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
28 template <class _Ap, class _Bp>
29 using _CopyConst _LIBCPP_NODEBUG = _If<is_const_v<_Ap>, const _Bp, _Bp>;
30
31 template <class _Ap, class _Bp>
32 using _OverrideRef _LIBCPP_NODEBUG = _If<is_rvalue_reference_v<_Ap>, remove_reference_t<_Bp>&&, _Bp&>;
33
34 template <class _Ap, class _Bp>
35 using _ForwardLike _LIBCPP_NODEBUG = _OverrideRef<_Ap&&, _CopyConst<remove_reference_t<_Ap>, remove_reference_t<_Bp>>>;
36
37 template <class _Tp, class _Up>
38 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto
39 forward_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 // };
52 template <class _Tp, class _As, class _Up>
53 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _ForwardLike<_Tp, _As>
__forward_as(_LIBCPP_LIFETIMEBOUND _Up && __val)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