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_base_of.h>
16#include <__type_traits/is_const.h>
17#include <__type_traits/is_reference.h>
18#include <__type_traits/remove_reference.h>
19
20#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
21# pragma GCC system_header
22#endif
23
24_LIBCPP_BEGIN_NAMESPACE_STD
25
26#if _LIBCPP_STD_VER >= 23
27
28template <class _Ap, class _Bp>
29using _CopyConst _LIBCPP_NODEBUG = _If<is_const_v<_Ap>, const _Bp, _Bp>;
30
31template <class _Ap, class _Bp>
32using _OverrideRef _LIBCPP_NODEBUG = _If<is_rvalue_reference_v<_Ap>, remove_reference_t<_Bp>&&, _Bp&>;
33
34template <class _Ap, class _Bp>
35using _ForwardLike _LIBCPP_NODEBUG = _OverrideRef<_Ap&&, _CopyConst<remove_reference_t<_Ap>, remove_reference_t<_Bp>>>;
36
37template <class _Tp, class _Up>
38[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto
39forward_like(_LIBCPP_LIFETIMEBOUND _Up&& __ux) noexcept -> _ForwardLike<_Tp, _Up> {
40 return static_cast<_ForwardLike<_Tp, _Up>>(__ux);
41}
42
43// This function is used for `deducing this` cases where you want to make sure the operation is performed on the class
44// itself and not on a derived class. For example
45// struct S {
46// template <class Self>
47// void func(Self&& self) {
48// // This will always call `do_something` of S instead of any class derived from S.
49// std::__forward_as<Self, S>(self).do_something();
50// }
51// };
52template <class _Tp, class _As, class _Up>
53[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _ForwardLike<_Tp, _As>
54__forward_as(_LIBCPP_LIFETIMEBOUND _Up&& __val) noexcept {
55 static_assert(is_base_of_v<_As, remove_reference_t<_Up>>);
56 return static_cast<_ForwardLike<_Tp, _As>>(__val);
57}
58
59#endif // _LIBCPP_STD_VER >= 23
60
61_LIBCPP_END_NAMESPACE_STD
62
63#endif // _LIBCPP___UTILITY_FORWARD_LIKE_H
64