Implement an _is_allocator type trait for use in deduction guides.

llvm-svn: 322306
This commit is contained in:
Marshall Clow 2018-01-11 19:36:22 +00:00
parent aac638eb1e
commit 0e22bf8cb9
2 changed files with 51 additions and 0 deletions

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@ -5597,6 +5597,16 @@ struct __temp_value {
};
#endif
#if _LIBCPP_STD_VER > 14
template<typename _Alloc, typename = void>
struct __is_allocator : false_type {};
template<typename _Alloc>
struct __is_allocator<_Alloc,
void_t<typename _Alloc::value_type, decltype(_VSTD::declval<_Alloc&>().allocate(size_t{}))>>
: true_type {};
#endif
_LIBCPP_END_NAMESPACE_STD
_LIBCPP_POP_MACROS

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@ -0,0 +1,41 @@
//===----------------------------------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// <memory>
// UNSUPPORTED: c++98, c++03, c++11, c++14
// template<typename _Alloc>
// struct __is_allocator;
// Is either true_type or false_type depending on if A is an allocator.
#include <memory>
#include <string>
#include "test_macros.h"
#include "min_allocator.h"
#include "test_allocator.h"
template <typename T>
void test_allocators()
{
static_assert( std::__is_allocator<std::allocator<T>>::value, "" );
static_assert( std::__is_allocator<test_allocator<T>>::value, "" );
static_assert( std::__is_allocator<min_allocator<T>>::value, "" );
}
int main()
{
// test_allocators<void>();
test_allocators<char>();
test_allocators<int>();
test_allocators<std::string>();
}