From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2181) id 455973858C3A; Fri, 15 Sep 2023 09:24:52 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 455973858C3A DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1694769892; bh=VOe3tTSCEBdlxE7fzCYs3ifeDx7z6HnUKTdrpFOpqew=; h=From:To:Subject:Date:From; b=Lg4dkGOV3wzwgvp+p2pHHd3LpF3VwJC2yWWnWdwwbCn0B2gyIC6dvrJPJOaDn3mg0 30H8f6iVfoDYFmqAnIl0Hphb+3bG+jXI7ApgWq6NwI0mqztR5g84k6/yXwJKisWd/J NWTpDSOsjLuqype3Hc+wGLjjlx/0uMnSJgTIQ8aY= MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Jonathan Wakely To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r14-4013] libstdc++: Fix constraints for std::variant default constructor X-Act-Checkin: gcc X-Git-Author: Jonathan Wakely X-Git-Refname: refs/heads/master X-Git-Oldrev: d19bdf8874059457fdfe50a9e14dad8f8b8cecbb X-Git-Newrev: 5daeda573cedc2910ecee7f1b3168210143dc026 Message-Id: <20230915092452.455973858C3A@sourceware.org> Date: Fri, 15 Sep 2023 09:24:52 +0000 (GMT) List-Id: https://gcc.gnu.org/g:5daeda573cedc2910ecee7f1b3168210143dc026 commit r14-4013-g5daeda573cedc2910ecee7f1b3168210143dc026 Author: Jonathan Wakely Date: Thu Sep 14 10:27:09 2023 +0100 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. Diff: --- libstdc++-v3/include/std/variant | 24 +++++++++++----------- .../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 36eec8d829b..c0e41740dcf 100644 --- a/libstdc++-v3/include/std/variant +++ b/libstdc++-v3/include/std/variant @@ -1332,9 +1332,6 @@ namespace __variant template 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 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 = enable_if_t>> + 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>> 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, 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 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 00000000000..d0d9235a59c --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/variant/default_ctor.cc @@ -0,0 +1,11 @@ +// { dg-do compile { target c++17 } } + +#include + +struct A{ A(int); }; +struct B{ B(){}; }; + +void f(std::variant); +int f(B); + +int unambiguous = f({}); // { dg-bogus "ambiguous" }