Correct CMake version check; VERSION_GREATER 3.18 is true for 3.18.1

.github/workflows/ci.yml

@@ -43,22 +43,27 @@ jobs:
             os: ubuntu-latest
           - toolset: gcc-8
             cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
             install: g++-8
           - toolset: gcc-9
             cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
           - toolset: gcc-10
             cxxstd: "11,14,17,2a"
-            os: ubuntu-22.04
+            container: ubuntu:22.04
+            os: ubuntu-latest
             install: g++-10
           - toolset: gcc-11
             cxxstd: "11,14,17,2a"
-            os: ubuntu-22.04
+            container: ubuntu:22.04
+            os: ubuntu-latest
             install: g++-11
           - toolset: gcc-12
             cxxstd: "11,14,17,20,2b"
-            os: ubuntu-22.04
+            container: ubuntu:22.04
+            os: ubuntu-latest
             install: g++-12
           - toolset: gcc-13
             cxxstd: "11,14,17,20,2b"
@@ -70,6 +75,11 @@ jobs:
             container: ubuntu:24.04
             os: ubuntu-latest
             install: g++-14
+          - toolset: gcc-15
+            cxxstd: "11,14,17,20,23,2c"
+            container: ubuntu:25.04
+            os: ubuntu-latest
+            install: g++-15
           - toolset: clang
             compiler: clang++-3.9
             cxxstd: "11,14"
@@ -91,37 +101,44 @@ jobs:
           - toolset: clang
             compiler: clang++-6.0
             cxxstd: "11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
             install: clang-6.0
           - toolset: clang
             compiler: clang++-7
             cxxstd: "11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
             install: clang-7
           - toolset: clang
             compiler: clang++-8
             cxxstd: "11,14,17"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
             install: clang-8
           - toolset: clang
             compiler: clang++-9
             cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
             install: clang-9
           - toolset: clang
             compiler: clang++-10
             cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
             install: clang-10
           - toolset: clang
             compiler: clang++-11
             cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
             install: clang-11
           - toolset: clang
             compiler: clang++-12
             cxxstd: "11,14,17,2a"
-            os: ubuntu-20.04
+            container: ubuntu:20.04
+            os: ubuntu-latest
             install: clang-12
           - toolset: clang
             compiler: clang++-13
@@ -162,9 +179,15 @@ jobs:
           - toolset: clang
             compiler: clang++-19
             cxxstd: "11,14,17,20,2b"
-            container: ubuntu:24.10
+            container: ubuntu:24.04
             os: ubuntu-latest
             install: clang-19
+          - toolset: clang
+            compiler: clang++-20
+            cxxstd: "11,14,17,20,23,2c"
+            container: ubuntu:25.04
+            os: ubuntu-latest
+            install: clang-20
           - toolset: clang
             cxxstd: "11,14,17,20,2b"
             os: macos-13
@@ -246,14 +269,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - toolset: msvc-14.0
-            cxxstd: "14,latest"
-            addrmd: 32,64
-            os: windows-2019
-          - toolset: msvc-14.2
-            cxxstd: "14,17,20,latest"
-            addrmd: 32,64
-            os: windows-2019
           - toolset: msvc-14.3
             cxxstd: "14,17,20,latest"
             addrmd: 32,64
@@ -265,7 +280,7 @@ jobs:
           - toolset: gcc
             cxxstd: "11,14,17,2a"
             addrmd: 64
-            os: windows-2019
+            os: windows-2022
 
     runs-on: ${{matrix.os}}
 
@@ -305,7 +320,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-20.04
           - os: ubuntu-22.04
           - os: ubuntu-24.04
           - os: macos-13
@@ -354,7 +368,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-20.04
           - os: ubuntu-22.04
           - os: ubuntu-24.04
           - os: macos-13
@@ -413,7 +426,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-20.04
           - os: ubuntu-22.04
           - os: ubuntu-24.04
           - os: macos-13
@@ -470,8 +482,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: windows-2019
-          - os: windows-2022
+          - os: windows-latest
 
     runs-on: ${{matrix.os}}
 
@@ -519,8 +530,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: windows-2019
-          - os: windows-2022
+          - os: windows-latest
 
     runs-on: ${{matrix.os}}
 
@@ -586,8 +596,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: windows-2019
-          - os: windows-2022
+          - os: windows-latest
 
     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")

include/boost/variant2/variant.hpp

@@ -30,6 +30,15 @@
 
 //
 
+// constexpr destructors
+#if defined(__cpp_constexpr_dynamic_alloc) && __cpp_constexpr_dynamic_alloc >= 201907L
+# define BOOST_VARIANT2_CXX20_CONSTEXPR constexpr
+#else
+# define BOOST_VARIANT2_CXX20_CONSTEXPR
+#endif
+
+//
+
 namespace boost
 {
 
@@ -557,16 +566,16 @@ template<class T1, class... T> union variant_storage_impl<mp11::mp_false, T1, T.
     {
     }
 
-    ~variant_storage_impl()
+    BOOST_VARIANT2_CXX20_CONSTEXPR ~variant_storage_impl()
     {
     }
 
-    template<class... A> void emplace( mp11::mp_size_t<0>, A&&... a )
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<0>, A&&... a )
     {
         ::new( &first_ ) T1( std::forward<A>(a)... );
     }
 
-    template<std::size_t I, class... A> void emplace( mp11::mp_size_t<I>, A&&... a )
+    template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<I>, A&&... a )
     {
         rest_.emplace( mp11::mp_size_t<I-1>(), std::forward<A>(a)... );
     }
@@ -606,22 +615,22 @@ template<class T0, class T1, class T2, class T3, class T4, class T5, class T6, c
 
     template<std::size_t I, class... A> constexpr variant_storage_impl( mp11::mp_size_t<I>, A&&... a ): rest_( mp11::mp_size_t<I-10>(), std::forward<A>(a)... ) {}
 
-    ~variant_storage_impl()
+    BOOST_VARIANT2_CXX20_CONSTEXPR ~variant_storage_impl()
     {
     }
 
-    template<class... A> void emplace( mp11::mp_size_t<0>, A&&... a ) { ::new( &t0_ ) T0( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<1>, A&&... a ) { ::new( &t1_ ) T1( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<2>, A&&... a ) { ::new( &t2_ ) T2( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<3>, A&&... a ) { ::new( &t3_ ) T3( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<4>, A&&... a ) { ::new( &t4_ ) T4( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<5>, A&&... a ) { ::new( &t5_ ) T5( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<6>, A&&... a ) { ::new( &t6_ ) T6( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<7>, A&&... a ) { ::new( &t7_ ) T7( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<8>, A&&... a ) { ::new( &t8_ ) T8( std::forward<A>(a)... ); }
-    template<class... A> void emplace( mp11::mp_size_t<9>, A&&... a ) { ::new( &t9_ ) T9( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<0>, A&&... a ) { ::new( &t0_ ) T0( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<1>, A&&... a ) { ::new( &t1_ ) T1( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<2>, A&&... a ) { ::new( &t2_ ) T2( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<3>, A&&... a ) { ::new( &t3_ ) T3( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<4>, A&&... a ) { ::new( &t4_ ) T4( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<5>, A&&... a ) { ::new( &t5_ ) T5( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<6>, A&&... a ) { ::new( &t6_ ) T6( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<7>, A&&... a ) { ::new( &t7_ ) T7( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<8>, A&&... a ) { ::new( &t8_ ) T8( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<9>, A&&... a ) { ::new( &t9_ ) T9( std::forward<A>(a)... ); }
 
-    template<std::size_t I, class... A> void emplace( mp11::mp_size_t<I>, A&&... a )
+    template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( mp11::mp_size_t<I>, A&&... a )
     {
         rest_.emplace( mp11::mp_size_t<I-10>(), std::forward<A>(a)... );
     }
@@ -674,7 +683,7 @@ template<class T1, class... T> union variant_storage_impl<mp11::mp_true, T1, T..
     {
     }
 
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<0>, A&&... a )
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<0>, A&&... a )
     {
         ::new( &first_ ) T1( std::forward<A>(a)... );
     }
@@ -742,16 +751,16 @@ template<class T0, class T1, class T2, class T3, class T4, class T5, class T6, c
 
     template<std::size_t I, class... A> constexpr variant_storage_impl( mp11::mp_size_t<I>, A&&... a ): rest_( mp11::mp_size_t<I-10>(), std::forward<A>(a)... ) {}
 
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<0>, A&&... a ) { ::new( &t0_ ) T0( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<1>, A&&... a ) { ::new( &t1_ ) T1( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<2>, A&&... a ) { ::new( &t2_ ) T2( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<3>, A&&... a ) { ::new( &t3_ ) T3( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<4>, A&&... a ) { ::new( &t4_ ) T4( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<5>, A&&... a ) { ::new( &t5_ ) T5( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<6>, A&&... a ) { ::new( &t6_ ) T6( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<7>, A&&... a ) { ::new( &t7_ ) T7( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<8>, A&&... a ) { ::new( &t8_ ) T8( std::forward<A>(a)... ); }
-    template<class... A> void emplace_impl( mp11::mp_false, mp11::mp_size_t<9>, A&&... a ) { ::new( &t9_ ) T9( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<0>, A&&... a ) { ::new( &t0_ ) T0( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<1>, A&&... a ) { ::new( &t1_ ) T1( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<2>, A&&... a ) { ::new( &t2_ ) T2( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<3>, A&&... a ) { ::new( &t3_ ) T3( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<4>, A&&... a ) { ::new( &t4_ ) T4( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<5>, A&&... a ) { ::new( &t5_ ) T5( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<6>, A&&... a ) { ::new( &t6_ ) T6( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<7>, A&&... a ) { ::new( &t7_ ) T7( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<8>, A&&... a ) { ::new( &t8_ ) T8( std::forward<A>(a)... ); }
+    template<class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<9>, A&&... a ) { ::new( &t9_ ) T9( std::forward<A>(a)... ); }
 
     template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_size_t<I>, A&&... a )
     {
@@ -890,7 +899,7 @@ template<class... T> struct variant_base_impl<true, true, T...>
     }
 
     // requires: ix_ == 0
-    template<class I, class... A> void _replace( I, A&&... a )
+    template<class I, class... A> BOOST_CXX14_CONSTEXPR void _replace( I, A&&... a )
     {
         ::new( &st_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
 
@@ -974,7 +983,7 @@ template<class... T> struct variant_base_impl<true, false, T...>
     }
 
     // requires: ix_ == 0
-    template<class I, class... A> void _replace( I, A&&... a )
+    template<class I, class... A> BOOST_CXX14_CONSTEXPR void _replace( I, A&&... a )
     {
         ::new( &st_[ 0 ] ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
 
@@ -1042,7 +1051,7 @@ template<class... T> struct variant_base_impl<false, true, T...>
     }
 
     // requires: ix_ == 0
-    template<class I, class... A> void _replace( I, A&&... a )
+    template<class I, class... A> BOOST_CXX14_CONSTEXPR void _replace( I, A&&... a )
     {
         ::new( &st_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
 
@@ -1059,14 +1068,14 @@ template<class... T> struct variant_base_impl<false, true, T...>
     {
         variant_base_impl * this_;
 
-        template<class I> void operator()( I ) const noexcept
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I ) const noexcept
         {
             using U = mp11::mp_at<mp11::mp_list<none, T...>, I>;
             this_->st_.get( I() ).~U();
         }
     };
 
-    void _destroy() noexcept
+    BOOST_CXX14_CONSTEXPR void _destroy() noexcept
     {
         if( ix_ > 0 )
         {
@@ -1074,7 +1083,7 @@ template<class... T> struct variant_base_impl<false, true, T...>
         }
     }
 
-    ~variant_base_impl() noexcept
+    BOOST_VARIANT2_CXX20_CONSTEXPR ~variant_base_impl() noexcept
     {
         _destroy();
     }
@@ -1102,7 +1111,7 @@ template<class... T> struct variant_base_impl<false, true, T...>
         return st_.get( mp11::mp_size_t<I+1>() );
     }
 
-    template<std::size_t I, class... A> void emplace( A&&... a )
+    template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( A&&... a )
     {
         std::size_t const J = I+1;
 
@@ -1182,7 +1191,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
 #endif
 
     // requires: ix_ == 0
-    template<class I, class... A> void _replace( I, A&&... a )
+    template<class I, class... A> BOOST_CXX14_CONSTEXPR void _replace( I, A&&... a )
     {
         ::new( &storage( 0 ) ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
 
@@ -1200,19 +1209,19 @@ template<class... T> struct variant_base_impl<false, false, T...>
         variant_base_impl * this_;
         unsigned i2_;
 
-        template<class I> void operator()( I ) const noexcept
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I ) const noexcept
         {
             using U = mp11::mp_at<mp11::mp_list<none, T...>, I>;
             this_->storage( i2_ ).get( I() ).~U();
         }
     };
 
-    void _destroy() noexcept
+    BOOST_CXX14_CONSTEXPR void _destroy() noexcept
     {
         mp11::mp_with_index<1 + sizeof...(T)>( ix_ / 2, _destroy_L1{ this, static_cast<unsigned>( ix_ & 1 ) } );
     }
 
-    ~variant_base_impl() noexcept
+    BOOST_VARIANT2_CXX20_CONSTEXPR ~variant_base_impl() noexcept
     {
         _destroy();
     }
@@ -1242,7 +1251,7 @@ template<class... T> struct variant_base_impl<false, false, T...>
         return storage( ix_ & 1 ).get( mp11::mp_size_t<I+1>() );
     }
 
-    template<std::size_t I, class... A> void emplace( A&&... a )
+    template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( A&&... a )
     {
         std::size_t const J = I+1;
 
@@ -1403,7 +1412,7 @@ private:
         variant_base * this_;
         variant_base const & r;
 
-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
         {
             this_->_replace( i, r._get_impl( i ) );
         }
@@ -1411,7 +1420,7 @@ private:
 
 public:
 
-    variant_cc_base_impl( variant_cc_base_impl const& r )
+    BOOST_CXX14_CONSTEXPR variant_cc_base_impl( variant_cc_base_impl const& r )
         noexcept( mp11::mp_all<std::is_nothrow_copy_constructible<T>...>::value )
         : variant_base()
     {
@@ -1483,7 +1492,7 @@ private:
         variant_base * this_;
         variant_base const & r;
 
-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
         {
             this_->template emplace<I::value>( r._get_impl( i ) );
         }
@@ -1557,7 +1566,7 @@ private:
         variant_base * this_;
         variant_base & r;
 
-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
         {
             this_->_replace( i, std::move( r._get_impl( i ) ) );
         }
@@ -1565,7 +1574,7 @@ private:
 
 public:
 
-    variant_mc_base_impl( variant_mc_base_impl && r )
+    BOOST_CXX14_CONSTEXPR variant_mc_base_impl( variant_mc_base_impl && r )
         noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>...>::value )
     {
         mp11::mp_with_index<sizeof...(T)>( r.index(), L2{ this, r } );
@@ -1636,7 +1645,7 @@ private:
         variant_base * this_;
         variant_base & r;
 
-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
         {
             this_->template emplace<I::value>( std::move( r._get_impl( i ) ) );
         }
@@ -1644,7 +1653,7 @@ private:
 
 public:
 
-    variant_ma_base_impl& operator=( variant_ma_base_impl && r )
+    BOOST_CXX14_CONSTEXPR variant_ma_base_impl& operator=( variant_ma_base_impl && r )
         noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>...>::value )
     {
         mp11::mp_with_index<sizeof...(T)>( r.index(), L4{ this, r } );
@@ -1790,7 +1799,7 @@ private:
         variant * this_;
         variant & r;
 
-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
         {
             using std::swap;
             swap( this_->_get_impl( i ), r._get_impl( i ) );
@@ -1799,7 +1808,7 @@ private:
 
 public:
 
-    void swap( variant& r ) noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>..., detail::is_nothrow_swappable<T>...>::value )
+    BOOST_CXX14_CONSTEXPR void swap( variant& r ) noexcept( mp11::mp_all<std::is_nothrow_move_constructible<T>..., detail::is_nothrow_swappable<T>...>::value )
     {
         if( index() == r.index() )
         {
@@ -1826,7 +1835,7 @@ private:
         variant_base * this_;
         variant<U...> const & r;
 
-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
         {
             using J = mp11::mp_find<mp11::mp_list<T...>, mp11::mp_at<mp11::mp_list<U...>, I>>;
             this_->_replace( J{}, r._get_impl( i ) );
@@ -1837,7 +1846,7 @@ public:
 
     template<class... U,
         class E2 = mp11::mp_if<mp11::mp_all<std::is_copy_constructible<U>..., mp11::mp_contains<mp11::mp_list<T...>, U>...>, void> >
-    variant( variant<U...> const& r )
+    BOOST_CXX14_CONSTEXPR variant( variant<U...> const& r )
         noexcept( mp11::mp_all<std::is_nothrow_copy_constructible<U>...>::value )
     {
         mp11::mp_with_index<sizeof...(U)>( r.index(), L6<U...>{ this, r } );
@@ -1850,7 +1859,7 @@ private:
         variant_base * this_;
         variant<U...> & r;
 
-        template<class I> void operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR void operator()( I i ) const
         {
             using J = mp11::mp_find<mp11::mp_list<T...>, mp11::mp_at<mp11::mp_list<U...>, I>>;
             this_->_replace( J{}, std::move( r._get_impl( i ) ) );
@@ -1861,7 +1870,7 @@ public:
 
     template<class... U,
         class E2 = mp11::mp_if<mp11::mp_all<std::is_move_constructible<U>..., mp11::mp_contains<mp11::mp_list<T...>, U>...>, void> >
-    variant( variant<U...> && r )
+    BOOST_CXX14_CONSTEXPR variant( variant<U...> && r )
         noexcept( mp11::mp_all<std::is_nothrow_move_constructible<U>...>::value )
     {
         mp11::mp_with_index<sizeof...(U)>( r.index(), L7<U...>{ this, r } );
@@ -1887,7 +1896,7 @@ private:
     {
         variant * this_;
 
-        template<class I> variant<U...> operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR variant<U...> operator()( I i ) const
         {
             using J = mp11::mp_find<mp11::mp_list<U...>, mp11::mp_at<mp11::mp_list<T...>, I>>;
             return this_->_subset_impl<U...>( J{}, this_->_get_impl( i ) );
@@ -1909,7 +1918,7 @@ private:
     {
         variant const * this_;
 
-        template<class I> variant<U...> operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR variant<U...> operator()( I i ) const
         {
             using J = mp11::mp_find<mp11::mp_list<U...>, mp11::mp_at<mp11::mp_list<T...>, I>>;
             return this_->_subset_impl<U...>( J{}, this_->_get_impl( i ) );
@@ -1931,7 +1940,7 @@ private:
     {
         variant * this_;
 
-        template<class I> variant<U...> operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR variant<U...> operator()( I i ) const
         {
             using J = mp11::mp_find<mp11::mp_list<U...>, mp11::mp_at<mp11::mp_list<T...>, I>>;
             return this_->_subset_impl<U...>( J{}, std::move( this_->_get_impl( i ) ) );
@@ -1957,7 +1966,7 @@ private:
     {
         variant const * this_;
 
-        template<class I> variant<U...> operator()( I i ) const
+        template<class I> BOOST_CXX14_CONSTEXPR variant<U...> operator()( I i ) const
         {
             using J = mp11::mp_find<mp11::mp_list<U...>, mp11::mp_at<mp11::mp_list<T...>, I>>;
             return this_->_subset_impl<U...>( J{}, std::move( this_->_get_impl( i ) ) );
@@ -2293,7 +2302,7 @@ template<class R = detail::deduced, class F, class V1, class V2, class... V> con
 // specialized algorithms
 template<class... T,
     class E = typename std::enable_if<mp11::mp_all<std::is_move_constructible<T>..., detail::is_swappable<T>...>::value>::type>
-void swap( variant<T...> & v, variant<T...> & w )
+BOOST_CXX14_CONSTEXPR void swap( variant<T...> & v, variant<T...> & w )
     noexcept( noexcept(v.swap(w)) )
 {
     v.swap( w );

test/Jamfile

@@ -157,3 +157,12 @@ 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) ;
 }
+
+compile variant_default_construct_cx_2.cpp ;
+compile variant_default_construct_cx_3.cpp ;
+compile variant_default_construct_cx_4.cpp ;
+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 ;

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_default_construct_cx_2.cpp

@@ -0,0 +1,32 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+    constexpr ~X() {}
+};
+
+int main()
+{
+    constexpr variant<int, X> v;
+
+    STATIC_ASSERT( v.index() == 0 );
+    STATIC_ASSERT( get<0>(v) == 0 );
+}
+
+#endif

test/variant_default_construct_cx_3.cpp

@@ -0,0 +1,37 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+	~X() {}
+};
+
+int main()
+{
+    constexpr variant<int, X> v;
+
+    STATIC_ASSERT( v.index() == 0 );
+    STATIC_ASSERT( get<0>(v) == 0 );
+}
+
+#endif

test/variant_default_construct_cx_4.cpp

@@ -0,0 +1,33 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <string>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+int main()
+{
+    constexpr variant<int, std::string> v;
+
+    STATIC_ASSERT( v.index() == 0 );
+    STATIC_ASSERT( get<0>(v) == 0 );
+}
+
+#endif

test/variant_default_construct_cx_5.cpp

@@ -0,0 +1,49 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_MSVC) && BOOST_MSVC < 1950
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_MSVC < 1950")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr destructor test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+};
+
+struct Y
+{
+    constexpr ~Y() {}
+};
+
+struct Z
+{
+    ~Z() {}
+};
+
+int main()
+{
+    constexpr variant<X, Y, Z> v;
+    STATIC_ASSERT( v.index() == 0 );
+}
+
+#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_value_construct_cx_2.cpp

@@ -0,0 +1,32 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+    constexpr ~X() {}
+};
+
+int main()
+{
+    constexpr variant<X, int> v( 5 );
+
+    STATIC_ASSERT( v.index() == 1 );
+    STATIC_ASSERT( get<1>(v) == 5 );
+}
+
+#endif

test/variant_value_construct_cx_3.cpp

@@ -0,0 +1,37 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+	~X() {}
+};
+
+int main()
+{
+    constexpr variant<X, int> v( 5 );
+
+    STATIC_ASSERT( v.index() == 1 );
+    STATIC_ASSERT( get<1>(v) == 5 );
+}
+
+#endif

test/variant_value_construct_cx_4.cpp

@@ -0,0 +1,56 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/variant2/variant.hpp>
+#include <boost/config/pragma_message.hpp>
+
+#if !defined(__cpp_constexpr_dynamic_alloc) || __cpp_constexpr_dynamic_alloc < 201907L
+
+BOOST_PRAGMA_MESSAGE("Skipping test because __cpp_constexpr_dynamic_alloc < 201907L")
+int main() {}
+
+#elif defined(BOOST_MSVC) && BOOST_MSVC < 1950
+
+BOOST_PRAGMA_MESSAGE("Skipping test because BOOST_MSVC < 1950")
+int main() {}
+
+#elif defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 180000
+
+BOOST_PRAGMA_MESSAGE("Skipping test because BOOST_CLANG_VERSION < 180000")
+int main() {}
+
+#else
+
+using namespace boost::variant2;
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+struct X
+{
+};
+
+struct Y
+{
+    constexpr ~Y() {}
+};
+
+struct Z
+{
+    ~Z() {}
+};
+
+int main()
+{
+    {
+        constexpr variant<X, Y, Z> v( X{} );
+        STATIC_ASSERT( v.index() == 0 );
+    }
+
+    {
+        constexpr variant<X, Y, Z> v( Y{} );
+        STATIC_ASSERT( v.index() == 1 );
+    }
+}
+
+#endif