_NO_CXX11_HDR_MUTEX)
-# define BOOST_SYSTEM_HAS_SYSTEM_ERROR
-#endif
+// The macro BOOST_SYSTEM_DISABLE_THREADS can be defined on configurations
+// that provide <system_error> and <atomic>, but not <mutex>, such as the
+// single-threaded libstdc++.
+//
+// https://github.com/boostorg/system/issues/92
 
 // BOOST_SYSTEM_NOEXCEPT
 // Retained for backward compatibility
 
-#define BOOST_SYSTEM_NOEXCEPT BOOST_NOEXCEPT
+#define BOOST_SYSTEM_NOEXCEPT noexcept
 
 // BOOST_SYSTEM_HAS_CONSTEXPR
 
@@ -58,7 +58,9 @@
 
 // BOOST_SYSTEM_CLANG_6
 
-#if defined(__clang__) && (__clang_major__ < 7 || (defined(__APPLE__) && __clang_major__ < 11))
+// Android NDK r18b has Clang 7.0.2 that still needs the workaround
+// https://github.com/boostorg/system/issues/100
+#if defined(__clang__) && (__clang_major__ < 7 || (defined(__APPLE__) && __clang_major__ < 11) || (defined(__ANDROID__) && __clang_major__ == 7))
 # define BOOST_SYSTEM_CLANG_6
 #endif
 

include/boost/system/detail/enable_if.hpp

@@ -5,28 +5,19 @@
 // Distributed under the Boost Software License, Version 1.0
 // http://www.boost.org/LICENSE_1_0.txt
 
+#include <type_traits>
+
 namespace boost
 {
-
 namespace system
 {
-
 namespace detail
 {
 
-template<bool C, class T = void> struct enable_if
-{
-    typedef T type;
-};
-
-template<class T> struct enable_if<false, T>
-{
-};
+using std::enable_if;
 
 } // namespace detail
-
 } // namespace system
-
 } // namespace boost
 
 #endif // #ifndef BOOST_SYSTEM_DETAIL_ENABLE_IF_HPP_INCLUDED

include/boost/system/detail/error_category.hpp

@@ -13,14 +13,12 @@
 #include <boost/system/detail/config.hpp>
 #include <boost/cstdint.hpp>
 #include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
 #include <string>
 #include <functional>
 #include <cstddef>
-
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-# include <system_error>
-# include <atomic>
-#endif
+#include <system_error>
+#include <atomic>
 
 namespace boost
 {
@@ -48,7 +46,7 @@ class std_category;
 #pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
 #endif
 
-#if defined(BOOST_MSVC)
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1900
 #pragma warning(push)
 #pragma warning(disable: 4351) //  new behavior: elements of array will be default initialized
 #endif
@@ -63,20 +61,11 @@ private:
     friend class error_code;
     friend class error_condition;
 
-#if !defined(BOOST_NO_CXX11_DELETED_FUNCTIONS)
 public:
 
     error_category( error_category const & ) = delete;
     error_category& operator=( error_category const & ) = delete;
 
-#else
-private:
-
-    error_category( error_category const & );
-    error_category& operator=( error_category const & );
-
-#endif
-
 private:
 
     boost::ulong_long_type id_;
@@ -89,68 +78,47 @@ private:
         void const* stdcat_align_;
     };
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
     mutable std::atomic< unsigned > sc_init_;
 
-#else
-
-    unsigned sc_init_;
-
-#endif
-
 protected:
 
-#if !defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) && !defined(BOOST_NO_CXX11_NON_PUBLIC_DEFAULTED_FUNCTIONS)
-
     ~error_category() = default;
 
-#else
-
-    // We'd like to make the destructor protected, to make code that deletes
-    // an error_category* not compile; unfortunately, doing the below makes
-    // the destructor user-provided and hence breaks use after main, as the
-    // categories may get destroyed before code that uses them
-
-    // ~error_category() {}
-
-#endif
-
-    BOOST_SYSTEM_CONSTEXPR error_category() BOOST_NOEXCEPT: id_( 0 ), stdcat_(), sc_init_()
+    constexpr error_category() noexcept: id_( 0 ), stdcat_(), sc_init_()
     {
     }
 
-    explicit BOOST_SYSTEM_CONSTEXPR error_category( boost::ulong_long_type id ) BOOST_NOEXCEPT: id_( id ), stdcat_(), sc_init_()
+    explicit constexpr error_category( boost::ulong_long_type id ) noexcept: id_( id ), stdcat_(), sc_init_()
     {
     }
 
 public:
 
-    virtual const char * name() const BOOST_NOEXCEPT = 0;
+    virtual const char * name() const noexcept = 0;
 
-    virtual error_condition default_error_condition( int ev ) const BOOST_NOEXCEPT;
-    virtual bool equivalent( int code, const error_condition & condition ) const BOOST_NOEXCEPT;
-    virtual bool equivalent( const error_code & code, int condition ) const BOOST_NOEXCEPT;
+    virtual error_condition default_error_condition( int ev ) const noexcept;
+    virtual bool equivalent( int code, const error_condition & condition ) const noexcept;
+    virtual bool equivalent( const error_code & code, int condition ) const noexcept;
 
     virtual std::string message( int ev ) const = 0;
-    virtual char const * message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT;
+    virtual char const * message( int ev, char * buffer, std::size_t len ) const noexcept;
 
-    virtual bool failed( int ev ) const BOOST_NOEXCEPT
+    virtual bool failed( int ev ) const noexcept
     {
         return ev != 0;
     }
 
-    friend BOOST_SYSTEM_CONSTEXPR bool operator==( error_category const & lhs, error_category const & rhs ) BOOST_NOEXCEPT
+    friend BOOST_SYSTEM_CONSTEXPR bool operator==( error_category const & lhs, error_category const & rhs ) noexcept
     {
         return rhs.id_ == 0? &lhs == &rhs: lhs.id_ == rhs.id_;
     }
 
-    friend BOOST_SYSTEM_CONSTEXPR bool operator!=( error_category const & lhs, error_category const & rhs ) BOOST_NOEXCEPT
+    friend BOOST_SYSTEM_CONSTEXPR bool operator!=( error_category const & lhs, error_category const & rhs ) noexcept
     {
         return !( lhs == rhs );
     }
 
-    friend BOOST_SYSTEM_CONSTEXPR bool operator<( error_category const & lhs, error_category const & rhs ) BOOST_NOEXCEPT
+    friend BOOST_SYSTEM_CONSTEXPR bool operator<( error_category const & lhs, error_category const & rhs ) noexcept
     {
         if( lhs.id_ < rhs.id_ )
         {
@@ -170,8 +138,6 @@ public:
         return std::less<error_category const *>()( &lhs, &rhs );
     }
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
     void init_stdcat() const;
 
 # if defined(__SUNPRO_CC) // trailing __global is not supported
@@ -179,11 +145,9 @@ public:
 # else
     operator std::error_category const & () const BOOST_SYMBOL_VISIBLE;
 # endif
-
-#endif
 };
 
-#if defined(BOOST_MSVC)
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1900
 #pragma warning(pop)
 #endif
 

include/boost/system/detail/error_category_impl.hpp

@@ -26,22 +26,22 @@ namespace system
 
 // error_category default implementation
 
-inline error_condition error_category::default_error_condition( int ev ) const BOOST_NOEXCEPT
+inline error_condition error_category::default_error_condition( int ev ) const noexcept
 {
     return error_condition( ev, *this );
 }
 
-inline bool error_category::equivalent( int code, const error_condition & condition ) const BOOST_NOEXCEPT
+inline bool error_category::equivalent( int code, const error_condition & condition ) const noexcept
 {
     return default_error_condition( code ) == condition;
 }
 
-inline bool error_category::equivalent( const error_code & code, int condition ) const BOOST_NOEXCEPT
+inline bool error_category::equivalent( const error_code & code, int condition ) const noexcept
 {
     return code.equals( condition, *this );
 }
 
-inline char const * error_category::message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT
+inline char const * error_category::message( int ev, char * buffer, std::size_t len ) const noexcept
 {
     if( len == 0 )
     {
@@ -58,27 +58,7 @@ inline char const * error_category::message( int ev, char * buffer, std::size_t
     try
 #endif
     {
-        std::string m = this->message( ev );
-
-# if defined( BOOST_MSVC )
-#  pragma warning( push )
-#  pragma warning( disable: 4996 )
-# elif defined(__clang__) && defined(__has_warning)
-#  pragma clang diagnostic push
-#  if __has_warning("-Wdeprecated-declarations")
-#   pragma clang diagnostic ignored "-Wdeprecated-declarations"
-#  endif
-# endif
-
-        std::strncpy( buffer, m.c_str(), len - 1 );
-        buffer[ len-1 ] = 0;
-
-# if defined( BOOST_MSVC )
-#  pragma warning( pop )
-# elif defined(__clang__) && defined(__has_warning)
-#  pragma clang diagnostic pop
-# endif
-
+        detail::snprintf( buffer, len, "%s", this->message( ev ).c_str() );
         return buffer;
     }
 #if !defined(BOOST_NO_EXCEPTIONS)
@@ -95,10 +75,8 @@ inline char const * error_category::message( int ev, char * buffer, std::size_t
 
 // interoperability with std::error_code, std::error_condition
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
 #include <boost/system/detail/std_category_impl.hpp>
-#include <mutex>
+#include <boost/system/detail/mutex.hpp>
 #include <new>
 
 namespace boost
@@ -106,18 +84,6 @@ namespace boost
 namespace system
 {
 
-namespace detail
-{
-
-template<class = void> struct stdcat_mx_holder
-{
-    static std::mutex mx_;
-};
-
-template<class T> std::mutex stdcat_mx_holder<T>::mx_;
-
-} // namespace detail
-
 inline void error_category::init_stdcat() const
 {
     static_assert( sizeof( stdcat_ ) >= sizeof( boost::system::detail::std_category ), "sizeof(stdcat_) is not enough for std_category" );
@@ -130,11 +96,17 @@ inline void error_category::init_stdcat() const
 
 #endif
 
-    std::lock_guard<std::mutex> lk( boost::system::detail::stdcat_mx_holder<>::mx_ );
+    // detail::mutex has a constexpr default constructor,
+    // and therefore guarantees static initialization, on
+    // everything except VS 2013 (msvc-12.0)
+
+    static system::detail::mutex mx_;
+
+    system::detail::lock_guard<system::detail::mutex> lk( mx_ );
 
     if( sc_init_.load( std::memory_order_acquire ) == 0 )
     {
-        ::new( static_cast<void*>( stdcat_ ) ) boost::system::detail::std_category( this, 0 );
+        ::new( static_cast<void*>( stdcat_ ) ) boost::system::detail::std_category( this, system::detail::id_wrapper<0>() );
         sc_init_.store( 1, std::memory_order_release );
     }
 }
@@ -151,7 +123,7 @@ inline BOOST_NOINLINE error_category::operator std::error_category const & () co
 // This condition must be the same as the one in error_condition.hpp
 #if defined(BOOST_SYSTEM_AVOID_STD_GENERIC_CATEGORY)
 
-        static const boost::system::detail::std_category generic_instance( this, 0x1F4D3 );
+        static const boost::system::detail::std_category generic_instance( this, system::detail::id_wrapper<0x1F4D3>() );
         return generic_instance;
 
 #else
@@ -166,7 +138,7 @@ inline BOOST_NOINLINE error_category::operator std::error_category const & () co
 // This condition must be the same as the one in error_code.hpp
 #if defined(BOOST_SYSTEM_AVOID_STD_SYSTEM_CATEGORY)
 
-        static const boost::system::detail::std_category system_instance( this, 0x1F4D7 );
+        static const boost::system::detail::std_category system_instance( this, system::detail::id_wrapper<0x1F4D7>() );
         return system_instance;
 
 #else
@@ -191,6 +163,4 @@ inline BOOST_NOINLINE error_category::operator std::error_category const & () co
 } // 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

@@ -21,21 +21,15 @@
 #include <boost/system/detail/append_int.hpp>
 #include <boost/system/detail/snprintf.hpp>
 #include <boost/system/detail/config.hpp>
-
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-# include <boost/system/detail/std_category.hpp>
-#endif
-
+#include <boost/system/detail/std_category.hpp>
 #include <boost/assert/source_location.hpp>
 #include <boost/cstdint.hpp>
 #include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
 #include <ostream>
 #include <new>
 #include <cstdio>
-
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-# include <system_error>
-#endif
+#include <system_error>
 
 #if defined(BOOST_GCC) && BOOST_GCC >= 40600 && BOOST_GCC < 70000
 # pragma GCC diagnostic push
@@ -57,12 +51,14 @@ namespace system
 //  and error_code containing a pointer to an object of a type derived
 //  from error_category.
 
+bool operator==( const error_code & code, const error_condition & condition ) noexcept;
 std::size_t hash_value( error_code const & ec );
 
 class error_code
 {
 private:
 
+    friend bool operator==( const error_code & code, const error_condition & condition ) noexcept;
     friend std::size_t hash_value( error_code const & ec );
 
 private:
@@ -76,9 +72,7 @@ private:
     union
     {
         data d1_;
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
         unsigned char d2_[ sizeof(std::error_code) ];
-#endif
     };
 
     // 0: default constructed, d1_ value initialized
@@ -90,7 +84,7 @@ private:
 
 private:
 
-    char const* category_name() const BOOST_NOEXCEPT
+    char const* category_name() const noexcept
     {
         // return category().name();
 
@@ -114,19 +108,19 @@ public:
 
     // constructors:
 
-    BOOST_SYSTEM_CONSTEXPR error_code() BOOST_NOEXCEPT:
+    constexpr error_code() noexcept:
         d1_(), lc_flags_( 0 )
     {
     }
 
-    BOOST_SYSTEM_CONSTEXPR error_code( int val, const error_category & cat ) BOOST_NOEXCEPT:
+    BOOST_SYSTEM_CONSTEXPR error_code( int val, const error_category & cat ) noexcept:
         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:
+    error_code( int val, const error_category & cat, source_location const * loc ) noexcept:
         d1_(), lc_flags_( ( loc? reinterpret_cast<boost::uintptr_t>( loc ): 2 ) | +detail::failed_impl( val, cat ) )
     {
         d1_.val_ = val;
@@ -136,15 +130,13 @@ public:
     template<class ErrorCodeEnum> BOOST_SYSTEM_CONSTEXPR error_code( ErrorCodeEnum e,
         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 )
+        >::type* = 0 ) noexcept: d1_(), lc_flags_( 0 )
     {
         *this = make_error_code( e );
     }
 
-    error_code( error_code const& ec, source_location const * loc ) BOOST_NOEXCEPT:
+    error_code( error_code const& ec, source_location const * loc ) noexcept:
         d1_(), lc_flags_( 0 )
     {
         *this = ec;
@@ -155,9 +147,7 @@ public:
         }
     }
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
-    error_code( std::error_code const& ec ) BOOST_NOEXCEPT:
+    error_code( std::error_code const& ec ) noexcept:
         d1_(), lc_flags_( 0 )
     {
 #ifndef BOOST_NO_RTTI
@@ -175,41 +165,39 @@ public:
         }
     }
 
-#endif
-
     // modifiers:
 
-    BOOST_SYSTEM_CONSTEXPR void assign( int val, const error_category & cat ) BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR void assign( int val, const error_category & cat ) noexcept
     {
         *this = error_code( val, cat );
     }
 
-    void assign( int val, const error_category & cat, source_location const * loc ) BOOST_NOEXCEPT
+    void assign( int val, const error_category & cat, source_location const * loc ) noexcept
     {
         *this = error_code( val, cat, loc );
     }
 
-    void assign( error_code const& ec, source_location const * loc ) BOOST_NOEXCEPT
+    void assign( error_code const& ec, source_location const * loc ) noexcept
     {
         *this = error_code( ec, loc );
     }
 
     template<typename ErrorCodeEnum>
         BOOST_SYSTEM_CONSTEXPR typename detail::enable_if<is_error_code_enum<ErrorCodeEnum>::value, error_code>::type &
-        operator=( ErrorCodeEnum val ) BOOST_NOEXCEPT
+        operator=( ErrorCodeEnum val ) noexcept
     {
         *this = make_error_code( val );
         return *this;
     }
 
-    BOOST_SYSTEM_CONSTEXPR void clear() BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR void clear() noexcept
     {
         *this = error_code();
     }
 
     // observers:
 
-    BOOST_SYSTEM_CONSTEXPR int value() const BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR int value() const noexcept
     {
         if( lc_flags_ != 1 )
         {
@@ -217,22 +205,16 @@ public:
         }
         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
+    BOOST_SYSTEM_CONSTEXPR const error_category & category() const noexcept
     {
         if( lc_flags_ == 0 )
         {
@@ -249,24 +231,19 @@ public:
     }
 
     // deprecated?
-    error_condition default_error_condition() const BOOST_NOEXCEPT
+    error_condition default_error_condition() const noexcept
     {
         return category().default_error_condition( value() );
     }
 
     std::string message() const
     {
-#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 )
+        else if( lc_flags_ == 0 )
         {
             return detail::system_error_category_message( value() );
         }
@@ -276,9 +253,8 @@ public:
         }
     }
 
-    char const * message( char * buffer, std::size_t len ) const BOOST_NOEXCEPT
+    char const * message( char * buffer, std::size_t len ) const noexcept
     {
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
         if( lc_flags_ == 1 )
         {
             std::error_code const& ec = *reinterpret_cast<std::error_code const*>( d2_ );
@@ -298,9 +274,7 @@ public:
             }
 #endif
         }
-#endif
-
-        if( lc_flags_ == 0 )
+        else if( lc_flags_ == 0 )
         {
             return detail::system_error_category_message( value(), buffer, len );
         }
@@ -310,17 +284,16 @@ public:
         }
     }
 
-    BOOST_SYSTEM_CONSTEXPR bool failed() const BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR bool failed() const noexcept
     {
         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
@@ -329,36 +302,17 @@ public:
         }
     }
 
-#if !defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS)
-
-    BOOST_SYSTEM_CONSTEXPR explicit operator bool() const BOOST_NOEXCEPT  // true if error
+    BOOST_SYSTEM_CONSTEXPR explicit operator bool() const noexcept  // true if error
     {
         return failed();
     }
 
-#else
-
-    typedef void (*unspecified_bool_type)();
-    static void unspecified_bool_true() {}
-
-    BOOST_SYSTEM_CONSTEXPR operator unspecified_bool_type() const  BOOST_NOEXCEPT // true if error
-    {
-        return failed()? unspecified_bool_true: 0;
-    }
-
-    BOOST_SYSTEM_CONSTEXPR bool operator!() const BOOST_NOEXCEPT // true if no error
-    {
-        return !failed();
-    }
-
-#endif
-
-    bool has_location() const BOOST_NOEXCEPT
+    bool has_location() const noexcept
     {
         return lc_flags_ >= 4;
     }
 
-    source_location const & location() const BOOST_NOEXCEPT
+    source_location const & location() const 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;
@@ -372,7 +326,7 @@ private:
 
     friend class error_category;
 
-    BOOST_SYSTEM_CONSTEXPR bool equals( int val, error_category const& cat ) const BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR bool equals( int val, error_category const& cat ) const noexcept
     {
         if( lc_flags_ == 0 )
         {
@@ -393,11 +347,14 @@ 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
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( const error_code & lhs, const error_code & rhs ) noexcept
     {
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+        bool s1 = lhs.lc_flags_ == 1;
+        bool s2 = rhs.lc_flags_ == 1;
 
-        if( lhs.lc_flags_ == 1 && rhs.lc_flags_ == 1 )
+        if( s1 != s2 ) return false;
+
+        if( s1 && s2 )
         {
             std::error_code const& e1 = *reinterpret_cast<std::error_code const*>( lhs.d2_ );
             std::error_code const& e2 = *reinterpret_cast<std::error_code const*>( rhs.d2_ );
@@ -405,17 +362,20 @@ public:
             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
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator<( const error_code & lhs, const error_code & rhs ) noexcept
     {
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
+        bool s1 = lhs.lc_flags_ == 1;
+        bool s2 = rhs.lc_flags_ == 1;
 
-        if( lhs.lc_flags_ == 1 && rhs.lc_flags_ == 1 )
+        if( s1 < s2 ) return true;
+        if( s2 < s1 ) return false;
+
+        if( s1 && s2 )
         {
             std::error_code const& e1 = *reinterpret_cast<std::error_code const*>( lhs.d2_ );
             std::error_code const& e2 = *reinterpret_cast<std::error_code const*>( rhs.d2_ );
@@ -423,77 +383,32 @@ public:
             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
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( const error_code & lhs, const error_code & rhs ) 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)
-
-    inline friend bool operator==( std::error_code const & lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator==( std::error_code const & lhs, error_code const & rhs ) noexcept
     {
         return lhs == static_cast< std::error_code >( rhs );
     }
 
-    inline friend bool operator==( error_code const & lhs, std::error_code const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator==( error_code const & lhs, std::error_code const & rhs ) noexcept
     {
         return static_cast< std::error_code >( lhs ) == rhs;
     }
 
-    inline friend bool operator!=( std::error_code const & lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator!=( std::error_code const & lhs, error_code const & rhs ) noexcept
     {
         return !( lhs == rhs );
     }
 
-    inline friend bool operator!=( error_code const & lhs, std::error_code const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator!=( error_code const & lhs, std::error_code const & rhs ) noexcept
     {
         return !( lhs == rhs );
     }
@@ -501,25 +416,25 @@ public:
     //
 
     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
+    inline friend bool operator==( error_code const & lhs, E rhs ) 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
+    inline friend bool operator==( E lhs, error_code const & rhs ) 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
+    inline friend bool operator!=( error_code const & lhs, E rhs ) 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
+    inline friend bool operator!=( E lhs, error_code const & rhs ) noexcept
     {
         return !( lhs == rhs );
     }
@@ -527,47 +442,47 @@ public:
     //
 
     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
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( error_code const & lhs, E rhs ) 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
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( E lhs, error_code const & rhs ) 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
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( error_code const & lhs, E rhs ) 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
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( E lhs, error_code const & rhs ) 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
+    inline friend bool operator==( error_code const & lhs, std::error_condition const & rhs ) noexcept
     {
         return static_cast< std::error_code >( lhs ) == rhs;
     }
 
-    inline friend bool operator==( std::error_condition const & lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator==( std::error_condition const & lhs, error_code const & rhs ) noexcept
     {
         return lhs == static_cast< std::error_code >( rhs );
     }
 
-    inline friend bool operator!=( error_code const & lhs, std::error_condition const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator!=( error_code const & lhs, std::error_condition const & rhs ) noexcept
     {
         return !( lhs == rhs );
     }
 
-    inline friend bool operator!=( std::error_condition const & lhs, error_code const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator!=( std::error_condition const & lhs, error_code const & rhs ) noexcept
     {
         return !( lhs == rhs );
     }
@@ -626,14 +541,10 @@ public:
       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_ );
@@ -645,7 +556,6 @@ public:
             return r;
         }
         else
-#endif
         {
             std::string r = category_name();
             detail::append_int( r, value() );
@@ -678,18 +588,41 @@ public:
     }
 };
 
+inline bool operator==( const error_code & code, const error_condition & condition ) noexcept
+{
+    if( code.lc_flags_ == 1 )
+    {
+        return static_cast<std::error_code>( code ) == static_cast<std::error_condition>( condition );
+    }
+    else
+    {
+        return code.category().equivalent( code.value(), condition ) || condition.category().equivalent( code, condition.value() );
+    }
+}
+
+inline bool operator==( const error_condition & condition, const error_code & code ) noexcept
+{
+    return code == condition;
+}
+
+inline bool operator!=( const error_code & lhs, const error_condition & rhs ) noexcept
+{
+    return !( lhs == rhs );
+}
+
+inline bool operator!=( const error_condition & lhs, const error_code & rhs ) noexcept
+{
+    return !( lhs == rhs );
+}
+
 inline std::size_t hash_value( error_code const & ec )
 {
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
     if( ec.lc_flags_ == 1 )
     {
         std::error_code const& e2 = *reinterpret_cast<std::error_code const*>( ec.d2_ );
         return std::hash<std::error_code>()( e2 );
     }
 
-#endif
-
     error_category const & cat = ec.category();
 
     boost::ulong_long_type id_ = cat.id_;

include/boost/system/detail/error_condition.hpp

@@ -50,7 +50,7 @@ private:
 
 private:
 
-    boost::ulong_long_type cat_id() const BOOST_NOEXCEPT
+    boost::ulong_long_type cat_id() const noexcept
     {
         return cat_? cat_->id_: detail::generic_category_id;
     }
@@ -59,17 +59,17 @@ public:
 
     // constructors:
 
-    BOOST_SYSTEM_CONSTEXPR error_condition() BOOST_NOEXCEPT:
+    BOOST_SYSTEM_CONSTEXPR error_condition() noexcept:
         val_( 0 ), cat_( 0 )
     {
     }
 
-    BOOST_SYSTEM_CONSTEXPR error_condition( int val, const error_category & cat ) BOOST_NOEXCEPT:
+    BOOST_SYSTEM_CONSTEXPR error_condition( int val, const error_category & cat ) noexcept:
         val_( val ), cat_( &cat )
     {
     }
 
-    BOOST_SYSTEM_CONSTEXPR explicit error_condition( boost::system::detail::generic_value_tag vt ) BOOST_NOEXCEPT:
+    BOOST_SYSTEM_CONSTEXPR explicit error_condition( boost::system::detail::generic_value_tag vt ) noexcept:
         val_( vt.value ), cat_( 0 )
     {
     }
@@ -77,20 +77,20 @@ public:
     template<class ErrorConditionEnum> BOOST_SYSTEM_CONSTEXPR error_condition( ErrorConditionEnum e,
       typename detail::enable_if<
         is_error_condition_enum<ErrorConditionEnum>::value && !boost::system::detail::is_same<ErrorConditionEnum, errc::errc_t>::value
-      >::type* = 0) BOOST_NOEXCEPT
+      >::type* = 0) 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:
+      typename detail::enable_if<boost::system::detail::is_same<ErrorConditionEnum, errc::errc_t>::value>::type* = 0) noexcept:
         val_( e ), cat_( 0 )
     {
     }
 
     // modifiers:
 
-    BOOST_SYSTEM_CONSTEXPR void assign( int val, const error_category & cat ) BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR void assign( int val, const error_category & cat ) noexcept
     {
         val_ = val;
         cat_ = &cat;
@@ -98,13 +98,13 @@ public:
 
     template<typename ErrorConditionEnum>
         BOOST_SYSTEM_CONSTEXPR typename detail::enable_if<is_error_condition_enum<ErrorConditionEnum>::value, error_condition>::type &
-        operator=( ErrorConditionEnum val ) BOOST_NOEXCEPT
+        operator=( ErrorConditionEnum val ) noexcept
     {
         *this = error_condition( val );
         return *this;
     }
 
-    BOOST_SYSTEM_CONSTEXPR void clear() BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR void clear() noexcept
     {
         val_ = 0;
         cat_ = 0;
@@ -112,12 +112,12 @@ public:
 
     // observers:
 
-    BOOST_SYSTEM_CONSTEXPR int value() const BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR int value() const noexcept
     {
         return val_;
     }
 
-    BOOST_SYSTEM_CONSTEXPR const error_category & category() const BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR const error_category & category() const noexcept
     {
         return cat_? *cat_: generic_category();
     }
@@ -134,7 +134,7 @@ public:
         }
     }
 
-    char const * message( char * buffer, std::size_t len ) const BOOST_NOEXCEPT
+    char const * message( char * buffer, std::size_t len ) const noexcept
     {
         if( cat_ )
         {
@@ -146,7 +146,7 @@ public:
         }
     }
 
-    BOOST_SYSTEM_CONSTEXPR bool failed() const BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR bool failed() const noexcept
     {
         if( cat_ )
         {
@@ -158,35 +158,16 @@ public:
         }
     }
 
-#if !defined(BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS)
-
-    BOOST_SYSTEM_CONSTEXPR explicit operator bool() const BOOST_NOEXCEPT  // true if error
+    BOOST_SYSTEM_CONSTEXPR explicit operator bool() const noexcept  // true if error
     {
         return failed();
     }
 
-#else
-
-    typedef void (*unspecified_bool_type)();
-    static void unspecified_bool_true() {}
-
-    BOOST_SYSTEM_CONSTEXPR operator unspecified_bool_type() const BOOST_NOEXCEPT  // true if error
-    {
-        return failed()? unspecified_bool_true: 0;
-    }
-
-    BOOST_SYSTEM_CONSTEXPR bool operator!() const BOOST_NOEXCEPT  // true if no error
-    {
-        return !failed();
-    }
-
-#endif
-
     // relationals:
     //  the more symmetrical non-member syntax allows enum
     //  conversions work for both rhs and lhs.
 
-    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( const error_condition & lhs, const error_condition & rhs ) BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( const error_condition & lhs, const error_condition & rhs ) noexcept
     {
         if( lhs.val_ != rhs.val_ )
         {
@@ -206,20 +187,18 @@ public:
         }
     }
 
-    BOOST_SYSTEM_CONSTEXPR inline friend bool operator<( const error_condition & lhs, const error_condition & rhs ) BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator<( const error_condition & lhs, const error_condition & rhs ) noexcept
     {
         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
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( const error_condition & lhs, const error_condition & rhs ) 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
@@ -241,27 +220,77 @@ public:
 #endif
     }
 
-    inline friend bool operator==( std::error_code const & lhs, error_condition const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator==( std::error_code const & lhs, error_condition const & rhs ) noexcept
     {
         return lhs == static_cast< std::error_condition >( rhs );
     }
 
-    inline friend bool operator==( error_condition const & lhs, std::error_code const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator==( error_condition const & lhs, std::error_code const & rhs ) noexcept
     {
         return static_cast< std::error_condition >( lhs ) == rhs;
     }
 
-    inline friend bool operator!=( std::error_code const & lhs, error_condition const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator!=( std::error_code const & lhs, error_condition const & rhs ) noexcept
     {
         return !( lhs == rhs );
     }
 
-    inline friend bool operator!=( error_condition const & lhs, std::error_code const & rhs ) BOOST_NOEXCEPT
+    inline friend bool operator!=( error_condition const & lhs, std::error_code const & rhs ) noexcept
     {
         return !( lhs == rhs );
     }
 
-#endif
+    //
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( error_condition const & lhs, E rhs ) noexcept
+    {
+        return lhs == make_error_condition( rhs );
+    }
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator==( E lhs, error_condition const & rhs ) noexcept
+    {
+        return make_error_condition( lhs ) == rhs;
+    }
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( error_condition const & lhs, E rhs ) noexcept
+    {
+        return !( lhs == rhs );
+    }
+
+    template<class E, class N = typename detail::enable_if<std::is_error_condition_enum<E>::value>::type>
+    BOOST_SYSTEM_CONSTEXPR inline friend bool operator!=( E lhs, error_condition const & rhs ) noexcept
+    {
+        return !( lhs == rhs );
+    }
+
+    //
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    inline friend bool operator==( error_condition const & lhs, E rhs ) noexcept
+    {
+        return lhs == make_error_code( rhs );
+    }
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    inline friend bool operator==( E lhs, error_condition const & rhs ) noexcept
+    {
+        return make_error_code( lhs ) == rhs;
+    }
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    inline friend bool operator!=( error_condition const & lhs, E rhs ) noexcept
+    {
+        return !( lhs == rhs );
+    }
+
+    template<class E, class N1 = void, class N2 = typename detail::enable_if<std::is_error_code_enum<E>::value>::type>
+    inline friend bool operator!=( E lhs, error_condition const & rhs ) noexcept
+    {
+        return !( lhs == rhs );
+    }
 
     std::string to_string() const
     {

include/boost/system/detail/generic_category.hpp

@@ -35,18 +35,18 @@ class BOOST_SYMBOL_VISIBLE generic_error_category: public error_category
 {
 public:
 
-    BOOST_SYSTEM_CONSTEXPR generic_error_category() BOOST_NOEXCEPT:
+    BOOST_SYSTEM_CONSTEXPR generic_error_category() noexcept:
         error_category( detail::generic_category_id )
     {
     }
 
-    const char * name() const BOOST_NOEXCEPT BOOST_OVERRIDE
+    const char * name() const noexcept BOOST_OVERRIDE
     {
         return "generic";
     }
 
     std::string message( int ev ) const BOOST_OVERRIDE;
-    char const * message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
+    char const * message( int ev, char * buffer, std::size_t len ) const noexcept BOOST_OVERRIDE;
 };
 
 #if ( defined( BOOST_GCC ) && BOOST_GCC >= 40600 ) || defined( BOOST_CLANG )
@@ -55,7 +55,7 @@ public:
 
 // generic_error_category::message
 
-inline char const * generic_error_category::message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT
+inline char const * generic_error_category::message( int ev, char * buffer, std::size_t len ) const noexcept
 {
     return generic_error_category_message( ev, buffer, len );
 }
@@ -86,7 +86,7 @@ template<class T> constexpr generic_error_category generic_cat_holder<T>::instan
 
 } // namespace detail
 
-constexpr error_category const & generic_category() BOOST_NOEXCEPT
+constexpr error_category const & generic_category() noexcept
 {
     return detail::generic_cat_holder<void>::instance;
 }
@@ -94,10 +94,10 @@ constexpr error_category const & generic_category() BOOST_NOEXCEPT
 #else // #if defined(BOOST_SYSTEM_HAS_CONSTEXPR)
 
 #if !defined(__SUNPRO_CC) // trailing __global is not supported
-inline error_category const & generic_category() BOOST_NOEXCEPT BOOST_SYMBOL_VISIBLE;
+inline error_category const & generic_category() noexcept BOOST_SYMBOL_VISIBLE;
 #endif
 
-inline error_category const & generic_category() BOOST_NOEXCEPT
+inline error_category const & generic_category() noexcept
 {
     static const detail::generic_error_category instance;
     return instance;

include/boost/system/detail/generic_category_message.hpp

@@ -27,19 +27,31 @@ namespace detail
 
 // glibc has two incompatible strerror_r definitions
 
-inline char const * strerror_r_helper( char const * r, char const * ) BOOST_NOEXCEPT
+inline char const * strerror_r_helper( char const * r, char const * ) noexcept
 {
     return r;
 }
 
-inline char const * strerror_r_helper( int r, char const * buffer ) BOOST_NOEXCEPT
+inline char const * strerror_r_helper( int r, char const * buffer ) noexcept
 {
     return r == 0? buffer: "Unknown error";
 }
 
-inline char const * generic_error_category_message( int ev, char * buffer, std::size_t len ) BOOST_NOEXCEPT
+inline char const * generic_error_category_message( int ev, char * buffer, std::size_t len ) noexcept
 {
-    return strerror_r_helper( strerror_r( ev, buffer, len ), buffer );
+    if( buffer != nullptr )
+    {
+        return strerror_r_helper( strerror_r( ev, buffer, len ), buffer );
+    }
+    else
+    {
+        // strerror_r requires non-null buffer pointer
+
+        char tmp[ 1 ] = {};
+        char const* r = strerror_r_helper( strerror_r( ev, tmp, 0 ), buffer );
+
+        return r == tmp? nullptr: r;
+    }
 }
 
 inline std::string generic_error_category_message( int ev )
@@ -68,7 +80,7 @@ inline std::string generic_error_category_message( int ev )
     return m? m: "Unknown error";
 }
 
-inline char const * generic_error_category_message( int ev, char * buffer, std::size_t len ) BOOST_NOEXCEPT
+inline char const * generic_error_category_message( int ev, char * buffer, std::size_t len ) noexcept
 {
     if( len == 0 )
     {

include/boost/system/detail/interop_category.hpp

@@ -35,25 +35,25 @@ class BOOST_SYMBOL_VISIBLE interop_error_category: public error_category
 {
 public:
 
-    BOOST_SYSTEM_CONSTEXPR interop_error_category() BOOST_NOEXCEPT:
+    BOOST_SYSTEM_CONSTEXPR interop_error_category() noexcept:
         error_category( detail::interop_category_id )
     {
     }
 
-    const char * name() const BOOST_NOEXCEPT BOOST_OVERRIDE
+    const char * name() const 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;
+    char const * message( int ev, char * buffer, std::size_t len ) const 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
+inline char const * interop_error_category::message( int ev, char * buffer, std::size_t len ) const noexcept
 {
     detail::snprintf( buffer, len, "Unknown interop error %d", ev );
     return buffer;
@@ -79,7 +79,7 @@ template<class T> struct BOOST_SYMBOL_VISIBLE interop_cat_holder
 template<class T> constexpr interop_error_category interop_cat_holder<T>::instance;
 #endif
 
-constexpr error_category const & interop_category() BOOST_NOEXCEPT
+constexpr error_category const & interop_category() noexcept
 {
     return interop_cat_holder<void>::instance;
 }
@@ -87,10 +87,10 @@ constexpr error_category const & interop_category() BOOST_NOEXCEPT
 #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;
+inline error_category const & interop_category() noexcept BOOST_SYMBOL_VISIBLE;
 #endif
 
-inline error_category const & interop_category() BOOST_NOEXCEPT
+inline error_category const & interop_category() noexcept
 {
     static const detail::interop_error_category instance;
     return instance;

include/boost/system/detail/is_same.hpp

@@ -5,29 +5,19 @@
 // Distributed under the Boost Software License, Version 1.0
 // http://www.boost.org/LICENSE_1_0.txt
 
+#include <type_traits>
+
 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 };
-};
+using std::is_same;
 
 } // namespace detail
-
 } // namespace system
-
 } // namespace boost
 
 #endif // #ifndef BOOST_SYSTEM_DETAIL_IS_SAME_HPP_INCLUDED

include/boost/system/detail/mutex.hpp

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

include/boost/system/detail/snprintf.hpp

@@ -8,66 +8,21 @@
 //
 // 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
+using std::snprintf;
 
 } // namespace detail
-
 } // namespace system
-
 } // namespace boost
 
 #endif // #ifndef BOOST_SYSTEM_DETAIL_SNPRINTF_HPP_INCLUDED

include/boost/system/detail/std_category.hpp

@@ -11,6 +11,7 @@
 // See library home page at http://www.boost.org/libs/system
 
 #include <boost/system/detail/error_category.hpp>
+#include <boost/config.hpp>
 #include <system_error>
 
 //
@@ -24,6 +25,8 @@ namespace system
 namespace detail
 {
 
+template<unsigned Id> struct id_wrapper {};
+
 class BOOST_SYMBOL_VISIBLE std_category: public std::error_category
 {
 private:
@@ -32,30 +35,28 @@ private:
 
 public:
 
-    boost::system::error_category const & original_category() const BOOST_NOEXCEPT
+    boost::system::error_category const & original_category() const noexcept
     {
         return *pc_;
     }
 
 public:
 
-    explicit std_category( boost::system::error_category const * pc, unsigned id ): pc_( pc )
+    template<unsigned Id>
+    explicit std_category( boost::system::error_category const * pc, id_wrapper<Id> ): pc_( pc )
     {
-        if( id != 0 )
-        {
 #if defined(_MSC_VER) && defined(_CPPLIB_VER) && _MSC_VER >= 1900 && _MSC_VER < 2000
 
-            // Poking into the protected _Addr member of std::error_category
-            // is not a particularly good programming practice, but what can
-            // you do
+        // We used to assign to the protected _Addr member of std::error_category
+        // here when Id != 0, but this should never happen now because this code
+        // path is no longer used
 
-            _Addr = id;
+        static_assert( Id == 0, "This constructor should only be called with Id == 0 under MS STL 14.0+" );
 
 #endif
-        }
     }
 
-    const char * name() const BOOST_NOEXCEPT BOOST_OVERRIDE
+    const char * name() const noexcept BOOST_OVERRIDE
     {
         return pc_->name();
     }
@@ -65,13 +66,13 @@ public:
         return pc_->message( ev );
     }
 
-    std::error_condition default_error_condition( int ev ) const BOOST_NOEXCEPT BOOST_OVERRIDE
+    std::error_condition default_error_condition( int ev ) const noexcept BOOST_OVERRIDE
     {
         return pc_->default_error_condition( ev );
     }
 
-    inline bool equivalent( int code, const std::error_condition & condition ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
-    inline bool equivalent( const std::error_code & code, int condition ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
+    inline bool equivalent( int code, const std::error_condition & condition ) const noexcept BOOST_OVERRIDE;
+    inline bool equivalent( const std::error_code & code, int condition ) const noexcept BOOST_OVERRIDE;
 };
 
 } // namespace detail

include/boost/system/detail/std_category_impl.hpp

@@ -26,7 +26,7 @@ namespace system
 namespace detail
 {
 
-inline bool std_category::equivalent( int code, const std::error_condition & condition ) const BOOST_NOEXCEPT
+inline bool std_category::equivalent( int code, const std::error_condition & condition ) const noexcept
 {
     if( condition.category() == *this )
     {
@@ -55,7 +55,7 @@ inline bool std_category::equivalent( int code, const std::error_condition & con
     }
 }
 
-inline bool std_category::equivalent( const std::error_code & code, int condition ) const BOOST_NOEXCEPT
+inline bool std_category::equivalent( const std::error_code & code, int condition ) const noexcept
 {
     if( code.category() == *this )
     {

include/boost/system/detail/system_category.hpp

@@ -34,20 +34,20 @@ class BOOST_SYMBOL_VISIBLE system_error_category: public error_category
 {
 public:
 
-    BOOST_SYSTEM_CONSTEXPR system_error_category() BOOST_NOEXCEPT:
+    BOOST_SYSTEM_CONSTEXPR system_error_category() noexcept:
         error_category( detail::system_category_id )
     {
     }
 
-    const char * name() const BOOST_NOEXCEPT BOOST_OVERRIDE
+    const char * name() const noexcept BOOST_OVERRIDE
     {
         return "system";
     }
 
-    error_condition default_error_condition( int ev ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
+    error_condition default_error_condition( int ev ) const noexcept BOOST_OVERRIDE;
 
     std::string message( int ev ) const BOOST_OVERRIDE;
-    char const * message( int ev, char * buffer, std::size_t len ) const BOOST_NOEXCEPT BOOST_OVERRIDE;
+    char const * message( int ev, char * buffer, std::size_t len ) const noexcept BOOST_OVERRIDE;
 };
 
 #if ( defined( BOOST_GCC ) && BOOST_GCC >= 40600 ) || defined( BOOST_CLANG )
@@ -75,7 +75,7 @@ template<class T> constexpr system_error_category system_cat_holder<T>::instance
 
 } // namespace detail
 
-constexpr error_category const & system_category() BOOST_NOEXCEPT
+constexpr error_category const & system_category() noexcept
 {
     return detail::system_cat_holder<void>::instance;
 }
@@ -83,10 +83,10 @@ constexpr error_category const & system_category() BOOST_NOEXCEPT
 #else // #if defined(BOOST_SYSTEM_HAS_CONSTEXPR)
 
 #if !defined(__SUNPRO_CC) // trailing __global is not supported
-inline error_category const & system_category() BOOST_NOEXCEPT BOOST_SYMBOL_VISIBLE;
+inline error_category const & system_category() noexcept BOOST_SYMBOL_VISIBLE;
 #endif
 
-inline error_category const & system_category() BOOST_NOEXCEPT
+inline error_category const & system_category() noexcept
 {
     static const detail::system_error_category instance;
     return instance;

include/boost/system/detail/system_category_condition_win32.hpp

@@ -25,7 +25,7 @@ namespace system
 namespace detail
 {
 
-inline int system_category_condition_win32( int ev ) BOOST_NOEXCEPT
+inline int system_category_condition_win32( int ev ) noexcept
 {
     // When using the Windows Runtime, most system errors are reported as HRESULTs.
     // We want to map the common Win32 errors to their equivalent error condition,
@@ -59,6 +59,7 @@ inline int system_category_condition_win32( int ev ) BOOST_NOEXCEPT
     case ERROR_ACCESS_DENIED_: return permission_denied;
     case ERROR_ALREADY_EXISTS_: return file_exists;
     case ERROR_BAD_NETPATH_: return no_such_file_or_directory;
+    case ERROR_BAD_NET_NAME_: return no_such_file_or_directory;
     case ERROR_BAD_UNIT_: return no_such_device;
     case ERROR_BROKEN_PIPE_: return broken_pipe;
     case ERROR_BUFFER_OVERFLOW_: return filename_too_long;
@@ -75,6 +76,7 @@ inline int system_category_condition_win32( int ev ) BOOST_NOEXCEPT
     case ERROR_DIR_NOT_EMPTY_: return directory_not_empty;
     case ERROR_DIRECTORY_: return invalid_argument; // WinError.h: "The directory name is invalid"
     case ERROR_DISK_FULL_: return no_space_on_device;
+    case ERROR_FILENAME_EXCED_RANGE_: return filename_too_long;
     case ERROR_FILE_EXISTS_: return file_exists;
     case ERROR_FILE_NOT_FOUND_: return no_such_file_or_directory;
     case ERROR_HANDLE_DISK_FULL_: return no_space_on_device;
@@ -100,12 +102,16 @@ inline int system_category_condition_win32( int ev ) BOOST_NOEXCEPT
     case ERROR_REPARSE_TAG_INVALID_: return invalid_argument;
     case ERROR_RETRY_: return resource_unavailable_try_again;
     case ERROR_SEEK_: return io_error;
+    case ERROR_SEM_TIMEOUT_: return timed_out;
     case ERROR_SHARING_VIOLATION_: return permission_denied;
     case ERROR_NOT_SUPPORTED_: return not_supported; // WinError.h: "The request is not supported."
+    case ERROR_TIMEOUT_: return timed_out;
     case ERROR_TOO_MANY_OPEN_FILES_: return too_many_files_open;
     case ERROR_WRITE_FAULT_: return io_error;
     case ERROR_WRITE_PROTECT_: return permission_denied;
 
+    case 258: return timed_out; // WAIT_TIMEOUT
+
     case WSAEACCES_: return permission_denied;
     case WSAEADDRINUSE_: return address_in_use;
     case WSAEADDRNOTAVAIL_: return address_not_available;

include/boost/system/detail/system_category_impl.hpp

@@ -25,7 +25,7 @@
 
 #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
+inline boost::system::error_condition boost::system::detail::system_error_category::default_error_condition( int ev ) const noexcept
 {
     int e2 = system_category_condition_win32( ev );
 
@@ -41,7 +41,7 @@ inline boost::system::error_condition boost::system::detail::system_error_catego
 
 #else // #if defined(BOOST_WINDOWS_API)
 
-inline boost::system::error_condition boost::system::detail::system_error_category::default_error_condition( int ev ) const BOOST_NOEXCEPT
+inline boost::system::error_condition boost::system::detail::system_error_category::default_error_condition( int ev ) const noexcept
 {
     return error_condition( boost::system::detail::generic_value_tag( ev ) );
 }
@@ -53,7 +53,7 @@ inline std::string boost::system::detail::system_error_category::message( int ev
     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
+inline char const * boost::system::detail::system_error_category::message( int ev, char * buffer, std::size_t len ) const noexcept
 {
     return system_error_category_message( ev, buffer, len );
 }

include/boost/system/detail/system_category_message.hpp

@@ -32,7 +32,7 @@ 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
+inline char const * system_error_category_message( int ev, char * buffer, std::size_t len ) noexcept
 {
     return system_category_message_win32( ev, buffer, len );
 }
@@ -57,7 +57,7 @@ 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
+inline char const * system_error_category_message( int ev, char * buffer, std::size_t len ) noexcept
 {
     return generic_error_category_message( ev, buffer, len );
 }

include/boost/system/detail/system_category_message_win32.hpp

@@ -47,7 +47,7 @@ inline boost::winapi::UINT_ message_cp_win32()
 #endif
 }
 
-inline char const * system_category_message_win32( int ev, char * buffer, std::size_t len ) BOOST_NOEXCEPT
+inline char const * system_category_message_win32( int ev, char * buffer, std::size_t len ) noexcept
 {
     if( len == 0 )
     {

include/boost/system/errc.hpp

@@ -31,19 +31,19 @@ namespace errc
 {
 
 // explicit conversion:
-BOOST_SYSTEM_CONSTEXPR inline error_code make_error_code( errc_t e ) BOOST_NOEXCEPT
+BOOST_SYSTEM_CONSTEXPR inline error_code make_error_code( errc_t e ) noexcept
 {
     return error_code( e, generic_category() );
 }
 
 // explicit conversion:
-inline error_code make_error_code( errc_t e, boost::source_location const * loc ) BOOST_NOEXCEPT
+inline error_code make_error_code( errc_t e, boost::source_location const * loc ) noexcept
 {
     return error_code( e, generic_category(), loc );
 }
 
 // implicit conversion:
-BOOST_SYSTEM_CONSTEXPR inline error_condition make_error_condition( errc_t e ) BOOST_NOEXCEPT
+BOOST_SYSTEM_CONSTEXPR inline error_condition make_error_condition( errc_t e ) noexcept
 {
     return error_condition( e, generic_category() );
 }

include/boost/system/result.hpp

@@ -73,10 +73,10 @@ BOOST_NORETURN BOOST_NOINLINE inline void throw_exception_from_error( std::excep
 // in_place_*
 
 using in_place_value_t = variant2::in_place_index_t<0>;
-constexpr in_place_value_t in_place_value{};
+BOOST_INLINE_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{};
+BOOST_INLINE_CONSTEXPR in_place_error_t in_place_error{};
 
 namespace detail
 {
@@ -85,6 +85,10 @@ template<class T> using remove_cvref = typename std::remove_cv< typename std::re
 
 template<class... T> using is_errc_t = std::is_same<mp11::mp_list<remove_cvref<T>...>, mp11::mp_list<errc::errc_t>>;
 
+template<class T, class... A> struct is_constructible: std::is_constructible<T, A...> {};
+template<class A> struct is_constructible<bool, A>: std::is_convertible<A, bool> {};
+template<class A> struct is_constructible<bool const, A>: std::is_convertible<A, bool> {};
+
 } // namespace detail
 
 // result
@@ -95,6 +99,14 @@ private:
 
     variant2::variant<T, E> v_;
 
+public:
+
+    using value_type = T;
+    using error_type = E;
+
+    static constexpr in_place_value_t in_place_value{};
+    static constexpr in_place_error_t in_place_error{};
+
 public:
 
     // constructors
@@ -114,7 +126,7 @@ public:
     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>
+        !std::is_convertible<A, E>::value, int>::type = 0>
     constexpr result( A&& a )
         noexcept( std::is_nothrow_constructible<T, A>::value )
         : v_( in_place_value, std::forward<A>(a) )
@@ -124,7 +136,7 @@ public:
     // 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>
+        !std::is_convertible<A, T>::value, int>::type = 0>
     constexpr result( A&& a )
         noexcept( std::is_nothrow_constructible<E, A>::value )
         : v_( in_place_error, std::forward<A>(a) )
@@ -133,9 +145,10 @@ public:
 
     // explicit, value
     template<class... A, class En = typename std::enable_if<
-        std::is_constructible<T, A...>::value &&
+        detail::is_constructible<T, A...>::value &&
         !(detail::is_errc_t<A...>::value && std::is_arithmetic<T>::value) &&
-        !std::is_constructible<E, A...>::value
+        !detail::is_constructible<E, A...>::value &&
+        sizeof...(A) >= 1
         >::type>
     explicit constexpr result( A&&... a )
         noexcept( std::is_nothrow_constructible<T, A...>::value )
@@ -145,8 +158,9 @@ public:
 
     // 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
+        !detail::is_constructible<T, A...>::value &&
+        detail::is_constructible<E, A...>::value &&
+        sizeof...(A) >= 1
         >::type>
     explicit constexpr result( A&&... a )
         noexcept( std::is_nothrow_constructible<E, A...>::value )
@@ -177,7 +191,8 @@ public:
     // converting
     template<class T2, class E2, class En = typename std::enable_if<
         std::is_convertible<T2, T>::value &&
-        std::is_convertible<E2, E>::value
+        std::is_convertible<E2, E>::value &&
+        !std::is_convertible<result<T2, E2> const&, T>::value
         >::type>
     BOOST_CXX14_CONSTEXPR result( result<T2, E2> const& r2 )
         noexcept(
@@ -195,7 +210,8 @@ public:
 
     template<class T2, class E2, class En = typename std::enable_if<
         std::is_convertible<T2, T>::value &&
-        std::is_convertible<E2, E>::value
+        std::is_convertible<E2, E>::value &&
+        !std::is_convertible<result<T2, E2>&&, T>::value
         >::type>
     BOOST_CXX14_CONSTEXPR result( result<T2, E2>&& r2 )
         noexcept(
@@ -220,7 +236,7 @@ public:
 
     constexpr bool has_error() const noexcept
     {
-        return v_.index() != 0;
+        return v_.index() == 1;
     }
 
     constexpr explicit operator bool() const noexcept
@@ -385,12 +401,26 @@ public:
 
     // error access
 
-    constexpr E error() const
+    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();
     }
 
+    BOOST_CXX14_CONSTEXPR E error() &&
+        noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_move_constructible<E>::value )
+    {
+        return has_error()? std::move( variant2::unsafe_get<1>( v_ ) ): E();
+    }
+
+    // emplace
+
+    template<class... A>
+    BOOST_CXX14_CONSTEXPR T& emplace( A&&... a )
+    {
+        return v_.template emplace<0>( std::forward<A>(a)... );
+    }
+
     // swap
 
     BOOST_CXX14_CONSTEXPR void swap( result& r )
@@ -420,6 +450,13 @@ public:
     }
 };
 
+#if defined(BOOST_NO_CXX17_INLINE_VARIABLES)
+
+template<class T, class E> constexpr in_place_value_t result<T, E>::in_place_value;
+template<class T, class E> constexpr in_place_error_t result<T, E>::in_place_error;
+
+#endif
+
 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() )
@@ -442,6 +479,14 @@ private:
 
     variant2::variant<variant2::monostate, E> v_;
 
+public:
+
+    using value_type = void;
+    using error_type = E;
+
+    static constexpr in_place_value_t in_place_value{};
+    static constexpr in_place_error_t in_place_error{};
+
 public:
 
     // constructors
@@ -500,6 +545,23 @@ public:
     {
     }
 
+    // converting
+    template<class E2, class En = typename std::enable_if<
+        std::is_convertible<E2, E>::value
+        >::type>
+    BOOST_CXX14_CONSTEXPR result( result<void, E2> const& r2 )
+        noexcept(
+            std::is_nothrow_constructible<E, E2>::value &&
+            std::is_nothrow_default_constructible<E2>::value &&
+            std::is_nothrow_copy_constructible<E2>::value )
+        : v_( in_place_error, r2.error() )
+    {
+        if( r2 )
+        {
+            this->emplace();
+        }
+    }
+
     // queries
 
     constexpr bool has_value() const noexcept
@@ -509,7 +571,7 @@ public:
 
     constexpr bool has_error() const noexcept
     {
-        return v_.index() != 0;
+        return v_.index() == 1;
     }
 
     constexpr explicit operator bool() const noexcept
@@ -549,12 +611,25 @@ public:
 
     // error access
 
-    constexpr E error() const
+    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();
     }
 
+    BOOST_CXX14_CONSTEXPR E error() &&
+        noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_move_constructible<E>::value )
+    {
+        return has_error()? std::move( variant2::unsafe_get<1>( v_ ) ): E();
+    }
+
+    // emplace
+
+    BOOST_CXX14_CONSTEXPR void emplace()
+    {
+        v_.template emplace<0>();
+    }
+
     // swap
 
     BOOST_CXX14_CONSTEXPR void swap( result& r )
@@ -584,6 +659,13 @@ public:
     }
 };
 
+#if defined(BOOST_NO_CXX17_INLINE_VARIABLES)
+
+template<class E> constexpr in_place_value_t result<void, E>::in_place_value;
+template<class E> constexpr in_place_error_t result<void, E>::in_place_error;
+
+#endif
+
 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() )
@@ -598,6 +680,670 @@ template<class Ch, class Tr, class E> std::basic_ostream<Ch, Tr>& operator<<( st
     return os;
 }
 
+// result<T&, E>
+
+namespace detail
+{
+
+template<class U, class A> struct reference_to_temporary: std::integral_constant<bool,
+    !std::is_reference<A>::value ||
+    !std::is_convertible<typename std::remove_reference<A>::type*, U*>::value
+> {};
+
+} // namespace detail
+
+template<class U, class E> class result<U&, E>
+{
+private:
+
+    variant2::variant<U*, E> v_;
+
+public:
+
+    using value_type = U&;
+    using error_type = E;
+
+    static constexpr in_place_value_t in_place_value{};
+    static constexpr in_place_error_t in_place_error{};
+
+public:
+
+    // constructors
+
+    // implicit, value
+    template<class A, typename std::enable_if<
+        std::is_convertible<A, U&>::value &&
+        !detail::reference_to_temporary<U, A>::value &&
+        !std::is_convertible<A, E>::value, int>::type = 0>
+    constexpr result( A&& a )
+        noexcept( std::is_nothrow_constructible<U&, A>::value )
+        : v_( in_place_value, &static_cast<U&>( std::forward<A>(a) ) )
+    {
+    }
+
+    // implicit, error
+    template<class A = E, class = void, typename std::enable_if<
+        std::is_convertible<A, E>::value &&
+        !std::is_convertible<A, U&>::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<
+        detail::is_constructible<U&, A>::value &&
+        !std::is_convertible<A, U&>::value &&
+        !detail::reference_to_temporary<U, A>::value &&
+        !detail::is_constructible<E, A>::value
+        >::type>
+    explicit constexpr result( A&& a )
+        noexcept( std::is_nothrow_constructible<U&, A>::value )
+        : v_( in_place_value, &static_cast<U&>( std::forward<A>(a) ) )
+    {
+    }
+
+    // explicit, error
+    template<class... A, class En2 = void, class En = typename std::enable_if<
+        !detail::is_constructible<U&, A...>::value &&
+        detail::is_constructible<E, A...>::value &&
+        sizeof...(A) >= 1
+        >::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<U&, A>::value &&
+        !detail::reference_to_temporary<U, A>::value
+        >::type>
+    constexpr result( in_place_value_t, A&& a )
+        noexcept( std::is_nothrow_constructible<U&, A>::value )
+        : v_( in_place_value, &static_cast<U&>( 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)... )
+    {
+    }
+
+    // converting
+    template<class U2, class E2, class En = typename std::enable_if<
+        std::is_convertible<U2&, U&>::value &&
+        !detail::reference_to_temporary<U, U2&>::value &&
+        std::is_convertible<E2, E>::value &&
+        !std::is_convertible<result<U2&, E2> const&, U&>::value
+        >::type>
+    BOOST_CXX14_CONSTEXPR result( result<U2&, E2> const& r2 )
+        noexcept(
+            std::is_nothrow_constructible<U&, U2&>::value &&
+            std::is_nothrow_constructible<E, E2>::value &&
+            std::is_nothrow_default_constructible<E2>::value &&
+            std::is_nothrow_copy_constructible<E2>::value )
+        : v_( in_place_error, r2.error() )
+    {
+        if( r2 )
+        {
+            this->emplace( *r2 );
+        }
+    }
+
+    // queries
+
+    constexpr bool has_value() const noexcept
+    {
+        return v_.index() == 0;
+    }
+
+    constexpr bool has_error() const noexcept
+    {
+        return v_.index() == 1;
+    }
+
+    constexpr explicit operator bool() const noexcept
+    {
+        return v_.index() == 0;
+    }
+
+    // checked value access
+
+    BOOST_CXX14_CONSTEXPR U& value( boost::source_location const& loc = BOOST_CURRENT_LOCATION ) const
+    {
+        if( has_value() )
+        {
+            return *variant2::unsafe_get<0>( v_ );
+        }
+        else
+        {
+            throw_exception_from_error( variant2::unsafe_get<1>( v_ ), loc );
+        }
+    }
+
+    // unchecked value access
+
+    BOOST_CXX14_CONSTEXPR U* operator->() const noexcept
+    {
+        return has_value()? variant2::unsafe_get<0>( v_ ): 0;
+    }
+
+    BOOST_CXX14_CONSTEXPR U& operator*() const noexcept
+    {
+        U* p = operator->();
+
+        BOOST_ASSERT( p != 0 );
+
+        return *p;
+    }
+
+    // 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();
+    }
+
+    BOOST_CXX14_CONSTEXPR E error() &&
+        noexcept( std::is_nothrow_default_constructible<E>::value && std::is_nothrow_move_constructible<E>::value )
+    {
+        return has_error()? std::move( variant2::unsafe_get<1>( v_ ) ): E();
+    }
+
+    // emplace
+
+    template<class A, class En = typename std::enable_if<
+        detail::is_constructible<U&, A>::value &&
+        !detail::reference_to_temporary<U, A>::value
+        >::type>
+    BOOST_CXX14_CONSTEXPR U& emplace( A&& a )
+    {
+        return *v_.template emplace<0>( &static_cast<U&>( a ) );
+    }
+
+    // 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 && r2? *r1 == *r2: r1.v_ == r2.v_ ) )
+    {
+        return r1 && r2? *r1 == *r2: r1.v_ == r2.v_;
+    }
+
+    friend constexpr bool operator!=( result const & r1, result const & r2 )
+        noexcept( noexcept( !( r1 == r2 ) ) )
+    {
+        return !( r1 == r2 );
+    }
+};
+
+#if defined(BOOST_NO_CXX17_INLINE_VARIABLES)
+
+template<class U, class E> constexpr in_place_value_t result<U&, E>::in_place_value;
+template<class U, class E> constexpr in_place_error_t result<U&, E>::in_place_error;
+
+#endif
+
+// operator|
+
+namespace detail
+{
+
+// is_value_convertible_to
+
+template<class T, class U> struct is_value_convertible_to: std::is_convertible<T, U>
+{
+};
+
+template<class T, class U> struct is_value_convertible_to<T, U&>:
+    std::integral_constant<bool,
+        std::is_lvalue_reference<T>::value &&
+        std::is_convertible<typename std::remove_reference<T>::type*, U*>::value>
+{
+};
+
+// is_result
+
+template<class T> struct is_result: std::false_type {};
+template<class T, class E> struct is_result< result<T, E> >: std::true_type {};
+
+} // namespace detail
+
+// result | value
+
+template<class T, class E, class U,
+    class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
+>
+T operator|( result<T, E> const& r, U&& u )
+{
+    if( r )
+    {
+        return *r;
+    }
+    else
+    {
+        return std::forward<U>( u );
+    }
+}
+
+template<class T, class E, class U,
+    class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
+>
+T operator|( result<T, E>&& r, U&& u )
+{
+    if( r )
+    {
+        return *std::move( r );
+    }
+    else
+    {
+        return std::forward<U>( u );
+    }
+}
+
+// result | nullary-returning-value
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
+>
+T operator|( result<T, E> const& r, F&& f )
+{
+    if( r )
+    {
+        return *r;
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
+>
+T operator|( result<T, E>&& r, F&& f )
+{
+    if( r )
+    {
+        return *std::move( r );
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+// result | nullary-returning-result
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<detail::is_value_convertible_to<T, typename U::value_type>::value>::type
+>
+U operator|( result<T, E> const& r, F&& f )
+{
+    if( r )
+    {
+        return *r;
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<detail::is_value_convertible_to<T, typename U::value_type>::value>::type
+>
+U operator|( result<T, E>&& r, F&& f )
+{
+    if( r )
+    {
+        return *std::move( r );
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+template<class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<std::is_void<typename U::value_type>::value>::type
+>
+U operator|( result<void, E> const& r, F&& f )
+{
+    if( r )
+    {
+        return {};
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+template<class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<std::is_void<typename U::value_type>::value>::type
+>
+U operator|( result<void, E>&& r, F&& f )
+{
+    if( r )
+    {
+        return {};
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+// operator|=
+
+// result |= value
+
+template<class T, class E, class U,
+    class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
+>
+result<T, E>& operator|=( result<T, E>& r, U&& u )
+{
+    if( !r )
+    {
+        r = std::forward<U>( u );
+    }
+
+    return r;
+}
+
+// result |= nullary-returning-value
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
+>
+result<T, E>& operator|=( result<T, E>& r, F&& f )
+{
+    if( !r )
+    {
+        r = std::forward<F>( f )();
+    }
+
+    return r;
+}
+
+// result |= nullary-returning-result
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<detail::is_value_convertible_to<typename U::value_type, T>::value>::type,
+    class En3 = typename std::enable_if<std::is_convertible<typename U::error_type, E>::value>::type
+>
+result<T, E>& operator|=( result<T, E>& r, F&& f )
+{
+    if( !r )
+    {
+        r = std::forward<F>( f )();
+    }
+
+    return r;
+}
+
+// operator&
+
+// result & unary-returning-value
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T const&>() ) ),
+    class En1 = typename std::enable_if<!detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<!std::is_void<U>::value>::type
+>
+result<U, E> operator&( result<T, E> const& r, F&& f )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )( *r );
+    }
+}
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T>() ) ),
+    class En1 = typename std::enable_if<!detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<!std::is_void<U>::value>::type
+>
+result<U, E> operator&( result<T, E>&& r, F&& f )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )( *std::move( r ) );
+    }
+}
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T const&>() ) ),
+    class En = typename std::enable_if<std::is_void<U>::value>::type
+>
+result<U, E> operator&( result<T, E> const& r, F&& f )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        std::forward<F>( f )( *r );
+        return {};
+    }
+}
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T>() ) ),
+    class En = typename std::enable_if<std::is_void<U>::value>::type
+>
+result<U, E> operator&( result<T, E>&& r, F&& f )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        std::forward<F>( f )( *std::move( r ) );
+        return {};
+    }
+}
+
+template<class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En1 = typename std::enable_if<!detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<!std::is_void<U>::value>::type
+>
+result<U, E> operator&( result<void, E> const& r, F&& f )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+template<class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En = typename std::enable_if<std::is_void<U>::value>::type
+>
+result<U, E> operator&( result<void, E> const& r, F&& f )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        std::forward<F>( f )();
+        return {};
+    }
+}
+
+// result & unary-returning-result
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T const&>() ) ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<std::is_convertible<E, typename U::error_type>::value>::type
+>
+U operator&( result<T, E> const& r, F&& f )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )( *r );
+    }
+}
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T>() ) ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<std::is_convertible<E, typename U::error_type>::value>::type
+>
+U operator&( result<T, E>&& r, F&& f )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )( *std::move( r ) );
+    }
+}
+
+template<class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<std::is_convertible<E, typename U::error_type>::value>::type
+>
+U operator&( result<void, E> const& r, F&& f )
+{
+    if( r.has_error() )
+    {
+        return r.error();
+    }
+    else
+    {
+        return std::forward<F>( f )();
+    }
+}
+
+// operator&=
+
+// result &= unary-returning-value
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T>() ) ),
+    class En1 = typename std::enable_if<!detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<detail::is_value_convertible_to<U, T>::value>::type
+>
+result<T, E>& operator&=( result<T, E>& r, F&& f )
+{
+    if( r )
+    {
+        r = std::forward<F>( f )( *std::move( r ) );
+    }
+
+    return r;
+}
+
+template<class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En = typename std::enable_if<!detail::is_result<U>::value>::type
+>
+result<void, E>& operator&=( result<void, E>& r, F&& f )
+{
+    if( r )
+    {
+        std::forward<F>( f )();
+    }
+
+    return r;
+}
+
+// result &= unary-returning-result
+
+template<class T, class E, class F,
+    class U = decltype( std::declval<F>()( std::declval<T>() ) ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<detail::is_value_convertible_to<typename U::value_type, T>::value>::type,
+    class En3 = typename std::enable_if<std::is_convertible<typename U::error_type, E>::value>::type
+>
+result<T, E>& operator&=( result<T, E>& r, F&& f )
+{
+    if( r )
+    {
+        r = std::forward<F>( f )( *std::move( r ) );
+    }
+
+    return r;
+}
+
+template<class E, class F,
+    class U = decltype( std::declval<F>()() ),
+    class En1 = typename std::enable_if<detail::is_result<U>::value>::type,
+    class En2 = typename std::enable_if<std::is_void<typename U::value_type>::value>::type,
+    class En3 = typename std::enable_if<std::is_convertible<typename U::error_type, E>::value>::type
+>
+result<void, E>& operator&=( result<void, E>& r, F&& f )
+{
+    if( r )
+    {
+        r = std::forward<F>( f )();
+    }
+
+    return r;
+}
+
 } // namespace system
 } // namespace boost
 

include/boost/system/system_error.hpp

@@ -43,7 +43,7 @@ public:
     system_error( int ev, error_category const & ecat, char const * prefix ):
         std::runtime_error( std::string( prefix ) + ": " + error_code( ev, ecat ).what() ), code_( ev, ecat ) {}
 
-    error_code code() const BOOST_NOEXCEPT
+    error_code code() const noexcept
     {
         return code_;
     }

meta/libraries.json

@@ -13,5 +13,5 @@
         "Error-handling",
         "Programming"
     ],
-    "cxxstd": "03"
+    "cxxstd": "11"
 }

test/CMakeLists.txt

@@ -15,6 +15,7 @@ macro(system_run s1)
   boost_test(SOURCES ${s1} ${ARGN})
   boost_test(SOURCES ${s1} ${ARGN} COMPILE_DEFINITIONS BOOST_NO_ANSI_APIS NAME ${n1}_no_ansi)
   boost_test(SOURCES ${s1} ${ARGN} COMPILE_DEFINITIONS BOOST_SYSTEM_USE_UTF8 NAME ${n1}_utf8)
+  boost_test(SOURCES ${s1} ${ARGN} COMPILE_DEFINITIONS BOOST_SYSTEM_DISABLE_THREADS NAME ${n1}_nthr)
 
 endmacro()
 
@@ -83,7 +84,6 @@ 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)
@@ -124,9 +124,18 @@ boost_test(TYPE run SOURCES std_interop_test14.cpp)
 boost_test(TYPE run SOURCES ec_location_test3.cpp)
 boost_test(TYPE run SOURCES ec_location_test4.cpp)
 
-# result
+boost_test(TYPE compile SOURCES constexpr_test2.cpp)
 
-set(BOOST_TEST_COMPILE_FEATURES cxx_std_11)
+boost_test(TYPE run SOURCES error_code_test3.cpp)
+boost_test(TYPE run SOURCES std_interop_test15.cpp)
+
+boost_test(TYPE run SOURCES win32_generic_test.cpp)
+
+boost_test(TYPE run SOURCES ec_hash_value_test.cpp)
+
+boost_test(TYPE run SOURCES std_interop_test16.cpp)
+
+# result
 
 boost_test(TYPE run SOURCES result_default_construct.cpp)
 boost_test(TYPE run SOURCES result_value_construct.cpp)
@@ -142,4 +151,29 @@ boost_test(TYPE run SOURCES result_eq.cpp)
 boost_test(TYPE run SOURCES result_range_for.cpp)
 boost_test(TYPE run SOURCES result_value_construct2.cpp)
 boost_test(TYPE run SOURCES result_error_construct2.cpp)
+boost_test(TYPE run SOURCES result_errc_construct.cpp)
 boost_test(TYPE run SOURCES result_convert_construct.cpp)
+boost_test(TYPE run SOURCES result_typedefs.cpp)
+boost_test(TYPE run SOURCES result_value_construct3.cpp)
+boost_test(TYPE run SOURCES result_error_construct3.cpp)
+boost_test(TYPE run SOURCES result_emplace.cpp)
+boost_test(TYPE run SOURCES result_error_construct4.cpp)
+boost_test(TYPE run SOURCES result_value_construct4.cpp)
+boost_test(TYPE run SOURCES result_value_construct5.cpp)
+boost_test(TYPE run SOURCES result_error_move.cpp)
+boost_test(TYPE run SOURCES result_value_construct6.cpp)
+boost_test(TYPE run SOURCES result_value_construct7.cpp)
+boost_test(TYPE run SOURCES result_error_construct5.cpp)
+boost_test(TYPE run SOURCES result_or_value.cpp)
+boost_test(TYPE compile-fail SOURCES result_or_value_fail.cpp)
+boost_test(TYPE compile-fail SOURCES result_or_value_fail2.cpp)
+boost_test(TYPE run SOURCES result_or_fn0v.cpp)
+boost_test(TYPE run SOURCES result_or_fn0r.cpp)
+boost_test(TYPE run SOURCES result_and_fn1v.cpp)
+boost_test(TYPE run SOURCES result_and_fn1r.cpp)
+boost_test(TYPE run SOURCES result_and_eq_fn1v.cpp)
+boost_test(TYPE run SOURCES result_and_eq_fn1r.cpp)
+boost_test(TYPE run SOURCES result_in_place_use.cpp)
+boost_test(TYPE run SOURCES result_or_eq_value.cpp)
+boost_test(TYPE run SOURCES result_or_eq_fn0v.cpp)
+boost_test(TYPE run SOURCES result_or_eq_fn0r.cpp)

test/Jamfile.v2

@@ -33,6 +33,7 @@ rule system-run ( sources + )
     result += [ run $(sources) : : : <library>/boost/system//boost_system <link>shared : $(sources[1]:B)_shared ] ;
     result += [ run $(sources) : : : <define>BOOST_NO_ANSI_APIS : $(sources[1]:B)_no_ansi ] ;
     result += [ run $(sources) : : : <define>BOOST_SYSTEM_USE_UTF8 : $(sources[1]:B)_utf8 ] ;
+    result += [ run $(sources) : : : <define>BOOST_SYSTEM_DISABLE_THREADS : $(sources[1]:B)_nthr ] ;
 
     return $(result) ;
 }
@@ -74,7 +75,9 @@ system-run generic_category_test.cpp ;
 system-run system_category_test.cpp ;
 system-run after_main_test.cpp ;
 system-run failed_test.cpp ;
-system-run failed_constexpr_test.cpp ;
+run failed_constexpr_test.cpp : : :
+    # GCC w/ UBSAN doesn't consider `cat_ != 0` a constant expression
+    <toolset>gcc,<undefined-sanitizer>norecover:<build>no ;
 
 # Quick (CI) test
 run quick.cpp ;
@@ -105,7 +108,6 @@ 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 ;
@@ -152,25 +154,56 @@ run std_interop_test14.cpp ;
 run ec_location_test3.cpp ;
 run ec_location_test4.cpp ;
 
+compile constexpr_test2.cpp ;
+
+run error_code_test3.cpp ;
+run std_interop_test15.cpp ;
+
+run win32_generic_test.cpp ;
+
+run ec_hash_value_test.cpp ;
+
+run std_interop_test16.cpp ;
+
 # result
 
-import ../../config/checks/config : requires ;
-
-CPP11 = [ requires cxx11_variadic_templates cxx11_template_aliases cxx11_decltype cxx11_constexpr cxx11_noexcept ] <toolset>gcc-4.7:<build>no ;
-
-run result_default_construct.cpp : : : $(CPP11) ;
-run result_value_construct.cpp : : : $(CPP11) ;
-run result_error_construct.cpp : : : $(CPP11) ;
-run result_copy_construct.cpp : : : $(CPP11) ;
-run result_move_construct.cpp : : : $(CPP11) ;
-run result_copy_assign.cpp : : : $(CPP11) ;
-run result_move_assign.cpp : : : $(CPP11) ;
-run result_value_access.cpp : : : $(CPP11) ;
-run result_error_access.cpp : : : $(CPP11) ;
-run result_swap.cpp : : : $(CPP11) <toolset>gcc-10:<cxxflags>"-Wno-maybe-uninitialized" ;
-run result_eq.cpp : : : $(CPP11) ;
-run result_range_for.cpp : : : $(CPP11) ;
-run result_value_construct2.cpp : : : $(CPP11) ;
-run result_error_construct2.cpp : : : $(CPP11) ;
-run result_errc_construct.cpp : : : $(CPP11) ;
-run result_convert_construct.cpp : : : $(CPP11) ;
+run result_default_construct.cpp ;
+run result_value_construct.cpp ;
+run result_error_construct.cpp ;
+run result_copy_construct.cpp ;
+run result_move_construct.cpp ;
+run result_copy_assign.cpp ;
+run result_move_assign.cpp ;
+run result_value_access.cpp ;
+run result_error_access.cpp ;
+run result_swap.cpp : : : <toolset>gcc-10:<cxxflags>"-Wno-maybe-uninitialized" ;
+run result_eq.cpp ;
+run result_range_for.cpp ;
+run result_value_construct2.cpp ;
+run result_error_construct2.cpp ;
+run result_errc_construct.cpp ;
+run result_convert_construct.cpp ;
+run result_typedefs.cpp ;
+run result_value_construct3.cpp ;
+run result_error_construct3.cpp ;
+run result_emplace.cpp ;
+run result_error_construct4.cpp ;
+run result_value_construct4.cpp ;
+run result_value_construct5.cpp ;
+run result_error_move.cpp ;
+run result_value_construct6.cpp ;
+run result_value_construct7.cpp ;
+run result_error_construct5.cpp ;
+run result_or_value.cpp ;
+compile-fail result_or_value_fail.cpp ;
+compile-fail result_or_value_fail2.cpp ;
+run result_or_fn0v.cpp ;
+run result_or_fn0r.cpp ;
+run result_and_fn1v.cpp ;
+run result_and_fn1r.cpp ;
+run result_and_eq_fn1v.cpp ;
+run result_and_eq_fn1r.cpp ;
+run result_in_place_use.cpp ;
+run result_or_eq_value.cpp ;
+run result_or_eq_fn0v.cpp ;
+run result_or_eq_fn0r.cpp ;

test/config_test.cpp

@@ -50,16 +50,6 @@ int main()
   std::cout << "BOOST_NO_ANSI_APIS is defined" << std::endl;
 #else
   std::cout << "BOOST_NO_ANSI_APIS is not defined" << std::endl;
-#endif
-#ifdef BOOST_NO_CXX11_NOEXCEPT
-  std::cout << "BOOST_NO_CXX11_NOEXCEPT is defined" << std::endl;
-#else
-  std::cout << "BOOST_NO_CXX11_NOEXCEPT is not defined" << std::endl;
-#endif
-#ifdef BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS
-  std::cout << "BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS is defined" << std::endl;
-#else
-  std::cout << "BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS is not defined" << std::endl;
 #endif
   return 0;
 }

test/constexpr_test2.cpp

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

test/cygwin_error_test.cpp

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

test/ec_hash_value_test.cpp

@@ -0,0 +1,126 @@
+// Copyright 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_code.hpp>
+#include <boost/system/generic_category.hpp>
+#include <boost/system/system_category.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <cerrno>
+#include <system_error>
+
+namespace sys = boost::system;
+
+int main()
+{
+    // normal against normal (equal, system)
+    {
+        sys::error_code e2( 0, sys::system_category() );
+        sys::error_code e3( e2.value(), e2.category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal against normal (equal, generic)
+    {
+        sys::error_code e2( EINVAL, sys::generic_category() );
+        sys::error_code e3( e2.value(), e2.category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal against normal (inequal, value, generic)
+    {
+        sys::error_code e2( 0, sys::generic_category() );
+        sys::error_code e3( EINVAL, sys::generic_category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal against normal (inequal, value, system)
+    {
+        sys::error_code e2( 1, sys::system_category() );
+        sys::error_code e3( 2, sys::system_category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal against normal (inequal, category)
+    {
+        sys::error_code e2( 0, sys::system_category() );
+        sys::error_code e3( 0, sys::generic_category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // empty against normal
+    {
+        sys::error_code e2;
+        sys::error_code e3( e2.value(), e2.category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // std:: wrapping against normal
+    {
+        std::error_code e1( EINVAL, std::generic_category() );
+
+        sys::error_code e2( e1 );
+        sys::error_code e3( e2.value(), e2.category() );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // empty against wrapping std:: empty
+    {
+        std::error_code e1;
+
+        sys::error_code e2( e1 );
+        sys::error_code e3;
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // empty against roundtrip via std
+    {
+        sys::error_code e2;
+
+        std::error_code e1( e2 );
+        sys::error_code e3( e1 );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal/generic against roundtrip via std
+    {
+        sys::error_code e2( EINVAL, boost::system::generic_category() );
+
+        std::error_code e1( e2 );
+        sys::error_code e3( e1 );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    // normal/system against roundtrip via std
+    {
+        sys::error_code e2( 0, boost::system::system_category() );
+
+        std::error_code e1( e2 );
+        sys::error_code e3( e1 );
+
+        BOOST_TEST( e2 != e3 || hash_value( e2 ) == hash_value( e3 ) );
+        BOOST_TEST( e2 == e3 || hash_value( e2 ) != hash_value( e3 ) );
+    }
+
+    return boost::report_errors();
+}

test/ec_location_test.cpp

@@ -85,8 +85,6 @@ int main()
         BOOST_TEST_EQ( ec.location().line(), 75 );
     }
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
     {
         std::error_code e2( val, std::generic_category() );
 
@@ -107,10 +105,8 @@ int main()
         BOOST_TEST( ec.failed() );
 
         BOOST_TEST( ec.has_location() );
-        BOOST_TEST_EQ( ec.location().line(), 100 );
+        BOOST_TEST_EQ( ec.location().line(), 98 );
     }
 
-#endif
-
     return boost::report_errors();
 }

test/ec_location_test2.cpp

@@ -32,8 +32,6 @@ 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
@@ -57,8 +55,6 @@ std::error_code make_error_code( E2 e )
     return std::error_code( e, std::generic_category() );
 }
 
-#endif
-
 int main()
 {
     {
@@ -84,7 +80,7 @@ int main()
         BOOST_TEST( ec.failed() );
 
         BOOST_TEST( ec.has_location() );
-        BOOST_TEST_EQ( ec.location().line(), 77 );
+        BOOST_TEST_EQ( ec.location().line(), 73 );
     }
 
     {
@@ -134,7 +130,7 @@ int main()
         BOOST_TEST( ec.failed() );
 
         BOOST_TEST( ec.has_location() );
-        BOOST_TEST_EQ( ec.location().line(), 127 );
+        BOOST_TEST_EQ( ec.location().line(), 123 );
     }
 
     {
@@ -182,7 +178,7 @@ int main()
         BOOST_TEST( ec.failed() );
 
         BOOST_TEST( ec.has_location() );
-        BOOST_TEST_EQ( ec.location().line(), 175 );
+        BOOST_TEST_EQ( ec.location().line(), 171 );
     }
 
     {
@@ -209,8 +205,6 @@ int main()
         BOOST_TEST_EQ( ec.location().line(), 0 );
     }
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
     {
         sys::error_code ec( e2inval );
 
@@ -281,7 +275,5 @@ int main()
         BOOST_TEST_EQ( ec.location().line(), 0 );
     }
 
-#endif
-
     return boost::report_errors();
 }

test/ec_location_test3.cpp

@@ -57,8 +57,6 @@ int main()
         BOOST_TEST_EQ( ec3.location(), boost::source_location() );
     }
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
     {
         std::error_code e2( val, std::generic_category() );
 
@@ -84,7 +82,5 @@ int main()
         BOOST_TEST_EQ( ec3.location(), boost::source_location() );
     }
 
-#endif
-
     return boost::report_errors();
 }

test/ec_location_test4.cpp

@@ -59,8 +59,6 @@ int main()
         BOOST_TEST_EQ( ec.location(), boost::source_location() );
     }
 
-#if defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
     {
         std::error_code e2( val, std::generic_category() );
 
@@ -87,7 +85,5 @@ int main()
         BOOST_TEST_EQ( ec.location(), boost::source_location() );
     }
 
-#endif
-
     return boost::report_errors();
 }

test/ec_what_test.cpp

@@ -62,8 +62,6 @@ int main()
         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 );
@@ -85,7 +83,5 @@ int main()
         BOOST_TEST_EQ( ec2.what(), ec2.message() + " [std:system:5]" );
     }
 
-#endif
-
     return boost::report_errors();
 }

test/error_category_test.cpp

@@ -8,11 +8,9 @@
 
 // See library home page at http://www.boost.org/libs/system
 
-// Avoid spurious VC++ warnings
-# define _CRT_SECURE_NO_WARNINGS
-
 #include <boost/system/error_code.hpp>
 #include <boost/core/lightweight_test.hpp>
+#include <boost/core/snprintf.hpp>
 #include <cstdio>
 
 //
@@ -23,7 +21,7 @@ class user_category: public sys::error_category
 {
 public:
 
-    virtual const char * name() const BOOST_NOEXCEPT
+    virtual const char * name() const noexcept
     {
         return "user";
     }
@@ -31,7 +29,7 @@ public:
     virtual std::string message( int ev ) const
     {
         char buffer[ 256 ];
-        std::sprintf( buffer, "user message %d", ev );
+        boost::core::snprintf( buffer, sizeof( buffer ), "user message %d", ev );
 
         return buffer;
     }

test/error_category_test2.cpp

@@ -8,11 +8,9 @@
 
 // See library home page at http://www.boost.org/libs/system
 
-// Avoid spurious VC++ warnings
-#define _CRT_SECURE_NO_WARNINGS
-
 #include <boost/system/error_category.hpp>
 #include <boost/core/lightweight_test.hpp>
+#include <boost/core/snprintf.hpp>
 #include <cstdio>
 
 //
@@ -23,7 +21,7 @@ class user_category: public sys::error_category
 {
 public:
 
-    virtual const char * name() const BOOST_NOEXCEPT
+    virtual const char * name() const noexcept
     {
         return "user";
     }
@@ -31,7 +29,7 @@ public:
     virtual std::string message( int ev ) const
     {
         char buffer[ 256 ];
-        std::sprintf( buffer, "user message %d", ev );
+        boost::core::snprintf( buffer, sizeof( buffer ), "user message %d", ev );
 
         return buffer;
     }

test/error_code_test2.cpp

@@ -11,26 +11,53 @@ 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" ) );
+    char buffer[ 4096 ], buffer2[ 4096 ];
 
     {
+        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(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( ec.message( buffer, sizeof( buffer ) ), ec.message().c_str() );
+
+        {
+            char const* msg = ec.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, ec.message().c_str() );
+            }
+        }
+
+        BOOST_TEST( !ec.failed() );
+        BOOST_TEST( !ec );
+
+        BOOST_TEST_EQ( ec.to_string(), std::string( "system:0" ) );
+    }
+
+    {
+        sys::error_code ec;
         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_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.category().message( ec2.value(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.message().c_str() );
+
+        {
+            char const* msg = ec2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, ec2.message().c_str() );
+            }
+        }
+
         BOOST_TEST( !ec2.failed() );
         BOOST_TEST( !ec2 );
 
@@ -41,12 +68,25 @@ int main()
     }
 
     {
+        sys::error_code ec;
         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_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.category().message( ec2.value(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.message().c_str() );
+
+        {
+            char const* msg = ec2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, ec2.message().c_str() );
+            }
+        }
+
         BOOST_TEST( !ec2.failed() );
         BOOST_TEST( !ec2 );
 
@@ -61,34 +101,124 @@ int main()
 
         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_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.category().message( ec2.value(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.message().c_str() );
+
+        {
+            char const* msg = ec2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, ec2.message().c_str() );
+            }
+        }
+
         BOOST_TEST( ec2.failed() );
         BOOST_TEST( ec2 );
         BOOST_TEST_NOT( !ec2 );
 
+        sys::error_code ec;
+
         BOOST_TEST_NE( ec, ec2 );
         BOOST_TEST_NOT( ec == ec2 );
 
         BOOST_TEST_EQ( ec2.to_string(), std::string( "generic:5" ) );
     }
 
+    {
+        sys::error_code ec2( -4, sys::generic_category() );
+
+        BOOST_TEST_EQ( ec2.value(), -4 );
+        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(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.message().c_str() );
+
+        {
+            char const* msg = ec2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, ec2.message().c_str() );
+            }
+        }
+
+        BOOST_TEST( ec2.failed() );
+        BOOST_TEST( ec2 );
+        BOOST_TEST_NOT( !ec2 );
+
+        sys::error_code ec;
+
+        BOOST_TEST_NE( ec, ec2 );
+        BOOST_TEST_NOT( ec == ec2 );
+
+        BOOST_TEST_EQ( ec2.to_string(), std::string( "generic:-4" ) );
+    }
+
     {
         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_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.category().message( ec2.value(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.message().c_str() );
+
+        {
+            char const* msg = ec2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, ec2.message().c_str() );
+            }
+        }
+
         BOOST_TEST( ec2.failed() );
         BOOST_TEST( ec2 );
         BOOST_TEST_NOT( !ec2 );
 
+        sys::error_code ec;
+
         BOOST_TEST_NE( ec, ec2 );
         BOOST_TEST_NOT( ec == ec2 );
 
         BOOST_TEST_EQ( ec2.to_string(), std::string( "system:5" ) );
     }
 
+    {
+        sys::error_code ec2( -4, sys::system_category() );
+
+        BOOST_TEST_EQ( ec2.value(), -4 );
+        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(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( ec2.message( buffer, sizeof( buffer ) ), ec2.message().c_str() );
+
+        {
+            char const* msg = ec2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, ec2.message().c_str() );
+            }
+        }
+
+        BOOST_TEST( ec2.failed() );
+        BOOST_TEST( ec2 );
+        BOOST_TEST_NOT( !ec2 );
+
+        sys::error_code ec;
+
+        BOOST_TEST_NE( ec, ec2 );
+        BOOST_TEST_NOT( ec == ec2 );
+
+        BOOST_TEST_EQ( ec2.to_string(), std::string( "system:-4" ) );
+    }
+
     return boost::report_errors();
 }

test/error_code_test3.cpp

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

test/error_condition_test3.cpp

@@ -11,26 +11,53 @@ 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" ) );
+    char buffer[ 4096 ], buffer2[ 4096 ];
 
     {
+        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(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( en.message( buffer, sizeof( buffer ) ), en.message().c_str() );
+
+        {
+            char const* msg = en.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, en.message().c_str() );
+            }
+        }
+
+        BOOST_TEST( !en.failed() );
+        BOOST_TEST( !en );
+
+        BOOST_TEST_EQ( en.to_string(), std::string( "cond:generic:0" ) );
+    }
+
+    {
+        sys::error_condition en;
         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_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.category().message( en2.value(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.message().c_str() );
+
+        {
+            char const* msg = en2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, en2.message().c_str() );
+            }
+        }
+
         BOOST_TEST( !en2.failed() );
         BOOST_TEST( !en2 );
 
@@ -41,12 +68,25 @@ int main()
     }
 
     {
+        sys::error_condition en;
         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_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.category().message( en2.value(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.message().c_str() );
+
+        {
+            char const* msg = en2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, en2.message().c_str() );
+            }
+        }
+
         BOOST_TEST( !en2.failed() );
         BOOST_TEST( !en2 );
 
@@ -61,34 +101,124 @@ int main()
 
         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_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.category().message( en2.value(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.message().c_str() );
+
+        {
+            char const* msg = en2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, en2.message().c_str() );
+            }
+        }
+
         BOOST_TEST( en2.failed() );
         BOOST_TEST( en2 );
         BOOST_TEST_NOT( !en2 );
 
+        sys::error_condition en;
+
         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( -4, sys::generic_category() );
+
+        BOOST_TEST_EQ( en2.value(), -4 );
+        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(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.message().c_str() );
+
+        {
+            char const* msg = en2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, en2.message().c_str() );
+            }
+        }
+
+        BOOST_TEST( en2.failed() );
+        BOOST_TEST( en2 );
+        BOOST_TEST_NOT( !en2 );
+
+        sys::error_condition en;
+
+        BOOST_TEST_NE( en, en2 );
+        BOOST_TEST_NOT( en == en2 );
+
+        BOOST_TEST_EQ( en2.to_string(), std::string( "cond:generic:-4" ) );
+    }
+
     {
         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_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.category().message( en2.value(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.message().c_str() );
+
+        {
+            char const* msg = en2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, en2.message().c_str() );
+            }
+        }
+
         BOOST_TEST( en2.failed() );
         BOOST_TEST( en2 );
         BOOST_TEST_NOT( !en2 );
 
+        sys::error_condition en;
+
         BOOST_TEST_NE( en, en2 );
         BOOST_TEST_NOT( en == en2 );
 
         BOOST_TEST_EQ( en2.to_string(), std::string( "cond:system:5" ) );
     }
 
+    {
+        sys::error_condition en2( -4, sys::system_category() );
+
+        BOOST_TEST_EQ( en2.value(), -4 );
+        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(), buffer2, sizeof( buffer2 ) ) );
+        BOOST_TEST_CSTR_EQ( en2.message( buffer, sizeof( buffer ) ), en2.message().c_str() );
+
+        {
+            char const* msg = en2.message( nullptr, 0 );
+
+            if( msg != nullptr )
+            {
+                BOOST_TEST_CSTR_EQ( msg, en2.message().c_str() );
+            }
+        }
+
+        BOOST_TEST( en2.failed() );
+        BOOST_TEST( en2 );
+        BOOST_TEST_NOT( !en2 );
+
+        sys::error_condition en;
+
+        BOOST_TEST_NE( en, en2 );
+        BOOST_TEST_NOT( en == en2 );
+
+        BOOST_TEST_EQ( en2.to_string(), std::string( "cond:system:-4" ) );
+    }
+
     return boost::report_errors();
 }

test/failed_test.cpp

@@ -2,11 +2,9 @@
 // Copyright 2018 Peter Dimov.
 // Distributed under the Boost Software License, Version 1.0.
 
-// Avoid spurious VC++ warnings
-#define _CRT_SECURE_NO_WARNINGS
-
 #include <boost/system/error_code.hpp>
 #include <boost/core/lightweight_test.hpp>
+#include <boost/core/snprintf.hpp>
 #include <cstdio>
 
 using namespace boost::system;
@@ -15,11 +13,11 @@ struct http_category_impl: public error_category
 {
     // clang++ 3.8 and below: initialization of const object
     // requires a user-provided default constructor
-    BOOST_SYSTEM_CONSTEXPR http_category_impl() BOOST_NOEXCEPT
+    BOOST_SYSTEM_CONSTEXPR http_category_impl() noexcept
     {
     }
 
-    char const * name() const BOOST_NOEXCEPT
+    char const * name() const noexcept
     {
         return "http";
     }
@@ -28,11 +26,11 @@ struct http_category_impl: public error_category
     {
         char buffer[ 32 ];
 
-        std::sprintf( buffer, "HTTP/1.0 %d", ev );
+        boost::core::snprintf( buffer, sizeof( buffer ), "HTTP/1.0 %d", ev );
         return buffer;
     }
 
-    bool failed( int ev ) const BOOST_NOEXCEPT
+    bool failed( int ev ) const noexcept
     {
         return !( ev >= 200 && ev < 300 );
     }

test/result_and_eq_fn1r.cpp

@@ -0,0 +1,149 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& r )
+    {
+        if( &r != this )
+        {
+            v_ = r.v_;
+            r.v_ = 0;
+        }
+
+        return *this;
+    }
+};
+
+struct E
+{
+};
+
+struct E2
+{
+    E2() {}
+    E2( E ) {}
+};
+
+result<int, E> fi( int x )
+{
+    return 2 * x + 1;
+}
+
+result<int, E2> fi2( int )
+{
+    return E2();
+}
+
+result<X, E> fy( Y y )
+{
+    return X{ 2 * y.v_ + 1 };
+}
+
+result<Y, E2> fy2( Y )
+{
+    return E2();
+}
+
+result<int&, E> fri( int& )
+{
+    static int x = 2;
+    return x;
+}
+
+result<int&, E2> fri2( int& )
+{
+    return E2();
+}
+
+result<void, E2> fv()
+{
+    return {};
+}
+
+result<void, E2> fv2()
+{
+    return E2();
+}
+
+int main()
+{
+    {
+        result<int, E2> r( 1 );
+
+        r &= fi;
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 3 );
+
+        r &= fi2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fi;
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        result<Y, E2> r( in_place_value, 1 );
+
+        r &= fy;
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 3 );
+
+        r &= fy2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fy;
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        int x1 = 1;
+        result<int&, E2> r( x1 );
+
+        r &= fri;
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &*fri( x1 ) );
+
+        r &= fri2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fri;
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        result<void, E2> r;
+
+        r &= fv;
+        BOOST_TEST( r.has_value() );
+
+        r &= fv2;
+        BOOST_TEST( r.has_error() );
+
+        r &= fv;
+        BOOST_TEST( r.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_and_eq_fn1v.cpp

@@ -0,0 +1,141 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& r )
+    {
+        if( &r != this )
+        {
+            v_ = r.v_;
+            r.v_ = 0;
+        }
+
+        return *this;
+    }
+};
+
+struct E
+{
+};
+
+int f( int x )
+{
+    return x * 2 + 1;
+}
+
+X g( Y y )
+{
+    return X{ y.v_ * 2 + 1 };
+}
+
+int& h( int& )
+{
+    static int x = 2;
+    return x;
+}
+
+static int fv_called;
+
+void fv()
+{
+    ++fv_called;
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        r &= f;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 3 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        r &= f;
+
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        result<Y> r( in_place_value, 1 );
+
+        r &= g;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 3 );
+    }
+
+    {
+        result<Y, E> r( in_place_error );
+
+        r &= g;
+
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        int x1 = 1;
+        result<int&> r( x1 );
+
+        r &= h;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &h( x1 ) );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        r &= h;
+
+        BOOST_TEST( r.has_error() );
+    }
+
+    {
+        result<void> r;
+        fv_called = 0;
+
+        r &= fv;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST_EQ( fv_called, 1 );
+    }
+
+    {
+        result<void, E> r( in_place_error );
+        fv_called = 0;
+
+        r &= fv;
+
+        BOOST_TEST( r.has_error() );
+        BOOST_TEST_EQ( fv_called, 0 );
+    }
+
+    return boost::report_errors();
+}

test/result_and_fn1r.cpp

@@ -0,0 +1,503 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& ) = delete;
+};
+
+struct E
+{
+};
+
+struct E2
+{
+    E2() {}
+    E2( E ) {}
+};
+
+result<int, E2> fi( int x )
+{
+    return 2 * x + 1;
+}
+
+result<int, E2> fi2( int )
+{
+    return E2();
+}
+
+result<void, E2> fi3( int )
+{
+    return {};
+}
+
+result<X, E2> fy( Y y )
+{
+    return X{ 2 * y.v_ + 1 };
+}
+
+result<X, E2> fy2( Y )
+{
+    return E2();
+}
+
+result<void, E2> fy3( Y )
+{
+    return {};
+}
+
+result<int, E2> fri( int& x )
+{
+    return x * 2 + 1;
+}
+
+result<int&, E2> fri2( int& )
+{
+    return E2();
+}
+
+result<void, E2> fri3( int& )
+{
+    return {};
+}
+
+result<int, E2> fk()
+{
+    return 7;
+}
+
+result<int, E2> fk2()
+{
+    return E2();
+}
+
+result<void, E2> fk3()
+{
+    return {};
+}
+
+result<void, E2> fk4()
+{
+    return E2();
+}
+
+int main()
+{
+    {
+        result<int, E> r( 1 );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        result<int, E> const r( 1 );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( 1 ) & fi;
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( 1 ) & fi2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<int, E>( 1 ) & fi3;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fi;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & fi2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fi3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( in_place_error ) & fi;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E2> r2 = result<int, E>( in_place_error ) & fi2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<int, E>( in_place_error ) & fi3;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_value, 1 ) & fy;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2->v_, 3 );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_value, 1 ) & fy2;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<Y, E>( in_place_value, 1 ) & fy3;
+
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_error ) & fy;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<X, E2> r2 = result<Y, E>( in_place_error ) & fy2;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<Y, E>( in_place_error ) & fy3;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        int x1 = 1;
+        result<int&, E> r( x1 );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        int x1 = 1;
+        result<int&, E> const r( x1 );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_value() );
+        }
+    }
+
+    {
+        int x1 = 1;
+
+        result<int, E2> r2 = result<int&, E>( x1 ) & fri;
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&, E2> r2 = result<int&, E>( x1 ) & fri2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        int x1 = 1;
+
+        result<void, E2> r2 = result<int&, E>( x1 ) & fri3;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int&, E> const r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fri;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int&, E2> r2 = r & fri2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fri3;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<int&, E>( in_place_error ) & fri;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int&, E2> r2 = result<int&, E>( in_place_error ) & fri2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<int&, E>( in_place_error ) & fri3;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E> r;
+
+        {
+            result<int, E2> r2 = r & fk;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 7 );
+        }
+
+        {
+            result<int, E2> r2 = r & fk2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fk3;
+            BOOST_TEST( r2.has_value() );
+        }
+
+        {
+            result<void, E2> r2 = r & fk4;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<void, E> const r;
+
+        {
+            result<int, E2> r2 = r & fk;
+            BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 7 );
+        }
+
+        {
+            result<int, E2> r2 = r & fk2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fk3;
+            BOOST_TEST( r2.has_value() );
+        }
+
+        {
+            result<void, E2> r2 = r & fk4;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<void, E>() & fk;
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 7 );
+    }
+
+    {
+        result<int, E2> r2 = result<void, E>() & fk2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<void, E>() & fk3;
+        BOOST_TEST( r2.has_value() );
+    }
+
+    {
+        result<void, E2> r2 = result<void, E>() & fk4;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E> r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fk;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & fk2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fk3;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fk4;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<void, E> const r( in_place_error );
+
+        {
+            result<int, E2> r2 = r & fk;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<int, E2> r2 = r & fk2;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fk3;
+            BOOST_TEST( r2.has_error() );
+        }
+
+        {
+            result<void, E2> r2 = r & fk4;
+            BOOST_TEST( r2.has_error() );
+        }
+    }
+
+    {
+        result<int, E2> r2 = result<void, E>( in_place_error ) & fk;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E2> r2 = result<void, E>( in_place_error ) & fk2;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<void, E>( in_place_error ) & fk3;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E2> r2 = result<void, E>( in_place_error ) & fk4;
+        BOOST_TEST( r2.has_error() );
+    }
+
+    return boost::report_errors();
+}

test/result_and_fn1v.cpp

@@ -0,0 +1,331 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& ) = delete;
+};
+
+struct E
+{
+};
+
+int f( int x )
+{
+    return x * 2 + 1;
+}
+
+X g( Y y )
+{
+    return X{ y.v_ * 2 + 1 };
+}
+
+int& h( int& )
+{
+    static int x = 2;
+    return x;
+}
+
+int k()
+{
+    return 7;
+}
+
+static int fv1_called_with;
+
+void fv1( int x )
+{
+    fv1_called_with = x;
+}
+
+static int fv2_called;
+
+void fv2()
+{
+    ++fv2_called;
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+        result<int> r2 = r & f;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int> const r( 1 );
+        result<int> r2 = r & f;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int> r2 = result<int>( 1 ) & f;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 3 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+        result<int, E> r2 = r & f;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E> const r( in_place_error );
+        result<int, E> r2 = r & f;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E> r2 = result<int, E>( in_place_error ) & f;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<X> r2 = result<Y>( in_place_value, 1 ) & g;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2->v_, 3 );
+    }
+
+    {
+        result<X, E> r2 = result<Y, E>( in_place_error ) & g;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r( x1 );
+
+        result<int&> r2 = r & h;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &h( x1 ) );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r( x1 );
+
+        result<int&> r2 = r & h;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &h( x1 ) );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r2 = result<int&>( x1 ) & h;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( &*r2, &h( x1 ) );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        result<int&, E> r2 = r & h;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int&, E> const r( in_place_error );
+
+        result<int&, E> r2 = r & h;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int&, E> r2 = result<int&, E>( in_place_error ) & h;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void> r;
+        result<int> r2 = r & k;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 7 );
+    }
+
+    {
+        result<void> const r;
+        result<int> r2 = r & k;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 7 );
+    }
+
+    {
+        result<int> r2 = result<void>() & k;
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( *r2, 7 );
+    }
+
+    {
+        result<void, E> r( in_place_error );
+        result<int, E> r2 = r & k;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<void, E> const r( in_place_error );
+        result<int, E> r2 = r & k;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        result<int, E> r2 = result<void, E>( in_place_error ) & k;
+
+        BOOST_TEST( r2.has_error() );
+    }
+
+    {
+        fv1_called_with = 0;
+
+        result<int> r( 1 );
+        result<void> r2 = r & fv1;
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST_EQ( fv1_called_with, 1 );
+    }
+
+    {
+        result<int> const r( 1 );
+        result<void> r2 = r & fv1;
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST_EQ( fv1_called_with, 1 );
+    }
+
+    {
+        fv1_called_with = 0;
+
+        result<void> r2 = result<int>( 1 ) & fv1;
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST_EQ( fv1_called_with, 1 );
+    }
+
+    {
+        fv1_called_with = 0;
+
+        result<int, E> r( in_place_error );
+        result<void, E> r2 = r & fv1;
+
+        BOOST_TEST( r2.has_error() );
+        BOOST_TEST_EQ( fv1_called_with, 0 );
+    }
+
+    {
+        fv1_called_with = 0;
+
+        result<int, E> const r( in_place_error );
+        result<void, E> r2 = r & fv1;
+
+        BOOST_TEST( r2.has_error() );
+        BOOST_TEST_EQ( fv1_called_with, 0 );
+    }
+
+    {
+        fv1_called_with = 0;
+
+        result<void, E> r2 = result<int, E>( in_place_error ) & fv1;
+
+        BOOST_TEST( r2.has_error() );
+        BOOST_TEST_EQ( fv1_called_with, 0 );
+    }
+
+    {
+        result<void> r;
+        fv2_called = 0;
+
+        result<void> r2 = r & fv2;
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST_EQ( fv2_called, 1 );
+    }
+
+    {
+        result<void> const r;
+        fv2_called = 0;
+
+        result<void> r2 = r & fv2;
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST_EQ( fv2_called, 1 );
+    }
+
+    {
+        fv2_called = 0;
+
+        result<void> r2 = result<void>() & fv2;
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST_EQ( fv2_called, 1 );
+    }
+
+    {
+        result<void, E> r( in_place_error );
+        fv2_called = 0;
+
+        result<void, E> r2 = r & fv2;
+
+        BOOST_TEST( r2.has_error() );
+        BOOST_TEST_EQ( fv2_called, 0 );
+    }
+
+    {
+        result<void, E> const r( in_place_error );
+        fv2_called = 0;
+
+        result<void, E> r2 = r & fv2;
+
+        BOOST_TEST( r2.has_error() );
+        BOOST_TEST_EQ( fv2_called, 0 );
+    }
+
+    {
+        fv2_called = 0;
+
+        result<void, E> r2 = result<void, E>( in_place_error ) & fv2;
+
+        BOOST_TEST( r2.has_error() );
+        BOOST_TEST_EQ( fv2_called, 0 );
+    }
+
+    return boost::report_errors();
+}

test/result_convert_construct.cpp

@@ -181,6 +181,95 @@ int main()
 
     BOOST_TEST_EQ( X::instances, 0 );
 
+    //
+
+    {
+        result<void, int> r;
+        result<void, X> r2 = r;
+
+        BOOST_TEST( r2 );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, int> const r;
+        result<void, X> r2 = r;
+
+        BOOST_TEST( r2 );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, X> r2 = result<void, int>();
+
+        BOOST_TEST( r2 );
+        BOOST_TEST_EQ( X::instances, 0 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, int> r( 5 );
+        result<void, X> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(5) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        result<void, int> const r( 6 );
+        result<void, X> r2 = r;
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(6) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    {
+        result<void, X> r2 = result<void, int>( 7 );
+
+        BOOST_TEST( !r2 );
+        BOOST_TEST_EQ( r2.error(), X(7) );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
+    {
+        int x = 5;
+
+        result<int&> r( x );
+        result<int const&> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 5 );
+    }
+
+    {
+        int x = 6;
+
+        result<int&> const r( x );
+        result<int const&> r2 = r;
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 6 );
+    }
+
+    {
+        int x = 7;
+
+        result<int const&> r2 = result<int&>( x );
+
+        BOOST_TEST( r2 ) && BOOST_TEST_EQ( *r2, 7 );
+    }
+
     {
         BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<long>, result<int>>));
         BOOST_TEST_TRAIT_TRUE((std::is_convertible<result<int>, result<long>>));
@@ -196,6 +285,21 @@ int main()
 
         BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int, void*>, result<int, int>>));
         BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<int, int>, result<int, void*>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<void, void*>, result<void, int>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<void, int>, result<void, void*>>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<int const&>, result<int&>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<result<int&>, result<int const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&>, result<int>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<int>, result<int const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&>, result<long&>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<long&>, result<int const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&>, result<long const&>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<result<long const&>, result<int const&>>));
     }
 
     return boost::report_errors();

test/result_copy_assign.cpp

@@ -682,5 +682,151 @@ int main()
         BOOST_TEST_EQ( r, r2 );
     }
 
+    // reference
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r1( x1 );
+        result<int&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int const x1 = 1;
+        int const x2 = 2;
+
+        result<int const&> r1( x1 );
+        result<int const&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> const r1( x1 );
+        result<int&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int const x1 = 1;
+        int const x2 = 2;
+
+        result<int const &> const r1( x1 );
+        result<int const &> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r1( x1 );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x2 = 2;
+
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        int x2 = 2;
+
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> const r1( ec );
+        result<int&> r2( x2 );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> const r1( ec );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = r1;
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
     return boost::report_errors();
 }

test/result_copy_construct.cpp

@@ -145,6 +145,8 @@ int main()
 
     BOOST_TEST_EQ( X::instances, 0 );
 
+    //
+
     {
         result<void> r;
         result<void> r2( r );
@@ -177,5 +179,121 @@ int main()
         BOOST_TEST_EQ( r, r2 );
     }
 
+    //
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r1( x1 );
+        result<int&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int const x1 = 1;
+
+        result<int const&> r1( x1 );
+        result<int const&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int const x1 = 1;
+
+        result<int const&> const r1( x1 );
+        result<int const&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X x1( 1 );
+
+        result<X&> r1( x1 );
+        result<X&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X x1( 1 );
+
+        result<X&> const r1( x1 );
+        result<X&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X const x1( 1 );
+
+        result<X const&> r1( x1 );
+        result<X const&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X const x1( 1 );
+
+        result<X const&> const r1( x1 );
+        result<X const&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> const r1( ec );
+        result<int&> r2( r1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    //
+
     return boost::report_errors();
 }

test/result_default_construct.cpp

@@ -12,6 +12,11 @@ struct X
 {
 };
 
+struct Y
+{
+    Y( int );
+};
+
 int main()
 {
     {
@@ -23,6 +28,24 @@ int main()
         BOOST_TEST_EQ( r.value(), 0 );
     }
 
+    {
+        result<int> r{};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        result<int> r = {};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
     {
         result<X> r;
 
@@ -30,6 +53,20 @@ int main()
         BOOST_TEST( !r.has_error() );
     }
 
+    {
+        result<X> r{};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        result<X> r = {};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
     {
         result<void> r;
 
@@ -37,5 +74,34 @@ int main()
         BOOST_TEST( !r.has_error() );
     }
 
+    {
+        result<void> r{};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        result<void> r = {};
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<int>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<int, int>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<X>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<X, int>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<void>>));
+        BOOST_TEST_TRAIT_TRUE((std::is_default_constructible<result<void, int>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_default_constructible<result<Y>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_default_constructible<result<Y, int>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_default_constructible<result<int&>>));
+        BOOST_TEST_TRAIT_FALSE((std::is_default_constructible<result<int&, int>>));
+    }
+
     return boost::report_errors();
 }

test/result_emplace.cpp

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

test/result_eq.cpp

@@ -149,5 +149,83 @@ int main()
         BOOST_TEST_NE( r1, r2 );
     }
 
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r1( x1 );
+        result<int&> r2( x2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( x2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        result<int&> r1( 1, generic_category() );
+        result<int&> r2( 2, generic_category() );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( 2, generic_category() );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        X x1( 1 );
+        X x2( 2 );
+
+        result<X&, Y> r1( x1 );
+        result<X&, Y> r2( x2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        X x1( 1 );
+        X x2( 1 );
+
+        result<X&, Y> r1( x1 );
+        result<X&, Y> r2( x2 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        result<X&, Y> r1( in_place_error, 1 );
+        result<X&, Y> r2( in_place_error, 2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
+    {
+        X x1( 1 );
+
+        result<X&, Y> r1( x1 );
+        result<X&, Y> r2( in_place_error, 2 );
+
+        BOOST_TEST_EQ( r1, r1 );
+        BOOST_TEST_NE( r1, r2 );
+    }
+
     return boost::report_errors();
 }

test/result_errc_construct.cpp

@@ -19,5 +19,14 @@ int main()
     BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<bool>>));
     BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, errc::errc_t>));
 
+    BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<int const&>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&>, errc::errc_t>));
+
+    BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<double const&>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<double const&>, errc::errc_t>));
+
+    BOOST_TEST_TRAIT_FALSE((std::is_convertible<errc::errc_t, result<bool const&>>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const&>, errc::errc_t>));
+
     return boost::report_errors();
 }

test/result_error_access.cpp

@@ -152,6 +152,8 @@ int main()
         BOOST_TEST_EQ( (result<std::string, X>( "s" ).error().v_), 0 );
     }
 
+    //
+
     {
         result<void> r;
 
@@ -208,5 +210,71 @@ int main()
         BOOST_TEST_EQ( result<void>( ec ).error(), ec );
     }
 
+    //
+
+    {
+        int x1 = 1;
+
+        result<int&> r( x1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r( x1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), error_code() );
+    }
+
+    {
+        int x1 = 1;
+
+        BOOST_TEST( result<int&>( x1 ).has_value() );
+        BOOST_TEST( !result<int&>( x1 ).has_error() );
+
+        BOOST_TEST_EQ( result<int&>( x1 ).error(), error_code() );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> const r( ec );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        BOOST_TEST( !result<int&>( ec ).has_value() );
+        BOOST_TEST( result<int&>( ec ).has_error() );
+
+        BOOST_TEST_EQ( result<int&>( ec ).error(), ec );
+    }
+
+    //
+
     return boost::report_errors();
 }

test/result_error_construct.cpp

@@ -146,8 +146,14 @@ int main()
         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>>));
+        // We'd like this to be false due to the ambiguity caused by X having
+        // an explicit constructor taking an int, which should be viable in this
+        // context, but the implicit constructor is enabled, and there's no way to
+        // disallow it
+        //
+        // BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int, X>, int>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<int, result<int, X>>));
     }
 
     {

test/result_error_construct3.cpp

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

test/result_error_construct4.cpp

@@ -0,0 +1,45 @@
+// Copyright 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+// Eigen::Matrix4d has an explicit templated constructor
+// https://github.com/boostorg/system/issues/103
+// https://github.com/boostorg/json/issues/843
+
+struct X
+{
+    X() {}
+    template<class T> explicit X( T const& ) {}
+};
+
+int main()
+{
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<X> r = ec;
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( std::errc::invalid_argument );
+
+        result<X> r = ec;
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_EQ( r.error(), ec );
+    }
+
+    return boost::report_errors();
+}

test/result_error_construct5.cpp

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

test/result_error_move.cpp

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

test/result_in_place_use.cpp

@@ -0,0 +1,22 @@
+// Copyright 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+template<class T, class U> void test( T const& t, U const& u )
+{
+    BOOST_TEST_NE( static_cast<void const*>( &t ), static_cast<void const*>( &u ) );
+}
+
+int main()
+{
+    using namespace boost::system;
+
+    test( result<int>::in_place_value, result<int>::in_place_error );
+    test( result<void>::in_place_value, result<void>::in_place_error );
+    test( result<int&>::in_place_value, result<int&>::in_place_error );
+
+    return boost::report_errors();
+}

test/result_move_assign.cpp

@@ -508,6 +508,8 @@ int main()
 
     BOOST_TEST_EQ( Y::instances, 0 );
 
+    //
+
     {
         result<void> r;
         result<void> r2;
@@ -600,5 +602,110 @@ int main()
         BOOST_TEST_EQ( r2.error(), ec );
     }
 
+    //
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r1( x1 );
+        result<int&> r2( x2 );
+
+        r2 = std::move( r1 );
+
+        BOOST_TEST_EQ( x1, 1 );
+        BOOST_TEST_EQ( x2, 2 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+        BOOST_TEST_EQ( &*r1, &*r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = std::move( r1 );
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+
+        BOOST_TEST_EQ( r1, r2 );
+    }
+
+    {
+        int x1 = 1;
+
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( x1 );
+
+        r2 = std::move( r1 );
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        int x1 = 1;
+
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r2( x1 );
+
+        r2 = result<int&>( ec );
+
+        BOOST_TEST_EQ( x1, 1 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r1( ec );
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = std::move( r1 );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    {
+        auto ec = make_error_code( errc::invalid_argument );
+
+        result<int&> r2( ENOENT, generic_category() );
+
+        r2 = result<int&>( ec );
+
+        BOOST_TEST( !r2.has_value() );
+        BOOST_TEST( r2.has_error() );
+
+        BOOST_TEST_EQ( r2.error(), ec );
+    }
+
+    //
+
     return boost::report_errors();
 }

test/result_move_construct.cpp

@@ -207,6 +207,8 @@ int main()
 
     BOOST_TEST_EQ( X::instances, 0 );
 
+    //
+
     {
         result<void> r;
         result<void> r2( std::move( r ) );
@@ -245,5 +247,149 @@ int main()
         BOOST_TEST_EQ( r2.error(), ec );
     }
 
+    //
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 );
+        result<int&> r2( std::move( r1 ) );
+
+        BOOST_TEST( r1.has_value() );
+        BOOST_TEST( !r1.has_error() );
+
+        BOOST_TEST_EQ( r1.value(), 1 );
+        BOOST_TEST_EQ( &*r1, &x1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int const x1 = 1;
+
+        result<int const&> r1( x1 );
+        result<int const&> r2( std::move( r1 ) );
+
+        BOOST_TEST( r1.has_value() );
+        BOOST_TEST( !r1.has_error() );
+
+        BOOST_TEST_EQ( r1.value(), 1 );
+        BOOST_TEST_EQ( &*r1, &x1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r2(( result<int&>( x1 ) ));
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        int const x1 = 1;
+
+        result<int const&> r2(( result<int const&>( x1 ) ));
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value(), 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+    }
+
+    {
+        X x1( 1 );
+
+        result<X&> r1( x1 );
+        result<X&> r2( std::move( r1 ) );
+
+        BOOST_TEST( r1.has_value() );
+        BOOST_TEST( !r1.has_error() );
+
+        BOOST_TEST_EQ( r1.value().v_, 1 );
+        BOOST_TEST_EQ( &*r1, &x1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X x1( 1 );
+
+        result<X&> r2(( result<X&>( x1 ) ));
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X const x1( 1 );
+
+        result<X const&> r1( x1 );
+        result<X const&> r2( std::move( r1 ) );
+
+        BOOST_TEST( r1.has_value() );
+        BOOST_TEST( !r1.has_error() );
+
+        BOOST_TEST_EQ( r1.value().v_, 1 );
+        BOOST_TEST_EQ( &*r1, &x1 );
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X const x1( 1 );
+
+        result<X const&> r2(( result<X const&>( x1 ) ));
+
+        BOOST_TEST( r2.has_value() );
+        BOOST_TEST( !r2.has_error() );
+
+        BOOST_TEST_EQ( r2.value().v_, 1 );
+        BOOST_TEST_EQ( &*r2, &x1 );
+
+        BOOST_TEST_EQ( X::instances, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    //
+
     return boost::report_errors();
 }

test/result_or_eq_fn0r.cpp

@@ -0,0 +1,160 @@
+// Copyright 2017, 2021-2024 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& r )
+    {
+        if( &r != this )
+        {
+            v_ = r.v_;
+            r.v_ = 0;
+        }
+
+        return *this;
+    }
+};
+
+struct E
+{
+};
+
+struct E2
+{
+    E2() {}
+    E2( E ) {}
+};
+
+result<int, E> fi()
+{
+    return 2;
+}
+
+result<int, E2> fi2()
+{
+    return E2();
+}
+
+result<X, E> fy()
+{
+    return X{ 2 };
+}
+
+result<Y, E2> fy2()
+{
+    return E2();
+}
+
+result<int&, E> fri()
+{
+    static int x = 2;
+    return x;
+}
+
+result<int&, E2> fri2()
+{
+    return E2();
+}
+
+int main()
+{
+    {
+        result<int, E2> r( 1 );
+
+        r |= fi;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 1 );
+
+        r |= fi2;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 1 );
+    }
+
+    {
+        result<int, E2> r( in_place_error );
+
+        r |= fi2;
+
+        BOOST_TEST( r.has_error() );
+
+        r |= fi;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 2 );
+    }
+
+    {
+        result<Y, E2> r( in_place_value, 1 );
+
+        r |= fy;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 1 );
+
+        r |= fy2;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 1 );
+    }
+
+    {
+        result<Y, E2> r( in_place_error );
+
+        r |= fy2;
+
+        BOOST_TEST( r.has_error() );
+
+        r |= fy;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&, E2> r( x1 );
+
+        r |= fri;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &x1 );
+
+        r |= fri2;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &x1 );
+    }
+
+    {
+        result<int&, E2> r( in_place_error );
+
+        r |= fri2;
+
+        BOOST_TEST( r.has_error() );
+
+        r |= fri;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &*fri() );
+    }
+
+    return boost::report_errors();
+}

test/result_or_eq_fn0v.cpp

@@ -0,0 +1,115 @@
+// Copyright 2017, 2021-2024 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& r )
+    {
+        if( &r != this )
+        {
+            v_ = r.v_;
+            r.v_ = 0;
+        }
+
+        return *this;
+    }
+};
+
+struct E
+{
+};
+
+int f()
+{
+    return 2;
+}
+
+X g()
+{
+    return { 2 };
+}
+
+int& h()
+{
+    static int x = 2;
+    return x;
+}
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        r |= f;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 1 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        r |= f;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 2 );
+    }
+
+    {
+        result<Y> r( in_place_value, 1 );
+
+        r |= g;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 1 );
+    }
+
+    {
+        result<Y, E> r( in_place_error );
+
+        r |= g;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 2 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r( x1 );
+
+        r |= h;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &x1 );
+    }
+
+    {
+        result<int&, E> r( in_place_error );
+
+        r |= h;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &h() );
+    }
+
+    return boost::report_errors();
+}

test/result_or_eq_value.cpp

@@ -0,0 +1,102 @@
+// Copyright 2017, 2021-2024 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v_;
+};
+
+struct Y
+{
+    int v_;
+
+    explicit Y( int v ): v_( v ) {}
+    Y( X x ): v_( x.v_) {}
+
+    Y( Y const& ) = delete;
+    Y& operator=( Y const& ) = delete;
+
+    Y( Y&& r ): v_( r.v_ )
+    {
+        r.v_ = 0;
+    }
+
+    Y& operator=( Y&& r )
+    {
+        if( &r != this )
+        {
+            v_ = r.v_;
+            r.v_ = 0;
+        }
+
+        return *this;
+    }
+};
+
+struct E
+{
+};
+
+int main()
+{
+    {
+        result<int> r( 1 );
+
+        r |= 2;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 1 );
+    }
+
+    {
+        result<int, E> r( in_place_error );
+
+        r |= 2;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( *r, 2 );
+    }
+
+    {
+        result<Y> r( in_place_value, 1 );
+
+        r |= X{2};
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 1 );
+    }
+
+    {
+        result<Y, E> r( in_place_error );
+
+        r |= X{2};
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( r->v_, 2 );
+    }
+
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r( x1 );
+
+        r |= x2;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &x1 );
+    }
+
+    {
+        int x2 = 2;
+
+        result<int&, E> r( in_place_error );
+
+        r |= x2;
+
+        BOOST_TEST( r.has_value() ) && BOOST_TEST_EQ( &*r, &x2 );
+    }
+
+    return boost::report_errors();
+}

test/result_or_fn0r.cpp

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

test/result_or_fn0v.cpp

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

test/result_or_value.cpp

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

test/result_or_value_fail.cpp

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

test/result_or_value_fail2.cpp

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

test/result_swap.cpp

@@ -259,5 +259,55 @@ int main()
         BOOST_TEST_EQ( r2, r2c );
     }
 
+    {
+        int x1 = 1;
+        int x2 = 2;
+
+        result<int&> r1( x1 ), r1c( r1 );
+        result<int&> r2( x2 ), 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 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> r1( x1 ), 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 );
+    }
+
     return boost::report_errors();
 }

test/result_typedefs.cpp

@@ -0,0 +1,39 @@
+// Copyright 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+using namespace boost::system;
+
+struct X {};
+
+int main()
+{
+    BOOST_TEST_TRAIT_SAME( result<int>::value_type, int );
+    BOOST_TEST_TRAIT_SAME( result<int>::error_type, error_code );
+
+    BOOST_TEST_TRAIT_SAME( result<X>::value_type, X );
+    BOOST_TEST_TRAIT_SAME( result<X>::error_type, error_code );
+
+    BOOST_TEST_TRAIT_SAME( result<void>::value_type, void );
+    BOOST_TEST_TRAIT_SAME( result<void>::error_type, error_code );
+
+    BOOST_TEST_TRAIT_SAME( result<int&>::value_type, int& );
+    BOOST_TEST_TRAIT_SAME( result<int&>::error_type, error_code );
+
+    BOOST_TEST_TRAIT_SAME( result<int, X>::value_type, int );
+    BOOST_TEST_TRAIT_SAME( result<int, X>::error_type, X );
+
+    BOOST_TEST_TRAIT_SAME( result<X, X>::value_type, X );
+    BOOST_TEST_TRAIT_SAME( result<X, X>::error_type, X );
+
+    BOOST_TEST_TRAIT_SAME( result<void, X>::value_type, void );
+    BOOST_TEST_TRAIT_SAME( result<void, X>::error_type, X );
+
+    BOOST_TEST_TRAIT_SAME( result<int&, X>::value_type, int& );
+    BOOST_TEST_TRAIT_SAME( result<int&, X>::error_type, X );
+
+    return boost::report_errors();
+}

test/result_value_access.cpp

@@ -5,6 +5,7 @@
 #include <boost/system/result.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <boost/core/lightweight_test_trait.hpp>
+#include <boost/config.hpp>
 #include <system_error>
 
 using namespace boost::system;
@@ -223,7 +224,10 @@ int main()
         BOOST_TEST_NOT( r );
         BOOST_TEST( !r );
 
+#if defined(BOOST_CLANG_VERSION) && BOOST_CLANG_VERSION < 30600
+#else
         BOOST_TEST_THROWS( r.value(), E2 );
+#endif
 
         BOOST_TEST_EQ( r.operator->(), static_cast<int*>(0) );
     }
@@ -332,6 +336,8 @@ int main()
         BOOST_TEST_EQ( (result<X, Y>( ec ).operator->()), static_cast<X*>(0) );
     }
 
+    //
+
     {
         result<void> r;
 
@@ -471,7 +477,10 @@ int main()
         BOOST_TEST_NOT( r );
         BOOST_TEST( !r );
 
+#if defined(BOOST_CLANG_VERSION) && BOOST_CLANG_VERSION < 30600
+#else
         BOOST_TEST_THROWS( r.value(), E2 );
+#endif
 
         BOOST_TEST_EQ( r.operator->(), static_cast<void*>(0) );
     }
@@ -490,5 +499,179 @@ int main()
         BOOST_TEST_EQ( r.operator->(), static_cast<void*>(0) );
     }
 
+    //
+
+    {
+        int x1 = 1;
+
+        result<int&> r( x1 );
+
+        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 );
+    }
+
+    {
+        int x1 = 1;
+
+        result<int&> const r( x1 );
+
+        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 );
+    }
+
+    {
+        int x1 = 1;
+
+        BOOST_TEST( result<int&>( x1 ).has_value() );
+        BOOST_TEST( !result<int&>( x1 ).has_error() );
+
+        BOOST_TEST( result<int&>( x1 ) );
+        BOOST_TEST_NOT( !result<int&>( x1 ) );
+
+        BOOST_TEST_EQ( result<int&>( x1 ).value(), 1 );
+        BOOST_TEST_EQ( *result<int&>( x1 ), 1 );
+
+        BOOST_TEST_EQ( result<int&>( x1 ).operator->(), &x1 );
+    }
+
+    {
+        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) );
+    }
+
+    {
+        auto ec = make_error_code( std::errc::invalid_argument );
+
+        result<int&, std::error_code> 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(), std::system_error );
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<int*>(0) );
+    }
+
+    {
+        result<int&, errc::errc_t> const r( in_place_error, errc::invalid_argument );
+
+        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) );
+    }
+
+    {
+        result<int&, std::errc> const r( std::errc::invalid_argument );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_NOT( r );
+        BOOST_TEST( !r );
+
+        BOOST_TEST_THROWS( r.value(), std::system_error );
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<int*>(0) );
+    }
+
+    {
+        result<int&, std::exception_ptr> const r( std::make_exception_ptr( E2() ) );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_NOT( r );
+        BOOST_TEST( !r );
+
+#if defined(BOOST_CLANG_VERSION) && BOOST_CLANG_VERSION < 30600
+#else
+        BOOST_TEST_THROWS( r.value(), E2 );
+#endif
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<int*>(0) );
+    }
+
+    {
+        result<int&, std::exception_ptr> const r( in_place_error );
+
+        BOOST_TEST( !r.has_value() );
+        BOOST_TEST( r.has_error() );
+
+        BOOST_TEST_NOT( r );
+        BOOST_TEST( !r );
+
+        BOOST_TEST_THROWS( r.value(), std::bad_exception );
+
+        BOOST_TEST_EQ( r.operator->(), static_cast<int*>(0) );
+    }
+
+    //
+
     return boost::report_errors();
 }

test/result_value_construct2.cpp

@@ -69,6 +69,11 @@ result<std::vector<int>> fv2()
     return {{ 1, 2 }};
 }
 
+result<void> fw0()
+{
+    return {};
+}
+
 int main()
 {
     {
@@ -148,5 +153,12 @@ int main()
         BOOST_TEST_EQ( r->at(1), 2 );
     }
 
+    {
+        result<void> r = fw0();
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
     return boost::report_errors();
 }

test/result_value_construct3.cpp

@@ -0,0 +1,142 @@
+// Copyright 2017, 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    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()
+{
+    {
+        using R = result<int>;
+        R r( R::in_place_value, 0 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        using R = result<int, int>;
+        R r( 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 );
+
+    {
+        using R = result<X>;
+        R r( R::in_place_value, 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 );
+
+    {
+        using R = result<X>;
+        R r( R::in_place_value, 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 );
+
+    {
+        using R = result<X>;
+        R r( R::in_place_value, 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 );
+
+    {
+        using R = result<X, X>;
+        R r( 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 );
+
+    {
+        using R = result<void>;
+        R r( R::in_place_value );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+    }
+
+    {
+        int x1 = 1;
+
+        using R = result<int&>;
+        R r( R::in_place_value, x1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 1 );
+    }
+
+    {
+        int x1 = 1;
+
+        using R = result<int&, int>;
+        R r( R::in_place_value, x1 );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( *r, 1 );
+    }
+
+    return boost::report_errors();
+}

test/result_value_construct4.cpp

@@ -0,0 +1,59 @@
+// Copyright 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::system;
+
+// Tricky mixed construction cases
+// https://github.com/boostorg/system/issues/104
+// https://brevzin.github.io//c++/2023/01/18/optional-construction/
+
+int main()
+{
+    {
+        result<int> r( make_error_code( errc::invalid_argument ) );
+        result<result<int>> r2( r );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> r( 5 );
+        result<result<int>> r2( r );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> const r( make_error_code( errc::invalid_argument ) );
+        result<result<int>> r2( r );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> const r( 5 );
+        result<result<int>> r2( r );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> r( make_error_code( errc::invalid_argument ) );
+        result<result<int>> r2( std::move( r ) );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    {
+        result<int> r( 5 );
+        result<result<int>> r2( std::move( r ) );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), r );
+    }
+
+    return boost::report_errors();
+}

test/result_value_construct5.cpp

@@ -0,0 +1,86 @@
+// Copyright 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER) && _MSC_VER < 1910
+# pragma warning( disable: 4800 ) // forcing value to bool 'true' or 'false'
+#endif
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <utility>
+#include <type_traits>
+
+using namespace boost::system;
+
+// Tricky mixed construction cases
+// https://github.com/boostorg/system/issues/104
+// https://brevzin.github.io//c++/2023/01/18/optional-construction/
+
+template<class R1, class R2> void test()
+{
+    {
+        R1 r1( make_error_code( errc::invalid_argument ) );
+        R2 r2( r1 );
+
+        BOOST_TEST( !r2.has_value() );
+    }
+
+    {
+        R1 r1( 0 );
+        R2 r2( r1 );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), false );
+    }
+
+    {
+        R1 r1( 1 );
+        R2 r2( r1 );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), true );
+    }
+
+    {
+        R1 r1( make_error_code( errc::invalid_argument ) );
+        R2 r2( std::move( r1 ) );
+
+        BOOST_TEST( !r2.has_value() );
+    }
+
+    {
+        R1 r1( 0 );
+        R2 r2( std::move( r1 ) );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), false );
+    }
+
+    {
+        R1 r1( 1 );
+        R2 r2( std::move( r1 ) );
+
+        BOOST_TEST( r2.has_value() ) && BOOST_TEST_EQ( r2.value(), true );
+    }
+}
+
+struct X
+{
+};
+
+int main()
+{
+    test< result<int>, result<bool> >();
+    test< result<int> const, result<bool> >();
+
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, result<X>&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, result<X> const&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, result<X>&&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool>, result<X> const&&>));
+
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const>, result<X>&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const>, result<X> const&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const>, result<X>&&>));
+    BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<bool const>, result<X> const&&>));
+
+    return boost::report_errors();
+}

test/result_value_construct6.cpp

@@ -0,0 +1,121 @@
+// Copyright 2017, 2021, 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#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( X const& ) = delete;
+    X& operator=( X const& ) = delete;
+
+    ~X() { --instances; }
+};
+
+int X::instances = 0;
+
+int main()
+{
+    {
+        int x = 0;
+        result<int&> r( x );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        int x = 0;
+        result<int&> r = x;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        int x = 1;
+        result<int&, int> r( in_place_value, x );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( *r, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X x( 1 );
+        result<X&> r( x );
+
+        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 );
+
+    {
+        X x( 1 );
+        result<X&> r = x;
+
+        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 );
+
+    {
+        X x( 1 );
+        result<X&, X> r( in_place_value, x );
+
+        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 const&>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int const&, result<int&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int&>, int>));
+        BOOST_TEST_TRAIT_FALSE((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_FALSE((std::is_constructible<result<X&>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<X&>>));
+    }
+
+    return boost::report_errors();
+}

test/result_value_construct7.cpp

@@ -0,0 +1,211 @@
+// Copyright 2017, 2021, 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#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( X const& ) = delete;
+    X& operator=( X const& ) = delete;
+
+    ~X() { --instances; }
+};
+
+int X::instances = 0;
+
+int main()
+{
+    {
+        int x = 0;
+        result<int const&> r( x );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        int const x = 0;
+        result<int const&> r( x );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        int x = 0;
+        result<int const&> r = x;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        int const x = 0;
+        result<int const&> r = x;
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( r.value(), 0 );
+    }
+
+    {
+        int x = 1;
+        result<int const&, int> r( in_place_value, x );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( *r, 1 );
+    }
+
+    {
+        int const x = 1;
+        result<int const&, int> r( in_place_value, x );
+
+        BOOST_TEST( r.has_value() );
+        BOOST_TEST( !r.has_error() );
+
+        BOOST_TEST_EQ( *r, 1 );
+    }
+
+    BOOST_TEST_EQ( X::instances, 0 );
+
+    {
+        X x( 1 );
+        result<X const&> r( x );
+
+        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 );
+
+    {
+        X const x( 1 );
+        result<X const&> r( x );
+
+        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 );
+
+    {
+        X x( 1 );
+        result<X const&> r = x;
+
+        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 );
+
+    {
+        X const x( 1 );
+        result<X const&> r = x;
+
+        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 );
+
+    {
+        X x( 1 );
+        result<X const&, X> r( in_place_value, x );
+
+        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 );
+
+    {
+        X const x( 1 );
+        result<X const&, X> r( in_place_value, x );
+
+        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 const&>, int&>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<int&, result<int const&>>));
+
+        BOOST_TEST_TRAIT_TRUE((std::is_constructible<result<int const&>, int const&>));
+        BOOST_TEST_TRAIT_TRUE((std::is_convertible<int const&, result<int const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<int const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<double const&>, int&>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int&, result<double const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<double const&>, int const&>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int const&, result<double const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<double const&>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<double const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&, int>, int&>));
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&, float>, int&>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&, int>, int const&>));
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&, float>, int const&>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&, int>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<int const&, float>, int>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<X const&>, int>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<int, result<X const&>>));
+
+        BOOST_TEST_TRAIT_FALSE((std::is_constructible<result<X const&>, X const>));
+        BOOST_TEST_TRAIT_FALSE((std::is_convertible<X const, result<X const&>>));
+    }
+
+    return boost::report_errors();
+}

test/snprintf_test.cpp

@@ -2,6 +2,16 @@
 // Distributed under the Boost Software License, Version 1.0.
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined(__GNUC__) && __GNUC__ >= 7
+# pragma GCC diagnostic ignored "-Wformat-truncation"
+#endif
+
+#if defined(__clang__) && defined(__has_warning)
+# if __has_warning( "-Wformat-truncation" )
+#  pragma clang diagnostic ignored "-Wformat-truncation"
+# endif
+#endif
+
 #include <boost/system/detail/snprintf.hpp>
 #include <boost/core/lightweight_test.hpp>
 

test/std_interop_test.cpp

@@ -8,28 +8,9 @@
 
 // See library home page at http://www.boost.org/libs/system
 
-// Avoid spurious VC++ warnings
-# define _CRT_SECURE_NO_WARNINGS
-
 #include <boost/system/error_code.hpp>
-#include <boost/config.hpp>
-#include <boost/config/pragma_message.hpp>
-#include <iostream>
-
-#if !defined(BOOST_SYSTEM_HAS_SYSTEM_ERROR)
-
-BOOST_PRAGMA_MESSAGE( "BOOST_SYSTEM_HAS_SYSTEM_ERROR not defined, test will be skipped" )
-
-int main()
-{
-  std::cout
-    << "The version of the C++ standard library being used does not"
-    " support header <system_error> so interoperation will not be tested.\n";
-}
-
-#else
-
 #include <boost/core/lightweight_test.hpp>
+#include <boost/core/snprintf.hpp>
 #include <system_error>
 #include <cerrno>
 #include <string>
@@ -119,7 +100,7 @@ class user_category_impl: public boost::system::error_category
 {
 public:
 
-    virtual const char * name() const BOOST_NOEXCEPT
+    virtual const char * name() const noexcept
     {
         return "user";
     }
@@ -127,12 +108,12 @@ public:
     virtual std::string message( int ev ) const
     {
         char buffer[ 256 ];
-        std::sprintf( buffer, "user message %d", ev );
+        boost::core::snprintf( buffer, sizeof( buffer ), "user message %d", ev );
 
         return buffer;
     }
 
-    virtual boost::system::error_condition default_error_condition( int ev ) const BOOST_NOEXCEPT
+    virtual boost::system::error_condition default_error_condition( int ev ) const noexcept
     {
         if( ev == 4 )
         {
@@ -148,7 +129,7 @@ public:
         }
     }
 
-    virtual bool equivalent( int code, const boost::system::error_condition & condition ) const BOOST_NOEXCEPT
+    virtual bool equivalent( int code, const boost::system::error_condition & condition ) const noexcept
     {
         if( code == 4 && condition == make_error_condition( boost::system::errc::too_many_files_open_in_system ) )
         {
@@ -163,7 +144,7 @@ public:
         return default_error_condition( code ) == condition;
     }
 
-    // virtual bool equivalent( const error_code & code, int condition ) const BOOST_NOEXCEPT;
+    // virtual bool equivalent( const error_code & code, int condition ) const noexcept;
 };
 
 boost::system::error_category const & user_category()
@@ -259,7 +240,7 @@ class user2_category_impl: public boost::system::error_category
 {
 public:
 
-    virtual const char * name() const BOOST_NOEXCEPT
+    virtual const char * name() const noexcept
     {
         return "user2";
     }
@@ -267,22 +248,22 @@ public:
     virtual std::string message( int ev ) const
     {
         char buffer[ 256 ];
-        std::sprintf( buffer, "user2 message %d", ev );
+        boost::core::snprintf( buffer, sizeof( buffer ), "user2 message %d", ev );
 
         return buffer;
     }
 
-    virtual boost::system::error_condition default_error_condition( int ev ) const BOOST_NOEXCEPT
+    virtual boost::system::error_condition default_error_condition( int ev ) const noexcept
     {
         return boost::system::error_condition( ev, *this );
     }
 
-    virtual bool equivalent( int code, const boost::system::error_condition & condition ) const BOOST_NOEXCEPT
+    virtual bool equivalent( int code, const boost::system::error_condition & condition ) const noexcept
     {
         return default_error_condition( code ) == condition;
     }
 
-    virtual bool equivalent( const boost::system::error_code & code, int condition ) const BOOST_NOEXCEPT
+    virtual bool equivalent( const boost::system::error_code & code, int condition ) const noexcept
     {
         if( code.category() == *this )
         {
@@ -339,9 +320,6 @@ static void test_user2_category()
 
 int main()
 {
-    std::cout
-      << "The version of the C++ standard library being used"
-      " supports header <system_error> so interoperation will be tested.\n";
     test_generic_category();
     test_system_category();
     test_user_category();
@@ -349,5 +327,3 @@ int main()
 
     return boost::report_errors();
 }
-
-#endif

test/std_interop_test10.cpp

@@ -4,16 +4,7 @@
 
 #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()
@@ -62,5 +53,3 @@ int main()
 
     return boost::report_errors();
 }
-
-#endif

test/std_interop_test11.cpp

@@ -8,12 +8,7 @@
 #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
+#if defined(BOOST_LIBSTDCXX_VERSION) && BOOST_LIBSTDCXX_VERSION < 50000
 
 BOOST_PRAGMA_MESSAGE( "Skipping test, BOOST_LIBSTDCXX_VERSION < 50000" )
 int main() {}

test/std_interop_test12.cpp

@@ -6,17 +6,8 @@
 #include <boost/system/error_category.hpp>
 #include <boost/system/errc.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
@@ -28,12 +19,12 @@ class my_category: public boost::system::error_category
 {
 public:
 
-    char const* name() const BOOST_NOEXCEPT
+    char const* name() const noexcept
     {
         return "mycat";
     }
 
-    boost::system::error_condition default_error_condition( int ev ) const BOOST_NOEXCEPT
+    boost::system::error_condition default_error_condition( int ev ) const noexcept
     {
         switch( ev )
         {
@@ -123,5 +114,3 @@ int main()
 
     return boost::report_errors();
 }
-
-#endif

test/std_interop_test13.cpp

@@ -5,24 +5,15 @@
 #include <boost/system/error_code.hpp>
 #include <boost/system/error_category.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>
 
 class my_category_impl: public std::error_category
 {
 public:
 
-    char const* name() const BOOST_NOEXCEPT
+    char const* name() const noexcept
     {
         return "mycat";
     }
@@ -73,5 +64,3 @@ int main()
 
     return boost::report_errors();
 }
-
-#endif

test/std_interop_test14.cpp

@@ -5,24 +5,15 @@
 #include <boost/system/error_code.hpp>
 #include <boost/system/error_category.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>
 
 class my_category_impl: public boost::system::error_category
 {
 public:
 
-    char const* name() const BOOST_NOEXCEPT
+    char const* name() const noexcept
     {
         return "mycat";
     }
@@ -53,5 +44,3 @@ int main()
 
     return boost::report_errors();
 }
-
-#endif

test/std_interop_test15.cpp

@@ -0,0 +1,89 @@
+// Copyright 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_code.hpp>
+#include <boost/system/error_condition.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
+
+#if defined(BOOST_SYSTEM_AVOID_STD_GENERIC_CATEGORY)
+
+BOOST_PRAGMA_MESSAGE( "Skipping test, BOOST_SYSTEM_AVOID_STD_GENERIC_CATEGORY is defined" )
+int main() {}
+
+#else
+
+#include <system_error>
+
+namespace sys = boost::system;
+
+enum my_errc
+{
+    enomem_c = ENOMEM
+};
+
+enum my_errn
+{
+    enomem_n = ENOMEM
+};
+
+namespace std {
+
+template<> struct is_error_code_enum<my_errc>
+{
+    static const bool value = true;
+};
+
+template<> struct is_error_condition_enum<my_errn>
+{
+    static const bool value = true;
+};
+
+} // namespace std
+
+std::error_code make_error_code( my_errc e )
+{
+    return std::error_code( e, std::generic_category() );
+}
+
+std::error_condition make_error_condition( my_errn e )
+{
+    return std::error_condition( e, std::generic_category() );
+}
+
+int main()
+{
+    sys::error_code ec = make_error_code( sys::errc::not_enough_memory );
+    sys::error_condition en( sys::errc::not_enough_memory );
+
+    BOOST_TEST_EQ( ec, en );
+    BOOST_TEST_EQ( en, ec );
+
+    BOOST_TEST_EQ( ec, enomem_c );
+    BOOST_TEST_EQ( enomem_c, ec );
+
+    BOOST_TEST_EQ( ec, enomem_n );
+    BOOST_TEST_EQ( enomem_n, ec );
+
+    BOOST_TEST_EQ( en, enomem_c );
+    BOOST_TEST_EQ( enomem_c, en );
+
+#if BOOST_WORKAROUND(BOOST_MSVC, == 1800)
+
+    // msvc-12.0 has op== as a member of std::error_condition
+
+#else
+
+    BOOST_TEST_EQ( en, enomem_n );
+
+#endif
+
+    BOOST_TEST_EQ( enomem_n, en );
+
+    return boost::report_errors();
+}
+
+#endif

test/std_interop_test16.cpp

@@ -0,0 +1,46 @@
+// Copyright 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/error_category.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/snprintf.hpp>
+#include <system_error>
+
+// get_user_category
+
+class user_category: public boost::system::error_category
+{
+public:
+
+    virtual const char * name() const noexcept
+    {
+        return "user";
+    }
+
+    virtual std::string message( int ev ) const
+    {
+        char buffer[ 256 ];
+        boost::core::snprintf( buffer, sizeof( buffer ), "user message %d", ev );
+
+        return buffer;
+    }
+};
+
+boost::system::error_category const & get_user_category()
+{
+    static user_category instance;
+    return instance;
+}
+
+//
+
+bool init_lwt = (boost::core::lwt_init(), true);
+
+std::error_category const & cat = get_user_category();
+
+int main()
+{
+    BOOST_TEST_CSTR_EQ( cat.name(), "user" );
+    return boost::report_errors();
+}

test/std_interop_test2.cpp

@@ -6,16 +6,7 @@
 #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 )
@@ -94,5 +85,3 @@ int main()
 
     return boost::report_errors();
 }
-
-#endif

test/std_interop_test3.cpp

@@ -4,16 +4,7 @@
 
 #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()
@@ -75,5 +66,3 @@ int main()
 
     return boost::report_errors();
 }
-
-#endif

test/std_interop_test4.cpp

@@ -4,16 +4,7 @@
 
 #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 )
@@ -85,5 +76,3 @@ int main()
 
     return boost::report_errors();
 }
-
-#endif

test/std_interop_test5.cpp

@@ -4,16 +4,7 @@
 
 #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()
@@ -104,5 +95,3 @@ int main()
 
     return boost::report_errors();
 }
-
-#endif