1// -*- C++ -*-
2//===----------------------------------------------------------------------===//
3//
4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5// See https://llvm.org/LICENSE.txt for license information.
6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7//
8//===----------------------------------------------------------------------===//
9
10#ifndef _LIBCPP___UTILITY_FORWARD_LIKE_H
11#define _LIBCPP___UTILITY_FORWARD_LIKE_H
12
13#include <__config>
14#include <__type_traits/conditional.h>
15#include <__type_traits/is_const.h>
16#include <__type_traits/is_reference.h>
17#include <__type_traits/remove_reference.h>
18
19#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
20#  pragma GCC system_header
21#endif
22
23_LIBCPP_BEGIN_NAMESPACE_STD
24
25#if _LIBCPP_STD_VER > 20
26
27template <class _Ap, class _Bp>
28using _CopyConst = _If<is_const_v<_Ap>, const _Bp, _Bp>;
29
30template <class _Ap, class _Bp>
31using _OverrideRef = _If<is_rvalue_reference_v<_Ap>, remove_reference_t<_Bp>&&, _Bp&>;
32
33template <class _Ap, class _Bp>
34using _ForwardLike = _OverrideRef<_Ap&&, _CopyConst<remove_reference_t<_Ap>, remove_reference_t<_Bp>>>;
35
36template <class _Tp, class _Up>
37[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto forward_like(_LIBCPP_LIFETIMEBOUND _Up&& __ux) noexcept
38    -> _ForwardLike<_Tp, _Up> {
39  return static_cast<_ForwardLike<_Tp, _Up>>(__ux);
40}
41
42#endif // _LIBCPP_STD_VER > 20
43
44_LIBCPP_END_NAMESPACE_STD
45
46#endif // _LIBCPP___UTILITY_FORWARD_LIKE_H
47