Use the exact 3.125f in variant_visit_r.cpp

.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(
@@ -163,68 +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_pipeline(
-        "Linux 22.04 GCC 11* 64",
-        "cppalliance/droneubuntu2204:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '03,11,14,17,2a', ADDRMD: '64' },
-    ),
-
-    linux_pipeline(
-        "Linux 22.04 GCC 12",
-        "cppalliance/droneubuntu2204:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-12', CXXSTD: '03,11,14,17,20,2b' },
-        "g++-12",
-    ),
-
-    linux_pipeline(
-        "Linux 20.04 Clang 13",
+        "Linux 20.04 Clang 8",
         "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-13', CXXSTD: '03,11,14,17,20' },
+        { TOOLSET: 'clang', COMPILER: 'clang++-8', CXXSTD: '03,11,14,17' },
+        "clang-8",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 9",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-9', CXXSTD: '03,11,14,17,2a' },
+        "clang-9",
+    ),
+
+    linux_pipeline(
+        "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: '03,11,14,17,20,2b' },
         "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: '03,11,14,17,20,2b' },
         "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_pipeline(
-        "Linux 20.04 Clang 15",
-        "cppalliance/droneubuntu2004:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-15', CXXSTD: '03,11,14,17,20,2b' },
+        "Linux 22.04 Clang 15 UBSAN",
+        "cppalliance/droneubuntu2204:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-15', CXXSTD: '03,11,14,17,20,2b' } + ubsan,
         "clang-15",
-        ["deb http://apt.llvm.org/focal/ llvm-toolchain-focal-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(
@@ -237,6 +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)
 

CMakeLists.txt

@@ -19,6 +19,15 @@ target_link_libraries(boost_variant2
     Boost::mp11
 )
 
+if(CMAKE_VERSION VERSION_GREATER 3.18 AND CMAKE_GENERATOR MATCHES "Visual Studio")
+
+  file(GLOB_RECURSE boost_variant2_IDEFILES CONFIGURE_DEPENDS include/*.hpp)
+  source_group(TREE ${PROJECT_SOURCE_DIR}/include FILES ${boost_variant2_IDEFILES} PREFIX "Header Files")
+  list(APPEND boost_variant2_IDEFILES extra/boost_variant2.natvis)
+  target_sources(boost_variant2 PRIVATE ${boost_variant2_IDEFILES})
+
+endif()
+
 target_compile_features(boost_variant2 INTERFACE cxx_std_11)
 
 if(BUILD_TESTING AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/CMakeLists.txt")

appveyor.yml

@@ -30,14 +30,16 @@ environment:
       TOOLSET: clang-win
       ADDRMD: 64
       CXXSTD: 14,17,latest
-    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
-      TOOLSET: msvc-14.2
-      ADDRMD: 32,64
-      CXXSTD: 14,17,latest
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
       TOOLSET: clang-win
       ADDRMD: 64
       CXXSTD: 14,17,latest
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
+      CMAKE: 1
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      CMAKE_SUBDIR: 1
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      CMAKE_INSTALL: 1
 
 install:
   - set BOOST_BRANCH=develop
@@ -57,4 +59,27 @@ test_script:
   - if not "%CXXSTD%" == "" set CXXSTD=cxxstd=%CXXSTD%
   - if not "%ADDRMD%" == "" set ADDRMD=address-model=%ADDRMD%
   - if not "%CXXFLAGS%" == "" set CXXFLAGS=cxxflags=%CXXFLAGS%
-  - b2 -j3 libs/variant2/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% %CXXFLAGS% variant=debug,release embed-manifest-via=linker
+  - if "%CMAKE%%CMAKE_SUBDIR%%CMAKE_INSTALL%" == ""  b2 -j3 libs/variant2/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% %CXXFLAGS% variant=debug,release embed-manifest-via=linker
+
+  - if not "%CMAKE%" == ""  mkdir __build__ && cd __build__
+  - if not "%CMAKE%" == ""  cmake -DBUILD_TESTING=ON -DBOOST_INCLUDE_LIBRARIES=variant2 -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/variant2/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=variant2 -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/variant2/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

extra/boost_variant2.natvis

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="utf-8"?>
+<AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
+
+    <Type Name="boost::variant2::detail::variant_ma_base_impl&lt;*&gt;" Inheritable="true">
+        <Intrinsic Name="index" Expression="$T2==1?((int)ix_-1):((int)((ix_-2)/2))"/>
+        <DisplayString Condition="index()==0&amp;&amp;$T2==1" Optional="true">{st_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==1&amp;&amp;$T2==1" Optional="true">{st_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==2&amp;&amp;$T2==1" Optional="true">{st_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==3&amp;&amp;$T2==1" Optional="true">{st_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==4&amp;&amp;$T2==1" Optional="true">{st_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==5&amp;&amp;$T2==1" Optional="true">{st_.rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==6&amp;&amp;$T2==1" Optional="true">{st_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==7&amp;&amp;$T2==1" Optional="true">{st_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==8&amp;&amp;$T2==1" Optional="true">{st_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==9&amp;&amp;$T2==1" Optional="true">{st_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==0&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==1&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==2&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==3&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==4&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==5&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==6&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==7&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==8&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <DisplayString Condition="index()==9&amp;&amp;$T2==0" Optional="true">{st_[ix_%2].rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.rest_.first_} ({index()})</DisplayString>
+        <Expand>
+            <Item Name="[index]">index()</Item>
+            <Item Name="ix_">ix_</Item>
+        </Expand>
+    </Type>
+
+</AutoVisualizer>

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:

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 );
     }
 
     {