libcxx/include/__memory/uses_allocator.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___MEMORY_USES_ALLOCATOR_H
#define _LIBCPP___MEMORY_USES_ALLOCATOR_H

#include <__config>
#include <cstddef>
#include <type_traits>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp>
struct __has_allocator_type
{
private:
    struct __two {char __lx; char __lxx;};
    template <class _Up> static __two __test(...);
    template <class _Up> static char __test(typename _Up::allocator_type* = 0);
public:
    static const bool value = sizeof(__test<_Tp>(0)) == 1;
};

template <class _Tp, class _Alloc, bool = __has_allocator_type<_Tp>::value>
struct __uses_allocator
    : public integral_constant<bool,
        is_convertible<_Alloc, typename _Tp::allocator_type>::value>
{
};

template <class _Tp, class _Alloc>
struct __uses_allocator<_Tp, _Alloc, false>
    : public false_type
{
};

template <class _Tp, class _Alloc>
struct _LIBCPP_TEMPLATE_VIS uses_allocator
    : public __uses_allocator<_Tp, _Alloc>
{
};

#if _LIBCPP_STD_VER > 14
template <class _Tp, class _Alloc>
inline constexpr size_t uses_allocator_v = uses_allocator<_Tp, _Alloc>::value;
#endif

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___MEMORY_USES_ALLOCATOR_H