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Workaround GCC bug PR78489 - SFINAE order is not respected.

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This patch works around variant test failures which are new to
GCC 8. GCC 8 either doesn't perform SFINAE in lexical order, or
it doesn't halt after encountering the first failure. This
causes hard error to occur instead of substitution failure.

See gcc.gnu.org/PR78489

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@328261 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eric Fiselier
2018-03-22 22:32:55 +00:00
parent b06c8f07b2
commit 493b609b27
2 changed files with 18 additions and 17 deletions
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29
include/variant
View File

@@ -1156,29 +1156,24 @@ public:
: __impl(in_place_index<_Ip>, _VSTD::forward<_Arg>(__arg)) {} : __impl(in_place_index<_Ip>, _VSTD::forward<_Arg>(__arg)) {}
template <size_t _Ip, class... _Args, template <size_t _Ip, class... _Args,
class = enable_if_t<(_Ip < sizeof...(_Types)), int>, enable_if_t<(_Ip < sizeof...(_Types)), size_t> _Ip2 = _Ip,
class _Tp = variant_alternative_t<_Ip, variant<_Types...>>, class _Tp = variant_alternative_t<_Ip2, variant<_Types...>>,
enable_if_t<is_constructible_v<_Tp, _Args...>, int> = 0> enable_if_t<is_constructible<_Tp, _Args...>::value, int> = 0>
inline _LIBCPP_INLINE_VISIBILITY inline _LIBCPP_INLINE_VISIBILITY
explicit constexpr variant( explicit constexpr variant(in_place_index_t<_Ip>,
in_place_index_t<_Ip>, _Args&&... __args)
_Args&&... __args) noexcept(is_nothrow_constructible_v<_Tp, _Args...>) noexcept(is_nothrow_constructible_v<_Tp, _Args...>)
: __impl(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...) {} : __impl(in_place_index<_Ip>, _VSTD::forward<_Args>(__args)...) {}
template < template <size_t _Ip, class _Up, class... _Args,
size_t _Ip, enable_if_t<(_Ip < sizeof...(_Types)), size_t> _Ip2 = _Ip,
class _Up, class _Tp = variant_alternative_t<_Ip2, variant<_Types...>>,
class... _Args,
enable_if_t<(_Ip < sizeof...(_Types)), int> = 0,
class _Tp = variant_alternative_t<_Ip, variant<_Types...>>,
enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>, enable_if_t<is_constructible_v<_Tp, initializer_list<_Up>&, _Args...>,
int> = 0> int> = 0>
inline _LIBCPP_INLINE_VISIBILITY inline _LIBCPP_INLINE_VISIBILITY
explicit constexpr variant( explicit constexpr variant(in_place_index_t<_Ip>, initializer_list<_Up> __il,
in_place_index_t<_Ip>, _Args&&... __args)
initializer_list<_Up> __il, noexcept(is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
_Args&&... __args) noexcept(
is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>)
: __impl(in_place_index<_Ip>, __il, _VSTD::forward<_Args>(__args)...) {} : __impl(in_place_index<_Ip>, __il, _VSTD::forward<_Args>(__args)...) {}
template < template <

6
test/std/utilities/variant/variant.variant/variant.ctor/in_place_index_init_list_args.pass.cpp
View File

@@ -73,6 +73,12 @@ void test_ctor_sfinae() {
!std::is_constructible<V, std::in_place_index_t<2>, IL>::value, ""); !std::is_constructible<V, std::in_place_index_t<2>, IL>::value, "");
static_assert(!test_convertible<V, std::in_place_index_t<2>, IL>(), ""); static_assert(!test_convertible<V, std::in_place_index_t<2>, IL>(), "");
} }
{ // index not in variant
using V = std::variant<InitList, InitListArg, int>;
static_assert(
!std::is_constructible<V, std::in_place_index_t<3>, IL>::value, "");
static_assert(!test_convertible<V, std::in_place_index_t<3>, IL>(), "");
}
} }
void test_ctor_basic() { void test_ctor_basic() {