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| author | Jonathan Wakely <jwakely@redhat.com> | 2023-09-14 10:27:09 +0100 |
|---|---|---|
| committer | Jonathan Wakely <jwakely@redhat.com> | 2023-09-15 10:24:01 +0100 |
| commit | 5daeda573cedc2910ecee7f1b3168210143dc026 (patch) | |
| tree | 8d37d1acaca91dc735fe416371df021128e0f0c1 | |
| parent | d19bdf8874059457fdfe50a9e14dad8f8b8cecbb (diff) | |
| download | gcc-5daeda573cedc2910ecee7f1b3168210143dc026.zip gcc-5daeda573cedc2910ecee7f1b3168210143dc026.tar.gz gcc-5daeda573cedc2910ecee7f1b3168210143dc026.tar.bz2 | |
libstdc++: Fix constraints for std::variant default constructor
The standard says the default ctor should be constrained, not deleted.
Our use of a defaulted default ctor and _Enable_default_constructor base
class results in it being deleted.
libstdc++-v3/ChangeLog:
* include/std/variant (variant): Remove derivation from
_Enable_default_constructor base class.
(variant::variant()): Constrain.
* testsuite/20_util/variant/default_ctor.cc: New test.
| -rw-r--r-- | libstdc++-v3/include/std/variant | 24 | ||||
| -rw-r--r-- | libstdc++-v3/testsuite/20_util/variant/default_ctor.cc | 11 |
2 files changed, 23 insertions, 12 deletions
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant index 36eec8d..c0e4174 100644 --- a/libstdc++-v3/include/std/variant +++ b/libstdc++-v3/include/std/variant @@ -1332,9 +1332,6 @@ namespace __variant template<typename... _Types> class variant : private __detail::__variant::_Variant_base<_Types...>, - private _Enable_default_constructor< - __detail::__variant::_Traits<_Types...>::_S_default_ctor, - variant<_Types...>>, private _Enable_copy_move< __detail::__variant::_Traits<_Types...>::_S_copy_ctor, __detail::__variant::_Traits<_Types...>::_S_copy_assign, @@ -1355,10 +1352,6 @@ namespace __variant "variant must have no void alternative"); using _Base = __detail::__variant::_Variant_base<_Types...>; - using _Default_ctor_enabler = - _Enable_default_constructor< - __detail::__variant::_Traits<_Types...>::_S_default_ctor, - variant<_Types...>>; template<typename _Tp> static constexpr bool __not_self @@ -1396,7 +1389,16 @@ namespace __variant = !__is_in_place_tag<__remove_cvref_t<_Tp>>::value; public: - variant() = default; +#if __cpp_concepts + variant() requires is_default_constructible_v<__to_type<0>> = default; +#else + template<typename _Tp0 = __to_type<0>, + typename = enable_if_t<is_default_constructible_v<_Tp0>>> + constexpr + variant() noexcept(is_nothrow_default_constructible_v<__to_type<0>>) + { } +#endif + variant(const variant& __rhs) = default; variant(variant&&) = default; variant& operator=(const variant&) = default; @@ -1441,8 +1443,7 @@ namespace __variant typename = enable_if_t<is_constructible_v<_Tp, _Args...>>> constexpr explicit variant(in_place_index_t<_Np>, _Args&&... __args) - : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...), - _Default_ctor_enabler(_Enable_default_constructor_tag{}) + : _Base(in_place_index<_Np>, std::forward<_Args>(__args)...) { } template<size_t _Np, typename _Up, typename... _Args, @@ -1453,8 +1454,7 @@ namespace __variant constexpr explicit variant(in_place_index_t<_Np>, initializer_list<_Up> __il, _Args&&... __args) - : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...), - _Default_ctor_enabler(_Enable_default_constructor_tag{}) + : _Base(in_place_index<_Np>, __il, std::forward<_Args>(__args)...) { } template<typename _Tp> diff --git a/libstdc++-v3/testsuite/20_util/variant/default_ctor.cc b/libstdc++-v3/testsuite/20_util/variant/default_ctor.cc new file mode 100644 index 0000000..d0d9235 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/variant/default_ctor.cc @@ -0,0 +1,11 @@ +// { dg-do compile { target c++17 } } + +#include <variant> + +struct A{ A(int); }; +struct B{ B(){}; }; + +void f(std::variant<A>); +int f(B); + +int unambiguous = f({}); // { dg-bogus "ambiguous" } |