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___FUNCTIONAL_REFERENCE_WRAPPER_H
11 #define _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H
12 
13 #include <__config>
14 #include <__functional/invoke.h>
15 #include <__functional/weak_result_type.h>
16 #include <__memory/addressof.h>
17 #include <__type_traits/enable_if.h>
18 #include <__type_traits/remove_cvref.h>
19 #include <__utility/declval.h>
20 #include <__utility/forward.h>
21 
22 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
23 #  pragma GCC system_header
24 #endif
25 
26 _LIBCPP_BEGIN_NAMESPACE_STD
27 
28 template <class _Tp>
29 class _LIBCPP_TEMPLATE_VIS reference_wrapper : public __weak_result_type<_Tp> {
30 public:
31   // types
32   typedef _Tp type;
33 
34 private:
35   type* __f_;
36 
37   static void __fun(_Tp&) _NOEXCEPT;
38   static void __fun(_Tp&&) = delete;
39 
40 public:
41   template <
42       class _Up,
43       class = __enable_if_t<!__is_same_uncvref<_Up, reference_wrapper>::value, decltype(__fun(std::declval<_Up>())) > >
reference_wrapper(_Up && __u)44   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper(_Up&& __u)
45       _NOEXCEPT_(noexcept(__fun(std::declval<_Up>()))) {
46     type& __f = static_cast<_Up&&>(__u);
47     __f_      = std::addressof(__f);
48   }
49 
50   // access
51   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 operator type&() const _NOEXCEPT { return *__f_; }
get()52   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 type& get() const _NOEXCEPT { return *__f_; }
53 
54   // invoke
55   template <class... _ArgTypes>
56   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 typename __invoke_of<type&, _ArgTypes...>::type
operator()57   operator()(_ArgTypes&&... __args) const
58 #if _LIBCPP_STD_VER >= 17
59       // Since is_nothrow_invocable requires C++17 LWG3764 is not backported
60       // to earlier versions.
61       noexcept(is_nothrow_invocable_v<_Tp&, _ArgTypes...>)
62 #endif
63   {
64     return std::__invoke(get(), std::forward<_ArgTypes>(__args)...);
65   }
66 };
67 
68 #if _LIBCPP_STD_VER >= 17
69 template <class _Tp>
70 reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
71 #endif
72 
73 template <class _Tp>
ref(_Tp & __t)74 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper<_Tp> ref(_Tp& __t) _NOEXCEPT {
75   return reference_wrapper<_Tp>(__t);
76 }
77 
78 template <class _Tp>
79 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper<_Tp>
ref(reference_wrapper<_Tp> __t)80 ref(reference_wrapper<_Tp> __t) _NOEXCEPT {
81   return __t;
82 }
83 
84 template <class _Tp>
cref(const _Tp & __t)85 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper<const _Tp> cref(const _Tp& __t) _NOEXCEPT {
86   return reference_wrapper<const _Tp>(__t);
87 }
88 
89 template <class _Tp>
90 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 reference_wrapper<const _Tp>
cref(reference_wrapper<_Tp> __t)91 cref(reference_wrapper<_Tp> __t) _NOEXCEPT {
92   return __t;
93 }
94 
95 template <class _Tp>
96 void ref(const _Tp&&) = delete;
97 template <class _Tp>
98 void cref(const _Tp&&) = delete;
99 
100 _LIBCPP_END_NAMESPACE_STD
101 
102 #endif // _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H
103