Make tag_invoke_L2 more msvc-14.0-friendly

.drone.jsonnet

@@ -97,30 +97,30 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
 
 [
     linux_pipeline(
-        "Linux 14.04 GCC 4.8*",
+        "Linux 14.04 GCC 4.8* 32/64",
         "cppalliance/droneubuntu1404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11' },
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11', ADDRMD: '32,64' },
     ),
 
     linux_pipeline(
-        "Linux 14.04 GCC 4.9",
+        "Linux 14.04 GCC 4.9 32/64",
         "cppalliance/droneubuntu1404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-4.9', CXXSTD: '03,11' },
-        "g++-4.9",
+        { TOOLSET: 'gcc', COMPILER: 'g++-4.9', CXXSTD: '03,11', ADDRMD: '32,64' },
+        "g++-4.9-multilib",
         [ "ppa:ubuntu-toolchain-r/test" ],
     ),
 
     linux_pipeline(
-        "Linux 16.04 GCC 5*",
+        "Linux 16.04 GCC 5* 32/64",
         "cppalliance/droneubuntu1604:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14' },
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14', ADDRMD: '32,64' },
     ),
 
     linux_pipeline(
-        "Linux 18.04 GCC 6",
+        "Linux 18.04 GCC 6 32/64",
         "cppalliance/droneubuntu1804:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-6', CXXSTD: '03,11,14' },
-        "g++-6",
+        { TOOLSET: 'gcc', COMPILER: 'g++-6', CXXSTD: '03,11,14', ADDRMD: '32,64' },
+        "g++-6-multilib",
     ),
 
     linux_pipeline(
@@ -130,22 +130,16 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
     ),
 
     linux_pipeline(
-        "Linux 18.04 GCC 8",
+        "Linux 18.04 GCC 8 32/64",
         "cppalliance/droneubuntu1804:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-8', CXXSTD: '03,11,14,17' },
-        "g++-8",
+        { TOOLSET: 'gcc', COMPILER: 'g++-8', CXXSTD: '03,11,14,17', ADDRMD: '32,64' },
+        "g++-8-multilib",
     ),
 
     linux_pipeline(
-        "Linux 20.04 GCC 9* 32",
+        "Linux 20.04 GCC 9* 32/64",
         "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '32' },
-    ),
-
-    linux_pipeline(
-        "Linux 20.04 GCC 9* 64",
-        "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '64' },
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '32,64' },
     ),
 
     linux_pipeline(
@@ -163,65 +157,170 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
     ),
 
     linux_pipeline(
-        "Linux 20.04 GCC 10 32 ASAN",
+        "Linux 20.04 GCC 10 32/64",
         "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-10', CXXSTD: '03,11,14,17,20', ADDRMD: '32' } + asan,
+        { TOOLSET: 'gcc', COMPILER: 'g++-10', CXXSTD: '03,11,14,17,20', ADDRMD: '32,64' },
         "g++-10-multilib",
     ),
 
     linux_pipeline(
-        "Linux 20.04 GCC 10 64 ASAN",
+        "Linux 22.04 GCC 11* 32/64",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '32,64' },
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 GCC 12 32 ASAN",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-12', CXXSTD: '03,11,14,17,20,2b', ADDRMD: '32' } + asan,
+        "g++-12-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 GCC 12 64 ASAN",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-12', CXXSTD: '03,11,14,17,20,2b', ADDRMD: '64' } + asan,
+        "g++-12-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 GCC 13 32/64",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '03,11,14,17,20,2b', ADDRMD: '32,64' },
+        "g++-13-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.5",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.5', CXXSTD: '03,11' },
+        "clang-3.5",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.6",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.6', CXXSTD: '03,11,14' },
+        "clang-3.6",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.7",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.7', CXXSTD: '03,11,14' },
+        "clang-3.7",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.8",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.8', CXXSTD: '03,11,14' },
+        "clang-3.8",
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 Clang 3.9",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.9', CXXSTD: '03,11,14' },
+        "clang-3.9",
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 Clang 4.0",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-4.0', CXXSTD: '03,11,14' },
+        "clang-4.0",
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 Clang 5.0",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-5.0', CXXSTD: '03,11,14,1z' },
+        "clang-5.0",
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 Clang 6.0",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-6.0', CXXSTD: '03,11,14,17' },
+        "clang-6.0",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 7",
         "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-10', CXXSTD: '03,11,14,17,20', ADDRMD: '64' } + asan,
-        "g++-10-multilib",
+        { TOOLSET: 'clang', COMPILER: 'clang++-7', CXXSTD: '03,11,14,17' },
+        "clang-7",
     ),
 
     linux_pipeline(
-        "Linux 22.04 GCC 11* 32",
-        "cppalliance/droneubuntu2204:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '32' },
+        "Linux 20.04 Clang 8",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-8', CXXSTD: '03,11,14,17' },
+        "clang-8",
     ),
 
     linux_pipeline(
-        "Linux 22.04 GCC 11* 64",
-        "cppalliance/droneubuntu2204:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '64' },
+        "Linux 20.04 Clang 9",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-9', CXXSTD: '03,11,14,17,2a' },
+        "clang-9",
     ),
 
     linux_pipeline(
-        "Linux 22.04 GCC 12",
-        "cppalliance/droneubuntu2204:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-12', CXXSTD: '03,11,14,17,20,2b' },
-        "g++-12",
+        "Linux 20.04 Clang 10",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-10', CXXSTD: '03,11,14,17,2a' },
+        "clang-10",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 11",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-11', CXXSTD: '03,11,14,17,2a' },
+        "clang-11",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 12",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-12', CXXSTD: '03,11,14,17,2a' },
+        "clang-12",
     ),
 
     linux_pipeline(
         "Linux 22.04 Clang 13",
         "cppalliance/droneubuntu2204:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-13', CXXSTD: '03,11,14,17,20' },
+        { TOOLSET: 'clang', COMPILER: 'clang++-13', CXXSTD: '03,11,14,17,20,2b' },
         "clang-13",
     ),
 
     linux_pipeline(
-        "Linux 22.04 Clang 14 UBSAN",
+        "Linux 22.04 Clang 14",
         "cppalliance/droneubuntu2204:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-14', CXXSTD: '03,11,14,17,20' } + ubsan,
+        { TOOLSET: 'clang', COMPILER: 'clang++-14', CXXSTD: '03,11,14,17,20,2b' },
         "clang-14",
     ),
 
     linux_pipeline(
-        "Linux 22.04 Clang 14 ASAN",
+        "Linux 22.04 Clang 15 UBSAN",
         "cppalliance/droneubuntu2204:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-14', CXXSTD: '03,11,14,17,20' } + asan,
-        "clang-14",
-    ),
-
-    linux_pipeline(
-        "Linux 22.04 Clang 15",
-        "cppalliance/droneubuntu2204:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-15', CXXSTD: '03,11,14,17,20,2b' },
+        { TOOLSET: 'clang', COMPILER: 'clang++-15', CXXSTD: '03,11,14,17,20,2b' } + ubsan,
         "clang-15",
-        ["deb http://apt.llvm.org/jammy/ llvm-toolchain-jammy-15 main"],
+    ),
+
+    linux_pipeline(
+        "Linux 22.04 Clang 15 ASAN",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-15', CXXSTD: '03,11,14,17,20,2b' } + asan,
+        "clang-15",
+    ),
+
+    linux_pipeline(
+        "Linux 23.04 Clang 16",
+        "cppalliance/droneubuntu2304:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-16', CXXSTD: '03,11,14,17,20,2b' },
+        "clang-16",
     ),
 
     macos_pipeline(
@@ -234,6 +333,18 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,1z' } + asan,
     ),
 
+    macos_pipeline(
+        "MacOS 12.4 Xcode 13.4.1 UBSAN",
+        { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '03,11,14,17,20,2b' } + 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: '03,11,14,17,20,2b' } + asan,
+        xcode_version = "13.4.1", osx_version = "monterey", arch = "arm64",
+    ),
+
     windows_pipeline(
         "Windows VS2015 msvc-14.0",
         "cppalliance/dronevs2015",

.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

@@ -55,6 +55,11 @@ jobs:
             cxxstd: "03,11,14,17,20,2b"
             os: ubuntu-22.04
             install: g++-12
+          - toolset: gcc-13
+            cxxstd: "03,11,14,17,20,2b"
+            os: ubuntu-latest
+            container: ubuntu:23.04
+            install: g++-13
           - toolset: clang
             compiler: clang++-3.9
             cxxstd: "03,11,14"
@@ -118,9 +123,26 @@ jobs:
             cxxstd: "03,11,14,17,20,2b"
             os: ubuntu-22.04
             install: clang-14
+          - toolset: clang
+            compiler: clang++-15
+            cxxstd: "03,11,14,17,20,2b"
+            os: ubuntu-22.04
+            install: clang-15
+          - toolset: clang
+            compiler: clang++-16
+            cxxstd: "03,11,14,17,20,2b"
+            os: ubuntu-latest
+            container: ubuntu:23.04
+            install: clang-16
           - toolset: clang
             cxxstd: "03,11,14,17,2a"
             os: macos-11
+          - toolset: clang
+            cxxstd: "03,11,14,17,20,2b"
+            os: macos-12
+          - toolset: clang
+            cxxstd: "03,11,14,17,20,2b"
+            os: macos-13
 
     runs-on: ${{matrix.os}}
     container: ${{matrix.container}}
@@ -136,11 +158,13 @@ jobs:
         if: matrix.container
         run: |
           apt-get update
-          apt-get -y install sudo python git g++
+          apt-get -y install sudo python3 git g++
 
       - name: Install packages
         if: matrix.install
-        run: sudo apt-get -y install ${{matrix.install}}
+        run: |
+          sudo apt-get update
+          sudo apt-get -y install ${{matrix.install}}
 
       - name: Setup Boost
         run: |
@@ -160,7 +184,7 @@ 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
 
@@ -241,6 +265,8 @@ jobs:
           - os: ubuntu-20.04
           - os: ubuntu-22.04
           - os: macos-11
+          - os: macos-12
+          - os: macos-13
 
     runs-on: ${{matrix.os}}
 
@@ -287,6 +313,8 @@ jobs:
           - os: ubuntu-20.04
           - os: ubuntu-22.04
           - os: macos-11
+          - os: macos-12
+          - os: macos-13
 
     runs-on: ${{matrix.os}}
 
@@ -343,6 +371,8 @@ jobs:
           - os: ubuntu-20.04
           - os: ubuntu-22.04
           - os: macos-11
+          - os: macos-12
+          - os: macos-13
 
     runs-on: ${{matrix.os}}
 
@@ -388,3 +418,183 @@ 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@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Use library with add_subdirectory (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_subdir_test
+          mkdir __build__ && cd __build__
+          cmake ..
+          cmake --build . --config Debug
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Use library with add_subdirectory (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_subdir_test/__build__
+          cmake --build . --config Release
+          ctest --output-on-failure --no-tests=error -C Release
+
+  windows-cmake-install:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Configure
+        shell: cmd
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=%LIBRARY% -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+
+      - name: Install (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install --config Debug
+
+      - name: Install (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target install --config Release
+
+      - name: Use the installed library (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_install_test && mkdir __build__ && cd __build__
+          cmake -DCMAKE_INSTALL_PREFIX=C:/cmake-prefix ..
+          cmake --build . --config Debug
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Use the installed library (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/libs/%LIBRARY%/test/cmake_install_test/__build__
+          cmake --build . --config Release
+          ctest --output-on-failure --no-tests=error -C Release
+
+  windows-cmake-test:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: windows-2019
+          - os: windows-2022
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup Boost
+        shell: cmd
+        run: |
+          echo GITHUB_REPOSITORY: %GITHUB_REPOSITORY%
+          for /f %%i in ("%GITHUB_REPOSITORY%") do set LIBRARY=%%~nxi
+          echo LIBRARY: %LIBRARY%
+          echo LIBRARY=%LIBRARY%>>%GITHUB_ENV%
+          echo GITHUB_BASE_REF: %GITHUB_BASE_REF%
+          echo GITHUB_REF: %GITHUB_REF%
+          if "%GITHUB_BASE_REF%" == "" set GITHUB_BASE_REF=%GITHUB_REF%
+          set BOOST_BRANCH=develop
+          for /f %%i in ("%GITHUB_BASE_REF%") do if "%%~nxi" == "master" set BOOST_BRANCH=master
+          echo BOOST_BRANCH: %BOOST_BRANCH%
+          cd ..
+          git clone -b %BOOST_BRANCH% --depth 1 https://github.com/boostorg/boost.git boost-root
+          cd boost-root
+          xcopy /s /e /q %GITHUB_WORKSPACE% libs\%LIBRARY%\
+          git submodule update --init tools/boostdep
+          python tools/boostdep/depinst/depinst.py --git_args "--jobs 3" %LIBRARY%
+
+      - name: Configure
+        shell: cmd
+        run: |
+          cd ../boost-root
+          mkdir __build__ && cd __build__
+          cmake -DBOOST_INCLUDE_LIBRARIES=%LIBRARY% -DBUILD_TESTING=ON ..
+
+      - name: Build tests (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target tests --config Debug
+
+      - name: Run tests (Debug)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          ctest --output-on-failure --no-tests=error -C Debug
+
+      - name: Build tests (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          cmake --build . --target tests --config Release
+
+      - name: Run tests (Release)
+        shell: cmd
+        run: |
+          cd ../boost-root/__build__
+          ctest --output-on-failure --no-tests=error -C Release

doc/variant2/changelog.adoc

@@ -8,6 +8,10 @@ https://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix: changelog_
 
+## Changes in 1.83.0
+
+* Added `uses_double_storage()`.
+
 ## Changes in 1.81.0
 
 * Added support for `boost::json::value_from` and `boost::json::value_to`.

doc/variant2/reference.adoc

@@ -250,6 +250,8 @@ public:
   constexpr bool valueless_by_exception() const noexcept;
   constexpr size_t index() const noexcept;
 
+  static constexpr bool uses_double_storage() noexcept;
+
   // swap
 
   void swap( variant& r ) noexcept( /*see below*/ );
@@ -570,6 +572,18 @@ constexpr size_t index() const noexcept;
 Returns:  ::
   The zero-based index of the active alternative.
 
+```
+static constexpr bool uses_double_storage() noexcept;
+```
+[none]
+* {blank}
++
+Returns:  ::
+  `true` if the variant uses double storage to meet the never valueless
+  guarantee because one of the alternatives is not nothrow move constructible,
+  and `false` otherwise.
+
+
 #### Swap
 
 ```

include/boost/variant2/variant.hpp

@@ -920,6 +920,11 @@ template<class... T> struct variant_base_impl<true, true, T...>
 
         this->emplace_impl<J, U>( std::is_nothrow_constructible<U, A&&...>(), std::forward<A>(a)... );
     }
+
+    static constexpr bool uses_double_storage() noexcept
+    {
+        return false;
+    }
 };
 
 // trivially destructible, double buffered
@@ -978,6 +983,11 @@ template<class... T> struct variant_base_impl<true, false, T...>
 
         ix_ = J * 2 + i2;
     }
+
+    static constexpr bool uses_double_storage() noexcept
+    {
+        return true;
+    }
 };
 
 // not trivially destructible, single buffered
@@ -1068,6 +1078,11 @@ template<class... T> struct variant_base_impl<false, true, T...>
         st_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
         ix_ = J;
     }
+
+    static constexpr bool uses_double_storage() noexcept
+    {
+        return false;
+    }
 };
 
 // not trivially destructible, double buffered
@@ -1193,6 +1208,11 @@ template<class... T> struct variant_base_impl<false, false, T...>
 
         ix_ = J * 2 + i2;
     }
+
+    static constexpr bool uses_double_storage() noexcept
+    {
+        return true;
+    }
 };
 
 } // namespace detail
@@ -1703,6 +1723,8 @@ public:
 
     using variant_base::index;
 
+    using variant_base::uses_double_storage;
+
     // swap
 
 private:
@@ -2475,16 +2497,16 @@ template<class V> struct tag_invoke_L2
     boost::json::value const& v;
     typename boost::json::result_for<V, boost::json::value>::type& r;
 
-    template<class I> void operator()( I i ) const
+    template<class I> void operator()( I /*i*/ ) const
     {
         if( !r )
         {
-            using Ti = mp11::mp_at_c<V, i>;
+            using Ti = mp11::mp_at_c<V, I::value>;
             auto r2 = boost::json::try_value_to<Ti>( v );
 
             if( r2 )
             {
-                r.emplace( in_place_index_t<i>{}, std::move( *r2 ) );
+                r.emplace( in_place_index_t<I::value>{}, std::move( *r2 ) );
             }
         }
     }

test/Jamfile

@@ -127,7 +127,9 @@ run variant_visit_by_index.cpp ;
 run variant_ostream_insert.cpp ;
 run is_output_streamable.cpp ;
 
-local JSON = <library>/boost//json/<warnings>off "<toolset>msvc-14.0:<build>no" "<toolset>msvc-14.2:<cxxflags>-wd5104" ;
+local JSON = <library>/boost//json/<warnings>off "<toolset>msvc-14.0:<build>no" "<toolset>msvc-14.2:<cxxflags>-wd5104" "<undefined-sanitizer>norecover:<link>static" ;
 
 run variant_json_value_from.cpp : : : $(JSON) ;
 run variant_json_value_to.cpp : : : $(JSON) ;
+
+compile variant_uses_double_storage.cpp ;

test/variant_get_by_index_cx.cpp

@@ -58,7 +58,7 @@ int main()
     {
         constexpr variant<int, float> v( 3.14f );
 
-        STATIC_ASSERT( get<1>(v) == 3.14f );
+        STATIC_ASSERT( get<1>(v) == (float)3.14f ); // see FLT_EVAL_METHOD
 
         STATIC_ASSERT_IF( get_if<0>(&v) == nullptr );
         STATIC_ASSERT_IF( get_if<1>(&v) == &get<1>(v) );
@@ -87,7 +87,7 @@ int main()
     {
         constexpr variant<int, int, float> v( 3.14f );
 
-        STATIC_ASSERT( get<2>(v) == 3.14f );
+        STATIC_ASSERT( get<2>(v) == (float)3.14f );
 
         STATIC_ASSERT_IF( get_if<0>(&v) == nullptr );
         STATIC_ASSERT_IF( get_if<1>(&v) == nullptr );

test/variant_get_by_type_cx.cpp

@@ -58,7 +58,7 @@ int main()
     {
         constexpr variant<int, float> v( 3.14f );
 
-        STATIC_ASSERT( get<float>(v) == 3.14f );
+        STATIC_ASSERT( get<float>(v) == (float)3.14f ); // see FLT_EVAL_METHOD
 
         STATIC_ASSERT_IF( get_if<int>(&v) == nullptr );
         STATIC_ASSERT_IF( get_if<float>(&v) == &get<float>(v) );
@@ -83,7 +83,7 @@ int main()
     {
         constexpr variant<int, int, float> v( 3.14f );
 
-        STATIC_ASSERT( get<float>(v) == 3.14f );
+        STATIC_ASSERT( get<float>(v) == (float)3.14f );
 
         STATIC_ASSERT_IF( get_if<float>(&v) == &get<float>(v) );
     }

test/variant_in_place_index_construct_cx.cpp

@@ -68,7 +68,7 @@ int main()
         constexpr variant<int, float> v( in_place_index_t<1>{}, 3.14f );
 
         STATIC_ASSERT( v.index() == 1 );
-        STATIC_ASSERT( get<1>(v) == 3.14f );
+        STATIC_ASSERT( get<1>(v) == (float)3.14f ); // see FLT_EVAL_METHOD
     }
 
     {
@@ -89,14 +89,14 @@ int main()
         constexpr variant<int, int, float, float, X, X> v( in_place_index_t<2>{}, 3.14f );
 
         STATIC_ASSERT( v.index() == 2 );
-        STATIC_ASSERT( get<2>(v) == 3.14f );
+        STATIC_ASSERT( get<2>(v) == (float)3.14f );
     }
 
     {
         constexpr variant<int, int, float, float, X, X> v( in_place_index_t<3>{}, 3.14f );
 
         STATIC_ASSERT( v.index() == 3 );
-        STATIC_ASSERT( get<3>(v) == 3.14f );
+        STATIC_ASSERT( get<3>(v) == (float)3.14f );
     }
 
     {

test/variant_in_place_type_construct_cx.cpp

@@ -80,7 +80,7 @@ int main()
         constexpr variant<int, float> v( in_place_type_t<float>{}, 3.14f );
 
         STATIC_ASSERT( v.index() == 1 );
-        STATIC_ASSERT( get<1>(v) == 3.14f );
+        STATIC_ASSERT( get<1>(v) == (float)3.14f ); // see FLT_EVAL_METHOD
 
         STATIC_ASSERT( holds_alternative<float>(v) );
     }
@@ -89,7 +89,7 @@ int main()
         constexpr variant<int, int, float, X> v( in_place_type_t<float>{}, 3.14f );
 
         STATIC_ASSERT( v.index() == 2 );
-        STATIC_ASSERT( get<2>(v) == 3.14f );
+        STATIC_ASSERT( get<2>(v) == (float)3.14f );
 
         STATIC_ASSERT( holds_alternative<float>(v) );
     }

test/variant_uses_double_storage.cpp

@@ -0,0 +1,50 @@
+// Copyright 2023 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <type_traits>
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X1
+{
+};
+
+STATIC_ASSERT( std::is_nothrow_move_constructible<X1>::value );
+STATIC_ASSERT( std::is_trivially_destructible<X1>::value );
+
+struct X2
+{
+    ~X2() {}
+};
+
+STATIC_ASSERT( std::is_nothrow_move_constructible<X2>::value );
+STATIC_ASSERT( !std::is_trivially_destructible<X2>::value );
+
+struct X3
+{
+    X3( X3&& ) {}
+};
+
+STATIC_ASSERT( !std::is_nothrow_move_constructible<X3>::value );
+STATIC_ASSERT( std::is_trivially_destructible<X3>::value );
+
+struct X4
+{
+    ~X4() {}
+    X4( X4&& ) {}
+};
+
+STATIC_ASSERT( !std::is_nothrow_move_constructible<X4>::value );
+STATIC_ASSERT( !std::is_trivially_destructible<X4>::value );
+
+//
+
+STATIC_ASSERT( !variant<int, float>::uses_double_storage() );
+STATIC_ASSERT( !variant<int, float, X1>::uses_double_storage() );
+STATIC_ASSERT( !variant<int, float, X2>::uses_double_storage() );
+STATIC_ASSERT( variant<int, float, X3>::uses_double_storage() );
+STATIC_ASSERT( variant<int, float, X4>::uses_double_storage() );

test/variant_value_construct_cx.cpp

@@ -82,7 +82,7 @@ int main()
 
         STATIC_ASSERT( v.index() == 1 );
         STATIC_ASSERT( holds_alternative<float>(v) );
-        STATIC_ASSERT( get<1>(v) == 3.14f );
+        STATIC_ASSERT( get<1>(v) == (float)3.14f ); // see FLT_EVAL_METHOD
     }
 
     {
@@ -97,7 +97,7 @@ int main()
 
         STATIC_ASSERT( v.index() == 2 );
         STATIC_ASSERT( holds_alternative<float>(v) );
-        STATIC_ASSERT( get<2>(v) == 3.14f );
+        STATIC_ASSERT( get<2>(v) == (float)3.14f );
     }
 
     {

test/variant_visit_r.cpp

@@ -61,18 +61,18 @@ int main()
     }
 
     {
-        variant<int, float> const v( 3.14f );
+        variant<int, float> const v( 3.125f );
 
         BOOST_TEST_EQ( visit<int>( F1(), v ), 3 );
-        BOOST_TEST_EQ( visit<float>( F1(), v ), 3.14f );
+        BOOST_TEST_EQ( visit<float>( F1(), v ), 3.125f );
     }
 
     {
         variant<int, float> v1( 1 );
-        variant<int, float> const v2( 3.14f );
+        variant<int, float> const v2( 3.125f );
 
         BOOST_TEST_EQ( visit<int>( F2(), v1, v2 ), 4 );
-        BOOST_TEST_EQ( visit<float>( F2(), v1, v2 ), 1 + 3.14f );
+        BOOST_TEST_EQ( visit<float>( F2(), v1, v2 ), 1 + 3.125f );
     }
 
     {