Reference #57 and #58 in comments as well

fix: add missing -Wmaybe-uninitialized pragma to recursive variant_storage_impl

.drone.jsonnet

@@ -34,7 +34,6 @@ local linux_pipeline(name, image, environment, packages = "", sources = [], arch
                 '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 []) +
             (if packages != "" then [ 'apt-get update', 'apt-get -y install ' + packages ] else []) +
@@ -213,6 +212,13 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         "g++-14-multilib",
     ),
 
+    linux_pipeline(
+        "Linux 25.04 GCC 15 32/64",
+        "cppalliance/droneubuntu2504:1",
+        { TOOLSET: 'gcc', COMPILER: 'g++-15', CXXSTD: '11,14,17,20,23,2c', ADDRMD: '32,64' },
+        "g++-15-multilib",
+    ),
+
     linux_pipeline(
         "Linux 16.04 Clang 3.5",
         "cppalliance/droneubuntu1604:1",
@@ -340,40 +346,47 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
     ),
 
     linux_pipeline(
-        "Linux 24.04 Clang 17 UBSAN",
+        "Linux 24.04 Clang 17",
         "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' } + ubsan,
+        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' },
         "clang-17",
     ),
 
     linux_pipeline(
-        "Linux 24.04 Clang 17 ASAN",
+        "Linux 24.04 Clang 18",
         "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-17', CXXSTD: '11,14,17,20,2b' } + asan,
-        "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,
+        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' },
         "clang-18",
     ),
 
     linux_pipeline(
-        "Linux 24.04 Clang 18 ASAN",
+        "Linux 24.04 Clang 19",
         "cppalliance/droneubuntu2404:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-18', CXXSTD: '11,14,17,20,2b' } + asan,
-        "clang-18",
-    ),
-
-    linux_pipeline(
-        "Linux 24.10 Clang 19",
-        "cppalliance/droneubuntu2410:1",
-        { TOOLSET: 'clang', COMPILER: 'clang++-19', CXXSTD: '11,14,17,20,2b' } + asan,
+        { TOOLSET: 'clang', COMPILER: 'clang++-19', CXXSTD: '11,14,17,20,2b' },
         "clang-19",
     ),
 
+    linux_pipeline(
+        "Linux 24.04 Clang 20 UBSAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-20', CXXSTD: '11,14,17,20,23,2c' } + ubsan,
+        "clang-20",
+    ),
+
+    linux_pipeline(
+        "Linux 24.04 Clang 20 ASAN",
+        "cppalliance/droneubuntu2404:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-20', CXXSTD: '11,14,17,20,23,2c' } + asan,
+        "clang-20",
+    ),
+
+    linux_pipeline(
+        "Linux 25.10 Clang 21",
+        "cppalliance/droneubuntu2510:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-21', CXXSTD: '11,14,17,20,23,2c' },
+        "clang-21",
+    ),
+
     macos_pipeline(
         "MacOS 10.15 Xcode 12.2 UBSAN",
         { TOOLSET: 'clang', COMPILER: 'clang++', CXXSTD: '11,14,1z' } + ubsan,
@@ -437,4 +450,16 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         "cppalliance/dronevs2022:1",
         { TOOLSET: 'msvc-14.3', CXXSTD: '14,17', CXXFLAGS: '/permissive-' },
     ),
+
+    windows_pipeline(
+        "Windows VS2026 msvc-14.5",
+        "cppalliance/dronevs2026:1",
+        { TOOLSET: 'msvc-14.5', CXXSTD: '14,17,20,latest' },
+    ),
+
+    windows_pipeline(
+        "Windows VS2026 msvc-14.5 permissive-",
+        "cppalliance/dronevs2026:1",
+        { TOOLSET: 'msvc-14.5', CXXSTD: '14,17', CXXFLAGS: '/permissive-' },
+    ),
 ]

.github/workflows/ci.yml

@@ -185,18 +185,24 @@ jobs:
           - toolset: clang
             compiler: clang++-20
             cxxstd: "11,14,17,20,23,2c"
-            container: ubuntu:25.04
+            container: ubuntu:24.04
             os: ubuntu-latest
             install: clang-20
           - toolset: clang
-            cxxstd: "11,14,17,20,2b"
-            os: macos-13
+            compiler: clang++-21
+            cxxstd: "11,14,17,20,23,2c"
+            container: ubuntu:25.10
+            os: ubuntu-latest
+            install: clang-21
           - toolset: clang
             cxxstd: "11,14,17,20,2b"
             os: macos-14
           - toolset: clang
-            cxxstd: "11,14,17,20,2b"
+            cxxstd: "11,14,17,20,23,2c"
             os: macos-15
+          - toolset: clang
+            cxxstd: "11,14,17,20,23,2c"
+            os: macos-26
 
     runs-on: ${{matrix.os}}
 
@@ -322,9 +328,9 @@ jobs:
         include:
           - os: ubuntu-22.04
           - os: ubuntu-24.04
-          - os: macos-13
           - os: macos-14
           - os: macos-15
+          - os: macos-26
 
     runs-on: ${{matrix.os}}
 
@@ -370,9 +376,9 @@ jobs:
         include:
           - os: ubuntu-22.04
           - os: ubuntu-24.04
-          - os: macos-13
           - os: macos-14
           - os: macos-15
+          - os: macos-26
 
     runs-on: ${{matrix.os}}
 
@@ -428,9 +434,9 @@ jobs:
         include:
           - os: ubuntu-22.04
           - os: ubuntu-24.04
-          - os: macos-13
           - os: macos-14
           - os: macos-15
+          - os: macos-26
 
     runs-on: ${{matrix.os}}
 

CMakeLists.txt

@@ -19,7 +19,7 @@ target_link_libraries(boost_variant2
     Boost::mp11
 )
 
-if(CMAKE_VERSION VERSION_GREATER 3.18 AND CMAKE_GENERATOR MATCHES "Visual Studio")
+if(NOT CMAKE_VERSION VERSION_LESS 3.19 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")

doc/variant2/changelog.adoc

@@ -8,6 +8,15 @@ https://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix: changelog_
 
+## Changes in 1.91.0
+
+* `holds_alternative<T>` and `get<T>` have been relaxed to no longer require `T` to occur exactly once in the list of alternatives. It now must occur at least once.
+
+## Changes in 1.90.0
+
+* More functions have been marked as `constexpr`, including `~variant`.
+  This didn't matter before {cpp}20, but does now.
+
 ## Changes in 1.88.0
 
 * Use the smallest appropriate unsigned type for the index.

doc/variant2/reference.adoc

@@ -719,10 +719,8 @@ template<class U, class... T>
 [none]
 * {blank}
 +
-Requires: :: The type `U` occurs exactly once in `T...`. Otherwise, the
-  program is ill-formed.
-Returns:  :: `true` if `index()` is equal to the zero-based index of `U`
-  in `T...`.
+Requires: :: The type `U` must be present in `T...`. Otherwise, the program is ill-formed.
+Returns:  :: `true` if `v` holds a value of type `U`, otherwise `false`.
 
 ### get
 
@@ -773,10 +771,8 @@ template<class U, class... T>
 [none]
 * {blank}
 +
-Requires: :: The type `U` occurs exactly once in `T...`. Otherwise, the
-  program is ill-formed.
-Effects:  :: If `v` holds a value of type `U`, returns a reference to that value.
-  Otherwise, throws `bad_variant_access`.
+Requires: :: The type `U` must be present in `T...`. Otherwise, the program is ill-formed.
+Effects:  :: If `v` holds a value of type `U`, returns a reference to that value. Otherwise, throws `bad_variant_access`.
 
 ### get_if
 
@@ -793,10 +789,8 @@ template<size_t I, class... T>
 [none]
 * {blank}
 +
-Effects:  :: A pointer to the value stored in the variant, if
-  `v != nullptr && v\->index() == I`. Otherwise, `nullptr`.
-Remarks: :: These functions do not participate in overload resolution
-  unless `I` < `sizeof...(T)`.
+Returns:  :: A pointer to the value stored in `*v`, if `v != nullptr && v\->index() == I`. Otherwise, `nullptr`.
+Remarks: :: These functions do not participate in overload resolution unless `I` < `sizeof...(T)`.
 
 ```
 template<class U, class... T>
@@ -811,10 +805,8 @@ template<class U, class... T>
 [none]
 * {blank}
 +
-Requires: :: The type `U` occurs exactly once in `T...`. Otherwise, the
-  program is ill-formed.
-Effects:  :: Equivalent to: `return get_if<I>(v);` with `I` being
-  the zero-based index of `U` in `T...`.
+Requires: :: The type `U` must be present in `T...`. Otherwise, the program is ill-formed.
+Returns:  :: If `v != nullptr` and `*v` holds a value of type `U`, a pointer to that value. Otherwise, `nullptr`.
 
 ### unsafe_get (extension)
 

include/boost/variant2/variant.hpp

@@ -1,12 +1,9 @@
 #ifndef BOOST_VARIANT2_VARIANT_HPP_INCLUDED
 #define BOOST_VARIANT2_VARIANT_HPP_INCLUDED
 
-// Copyright 2017-2019 Peter Dimov.
-//
+// Copyright 2017-2026 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
 
 #if defined(_MSC_VER) && _MSC_VER < 1910
 # pragma warning( push )
@@ -93,7 +90,7 @@ struct monostate
 {
 };
 
-#if !BOOST_WORKAROUND(BOOST_MSVC, < 1950)
+#if !BOOST_WORKAROUND(BOOST_MSVC, < 1960)
 
 constexpr bool operator<(monostate, monostate) noexcept { return false; }
 constexpr bool operator>(monostate, monostate) noexcept { return false; }
@@ -324,12 +321,41 @@ constexpr std::size_t variant_npos = ~static_cast<std::size_t>( 0 );
 
 // holds_alternative
 
+#if !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
+
 template<class U, class... T> constexpr bool holds_alternative( variant<T...> const& v ) noexcept
 {
-    static_assert( mp11::mp_count<variant<T...>, U>::value == 1, "The type must occur exactly once in the list of variant alternatives" );
-    return v.index() == mp11::mp_find<variant<T...>, U>::value;
+    static_assert( mp11::mp_contains<variant<T...>, U>::value, "The type must be present in the list of variant alternatives" );
+
+    using A = bool[];
+    return A{ std::is_same<U, T>::value... }[ v.index() ];
 }
 
+#else
+
+namespace detail
+{
+
+template<class U, class V> struct holds_alternative_L
+{
+    template<class I> constexpr bool operator()( I ) const noexcept
+    {
+        return std::is_same< U, mp11::mp_at<V, I> >::value;
+    }
+};
+
+} // namespace detail
+
+template<class U, class... T> constexpr bool holds_alternative( variant<T...> const& v ) noexcept
+{
+    using V = variant<T...>;
+    static_assert( mp11::mp_contains<V, U>::value, "The type must be present in the list of variant alternatives" );
+
+    return mp11::mp_with_index<sizeof...(T)>( v.index(), detail::holds_alternative_L<U, V>() );
+}
+
+#endif
+
 // get (index)
 
 template<std::size_t I, class... T> constexpr variant_alternative_t<I, variant<T...>>& get(variant<T...>& v)
@@ -422,61 +448,106 @@ template<std::size_t I, class... T> constexpr variant_alternative_t<I, variant<T
 
 // get (type)
 
+namespace detail
+{
+
+template<class U, class V> struct get_if_impl_L1
+{
+    V& v_;
+
+    template<class I> constexpr U* fn( I, mp11::mp_true ) const noexcept
+    {
+        return &v_._get_impl( I() );
+    }
+
+    template<class I> constexpr U* fn( I, mp11::mp_false ) const noexcept
+    {
+        return nullptr;
+    }
+
+    template<class I> constexpr U* operator()( I ) const noexcept
+    {
+        return this->fn( I(), std::is_same<U, mp11::mp_at<V, I>>() );
+    }
+};
+
+template<class U, class... T> constexpr U* get_if_impl( variant<T...>& v ) noexcept
+{
+    return mp11::mp_with_index<sizeof...(T)>( v.index(), get_if_impl_L1< U, variant<T...> >{ v } );
+}
+
+template<class U, class V> struct get_if_impl_L2
+{
+    V const& v_;
+
+    template<class I> constexpr U const* fn( I, mp11::mp_true ) const noexcept
+    {
+        return &v_._get_impl( I() );
+    }
+
+    template<class I> constexpr U const* fn( I, mp11::mp_false ) const noexcept
+    {
+        return nullptr;
+    }
+
+    template<class I> constexpr U const* operator()( I ) const noexcept
+    {
+        return this->fn( I(), std::is_same<U, mp11::mp_at<V, I>>() );
+    }
+};
+
+template<class U, class... T> constexpr U const* get_if_impl( variant<T...> const& v ) noexcept
+{
+    return mp11::mp_with_index<sizeof...(T)>( v.index(), get_if_impl_L2< U, variant<T...> >{ v } );
+}
+
+} // namespace detail
+
 template<class U, class... T> constexpr U& get(variant<T...>& v)
 {
-    static_assert( mp11::mp_count<variant<T...>, U>::value == 1, "The type must occur exactly once in the list of variant alternatives" );
-
-    using I = mp11::mp_find<variant<T...>, U>;
-
-    return ( v.index() != I::value? detail::throw_bad_variant_access(): (void)0 ), v._get_impl( I() );
+    static_assert( mp11::mp_contains<variant<T...>, U>::value, "The type must be present in the list of variant alternatives" );
+    return ( !holds_alternative<U>( v )? detail::throw_bad_variant_access(): (void)0 ), *detail::get_if_impl<U>( v );
 }
 
 template<class U, class... T> constexpr U&& get(variant<T...>&& v)
 {
-    static_assert( mp11::mp_count<variant<T...>, U>::value == 1, "The type must occur exactly once in the list of variant alternatives" );
-
-    using I = mp11::mp_find<variant<T...>, U>;
+    static_assert( mp11::mp_contains<variant<T...>, U>::value, "The type must be present in the list of variant alternatives" );
 
 #if !BOOST_WORKAROUND(BOOST_MSVC, < 1930)
 
-    return ( v.index() != I::value? detail::throw_bad_variant_access(): (void)0 ), std::move( v._get_impl( I() ) );
+    return ( !holds_alternative<U>( v )? detail::throw_bad_variant_access(): (void)0 ), std::move( *detail::get_if_impl<U>( v ) );
 
 #else
 
-    if( v.index() != I::value ) detail::throw_bad_variant_access();
-    return std::move( v._get_impl( I() ) );
+    if( !holds_alternative<U>( v ) ) detail::throw_bad_variant_access();
+    return std::move( *detail::get_if_impl<U>( v ) );
 
 #endif
 }
 
 template<class U, class... T> constexpr U const& get(variant<T...> const& v)
 {
-    static_assert( mp11::mp_count<variant<T...>, U>::value == 1, "The type must occur exactly once in the list of variant alternatives" );
-
-    using I = mp11::mp_find<variant<T...>, U>;
-
-    return ( v.index() != I::value? detail::throw_bad_variant_access(): (void)0 ), v._get_impl( I() );
+    static_assert( mp11::mp_contains<variant<T...>, U>::value, "The type must be present in the list of variant alternatives" );
+    return ( !holds_alternative<U>( v )? detail::throw_bad_variant_access(): (void)0 ), *detail::get_if_impl<U>( v );
 }
 
 template<class U, class... T> constexpr U const&& get(variant<T...> const&& v)
 {
-    static_assert( mp11::mp_count<variant<T...>, U>::value == 1, "The type must occur exactly once in the list of variant alternatives" );
-
-    using I = mp11::mp_find<variant<T...>, U>;
+    static_assert( mp11::mp_contains<variant<T...>, U>::value, "The type must be present in the list of variant alternatives" );
 
 #if !BOOST_WORKAROUND(BOOST_MSVC, < 1930)
 
-    return ( v.index() != I::value? detail::throw_bad_variant_access(): (void)0 ), std::move( v._get_impl( I() ) );
+    return ( !holds_alternative<U>( v )? detail::throw_bad_variant_access(): (void)0 ), std::move( *detail::get_if_impl<U>( v ) );
 
 #else
 
-    if( v.index() != I::value ) detail::throw_bad_variant_access();
-    return std::move( v._get_impl( I() ) );
+    if( !holds_alternative<U>( v ) ) detail::throw_bad_variant_access();
+    return std::move( *detail::get_if_impl<U>( v ) );
 
 #endif
 }
 
-// get_if
+// get_if (index)
 
 template<std::size_t I, class... T> constexpr typename std::add_pointer<variant_alternative_t<I, variant<T...>>>::type get_if(variant<T...>* v) noexcept
 {
@@ -490,22 +561,18 @@ template<std::size_t I, class... T> constexpr typename std::add_pointer<const va
     return v && v->index() == I? &v->_get_impl( mp11::mp_size_t<I>() ): 0;
 }
 
+// get_if (type)
+
 template<class U, class... T> constexpr typename std::add_pointer<U>::type get_if(variant<T...>* v) noexcept
 {
-    static_assert( mp11::mp_count<variant<T...>, U>::value == 1, "The type must occur exactly once in the list of variant alternatives" );
-
-    using I = mp11::mp_find<variant<T...>, U>;
-
-    return v && v->index() == I::value? &v->_get_impl( I() ): 0;
+    static_assert( mp11::mp_contains<variant<T...>, U>::value, "The type must be present in the list of variant alternatives" );
+    return v && holds_alternative<U>( *v )? detail::get_if_impl<U>( *v ): 0;
 }
 
-template<class U, class... T> constexpr typename std::add_pointer<U const>::type get_if(variant<T...> const * v) noexcept
+template<class U, class... T> constexpr typename std::add_pointer<U const>::type get_if(variant<T...> const* v) noexcept
 {
-    static_assert( mp11::mp_count<variant<T...>, U>::value == 1, "The type must occur exactly once in the list of variant alternatives" );
-
-    using I = mp11::mp_find<variant<T...>, U>;
-
-    return v && v->index() == I::value? &v->_get_impl( I() ): 0;
+    static_assert( mp11::mp_contains<variant<T...>, U>::value, "The type must be present in the list of variant alternatives" );
+    return v && holds_alternative<U>( *v )? detail::get_if_impl<U>( *v ): 0;
 }
 
 //
@@ -558,10 +625,22 @@ template<class T1, class... T> union variant_storage_impl<mp11::mp_false, T1, T.
     T1 first_;
     variant_storage<T...> rest_;
 
+#if defined(BOOST_GCC) && (__GNUC__ >= 7)
+// false positive, see https://github.com/boostorg/variant2/issues/55
+// ... and https://github.com/boostorg/variant2/pull/57
+// ... and https://github.com/boostorg/variant2/pull/58
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
     template<class... A> constexpr variant_storage_impl( mp11::mp_size_t<0>, A&&... a ): first_( std::forward<A>(a)... )
     {
     }
 
+#if defined(BOOST_GCC) && (__GNUC__ >= 7)
+# pragma GCC diagnostic pop
+#endif
+
     template<std::size_t I, class... A> constexpr variant_storage_impl( mp11::mp_size_t<I>, A&&... a ): rest_( mp11::mp_size_t<I-1>(), std::forward<A>(a)... )
     {
     }
@@ -675,10 +754,22 @@ template<class T1, class... T> union variant_storage_impl<mp11::mp_true, T1, T..
     T1 first_;
     variant_storage<T...> rest_;
 
+#if defined(BOOST_GCC) && (__GNUC__ >= 7)
+// false positive, see https://github.com/boostorg/variant2/issues/55
+// ... and https://github.com/boostorg/variant2/pull/57
+// ... and https://github.com/boostorg/variant2/pull/58
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
     template<class... A> constexpr variant_storage_impl( mp11::mp_size_t<0>, A&&... a ): first_( std::forward<A>(a)... )
     {
     }
 
+#if defined(BOOST_GCC) && (__GNUC__ >= 7)
+# pragma GCC diagnostic pop
+#endif
+
     template<std::size_t I, class... A> constexpr variant_storage_impl( mp11::mp_size_t<I>, A&&... a ): rest_( mp11::mp_size_t<I-1>(), std::forward<A>(a)... )
     {
     }
@@ -704,6 +795,7 @@ template<class T1, class... T> union variant_storage_impl<mp11::mp_true, T1, T..
 # pragma GCC diagnostic ignored "-Wuninitialized"
 #endif
 #endif
+
         *this = variant_storage_impl( mp11::mp_size_t<I>(), std::forward<A>(a)... );
 
 #if defined(BOOST_GCC) && (__GNUC__ >= 7)
@@ -1071,7 +1163,18 @@ template<class... T> struct variant_base_impl<false, true, T...>
         template<class I> BOOST_CXX14_CONSTEXPR void operator()( I ) const noexcept
         {
             using U = mp11::mp_at<mp11::mp_list<none, T...>, I>;
+
+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+// false positive, see https://github.com/boostorg/variant2/issues/55
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
             this_->st_.get( I() ).~U();
+
+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+# pragma GCC diagnostic pop
+#endif
         }
     };
 
@@ -1119,8 +1222,18 @@ template<class... T> struct variant_base_impl<false, true, T...>
 
         static_assert( std::is_nothrow_move_constructible<U>::value, "Logic error: U must be nothrow move constructible" );
 
+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+// false positive, see https://github.com/boostorg/variant2/issues/55
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
         U tmp( std::forward<A>(a)... );
 
+#if defined(BOOST_GCC) && (__GNUC__ >= 12)
+# pragma GCC diagnostic pop
+#endif
+
         _destroy();
 
         st_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
@@ -1689,7 +1802,7 @@ public:
         class Ud = typename std::decay<U>::type,
         class E1 = typename std::enable_if< !std::is_same<Ud, variant>::value && !std::is_base_of<variant, Ud>::value && !detail::is_in_place_index<Ud>::value && !detail::is_in_place_type<Ud>::value >::type,
 
-#if BOOST_WORKAROUND(BOOST_MSVC, < 1950)
+#if BOOST_WORKAROUND(BOOST_MSVC, < 1960)
 
         class V = mp11::mp_apply_q< mp11::mp_bind_front<detail::resolve_overload_type, U&&>, variant >,
 

test/CMakeLists.txt

@@ -6,6 +6,6 @@ include(BoostTestJamfile OPTIONAL RESULT_VARIABLE HAVE_BOOST_TEST)
 
 if(HAVE_BOOST_TEST)
 
-boost_test_jamfile(FILE Jamfile LINK_LIBRARIES Boost::variant2 Boost::core Boost::container_hash)
+boost_test_jamfile(FILE Jamfile LINK_LIBRARIES Boost::variant2 Boost::core Boost::container_hash Boost::system)
 
 endif()

test/Jamfile

@@ -1,14 +1,8 @@
-#  Boost.Variant2 Library Test Jamfile
-#
-#  Copyright 2015-2019 Peter Dimov
-#
+#  Copyright 2015-2026 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
 
 import testing ;
-import-search /boost/config/checks ;
-import config : requires ;
 
 project
   : default-build
@@ -33,54 +27,54 @@ run variant_size.cpp ;
 run variant_alternative.cpp ;
 
 run variant_holds_alternative.cpp ;
-compile variant_holds_alternative_cx.cpp : <toolset>msvc-14.0:<build>no ;
+compile variant_holds_alternative_cx.cpp ;
 
 run variant_get_by_index.cpp ;
-compile variant_get_by_index_cx.cpp : <toolset>msvc-14.0:<build>no ;
+compile variant_get_by_index_cx.cpp ;
 
 run variant_get_by_type.cpp ;
-compile variant_get_by_type_cx.cpp : <toolset>msvc-14.0:<build>no ;
+compile variant_get_by_type_cx.cpp ;
 
 run variant_default_construct.cpp ;
-compile variant_default_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
+compile variant_default_construct_cx.cpp ;
 
 run variant_copy_construct.cpp ;
-compile variant_copy_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
+compile variant_copy_construct_cx.cpp ;
 
 run variant_move_construct.cpp ;
-compile variant_move_construct_cx.cpp : [ requires cxx14_constexpr ] ;
+compile variant_move_construct_cx.cpp ;
 
 run variant_value_construct.cpp ;
-compile variant_value_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
+compile variant_value_construct_cx.cpp ;
 
 run variant_in_place_index_construct.cpp ;
-compile variant_in_place_index_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
+compile variant_in_place_index_construct_cx.cpp ;
 
 run variant_in_place_type_construct.cpp ;
-compile variant_in_place_type_construct_cx.cpp : <toolset>msvc-14.0:<build>no ;
+compile variant_in_place_type_construct_cx.cpp ;
 
 run variant_copy_assign.cpp ;
-compile variant_copy_assign_cx.cpp : [ requires cxx14_constexpr ] <toolset>gcc-5:<build>no <toolset>gcc-6:<build>no ;
+compile variant_copy_assign_cx.cpp ;
 
 run variant_move_assign.cpp ;
-compile variant_move_assign_cx.cpp : [ requires cxx14_constexpr ] <toolset>gcc-5:<build>no <toolset>gcc-6:<build>no ;
+compile variant_move_assign_cx.cpp ;
 
 run variant_value_assign.cpp ;
-compile variant_value_assign_cx.cpp : [ requires cxx14_constexpr ] ;
+compile variant_value_assign_cx.cpp ;
 
 run variant_emplace_index.cpp ;
-compile variant_emplace_index_cx.cpp : [ requires cxx14_constexpr ] ;
+compile variant_emplace_index_cx.cpp ;
 
 run variant_emplace_type.cpp ;
-compile variant_emplace_type_cx.cpp : [ requires cxx14_constexpr ] ;
+compile variant_emplace_type_cx.cpp ;
 
 run variant_swap.cpp ;
 
 run variant_eq_ne.cpp ;
-compile variant_eq_ne_cx.cpp : [ requires cxx14_constexpr ] ;
+compile variant_eq_ne_cx.cpp ;
 
 run variant_lt_gt.cpp ;
-compile variant_lt_gt_cx.cpp : [ requires cxx14_constexpr ] ;
+compile variant_lt_gt_cx.cpp ;
 
 run variant_destroy.cpp ;
 run variant_visit.cpp ;
@@ -103,10 +97,10 @@ local NX =
     ;
 
 run variant_get_by_index.cpp throw_exception.cpp : : : $(NX) : variant_get_by_index_nx ;
-compile variant_get_by_index_cx.cpp : $(NX) <toolset>msvc-14.0:<build>no : variant_get_by_index_cx_nx ;
+compile variant_get_by_index_cx.cpp : $(NX) : variant_get_by_index_cx_nx ;
 
 run variant_get_by_type.cpp throw_exception.cpp : : : $(NX) : variant_get_by_type_nx ;
-compile variant_get_by_type_cx.cpp : $(NX) <toolset>msvc-14.0:<build>no : variant_get_by_type_cx_nx ;
+compile variant_get_by_type_cx.cpp : $(NX) : variant_get_by_type_cx_nx ;
 
 run variant_subset.cpp throw_exception.cpp : : : $(NX) : variant_subset_nx ;
 
@@ -117,7 +111,12 @@ run variant_special.cpp ;
 
 run variant_visit_derived.cpp ;
 
-run variant_many_types.cpp ;
+# These two tests require /bigobj under GCC/Windows and CMake/VS2022 (for some reason)
+
+run variant_many_types.cpp : : :
+    <toolset>gcc,<target-os>windows:<variant>release
+    <toolset>gcc,<target-os>cygwin:<variant>release
+    ;
 
 run variant_visit_r.cpp : : :
     <toolset>gcc,<target-os>windows:<variant>release
@@ -131,7 +130,13 @@ run variant_visit_by_index.cpp ;
 run variant_ostream_insert.cpp ;
 run is_output_streamable.cpp ;
 
-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" ;
+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"
+    "<toolset>gcc-4.9:<build>no"
+    ;
 
 run variant_json_value_from.cpp : : : $(JSON) ;
 run variant_json_value_to.cpp : : : $(JSON) ;
@@ -140,9 +145,9 @@ 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 ] ;
+compile variant_visit_cx.cpp ;
+compile variant_visit_cx_2.cpp ;
+compile variant_visit_r_cx.cpp ;
 
 local index-type-reqs =
 
@@ -166,3 +171,12 @@ compile variant_default_construct_cx_5.cpp ;
 compile variant_value_construct_cx_2.cpp ;
 compile variant_value_construct_cx_3.cpp ;
 compile variant_value_construct_cx_4.cpp ;
+
+# GCC 12+ false positive -Wmaybe-uninitialized with non-trivially-copyable types
+run variant_issue_55.cpp
+  : : :
+    <library>/boost/system//boost_system
+
+    # clang-cl 32 bit fails with an assertion in mp_with_index, likely due to a codegen bug
+    "<toolset>clang-win,<address-model>32:<build>no"
+  ;

test/variant_copy_assign_cx.cpp

@@ -1,12 +1,22 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+int main() {}
+
+#elif defined(BOOST_GCC) && BOOST_GCC < 70000
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_GCC < 70000" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -33,26 +43,26 @@ enum E
 
 #define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
 
-template<class V, class T, class A> constexpr T test( A const& a )
+template<class V, std::size_t I, class A> constexpr variant_alternative_t<I, V> test( A const& a )
 {
     V v;
 
     v = a;
 
-    return get<T>(v);
+    return get<I>(v);
 }
 
 int main()
 {
     {
         constexpr variant<int> v( 1 );
-        constexpr auto w = test<variant<int>, int>( v );
+        constexpr auto w = test<variant<int>, 0>( v );
         STATIC_ASSERT( w == 1 );
     }
 
     {
         constexpr variant<X> v( 1 );
-        constexpr auto w = test<variant<X>, X>( v );
+        constexpr auto w = test<variant<X>, 0>( v );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -61,7 +71,7 @@ int main()
 
     {
         constexpr variant<Y> v( 1 );
-        constexpr auto w = test<variant<Y>, Y>( v );
+        constexpr auto w = test<variant<Y>, 0>( v );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -69,31 +79,31 @@ int main()
 
     {
         constexpr variant<int, float> v( 1 );
-        constexpr auto w = test<variant<int, float>, int>( v );
+        constexpr auto w = test<variant<int, float>, 0>( v );
         STATIC_ASSERT( w == 1 );
     }
 
     {
         constexpr variant<int, float> v( 3.0f );
-        constexpr auto w = test<variant<int, float>, float>( v );
+        constexpr auto w = test<variant<int, float>, 1>( v );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
         constexpr variant<int, int, float> v( 3.0f );
-        constexpr auto w = test<variant<int, int, float>, float>( v );
+        constexpr auto w = test<variant<int, int, float>, 2>( v );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
         constexpr variant<E, E, X> v( 1 );
-        constexpr auto w = test<variant<E, E, X>, X>( v );
+        constexpr auto w = test<variant<E, E, X>, 2>( v );
         STATIC_ASSERT( w == 1 );
     }
 
     {
         constexpr variant<int, int, float, float, X> v( X(1) );
-        constexpr auto w = test<variant<int, int, float, float, X>, X>( v );
+        constexpr auto w = test<variant<int, int, float, float, X>, 4>( v );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -102,15 +112,17 @@ int main()
 
     {
         constexpr variant<E, E, Y> v( 1 );
-        constexpr auto w = test<variant<E, E, Y>, Y>( v );
+        constexpr auto w = test<variant<E, E, Y>, 2>( v );
         STATIC_ASSERT( w == 1 );
     }
 
     {
         constexpr variant<int, int, float, float, Y> v( Y(1) );
-        constexpr auto w = test<variant<int, int, float, float, Y>, Y>( v );
+        constexpr auto w = test<variant<int, int, float, float, Y>, 4>( v );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 }
+
+#endif

test/variant_copy_assign_throw.cpp

@@ -45,7 +45,7 @@ void test()
     variant<Y1, Y2> v1( in_place_type_t<Y1>{} );
     variant<Y1, Y2> v2( in_place_type_t<Y2>{} );
 
-    BOOST_TEST_THROWS( v1 = v2, std::runtime_error )
+    BOOST_TEST_THROWS( v1 = v2, std::runtime_error );
 }
 
 int main()

test/variant_copy_construct_cx.cpp

@@ -1,12 +1,17 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1910
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_MSVC < 1910" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -33,22 +38,22 @@ enum E
 
 #define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
 
-template<class T, class V> constexpr T test( V const v )
+template<std::size_t I, class V> constexpr variant_alternative_t<I, V> test( V const v )
 {
-    return get<T>( v );
+    return get<I>( v );
 }
 
 int main()
 {
     {
         constexpr variant<int> v( 1 );
-        constexpr auto w = test<int>( v );
+        constexpr auto w = test<0>( v );
         STATIC_ASSERT( w == 1 );
     }
 
     {
         constexpr variant<X> v( 1 );
-        constexpr auto w = test<X>( v );
+        constexpr auto w = test<0>( v );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -57,7 +62,7 @@ int main()
 
     {
         constexpr variant<Y> v( 1 );
-        constexpr auto w = test<Y>( v );
+        constexpr auto w = test<0>( v );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -65,31 +70,31 @@ int main()
 
     {
         constexpr variant<int, float> v( 1 );
-        constexpr auto w = test<int>( v );
+        constexpr auto w = test<0>( v );
         STATIC_ASSERT( w == 1 );
     }
 
     {
         constexpr variant<int, float> v( 3.0f );
-        constexpr auto w = test<float>( v );
+        constexpr auto w = test<1>( v );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
         constexpr variant<int, int, float> v( 3.0f );
-        constexpr auto w = test<float>( v );
+        constexpr auto w = test<2>( v );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
         constexpr variant<E, E, X> v( 1 );
-        constexpr auto w = test<X>( v );
+        constexpr auto w = test<2>( v );
         STATIC_ASSERT( w == 1 );
     }
 
     {
         constexpr variant<int, int, float, float, X> v( X(1) );
-        constexpr auto w = test<X>( v );
+        constexpr auto w = test<4>( v );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -98,15 +103,17 @@ int main()
 
     {
         constexpr variant<E, E, Y> v( 1 );
-        constexpr auto w = test<Y>( v );
+        constexpr auto w = test<2>( v );
         STATIC_ASSERT( w == 1 );
     }
 
     {
         constexpr variant<int, int, float, float, Y> v( Y(1) );
-        constexpr auto w = test<Y>( v );
+        constexpr auto w = test<4>( v );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 }
+
+#endif

test/variant_default_construct_cx.cpp

@@ -1,12 +1,17 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1910
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_MSVC < 1910" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -49,3 +54,5 @@ int main()
         STATIC_ASSERT( get<0>(v) == 0 );
     }
 }
+
+#endif

test/variant_default_construct_cx_5.cpp

@@ -10,9 +10,9 @@
 BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because __cpp_constexpr_dynamic_alloc < 201907L")
 int main() {}
 
-#elif defined(BOOST_MSVC) && BOOST_MSVC < 1950
+#elif defined(BOOST_MSVC) && BOOST_MSVC < 1960
 
-BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_MSVC < 1950")
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_MSVC < 1960")
 int main() {}
 
 #elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000

test/variant_emplace_index_cx.cpp

@@ -1,12 +1,17 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -134,3 +139,5 @@ int main()
 
 #endif
 }
+
+#endif

test/variant_emplace_type_cx.cpp

@@ -1,12 +1,17 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -28,24 +33,24 @@ struct Y
 
 #define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
 
-template<class V, class T, class A> constexpr A test( A const& a )
+template<class V, std::size_t I, class A, class T = variant_alternative_t<I, V>> constexpr T test( A const& a )
 {
     V v;
 
     v.template emplace<T>( a );
 
-    return get<T>(v);
+    return get<I>(v);
 }
 
 int main()
 {
     {
-        constexpr auto w = test<variant<int>, int>( 1 );
+        constexpr auto w = test<variant<int>, 0>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<X>, X>( 1 );
+        constexpr auto w = test<variant<X>, 0>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -53,29 +58,29 @@ int main()
 #else
 
     {
-        constexpr auto w = test<variant<Y>, Y>( 1 );
+        constexpr auto w = test<variant<Y>, 0>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 
     {
-        constexpr auto w = test<variant<int, float>, int>( 1 );
+        constexpr auto w = test<variant<int, float>, 0>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<int, float>, float>( 3.0f );
+        constexpr auto w = test<variant<int, float>, 1>( 3.0f );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
-        constexpr auto w = test<variant<int, int, float>, float>( 3.0f );
+        constexpr auto w = test<variant<int, int, float>, 2>( 3.0f );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
-        constexpr auto w = test<variant<int, int, float, float, X>, X>( 1 );
+        constexpr auto w = test<variant<int, int, float, float, X>, 4>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -83,9 +88,11 @@ int main()
 #else
 
     {
-        constexpr auto w = test<variant<int, int, float, float, Y>, Y>( 1 );
+        constexpr auto w = test<variant<int, int, float, float, Y>, 4>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 }
+
+#endif

test/variant_eq_ne_cx.cpp

@@ -1,24 +1,26 @@
-
 // Copyright 2017, 2019 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
 
 #include <boost/variant2/variant.hpp>
-using namespace boost::variant2;
-
-#if !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
-
+#include <boost/mp11.hpp>
+#include <boost/config.hpp>
 #include <boost/config/pragma_message.hpp>
 
-BOOST_PRAGMA_MESSAGE("Skipping constexpr op==, op!= test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
 
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+int main() {}
+
+#elif !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr op==, op!= test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
 int main() {}
 
 #else
 
+using namespace boost::variant2;
+
 struct X
 {
 };

test/variant_get_by_index_cx.cpp

@@ -1,13 +1,17 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
 #include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1910
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_MSVC < 1910" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -94,3 +98,5 @@ int main()
         STATIC_ASSERT_IF( get_if<2>(&v) == &get<2>(v) );
     }
 }
+
+#endif

test/variant_get_by_type.cpp

@@ -1,10 +1,6 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #if defined( __clang__ ) && defined( __has_warning )
 # if __has_warning( "-Wdeprecated-volatile" )
@@ -217,6 +213,9 @@ int main()
         BOOST_TEST_EQ( get<int>(v), 0 );
         BOOST_TEST_EQ( get_if<int>(&v), &get<int>(v) );
 
+        BOOST_TEST_THROWS( get<float>(v), bad_variant_access );
+        BOOST_TEST_EQ( get_if<float>(&v), nullptr );
+
         BOOST_TEST_EQ( get<int>(std::move(v)), 0 );
     }
 
@@ -226,6 +225,9 @@ int main()
         BOOST_TEST_EQ( get<int>(v), 0 );
         BOOST_TEST_EQ( get_if<int>(&v), &get<int>(v) );
 
+        BOOST_TEST_THROWS( get<float>(v), bad_variant_access );
+        BOOST_TEST_EQ( get_if<float>(&v), nullptr );
+
         BOOST_TEST_EQ( get<int>(std::move(v)), 0 );
     }
 
@@ -235,6 +237,9 @@ int main()
         BOOST_TEST_EQ( get<int>(v), 1 );
         BOOST_TEST_EQ( get_if<int>(&v), &get<int>(v) );
 
+        BOOST_TEST_THROWS( get<float>(v), bad_variant_access );
+        BOOST_TEST_EQ( get_if<float>(&v), nullptr );
+
         BOOST_TEST_EQ( get<int>(std::move(v)), 1 );
     }
 
@@ -244,12 +249,18 @@ int main()
         BOOST_TEST_EQ( get<int>(v), 1 );
         BOOST_TEST_EQ( get_if<int>(&v), &get<int>(v) );
 
+        BOOST_TEST_THROWS( get<float>(v), bad_variant_access );
+        BOOST_TEST_EQ( get_if<float>(&v), nullptr );
+
         BOOST_TEST_EQ( get<int>(std::move(v)), 1 );
     }
 
     {
         variant<int, int, float> v( 3.14f );
 
+        BOOST_TEST_THROWS( get<int>(v), bad_variant_access );
+        BOOST_TEST_EQ( get_if<int>(&v), nullptr );
+
         BOOST_TEST_EQ( get<float>(v), 3.14f );
         BOOST_TEST_EQ( get_if<float>(&v), &get<float>(v) );
 
@@ -259,6 +270,9 @@ int main()
     {
         variant<int, int, float> const v( 3.14f );
 
+        BOOST_TEST_THROWS( get<int>(v), bad_variant_access );
+        BOOST_TEST_EQ( get_if<int>(&v), nullptr );
+
         BOOST_TEST_EQ( get<float>(v), 3.14f );
         BOOST_TEST_EQ( get_if<float>(&v), &get<float>(v) );
 
@@ -301,11 +315,13 @@ int main()
 
     {
         variant<int, int, float> * p = 0;
+        BOOST_TEST_EQ( get_if<int>(p), nullptr );
         BOOST_TEST_EQ( get_if<float>(p), nullptr );
     }
 
     {
         variant<int, int, float> const * p = 0;
+        BOOST_TEST_EQ( get_if<int>(p), nullptr );
         BOOST_TEST_EQ( get_if<float>(p), nullptr );
     }
 

test/variant_get_by_type_cx.cpp

@@ -1,13 +1,18 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/mp11.hpp>
 #include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE("Test skipped because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -70,6 +75,7 @@ int main()
         STATIC_ASSERT( get<int>(v) == 0 );
 
         STATIC_ASSERT_IF( get_if<int>(&v) == &get<int>(v) );
+        STATIC_ASSERT_IF( get_if<float>(&v) == nullptr );
     }
 
     {
@@ -78,6 +84,7 @@ int main()
         STATIC_ASSERT( get<int>(v) == 1 );
 
         STATIC_ASSERT_IF( get_if<int>(&v) == &get<int>(v) );
+        STATIC_ASSERT_IF( get_if<float>(&v) == nullptr );
     }
 
     {
@@ -85,6 +92,9 @@ int main()
 
         STATIC_ASSERT( get<float>(v) == (float)3.14f );
 
+        STATIC_ASSERT_IF( get_if<int>(&v) == nullptr );
         STATIC_ASSERT_IF( get_if<float>(&v) == &get<float>(v) );
     }
 }
+
+#endif

test/variant_holds_alternative.cpp

@@ -1,10 +1,6 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
@@ -34,13 +30,27 @@ int main()
     {
         variant<int, float, float> v;
         BOOST_TEST( holds_alternative<int>( v ) );
+        BOOST_TEST( !holds_alternative<float>( v ) );
     }
 
     {
         variant<int, int, float> v( 3.14f );
+        BOOST_TEST( !holds_alternative<int>( v ) );
         BOOST_TEST( holds_alternative<float>( v ) );
     }
 
+    {
+        variant<int, int, float> v( in_place_index_t<0>{} );
+        BOOST_TEST( holds_alternative<int>( v ) );
+        BOOST_TEST( !holds_alternative<float>( v ) );
+    }
+
+    {
+        variant<int, int, float> v( in_place_index_t<1>{} );
+        BOOST_TEST( holds_alternative<int>( v ) );
+        BOOST_TEST( !holds_alternative<float>( v ) );
+    }
+
     {
         variant<int, float, std::string> v;
         BOOST_TEST( holds_alternative<int>( v ) );
@@ -64,15 +74,31 @@ int main()
 
     {
         variant<int, int, float, std::string> v( 3.14f );
+        BOOST_TEST( !holds_alternative<int>( v ) );
         BOOST_TEST( holds_alternative<float>( v ) );
         BOOST_TEST( !holds_alternative<std::string>( v ) );
     }
 
     {
         variant<int, int, float, std::string> v( "text" );
+        BOOST_TEST( !holds_alternative<int>( v ) );
         BOOST_TEST( !holds_alternative<float>( v ) );
         BOOST_TEST( holds_alternative<std::string>( v ) );
     }
 
+    {
+        variant<int, int, float, std::string> v( in_place_index_t<0>{} );
+        BOOST_TEST( holds_alternative<int>( v ) );
+        BOOST_TEST( !holds_alternative<float>( v ) );
+        BOOST_TEST( !holds_alternative<std::string>( v ) );
+    }
+
+    {
+        variant<int, int, float, std::string> v( in_place_index_t<1>{} );
+        BOOST_TEST( holds_alternative<int>( v ) );
+        BOOST_TEST( !holds_alternative<float>( v ) );
+        BOOST_TEST( !holds_alternative<std::string>( v ) );
+    }
+
     return boost::report_errors();
 }

test/variant_holds_alternative_cx.cpp

@@ -1,12 +1,17 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1910
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_MSVC < 1910" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -34,10 +39,20 @@ int main()
     {
         constexpr variant<int, float, float> v;
         STATIC_ASSERT( holds_alternative<int>( v ) );
+        STATIC_ASSERT( !holds_alternative<float>( v ) );
     }
 
     {
         constexpr variant<int, int, float> v( 3.14f );
+        STATIC_ASSERT( !holds_alternative<int>( v ) );
         STATIC_ASSERT( holds_alternative<float>( v ) );
     }
+
+    {
+        constexpr variant<int, int, float> v;
+        STATIC_ASSERT( holds_alternative<int>( v ) );
+        STATIC_ASSERT( !holds_alternative<float>( v ) );
+    }
 }
+
+#endif

test/variant_in_place_index_construct_cx.cpp

@@ -1,14 +1,18 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
 #include <boost/config.hpp>
 #include <boost/config/workaround.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1910
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_MSVC < 1910" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -119,3 +123,5 @@ int main()
 
 #endif
 }
+
+#endif

test/variant_in_place_type_construct_cx.cpp

@@ -1,14 +1,18 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
 #include <boost/config.hpp>
 #include <boost/config/workaround.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1910
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_MSVC < 1910" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -118,3 +122,5 @@ int main()
 
 #endif
 }
+
+#endif

test/variant_issue_55.cpp

@@ -0,0 +1,194 @@
+// Copyright 2025 Peter Dimov
+// Copyright 2025 Vinnie Falco
+//
+// 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
+
+// GCC 12+ -Wmaybe-uninitialized false positive tests
+// https://github.com/boostorg/variant2/issues/55
+//
+// GCC 12+'s improved dataflow analysis sees code paths for all alternatives
+// in mp_with_index and warns that members may be uninitialized, even though
+// the variant's discriminator guarantees only initialized alternatives are
+// accessed.
+
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <exception>
+#include <string>
+
+// Check for C++17 std::optional support
+#if BOOST_CXX_VERSION >= 201703L
+# include <optional>
+# define BOOST_VARIANT2_TEST_HAS_OPTIONAL 1
+#endif
+
+// Check for C++20 coroutine support
+#if defined(__cpp_impl_coroutine) && __cpp_impl_coroutine >= 201902L
+# include <coroutine>
+# define BOOST_VARIANT2_TEST_HAS_CORO 1
+#endif
+
+using result_void = boost::system::result<void, std::exception_ptr>;
+using result_string = boost::system::result<std::string, std::exception_ptr>;
+
+void testGccUninitialized()
+{
+    // Test 1: Simple copy construction
+    {
+        result_void r1;
+        result_void r2(r1);
+        (void)r2;
+    }
+
+    // Test 2: Copy assignment
+    {
+        result_void r1;
+        result_void r2;
+        r2 = r1;
+        (void)r2;
+    }
+
+#ifdef BOOST_VARIANT2_TEST_HAS_OPTIONAL
+    // Test 3: std::optional assignment (matches spawn pattern)
+    {
+        std::optional<result_void> opt;
+        opt = result_void{};
+        (void)opt;
+    }
+#endif
+
+    // Test 4: Pass to function via copy
+    {
+        auto fn = [](result_void r) { (void)r; };
+        fn(result_void{});
+    }
+
+#ifdef BOOST_VARIANT2_TEST_HAS_OPTIONAL
+    // Test 5: Lambda capture + optional (closest to spawn)
+    {
+        auto fn = [](result_void r) {
+            std::optional<result_void> opt;
+            opt = r;
+            return opt.has_value();
+        };
+        (void)fn(result_void{});
+    }
+#endif
+
+    // Test 6: Non-void result with string (triggers string warning)
+    {
+        result_string r1;
+        result_string r2(r1);
+        (void)r2;
+    }
+
+    // Test 7: Assign exception to result holding value
+    {
+        result_string r1{"hello"};
+        r1 = std::make_exception_ptr(std::runtime_error("test"));
+        (void)r1;
+    }
+
+#ifdef BOOST_VARIANT2_TEST_HAS_OPTIONAL
+    // Test 8: Optional with string result
+    {
+        std::optional<result_string> opt;
+        opt = result_string{};
+        (void)opt;
+    }
+#endif
+
+#ifdef BOOST_VARIANT2_TEST_HAS_CORO
+    // Minimal fire-and-forget coroutine for testing
+    struct fire_and_forget
+    {
+        struct promise_type
+        {
+            fire_and_forget get_return_object() { return {}; }
+            std::suspend_never initial_suspend() noexcept { return {}; }
+            std::suspend_never final_suspend() noexcept { return {}; }
+            void return_void() {}
+            void unhandled_exception() { std::terminate(); }
+        };
+    };
+
+    // Test 9: Coroutine returning result (mimics spawn)
+    {
+        auto coro = []() -> fire_and_forget {
+            result_void r{};
+            (void)r;
+            co_return;
+        };
+        coro();
+    }
+
+    // Test 10: Coroutine with handler call (closest to actual spawn)
+    {
+        std::optional<result_void> received;
+        auto handler = [&](result_void r) {
+            received = r;
+        };
+        auto coro = [&]() -> fire_and_forget {
+            handler(result_void{});
+            co_return;
+        };
+        coro();
+        (void)received;
+    }
+
+    // Test 11: Coroutine with try/catch like spawn
+    {
+        std::optional<result_void> received;
+        auto handler = [&](result_void r) {
+            received = r;
+        };
+        auto coro = [&]() -> fire_and_forget {
+            try
+            {
+                handler(result_void{});
+            }
+            catch (...)
+            {
+                handler(result_void{std::current_exception()});
+            }
+            co_return;
+        };
+        coro();
+        (void)received;
+    }
+
+    // Test 12: Coroutine with string result
+    {
+        std::optional<result_string> received;
+        auto handler = [&](result_string r) {
+            received = r;
+        };
+        auto coro = [&]() -> fire_and_forget {
+            try
+            {
+                handler(result_string{"test"});
+            }
+            catch (...)
+            {
+                handler(result_string{std::current_exception()});
+            }
+            co_return;
+        };
+        coro();
+        (void)received;
+    }
+#endif
+}
+
+int main()
+{
+    boost::core::lwt_init();
+
+    testGccUninitialized();
+
+    return boost::report_errors();
+}

test/variant_lt_gt_cx.cpp

@@ -1,24 +1,26 @@
-
 // Copyright 2017, 2019 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
 
 #include <boost/variant2/variant.hpp>
-using namespace boost::variant2;
-
-#if !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
-
+#include <boost/mp11.hpp>
+#include <boost/config.hpp>
 #include <boost/config/pragma_message.hpp>
 
-BOOST_PRAGMA_MESSAGE("Skipping constexpr op<, op<= test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
 
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+int main() {}
+
+#elif !defined(BOOST_MP11_HAS_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr op<, op<= test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
 int main() {}
 
 #else
 
+using namespace boost::variant2;
+
 struct X
 {
 };

test/variant_move_assign_cx.cpp

@@ -1,14 +1,24 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
 #include <utility>
 
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+int main() {}
+
+#elif defined(BOOST_GCC) && BOOST_GCC < 70000
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_GCC < 70000" )
+int main() {}
+
+#else
+
 using namespace boost::variant2;
 
 struct X
@@ -34,24 +44,24 @@ enum E
 
 #define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
 
-template<class V, class T, class A> constexpr T test( A&& a )
+template<class V, std::size_t I, class A> constexpr variant_alternative_t<I, V> test( A&& a )
 {
     V v;
 
     v = std::forward<A>(a);
 
-    return get<T>(v);
+    return get<I>(v);
 }
 
 int main()
 {
     {
-        constexpr auto w = test<variant<int>, int>( variant<int>( 1 ) );
+        constexpr auto w = test<variant<int>, 0>( variant<int>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<X>, X>( variant<X>( 1 ) );
+        constexpr auto w = test<variant<X>, 0>( variant<X>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -59,34 +69,34 @@ int main()
 #else
 
     {
-        constexpr auto w = test<variant<Y>, Y>( variant<Y>( 1 ) );
+        constexpr auto w = test<variant<Y>, 0>( variant<Y>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 
     {
-        constexpr auto w = test<variant<int, float>, int>( variant<int, float>( 1 ) );
+        constexpr auto w = test<variant<int, float>, 0>( variant<int, float>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<int, float>, float>( variant<int, float>( 3.0f ) );
+        constexpr auto w = test<variant<int, float>, 1>( variant<int, float>( 3.0f ) );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
-        constexpr auto w = test<variant<int, int, float>, float>( variant<int, int, float>( 3.0f ) );
+        constexpr auto w = test<variant<int, int, float>, 2>( variant<int, int, float>( 3.0f ) );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
-        constexpr auto w = test<variant<E, E, X>, X>( variant<E, E, X>( 1 ) );
+        constexpr auto w = test<variant<E, E, X>, 2>( variant<E, E, X>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<int, int, float, float, X>, X>( variant<int, int, float, float, X>( X(1) ) );
+        constexpr auto w = test<variant<int, int, float, float, X>, 4>( variant<int, int, float, float, X>( X(1) ) );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -94,14 +104,16 @@ int main()
 #else
 
     {
-        constexpr auto w = test<variant<E, E, Y>, Y>( variant<E, E, Y>( 1 ) );
+        constexpr auto w = test<variant<E, E, Y>, 2>( variant<E, E, Y>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<int, int, float, float, Y>, Y>( variant<int, int, float, float, Y>( Y(1) ) );
+        constexpr auto w = test<variant<int, int, float, float, Y>, 4>( variant<int, int, float, float, Y>( Y(1) ) );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 }
+
+#endif

test/variant_move_assign_throw.cpp

@@ -45,7 +45,7 @@ void test()
     variant<Y1, Y2> v1( in_place_type_t<Y1>{} );
     variant<Y1, Y2> v2( in_place_type_t<Y2>{} );
 
-    BOOST_TEST_THROWS( v1 = std::move( v2 ), std::runtime_error )
+    BOOST_TEST_THROWS( v1 = std::move( v2 ), std::runtime_error );
 }
 
 int main()

test/variant_move_construct_cx.cpp

@@ -1,14 +1,19 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
 #include <utility>
 
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+int main() {}
+
+#else
+
 using namespace boost::variant2;
 
 struct X
@@ -34,21 +39,21 @@ enum E
 
 #define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
 
-template<class T, class V> constexpr T test( V&& v )
+template<std::size_t I, class V> constexpr variant_alternative_t<I, V> test( V&& v )
 {
     V v2( std::forward<V>(v) );
-    return get<T>( v2 );
+    return get<I>( v2 );
 }
 
 int main()
 {
     {
-        constexpr auto w = test<int>( variant<int>( 1 ) );
+        constexpr auto w = test<0>( variant<int>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<X>( variant<X>( 1 ) );
+        constexpr auto w = test<0>( variant<X>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -56,34 +61,34 @@ int main()
 #else
 
     {
-        constexpr auto w = test<Y>( variant<Y>( 1 ) );
+        constexpr auto w = test<0>( variant<Y>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 
     {
-        constexpr auto w = test<int>( variant<int, float>( 1 ) );
+        constexpr auto w = test<0>( variant<int, float>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<float>( variant<int, float>( 3.0f ) );
+        constexpr auto w = test<1>( variant<int, float>( 3.0f ) );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
-        constexpr auto w = test<float>( variant<int, int, float>( 3.0f ) );
+        constexpr auto w = test<2>( variant<int, int, float>( 3.0f ) );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
-        constexpr auto w = test<X>( variant<E, E, X>( 1 ) );
+        constexpr auto w = test<2>( variant<E, E, X>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<X>( variant<int, int, float, float, X>( X(1) ) );
+        constexpr auto w = test<4>( variant<int, int, float, float, X>( X(1) ) );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -91,14 +96,16 @@ int main()
 #else
 
     {
-        constexpr auto w = test<Y>( variant<E, E, Y>( 1 ) );
+        constexpr auto w = test<2>( variant<E, E, Y>( 1 ) );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<Y>( variant<int, int, float, float, Y>( Y(1) ) );
+        constexpr auto w = test<4>( variant<int, int, float, float, Y>( Y(1) ) );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 }
+
+#endif

test/variant_value_assign_cx.cpp

@@ -1,12 +1,17 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -33,24 +38,24 @@ enum E
 
 #define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
 
-template<class V, class T, class A> constexpr A test( A const& a )
+template<class V, std::size_t I, class A> constexpr variant_alternative_t<I, V> test( A const& a )
 {
     V v;
 
     v = a;
 
-    return get<T>(v);
+    return get<I>(v);
 }
 
 int main()
 {
     {
-        constexpr auto w = test<variant<int>, int>( 1 );
+        constexpr auto w = test<variant<int>, 0>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<X>, X>( 1 );
+        constexpr auto w = test<variant<X>, 0>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -58,34 +63,34 @@ int main()
 #else
 
     {
-        constexpr auto w = test<variant<Y>, Y>( 1 );
+        constexpr auto w = test<variant<Y>, 0>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 
     {
-        constexpr auto w = test<variant<int, float>, int>( 1 );
+        constexpr auto w = test<variant<int, float>, 0>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<int, float>, float>( 3.0f );
+        constexpr auto w = test<variant<int, float>, 1>( 3.0f );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
-        constexpr auto w = test<variant<int, int, float>, float>( 3.0f );
+        constexpr auto w = test<variant<int, int, float>, 2>( 3.0f );
         STATIC_ASSERT( w == 3.0f );
     }
 
     {
-        constexpr auto w = test<variant<E, E, X>, X>( 1 );
+        constexpr auto w = test<variant<E, E, X>, 2>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<int, int, float, float, X>, X>( X(1) );
+        constexpr auto w = test<variant<int, int, float, float, X>, 4>( X(1) );
         STATIC_ASSERT( w == 1 );
     }
 
@@ -93,14 +98,16 @@ int main()
 #else
 
     {
-        constexpr auto w = test<variant<E, E, Y>, Y>( 1 );
+        constexpr auto w = test<variant<E, E, Y>, 2>( 1 );
         STATIC_ASSERT( w == 1 );
     }
 
     {
-        constexpr auto w = test<variant<int, int, float, float, Y>, Y>( Y(1) );
+        constexpr auto w = test<variant<int, int, float, float, Y>, 4>( Y(1) );
         STATIC_ASSERT( w == 1 );
     }
 
 #endif
 }
+
+#endif

test/variant_value_construct_cx.cpp

@@ -1,12 +1,17 @@
-
-// Copyright 2017 Peter Dimov.
-//
+// Copyright 2017, 2026 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
 
 #include <boost/variant2/variant.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if defined(BOOST_MSVC) && BOOST_MSVC < 1910
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_MSVC < 1910" )
+int main() {}
+
+#else
 
 using namespace boost::variant2;
 
@@ -107,3 +112,5 @@ int main()
         STATIC_ASSERT( holds_alternative<X>(v) );
     }
 }
+
+#endif

test/variant_value_construct_cx_4.cpp

@@ -10,9 +10,9 @@
 BOOST_PRAGMA_MESSAGE("Skipping test because __cpp_constexpr_dynamic_alloc < 201907L")
 int main() {}
 
-#elif defined(BOOST_MSVC) && BOOST_MSVC < 1950
+#elif defined(BOOST_MSVC) && BOOST_MSVC < 1960
 
-BOOST_PRAGMA_MESSAGE("Skipping test because BOOST_MSVC < 1950")
+BOOST_PRAGMA_MESSAGE("Skipping test because BOOST_MSVC < 1960")
 int main() {}
 
 #elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000

test/variant_visit_cx.cpp

@@ -1,20 +1,26 @@
-// Copyright 2017, 2024 Peter Dimov
+// Copyright 2017, 2024, 2026 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/mp11.hpp>
+#include <boost/config.hpp>
 #include <boost/config/pragma_message.hpp>
 
-BOOST_PRAGMA_MESSAGE("Skipping constexpr visit test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
 
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+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 X
 {
     constexpr operator int() const { return 2; }

test/variant_visit_r_cx.cpp

@@ -1,20 +1,26 @@
-// Copyright 2017, 2024 Peter Dimov
+// Copyright 2017, 2024, 2026 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/mp11.hpp>
+#include <boost/config.hpp>
 #include <boost/config/pragma_message.hpp>
 
-BOOST_PRAGMA_MESSAGE("Skipping constexpr visit test because BOOST_MP11_HAS_CXX14_CONSTEXPR is not defined")
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
 
+BOOST_PRAGMA_MESSAGE( "Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined" )
+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 X
 {
     int v;