constexpr the copy/move constructors; change copy/move assign to not require constexpr lambdas

include/boost/variant2/variant.hpp

@@ -868,8 +868,19 @@ public:
     {
     }
 
-    template<class E1 = void, class E2 = mp_if<mp_all<std::is_copy_constructible<T>...>, E1>>
-    constexpr variant( variant const& r )
+    template<class E1 = void,
+        class E2 = mp_if<mp_all<std::is_trivially_copy_constructible<T>...>, E1>
+    >
+    constexpr variant( variant const& r ) noexcept
+        : variant_base( static_cast<variant_base const&>(r) )
+    {
+    }
+
+    template<class E1 = void,
+        class E2 = mp_if<mp_not<mp_all<std::is_trivially_copy_constructible<T>...>>, E1>,
+        class E3 = mp_if<mp_all<std::is_copy_constructible<T>...>, E1>
+    >
+    variant( variant const& r )
         noexcept( mp_all<std::is_nothrow_copy_constructible<T>...>::value )
     {
         mp_with_index<sizeof...(T)>( r.index(), [&]( auto I ){
@@ -879,8 +890,19 @@ public:
         });
     }
 
-    template<class E1 = void, class E2 = mp_if<mp_all<std::is_move_constructible<T>...>, E1>>
-    constexpr variant( variant && r )
+    template<class E1 = void,
+        class E2 = mp_if<mp_all<std::is_trivially_move_constructible<T>...>, E1>
+    >
+    constexpr variant( variant && r ) noexcept
+        : variant_base( static_cast<variant_base&&>(r) )
+    {
+    }
+
+    template<class E1 = void,
+        class E2 = mp_if<mp_not<mp_all<std::is_trivially_move_constructible<T>...>>, E1>,
+        class E3 = mp_if<mp_all<std::is_move_constructible<T>...>, E1>
+    >
+    variant( variant && r )
         noexcept( mp_all<std::is_nothrow_move_constructible<T>...>::value )
     {
         mp_with_index<sizeof...(T)>( r.index(), [&]( auto I ){
@@ -923,7 +945,19 @@ public:
     }
 
     // assignment
-    template<class E1 = void, class E2 = mp_if<mp_all<std::is_copy_constructible<T>..., std::is_copy_assignable<T>...>, E1>>
+    template<class E1 = void,
+        class E2 = mp_if<mp_all<std::is_trivially_destructible<T>..., std::is_trivially_copy_assignable<T>...>, E1>
+    >
+    constexpr variant& operator=( variant const & r ) noexcept
+    {
+        static_cast<variant_base&>( *this ) = static_cast<variant_base const&>( r );
+        return *this;
+    }
+
+    template<class E1 = void,
+        class E2 = mp_if<mp_not<mp_all<std::is_trivially_destructible<T>..., std::is_trivially_copy_assignable<T>...>>, E1>,
+        class E3 = mp_if<mp_all<std::is_copy_constructible<T>..., std::is_copy_assignable<T>...>, E1>
+    >
     constexpr variant& operator=( variant const & r )
         noexcept( mp_all<std::is_nothrow_copy_constructible<T>..., std::is_nothrow_copy_assignable<T>...>::value )
     {
@@ -943,8 +977,20 @@ public:
         return *this;
     }
 
-    template<class E1 = void, class E2 = mp_if<mp_all<std::is_move_constructible<T>..., std::is_move_assignable<T>...>, E1>>
-    constexpr variant& operator=( variant && r )
+    template<class E1 = void,
+        class E2 = mp_if<mp_all<std::is_trivially_destructible<T>..., std::is_trivially_move_assignable<T>...>, E1>
+    >
+    constexpr variant& operator=( variant && r ) noexcept
+    {
+        static_cast<variant_base&>( *this ) = static_cast<variant_base&&>( r );
+        return *this;
+    }
+
+    template<class E1 = void,
+        class E2 = mp_if<mp_not<mp_all<std::is_trivially_destructible<T>..., std::is_trivially_move_assignable<T>...>>, E1>,
+        class E3 = mp_if<mp_all<std::is_move_constructible<T>..., std::is_move_assignable<T>...>, E1>
+    >
+    variant& operator=( variant && r )
         noexcept( mp_all<std::is_nothrow_move_constructible<T>..., std::is_nothrow_move_assignable<T>...>::value )
     {
         mp_with_index<sizeof...(T)>( r.index(), [&]( auto I ){

test/Jamfile

@@ -27,7 +27,10 @@ run variant_default_construct.cpp : : : $(REQ) ;
 compile variant_default_construct_cx.cpp : : : $(REQ) ;
 
 run variant_copy_construct.cpp : : : $(REQ) ;
+compile variant_copy_construct_cx.cpp : : : $(REQ) ;
+
 run variant_move_construct.cpp : : : $(REQ) ;
+compile variant_move_construct_cx.cpp : : : $(REQ) ;
 
 run variant_value_construct.cpp : : : $(REQ) ;
 compile variant_value_construct_cx.cpp : : : $(REQ) ;

test/variant_copy_assign_cx.cpp

@@ -6,13 +6,6 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
-#if !defined( __cpp_constexpr ) || __cpp_constexpr < 201603
-
-// no constexpr lambda support
-int main() {}
-
-#else
-
 #include <boost/variant2/variant.hpp>
 
 using namespace boost::variant2;
@@ -121,5 +114,3 @@ int main()
 
 #endif
 }
-
-#endif // constexpr lambda support

test/variant_copy_construct_cx.cpp

@@ -0,0 +1,122 @@
+
+// Copyright 2017 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
+
+#if !defined( __cpp_constexpr ) || __cpp_constexpr < 201603
+
+// no constexpr lambda support
+int main() {}
+
+#else
+
+#include <boost/variant2/variant.hpp>
+
+using namespace boost::variant2;
+
+struct X
+{
+    int v;
+    X() = default;
+    constexpr X( int v ): v( v ) {}
+    constexpr operator int() const { return v; }
+};
+
+struct Y
+{
+    int v;
+    constexpr Y(): v() {}
+    constexpr Y( int v ): v( v ) {}
+    constexpr operator int() const { return v; }
+};
+
+enum E
+{
+    v
+};
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+template<class T, class V> constexpr T test( V const& v )
+{
+    V v2( v );
+    return get<T>(v);
+}
+
+int main()
+{
+    {
+        constexpr variant<int> v( 1 );
+        constexpr auto w = test<int>( v );
+        STATIC_ASSERT( w == 1 );
+    }
+
+    {
+        constexpr variant<X> v( 1 );
+        constexpr auto w = test<X>( v );
+        STATIC_ASSERT( w == 1 );
+    }
+
+#if defined( BOOST_LIBSTDCXX_VERSION ) && BOOST_LIBSTDCXX_VERSION < 50000
+#else
+
+    {
+        constexpr variant<Y> v( 1 );
+        constexpr auto w = test<Y>( v );
+        STATIC_ASSERT( w == 1 );
+    }
+
+#endif
+
+    {
+        constexpr variant<int, float> v( 1 );
+        constexpr auto w = test<int>( v );
+        STATIC_ASSERT( w == 1 );
+    }
+
+    {
+        constexpr variant<int, float> v( 3.0f );
+        constexpr auto w = test<float>( v );
+        STATIC_ASSERT( w == 3.0f );
+    }
+
+    {
+        constexpr variant<int, int, float> v( 3.0f );
+        constexpr auto w = test<float>( v );
+        STATIC_ASSERT( w == 3.0f );
+    }
+
+    {
+        constexpr variant<E, E, X> v( 1 );
+        constexpr auto w = test<X>( v );
+        STATIC_ASSERT( w == 1 );
+    }
+
+    {
+        constexpr variant<int, int, float, float, X> v( X(1) );
+        constexpr auto w = test<X>( v );
+        STATIC_ASSERT( w == 1 );
+    }
+
+#if defined( BOOST_LIBSTDCXX_VERSION ) && BOOST_LIBSTDCXX_VERSION < 50000
+#else
+
+    {
+        constexpr variant<E, E, Y> v( 1 );
+        constexpr auto w = test<Y>( v );
+        STATIC_ASSERT( w == 1 );
+    }
+
+    {
+        constexpr variant<int, int, float, float, Y> v( Y(1) );
+        constexpr auto w = test<Y>( v );
+        STATIC_ASSERT( w == 1 );
+    }
+
+#endif
+}
+
+#endif // constexpr lambda support

test/variant_move_assign_cx.cpp

@@ -6,13 +6,6 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
-#if !defined( __cpp_constexpr ) || __cpp_constexpr < 201603
-
-// no constexpr lambda support
-int main() {}
-
-#else
-
 #include <boost/variant2/variant.hpp>
 #include <utility>
 
@@ -112,5 +105,3 @@ int main()
 
 #endif
 }
-
-#endif // constexpr lambda support

test/variant_move_construct_cx.cpp

@@ -0,0 +1,113 @@
+
+// Copyright 2017 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
+
+#if !defined( __cpp_constexpr ) || __cpp_constexpr < 201603
+
+// no constexpr lambda support
+int main() {}
+
+#else
+
+#include <boost/variant2/variant.hpp>
+#include <utility>
+
+using namespace boost::variant2;
+
+struct X
+{
+    int v;
+    X() = default;
+    constexpr X( int v ): v( v ) {}
+    constexpr operator int() const { return v; }
+};
+
+struct Y
+{
+    int v;
+    constexpr Y(): v() {}
+    constexpr Y( int v ): v( v ) {}
+    constexpr operator int() const { return v; }
+};
+
+enum E
+{
+    v
+};
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+template<class T, class V> constexpr T test( V&& v )
+{
+    V v2( std::forward<V>(v) );
+    return get<T>(v);
+}
+
+int main()
+{
+    {
+        constexpr auto w = test<int>( variant<int>( 1 ) );
+        STATIC_ASSERT( w == 1 );
+    }
+
+    {
+        constexpr auto w = test<X>( variant<X>( 1 ) );
+        STATIC_ASSERT( w == 1 );
+    }
+
+#if defined( BOOST_LIBSTDCXX_VERSION ) && BOOST_LIBSTDCXX_VERSION < 50000
+#else
+
+    {
+        constexpr auto w = test<Y>( variant<Y>( 1 ) );
+        STATIC_ASSERT( w == 1 );
+    }
+
+#endif
+
+    {
+        constexpr auto w = test<int>( variant<int, float>( 1 ) );
+        STATIC_ASSERT( w == 1 );
+    }
+
+    {
+        constexpr auto w = test<float>( variant<int, float>( 3.0f ) );
+        STATIC_ASSERT( w == 3.0f );
+    }
+
+    {
+        constexpr auto w = test<float>( variant<int, int, float>( 3.0f ) );
+        STATIC_ASSERT( w == 3.0f );
+    }
+
+    {
+        constexpr auto w = test<X>( variant<E, E, X>( 1 ) );
+        STATIC_ASSERT( w == 1 );
+    }
+
+    {
+        constexpr auto w = test<X>( variant<int, int, float, float, X>( X(1) ) );
+        STATIC_ASSERT( w == 1 );
+    }
+
+#if defined( BOOST_LIBSTDCXX_VERSION ) && BOOST_LIBSTDCXX_VERSION < 50000
+#else
+
+    {
+        constexpr auto w = test<Y>( variant<E, E, Y>( 1 ) );
+        STATIC_ASSERT( w == 1 );
+    }
+
+    {
+        constexpr auto w = test<Y>( variant<int, int, float, float, Y>( Y(1) ) );
+        STATIC_ASSERT( w == 1 );
+    }
+
+#endif
+}
+
+#endif // constexpr lambda support