Update revision history

Add missing std namespace qualifiers

.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 []) +
@@ -99,7 +101,7 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
     linux_pipeline(
         "Linux 16.04 GCC 4.8 32/64",
         "cppalliance/droneubuntu1604:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++', CXXSTD: '11', ADDRMD: '32,64' },
+        { TOOLSET: 'gcc', COMPILER: 'g++-4.8', CXXSTD: '11', ADDRMD: '32,64' },
         "g++-4.8-multilib",
     ),
 
@@ -177,44 +179,37 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
     ),
 
     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 23.04 GCC 13 64 ASAN",
-        "cppalliance/droneubuntu2304:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '11,14,17,20,2b', ADDRMD: '64' } + asan,
-        "g++-13-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 24.04 GCC 14 32",
+        "Linux 24.04 GCC 13 32/64",
         "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '32' },
+        { TOOLSET: 'gcc', COMPILER: 'g++-13', CXXSTD: '11,14,17,20,2b', ADDRMD: '32,64' },
+        "g++-13-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 GCC 14 32 ASAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '32' } + asan,
         "g++-14-multilib",
     ),
 
     linux_pipeline(
-        "Linux 24.04 GCC 14 64",
+        "Linux 24.04 GCC 14 64 ASAN",
         "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '64' },
+        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '64' } + asan,
+        "g++-14-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 GCC 14 32 UBSAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '32' } + ubsan,
+        "g++-14-multilib",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 GCC 14 64 UBSAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-14', CXXSTD: '11,14,17,20,2b', ADDRMD: '64' } + ubsan,
         "g++-14-multilib",
     ),
 
@@ -263,7 +258,7 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
     linux_pipeline(
         "Linux 18.04 Clang 5.0",
         "cppalliance/droneubuntu1804:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-5.0', CXXSTD: '11,14,1z' },
+        { TOOLSET: 'clang', COMPILER: 'clang++-5.0', CXXSTD: '11,14' },
         "clang-5.0",
     ),
 
@@ -338,22 +333,22 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
     ),
 
     linux_pipeline(
-        "Linux 23.04 Clang 16",
-        "cppalliance/droneubuntu2304:1",
+        "Linux 24.04 Clang 16",
+        "cppalliance/droneubuntu2404:1",
         { TOOLSET: 'clang', COMPILER: 'clang++-16', CXXSTD: '11,14,17,20,2b' },
         "clang-16",
     ),
 
     linux_pipeline(
-        "Linux 23.10 Clang 17 UBSAN",
-        "cppalliance/droneubuntu2310:1",
+        "Linux 24.04 Clang 17 UBSAN",
+        "cppalliance/droneubuntu2404:1",
         { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' } + ubsan,
         "clang-17",
     ),
 
     linux_pipeline(
-        "Linux 23.10 Clang 17 ASAN",
-        "cppalliance/droneubuntu2310:1",
+        "Linux 24.04 Clang 17 ASAN",
+        "cppalliance/droneubuntu2404:1",
         { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' } + asan,
         "clang-17",
     ),
@@ -372,6 +367,13 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         "clang-18",
     ),
 
+    linux_pipeline(
+        "Linux 24.10 Clang 19",
+        "cppalliance/droneubuntu2410:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-19', CXXSTD: '11,14,17,20,2b' } + asan,
+        "clang-19",
+    ),
+
     macos_pipeline(
         "MacOS 10.15 Xcode 12.2 UBSAN",
         { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,1z' } + ubsan,

.github/workflows/ci.yml

@@ -62,7 +62,7 @@ jobs:
             install: g++-12
           - toolset: gcc-13
             cxxstd: "11,14,17,20,2b"
-            container: ubuntu:23.04
+            container: ubuntu:24.04
             os: ubuntu-latest
             install: g++-13
           - toolset: gcc-14
@@ -84,7 +84,7 @@ jobs:
             install: clang-4.0
           - toolset: clang
             compiler: clang++-5.0
-            cxxstd: "11,14,1z"
+            cxxstd: "11,14"
             container: ubuntu:18.04
             os: ubuntu-latest
             install: clang-5.0
@@ -144,13 +144,13 @@ jobs:
           - toolset: clang
             compiler: clang++-16
             cxxstd: "11,14,17,20,2b"
-            container: ubuntu:23.04
+            container: ubuntu:24.04
             os: ubuntu-latest
             install: clang-16
           - toolset: clang
             compiler: clang++-17
             cxxstd: "11,14,17,20,2b"
-            container: ubuntu:23.10
+            container: ubuntu:24.04
             os: ubuntu-latest
             install: clang-17
           - toolset: clang
@@ -160,33 +160,48 @@ jobs:
             os: ubuntu-latest
             install: clang-18
           - toolset: clang
-            cxxstd: "11,14,17,2a"
-            os: macos-11
-          - toolset: clang
+            compiler: clang++-19
             cxxstd: "11,14,17,20,2b"
-            os: macos-12
+            container: ubuntu:24.10
+            os: ubuntu-latest
+            install: clang-19
           - toolset: clang
             cxxstd: "11,14,17,20,2b"
             os: macos-13
           - toolset: clang
             cxxstd: "11,14,17,20,2b"
             os: macos-14
+          - toolset: clang
+            cxxstd: "11,14,17,20,2b"
+            os: macos-15
 
     runs-on: ${{matrix.os}}
-    container: ${{matrix.container}}
+
+    container:
+      image: ${{matrix.container}}
+      volumes:
+        - /node20217:/node20217:rw,rshared
+        - ${{ startsWith(matrix.container, 'ubuntu:1') && '/node20217:/__e/node20:ro,rshared' || ' ' }}
 
     defaults:
       run:
         shell: bash
 
     steps:
-      - uses: actions/checkout@v3
-
       - name: Setup container environment
         if: matrix.container
         run: |
           apt-get update
-          apt-get -y install sudo python3 git g++
+          apt-get -y install sudo python3 git g++ curl xz-utils
+
+      - name: Install nodejs20glibc2.17
+        if: ${{ startsWith( matrix.container, 'ubuntu:1' ) }}
+        run: |
+          curl -LO https://archives.boost.io/misc/node/node-v20.9.0-linux-x64-glibc-217.tar.xz
+          tar -xf node-v20.9.0-linux-x64-glibc-217.tar.xz --strip-components 1 -C /node20217
+          ldd /__e/node20/bin/node
+
+      - uses: actions/checkout@v4
 
       - name: Install packages
         if: matrix.install
@@ -283,7 +298,7 @@ jobs:
         shell: cmd
         run: |
           cd ../boost-root
-          b2 -j3 libs/%LIBRARY%/test toolset=${{matrix.toolset}} cxxstd=${{matrix.cxxstd}} address-model=${{matrix.addrmd}} variant=debug,release embed-manifest-via=linker
+          b2 -j2 libs/%LIBRARY%/test toolset=${{matrix.toolset}} cxxstd=${{matrix.cxxstd}} address-model=${{matrix.addrmd}} variant=debug,release embed-manifest-via=linker
 
   posix-cmake-subdir:
     strategy:
@@ -292,9 +307,10 @@ jobs:
         include:
           - os: ubuntu-20.04
           - os: ubuntu-22.04
-          - os: macos-11
-          - os: macos-12
+          - os: ubuntu-24.04
           - os: macos-13
+          - os: macos-14
+          - os: macos-15
 
     runs-on: ${{matrix.os}}
 
@@ -340,9 +356,10 @@ jobs:
         include:
           - os: ubuntu-20.04
           - os: ubuntu-22.04
-          - os: macos-11
-          - os: macos-12
+          - os: ubuntu-24.04
           - os: macos-13
+          - os: macos-14
+          - os: macos-15
 
     runs-on: ${{matrix.os}}
 
@@ -398,9 +415,10 @@ jobs:
         include:
           - os: ubuntu-20.04
           - os: ubuntu-22.04
-          - os: macos-11
-          - os: macos-12
+          - os: ubuntu-24.04
           - os: macos-13
+          - os: macos-14
+          - os: macos-15
 
     runs-on: ${{matrix.os}}
 

appveyor.yml

@@ -59,7 +59,7 @@ test_script:
   - if not "%CXXSTD%" == "" set CXXSTD=cxxstd=%CXXSTD%
   - if not "%ADDRMD%" == "" set ADDRMD=address-model=%ADDRMD%
   - if not "%CXXFLAGS%" == "" set CXXFLAGS=cxxflags=%CXXFLAGS%
-  - if "%CMAKE%%CMAKE_SUBDIR%%CMAKE_INSTALL%" == ""  b2 -j3 libs/variant2/test toolset=%TOOLSET% %CXXSTD% %ADDRMD% %CXXFLAGS% variant=debug,release embed-manifest-via=linker
+  - if "%CMAKE%%CMAKE_SUBDIR%%CMAKE_INSTALL%" == ""  b2 -j2 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 ..

build.jam

@@ -0,0 +1,22 @@
+# Copyright 2023-2024 René Ferdinand Rivera Morell
+# Copyright 2024 Peter Dimov
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+require-b2 5.2 ;
+
+constant boost_dependencies :
+    /boost/assert//boost_assert
+    /boost/config//boost_config
+    /boost/mp11//boost_mp11
+    ;
+
+project /boost/variant2 ;
+
+explicit
+    [ alias boost_variant2 : : : : <include>include <library>$(boost_dependencies) ]
+    [ alias all : boost_variant2 test ]
+    ;
+
+call-if : boost-library variant2
+    ;

doc/variant2/changelog.adoc

@@ -1,5 +1,5 @@
 ////
-Copyright 2019-2022 Peter Dimov
+Copyright 2019-2025 Peter Dimov
 Distributed under the Boost Software License, Version 1.0.
 https://www.boost.org/LICENSE_1_0.txt
 ////
@@ -8,6 +8,10 @@ https://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix: changelog_
 
+## Changes in 1.88.0
+
+* Use the smallest appropriate unsigned type for the index.
+
 ## Changes in 1.83.0
 
 * Added `uses_double_storage()`.

include/boost/variant2/variant.hpp

@@ -26,6 +26,7 @@
 #include <iosfwd>
 #include <cstdint>
 #include <cerrno>
+#include <limits>
 
 //
 
@@ -83,7 +84,7 @@ struct monostate
 {
 };
 
-#if !BOOST_WORKAROUND(BOOST_MSVC, < 1940)
+#if !BOOST_WORKAROUND(BOOST_MSVC, < 1950)
 
 constexpr bool operator<(monostate, monostate) noexcept { return false; }
 constexpr bool operator>(monostate, monostate) noexcept { return false; }
@@ -845,6 +846,26 @@ template<class U, class... T> using resolve_overload_type = typename decltype( o
 
 template<class U, class... T> using resolve_overload_index = mp11::mp_find<mp11::mp_list<T...>, resolve_overload_type<U, T...>>;
 
+// index_type
+
+template<std::size_t N> using get_smallest_unsigned_type = mp11::mp_cond<
+
+    mp11::mp_bool< N <= (std::numeric_limits<unsigned char>::max)() >, unsigned char,
+    mp11::mp_bool< N <= (std::numeric_limits<unsigned short>::max)() >, unsigned short,
+    mp11::mp_true, unsigned
+
+>;
+
+#if BOOST_WORKAROUND( BOOST_CLANG_VERSION, < 30800 )
+
+template<bool Double, class... T> using get_index_type = unsigned short;
+
+#else
+
+template<bool Double, class... T> using get_index_type = get_smallest_unsigned_type< (Double + 1) * sizeof...(T) >;
+
+#endif
+
 // variant_base
 
 template<bool is_trivially_destructible, bool is_single_buffered, class... T> struct variant_base_impl;
@@ -855,8 +876,10 @@ struct none {};
 // trivially destructible, single buffered
 template<class... T> struct variant_base_impl<true, true, T...>
 {
+    using index_type = get_index_type<false, T...>;
+
     variant_storage<none, T...> st_;
-    unsigned ix_;
+    index_type ix_;
 
     constexpr variant_base_impl(): st_( mp11::mp_size_t<0>() ), ix_( 0 )
     {
@@ -870,6 +893,8 @@ template<class... T> struct variant_base_impl<true, true, T...>
     template<class I, class... A> void _replace( I, A&&... a )
     {
         ::new( &st_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
+
+        static_assert( I::value + 1 <= (std::numeric_limits<index_type>::max)(), "" );
         ix_ = I::value + 1;
     }
 
@@ -880,7 +905,7 @@ template<class... T> struct variant_base_impl<true, true, T...>
 
     template<std::size_t I> BOOST_CXX14_CONSTEXPR mp11::mp_at_c<variant<T...>, I>& _get_impl( mp11::mp_size_t<I> ) noexcept
     {
-        size_t const J = I+1;
+        std::size_t const J = I+1;
 
         BOOST_ASSERT( ix_ == J );
 
@@ -889,7 +914,7 @@ template<class... T> struct variant_base_impl<true, true, T...>
 
     template<std::size_t I> constexpr mp11::mp_at_c<variant<T...>, I> const& _get_impl( mp11::mp_size_t<I> ) const noexcept
     {
-        // size_t const J = I+1;
+        // std::size_t const J = I+1;
 
         BOOST_VARIANT2_CX14_ASSERT( ix_ == I+1 )
 
@@ -901,6 +926,8 @@ template<class... T> struct variant_base_impl<true, true, T...>
         static_assert( std::is_nothrow_constructible<U, A&&...>::value, "Logic error: U must be nothrow constructible from A&&..." );
 
         st_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
+
+        static_assert( J <= (std::numeric_limits<index_type>::max)(), "" );
         ix_ = J;
     }
 
@@ -911,6 +938,8 @@ template<class... T> struct variant_base_impl<true, true, T...>
         U tmp( std::forward<A>(a)... );
 
         st_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
+
+        static_assert( J <= (std::numeric_limits<index_type>::max)(), "" );
         ix_ = J;
     }
 
@@ -931,8 +960,10 @@ template<class... T> struct variant_base_impl<true, true, T...>
 // trivially destructible, double buffered
 template<class... T> struct variant_base_impl<true, false, T...>
 {
+    using index_type = get_index_type<true, T...>;
+
     variant_storage<none, T...> st_[ 2 ];
-    unsigned ix_;
+    index_type ix_;
 
     constexpr variant_base_impl(): st_{ { mp11::mp_size_t<0>() }, { mp11::mp_size_t<0>() } }, ix_( 0 )
     {
@@ -946,6 +977,8 @@ template<class... T> struct variant_base_impl<true, false, T...>
     template<class I, class... A> void _replace( I, A&&... a )
     {
         ::new( &st_[ 0 ] ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
+
+        static_assert( ( I::value + 1 ) * 2 <= (std::numeric_limits<index_type>::max)(), "" );
         ix_ = ( I::value + 1 ) * 2;
     }
 
@@ -958,7 +991,7 @@ template<class... T> struct variant_base_impl<true, false, T...>
     {
         BOOST_ASSERT( index() == I );
 
-        size_t const J = I+1;
+        std::size_t const J = I+1;
 
         constexpr mp11::mp_size_t<J> j{};
         return st_[ ix_ & 1 ].get( j );
@@ -968,7 +1001,7 @@ template<class... T> struct variant_base_impl<true, false, T...>
     {
         BOOST_VARIANT2_CX14_ASSERT( index() == I )
 
-        // size_t const J = I+1;
+        // std::size_t const J = I+1;
         // constexpr mp_size_t<J> j{};
 
         return st_[ ix_ & 1 ].get( mp11::mp_size_t<I+1>() );
@@ -976,13 +1009,14 @@ template<class... T> struct variant_base_impl<true, false, T...>
 
     template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( A&&... a )
     {
-        size_t const J = I+1;
+        std::size_t const J = I+1;
 
         unsigned i2 = 1 - ( ix_ & 1 );
 
         st_[ i2 ].emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
 
-        ix_ = J * 2 + i2;
+        static_assert( J * 2 + 1 <= (std::numeric_limits<index_type>::max)(), "" );
+        ix_ = static_cast<index_type>( J * 2 + i2 );
     }
 
     static constexpr bool uses_double_storage() noexcept
@@ -994,8 +1028,10 @@ template<class... T> struct variant_base_impl<true, false, T...>
 // not trivially destructible, single buffered
 template<class... T> struct variant_base_impl<false, true, T...>
 {
+    using index_type = get_index_type<false, T...>;
+
     variant_storage<none, T...> st_;
-    unsigned ix_;
+    index_type ix_;
 
     constexpr variant_base_impl(): st_( mp11::mp_size_t<0>() ), ix_( 0 )
     {
@@ -1009,6 +1045,8 @@ template<class... T> struct variant_base_impl<false, true, T...>
     template<class I, class... A> void _replace( I, A&&... a )
     {
         ::new( &st_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
+
+        static_assert( I::value + 1 <= (std::numeric_limits<index_type>::max)(), "" );
         ix_ = I::value + 1;
     }
 
@@ -1048,7 +1086,7 @@ template<class... T> struct variant_base_impl<false, true, T...>
 
     template<std::size_t I> BOOST_CXX14_CONSTEXPR mp11::mp_at_c<variant<T...>, I>& _get_impl( mp11::mp_size_t<I> ) noexcept
     {
-        size_t const J = I+1;
+        std::size_t const J = I+1;
 
         BOOST_ASSERT( ix_ == J );
 
@@ -1057,7 +1095,7 @@ template<class... T> struct variant_base_impl<false, true, T...>
 
     template<std::size_t I> constexpr mp11::mp_at_c<variant<T...>, I> const& _get_impl( mp11::mp_size_t<I> ) const noexcept
     {
-        // size_t const J = I+1;
+        // std::size_t const J = I+1;
 
         BOOST_VARIANT2_CX14_ASSERT( ix_ == I+1 )
 
@@ -1066,7 +1104,7 @@ template<class... T> struct variant_base_impl<false, true, T...>
 
     template<std::size_t I, class... A> void emplace( A&&... a )
     {
-        size_t const J = I+1;
+        std::size_t const J = I+1;
 
         using U = mp11::mp_at_c<variant<T...>, I>;
 
@@ -1077,6 +1115,8 @@ template<class... T> struct variant_base_impl<false, true, T...>
         _destroy();
 
         st_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
+
+        static_assert( J <= (std::numeric_limits<index_type>::max)(), "" );
         ix_ = J;
     }
 
@@ -1089,12 +1129,14 @@ template<class... T> struct variant_base_impl<false, true, T...>
 // not trivially destructible, double buffered
 template<class... T> struct variant_base_impl<false, false, T...>
 {
+    using index_type = get_index_type<true, T...>;
+
 #if defined(__GNUC__) && __GNUC__ < 11 && !defined(__clang__) && !defined(__INTEL_COMPILER)
 
     // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63707 :-(
 
     variant_storage<none, T...> st1_, st2_;
-    unsigned ix_;
+    index_type ix_;
 
     constexpr variant_base_impl(): st1_( mp11::mp_size_t<0>() ), st2_( mp11::mp_size_t<0>() ), ix_( 0 )
     {
@@ -1117,7 +1159,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
 #else
 
     variant_storage<none, T...> st_[ 2 ];
-    unsigned ix_;
+    index_type ix_;
 
     constexpr variant_base_impl(): st_{ { mp11::mp_size_t<0>() }, { mp11::mp_size_t<0>() } }, ix_( 0 )
     {
@@ -1143,6 +1185,8 @@ template<class... T> struct variant_base_impl<false, false, T...>
     template<class I, class... A> void _replace( I, A&&... a )
     {
         ::new( &storage( 0 ) ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
+
+        static_assert( ( I::value + 1 ) * 2 <= (std::numeric_limits<index_type>::max)(), "" );
         ix_ = ( I::value + 1 ) * 2;
     }
 
@@ -1165,7 +1209,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
 
     void _destroy() noexcept
     {
-        mp11::mp_with_index<1 + sizeof...(T)>( ix_ / 2, _destroy_L1{ this, ix_ & 1 } );
+        mp11::mp_with_index<1 + sizeof...(T)>( ix_ / 2, _destroy_L1{ this, static_cast<unsigned>( ix_ & 1 ) } );
     }
 
     ~variant_base_impl() noexcept
@@ -1182,7 +1226,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
     {
         BOOST_ASSERT( index() == I );
 
-        size_t const J = I+1;
+        std::size_t const J = I+1;
 
         constexpr mp11::mp_size_t<J> j{};
         return storage( ix_ & 1 ).get( j );
@@ -1192,7 +1236,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
     {
         BOOST_VARIANT2_CX14_ASSERT( index() == I )
 
-        // size_t const J = I+1;
+        // std::size_t const J = I+1;
         // constexpr mp_size_t<J> j{};
 
         return storage( ix_ & 1 ).get( mp11::mp_size_t<I+1>() );
@@ -1200,14 +1244,15 @@ template<class... T> struct variant_base_impl<false, false, T...>
 
     template<std::size_t I, class... A> void emplace( A&&... a )
     {
-        size_t const J = I+1;
+        std::size_t const J = I+1;
 
         unsigned i2 = 1 - ( ix_ & 1 );
 
         storage( i2 ).emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
         _destroy();
 
-        ix_ = J * 2 + i2;
+        static_assert( J * 2 + 1 <= (std::numeric_limits<index_type>::max)(), "" );
+        ix_ = static_cast<index_type>( J * 2 + i2 );
     }
 
     static constexpr bool uses_double_storage() noexcept
@@ -2125,7 +2170,7 @@ template<class R, class F, class V1> struct visit_L1
     F&& f;
     V1&& v1;
 
-    template<class I> auto operator()( I ) const -> Vret<R, F, V1>
+    template<class I> constexpr auto operator()( I ) const -> Vret<R, F, V1>
     {
         return std::forward<F>(f)( unsafe_get<I::value>( std::forward<V1>(v1) ) );
     }

test/Jamfile

@@ -7,7 +7,8 @@
 #  http://www.boost.org/LICENSE_1_0.txt
 
 import testing ;
-import ../../config/checks/config : requires ;
+import-search /boost/config/checks ;
+import config : requires ;
 
 project
   : default-build
@@ -16,9 +17,14 @@ project
 
   : requirements
 
+    <library>/boost/variant2//boost_variant2
+    <library>/boost/core//boost_core
+    <library>/boost/container_hash//boost_container_hash
+
     <toolset>msvc:<warnings-as-errors>on
     <toolset>gcc:<warnings-as-errors>on
     <toolset>clang:<warnings-as-errors>on
+
   ;
 
 run quick.cpp ;
@@ -54,10 +60,10 @@ run variant_in_place_type_construct.cpp ;
 compile variant_in_place_type_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
 
 run variant_copy_assign.cpp ;
-compile variant_copy_assign_cx.cpp : [ requires cxx14_constexpr ] ;
+compile variant_copy_assign_cx.cpp : [ requires cxx14_constexpr ] <toolset>gcc-5:<build>no <toolset>gcc-6:<build>no ;
 
 run variant_move_assign.cpp ;
-compile variant_move_assign_cx.cpp : [ requires cxx14_constexpr ] ;
+compile variant_move_assign_cx.cpp : [ requires cxx14_constexpr ] <toolset>gcc-5:<build>no <toolset>gcc-6:<build>no ;
 
 run variant_value_assign.cpp ;
 compile variant_value_assign_cx.cpp : [ requires cxx14_constexpr ] ;
@@ -125,7 +131,7 @@ 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" "<undefined-sanitizer>norecover:<link>static" ;
+local JSON = <library>/boost/json//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) ;
@@ -133,3 +139,21 @@ run variant_json_value_to.cpp : : : $(JSON) ;
 compile variant_uses_double_storage.cpp ;
 
 run variant_derived_construct2.cpp ;
+
+compile variant_visit_cx.cpp : [ requires cxx14_constexpr ] ;
+compile variant_visit_cx_2.cpp : [ requires cxx14_constexpr ] ;
+compile variant_visit_r_cx.cpp : [ requires cxx14_constexpr ] ;
+
+local index-type-reqs =
+
+  <variant>release
+  <toolset>msvc,<address-model>32:<build>no
+  <toolset>clang,<target-os>linux:<cxxflags>-ftemplate-depth=1024 # for Clang 3.x
+;
+
+local list-sizes = 126 127 128 129 254 255 256 257 ;
+
+for local list-size in $(list-sizes)
+{
+    run variant_index_type.cpp : : : $(index-type-reqs) <define>LIST_SIZE=$(list-size) : variant_index_type_$(list-size) ;
+}

test/cmake_install_test/CMakeLists.txt

@@ -14,4 +14,4 @@ target_link_libraries(quick Boost::variant2)
 enable_testing()
 add_test(quick quick)
 
-add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)
+add_custom_target(check VERBATIM COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)

test/cmake_subdir_test/CMakeLists.txt

@@ -18,4 +18,4 @@ target_link_libraries(quick Boost::variant2)
 enable_testing()
 add_test(quick quick)
 
-add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)
+add_custom_target(check VERBATIM COMMAND ${CMAKE_CTEST_COMMAND} --output-on-failure -C $<CONFIG>)

test/variant_index_type.cpp

@@ -0,0 +1,86 @@
+// Copyright 2024 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#if defined(_MSC_VER)
+# pragma warning( disable: 4503 ) // decorated name length exceeded
+#endif
+
+#include <boost/variant2/variant.hpp>
+#include <boost/mp11.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+using namespace boost::mp11;
+
+template<std::size_t I> struct X
+{
+};
+
+template<class N> using Xf = X< N::value >;
+
+template<std::size_t I> struct Y
+{
+    Y() = default;
+    Y( Y&& ) {}
+};
+
+template<class N> using Yf = Y< N::value >;
+
+template<std::size_t I> struct Z
+{
+    ~Z() {}
+};
+
+template<class N> using Zf = Z< N::value >;
+
+template<std::size_t I> struct W
+{
+    ~W() {}
+
+    W() = default;
+    W( W&& ) {}
+};
+
+template<class N> using Wf = W< N::value >;
+
+template<class L, template<class...> class F> void test()
+{
+    using V = mp_rename< mp_transform<F, L>, boost::variant2::variant >;
+
+    constexpr std::size_t N = mp_size<L>::value;
+
+    using last_type = F<mp_size_t<N-1>>;
+
+    {
+        V v( last_type{} );
+        BOOST_TEST_EQ( v.index(), N-1 );
+    }
+
+    {
+        V v;
+        BOOST_TEST_EQ( v.index(), 0 );
+
+        v.template emplace<last_type>();
+        BOOST_TEST_EQ( v.index(), N-1 );
+    }
+}
+
+int main()
+{
+    constexpr std::size_t N = LIST_SIZE;
+    using L = mp_iota_c<N>;
+
+    static_assert( !boost::variant2::variant< X<0>, X<1> >::uses_double_storage(), "" );
+    test<L, Xf>();
+
+    static_assert( boost::variant2::variant< Y<0>, Y<1> >::uses_double_storage(), "" );
+    test<L, Yf>();
+
+    static_assert( !boost::variant2::variant< Z<0>, Z<1> >::uses_double_storage(), "" );
+    test<L, Zf>();
+
+    static_assert( boost::variant2::variant< W<0>, W<1> >::uses_double_storage(), "" );
+    test<L, Wf>();
+
+    return boost::report_errors();
+}

test/variant_json_value_from.cpp

@@ -2,6 +2,12 @@
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
+#include <boost/config.hpp>
+
+#if defined(BOOST_GCC) && BOOST_GCC < 50000
+# define BOOST_ALLOW_DEPRECATED
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/json/value_from.hpp>
 #include <boost/json/serialize.hpp>

test/variant_json_value_to.cpp

@@ -2,6 +2,12 @@
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
+#include <boost/config.hpp>
+
+#if defined(BOOST_GCC) && BOOST_GCC < 50000
+# define BOOST_ALLOW_DEPRECATED
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/json/value_to.hpp>
 #include <boost/json/serialize.hpp>

test/variant_visit_cx.cpp

@@ -0,0 +1,51 @@
+// Copyright 2017, 2024 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+using namespace boost::variant2;
+
+#if !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
+
+#include <boost/config/pragma_message.hpp>
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr visit test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
+
+int main() {}
+
+#else
+
+struct X
+{
+    constexpr operator int() const { return 2; }
+};
+
+struct F
+{
+    constexpr int operator()( int x ) const
+    {
+        return x;
+    }
+};
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+int main()
+{
+    {
+        constexpr variant<int> v( 1 );
+        STATIC_ASSERT( visit( F(), v ) == 1 );
+    }
+
+    {
+        constexpr variant<char, int> v( 'a' );
+        STATIC_ASSERT( visit( F(), v ) == 'a' );
+    }
+
+    {
+        constexpr variant<char, int, X> v( X{} );
+        STATIC_ASSERT( visit( F(), v ) == 2 );
+    }
+}
+
+#endif

test/variant_visit_cx_2.cpp

@@ -0,0 +1,53 @@
+// Copyright 2017, 2024 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !( defined(__cpp_constexpr) && __cpp_constexpr >= 201603L )
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr visit test because __cpp_constexpr < 201603L")
+int main() {}
+
+#elif !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr visit test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+struct F
+{
+    constexpr int operator()( int x1, int x2 ) const
+    {
+        return x1 + x2;
+    }
+
+    constexpr int operator()( int x1, int x2, int x3 ) const
+    {
+        return x1 + x2 + x3;
+    }
+};
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+int main()
+{
+    {
+        constexpr variant<char, int> v1( 1 );
+        constexpr variant<char, int> v2( '2' );
+        STATIC_ASSERT( visit( F(), v1, v2 ) == 1 + '2' );
+    }
+
+    {
+        constexpr variant<char, int> v1( 1 );
+        constexpr variant<char, int> v2( 2 );
+        constexpr variant<char, int> v3( '3' );
+        STATIC_ASSERT( visit( F(), v1, v2, v3 ) == 1 + 2 + '3' );
+    }
+}
+
+#endif

test/variant_visit_r_cx.cpp

@@ -0,0 +1,52 @@
+// Copyright 2017, 2024 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+using namespace boost::variant2;
+
+#if !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
+
+#include <boost/config/pragma_message.hpp>
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr visit test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
+
+int main() {}
+
+#else
+
+struct X
+{
+    int v;
+    constexpr operator int() const { return v; }
+};
+
+struct F
+{
+    template<class T> constexpr T operator()( T x ) const
+    {
+        return x;
+    }
+};
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+int main()
+{
+    {
+        constexpr variant<int> v( 1 );
+        STATIC_ASSERT( visit<int>( F(), v ) == 1 );
+    }
+
+    {
+        constexpr variant<char, int> v( 'a' );
+        STATIC_ASSERT( visit<int>( F(), v ) == 'a' );
+    }
+
+    {
+        constexpr variant<char, int, X> v( X{2} );
+        STATIC_ASSERT( visit<int>( F(), v ) == 2 );
+    }
+}
+
+#endif