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re PR libstdc++/78441 ([variant] variant_alternative doesn't allow cv qualifiers) 

PR libstdc++/78441
	* include/std/variant: Propagate cv qualifications to types returned
	by variant_alternative.
	* testsuite/20_util/variant/compile.cc: Tests.

From-SVN: r242892
This commit is contained in:
Tim Shen 2016-11-27 00:32:04 +00:00 committed by Tim Shen
parent 216c1ee838
commit 3203ed5f01
3 changed files with 28 additions and 0 deletions
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7
libstdc++-v3/ChangeLog
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@ -1,3 +1,10 @@
2016-11-26 Tim Shen <timshen@google.com>
PR libstdc++/78441
* include/std/variant: Propagate cv qualifications to types returned
by variant_alternative.
* testsuite/20_util/variant/compile.cc: Tests.
2016-11-23 Felix Morgner <felix.morgner@gmail.com>
Jonathan Wakely <jwakely@redhat.com>

12
libstdc++-v3/include/std/variant
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@ -85,6 +85,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
using variant_alternative_t =
typename variant_alternative<_Np, _Variant>::type;
template<size_t _Np, typename _Variant>
struct variant_alternative<_Np, const _Variant>
{ using type = add_const_t<variant_alternative_t<_Np, _Variant>>; };
template<size_t _Np, typename _Variant>
struct variant_alternative<_Np, volatile _Variant>
{ using type = add_volatile_t<variant_alternative_t<_Np, _Variant>>; };
template<size_t _Np, typename _Variant>
struct variant_alternative<_Np, const volatile _Variant>
{ using type = add_cv_t<variant_alternative_t<_Np, _Variant>>; };
constexpr size_t variant_npos = -1;
_GLIBCXX_END_NAMESPACE_VERSION

9
libstdc++-v3/testsuite/20_util/variant/compile.cc
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@ -330,3 +330,12 @@ void test_adl()
variant<X> v8{allocator_arg, a, in_place_type<X>, il, x};
variant<X> v9{allocator_arg, a, in_place_type<X>, 1};
}
void test_variant_alternative() {
static_assert(is_same_v<variant_alternative_t<0, variant<int, string>>, int>, "");
static_assert(is_same_v<variant_alternative_t<1, variant<int, string>>, string>, "");
static_assert(is_same_v<variant_alternative_t<0, const variant<int>>, const int>, "");
static_assert(is_same_v<variant_alternative_t<0, volatile variant<int>>, volatile int>, "");
static_assert(is_same_v<variant_alternative_t<0, const volatile variant<int>>, const volatile int>, "");
}