chromium/third_party/libc++/src/include/__memory/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_ALLOCATOR_H
#define _LIBCPP___MEMORY_ALLOCATOR_H

#include <__config>
#include <__memory/addressof.h>
#include <__memory/allocate_at_least.h>
#include <__memory/allocator_traits.h>
#include <__type_traits/is_const.h>
#include <__type_traits/is_constant_evaluated.h>
#include <__type_traits/is_same.h>
#include <__type_traits/is_void.h>
#include <__type_traits/is_volatile.h>
#include <__utility/forward.h>
#include <cstddef>
#include <new>

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

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp>
class allocator;

#if _LIBCPP_STD_VER <= 17
// These specializations shouldn't be marked _LIBCPP_DEPRECATED_IN_CXX17.
// Specializing allocator<void> is deprecated, but not using it.
template <>
class _LIBCPP_TEMPLATE_VIS allocator<void> {
public:
  _LIBCPP_DEPRECATED_IN_CXX17 typedef void* pointer;
  _LIBCPP_DEPRECATED_IN_CXX17 typedef const void* const_pointer;
  _LIBCPP_DEPRECATED_IN_CXX17 typedef void value_type;

  template <class _Up>
  struct _LIBCPP_DEPRECATED_IN_CXX17 rebind {
    typedef allocator<_Up> other;
  };
};
#endif // _LIBCPP_STD_VER <= 17

// This class provides a non-trivial default constructor to the class that derives from it
// if the condition is satisfied.
//
// The second template parameter exists to allow giving a unique type to __non_trivial_if,
// which makes it possible to avoid breaking the ABI when making this a base class of an
// existing class. Without that, imagine we have classes D1 and D2, both of which used to
// have no base classes, but which now derive from __non_trivial_if. The layout of a class
// that inherits from both D1 and D2 will change because the two __non_trivial_if base
// classes are not allowed to share the same address.
//
// By making those __non_trivial_if base classes unique, we work around this problem and
// it is safe to start deriving from __non_trivial_if in existing classes.
template <bool _Cond, class _Unique>
struct __non_trivial_if { … };

__non_trivial_if<true, _Unique>;

// allocator
//
// Note: For ABI compatibility between C++20 and previous standards, we make
//       allocator<void> trivial in C++20.

template <class _Tp>
class _LIBCPP_TEMPLATE_VIS allocator : private __non_trivial_if<!is_void<_Tp>::value, allocator<_Tp> > { … };

template <class _Tp, class _Up>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
operator==(const allocator<_Tp>&, const allocator<_Up>&) _NOEXCEPT { … }

#if _LIBCPP_STD_VER <= 17

template <class _Tp, class _Up>
inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const allocator<_Tp>&, const allocator<_Up>&) _NOEXCEPT {
  return false;
}

#endif

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___MEMORY_ALLOCATOR_H