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 {
31 public:
32     // types
33     typedef _Tp type;
34 private:
35     type* __f_;
36 
37     static void __fun(_Tp&) _NOEXCEPT;
38     static void __fun(_Tp&&) = delete;
39 
40 public:
41     template <class _Up, class = __enable_if_t<!__is_same_uncvref<_Up, reference_wrapper>::value, decltype(__fun(std::declval<_Up>())) > >
42     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
43     reference_wrapper(_Up&& __u) _NOEXCEPT_(noexcept(__fun(std::declval<_Up>()))) {
44         type& __f = static_cast<_Up&&>(__u);
45         __f_ = _VSTD::addressof(__f);
46     }
47 
48     // access
49     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
50     operator type&() const _NOEXCEPT {return *__f_;}
51     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
52     type& get() const _NOEXCEPT {return *__f_;}
53 
54     // invoke
55     template <class... _ArgTypes>
56     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
57     typename __invoke_of<type&, _ArgTypes...>::type
58     operator() (_ArgTypes&&... __args) const
59 #if _LIBCPP_STD_VER >= 17
60         // Since is_nothrow_invocable requires C++17 LWG3764 is not backported
61         // to earlier versions.
62         noexcept(is_nothrow_invocable_v<_Tp&, _ArgTypes...>)
63 #endif
64     {
65         return std::__invoke(get(), std::forward<_ArgTypes>(__args)...);
66     }
67 };
68 
69 #if _LIBCPP_STD_VER >= 17
70 template <class _Tp>
71 reference_wrapper(_Tp&) -> reference_wrapper<_Tp>;
72 #endif
73 
74 template <class _Tp>
75 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
76 reference_wrapper<_Tp>
77 ref(_Tp& __t) _NOEXCEPT
78 {
79     return reference_wrapper<_Tp>(__t);
80 }
81 
82 template <class _Tp>
83 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
84 reference_wrapper<_Tp>
85 ref(reference_wrapper<_Tp> __t) _NOEXCEPT
86 {
87     return __t;
88 }
89 
90 template <class _Tp>
91 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
92 reference_wrapper<const _Tp>
93 cref(const _Tp& __t) _NOEXCEPT
94 {
95     return reference_wrapper<const _Tp>(__t);
96 }
97 
98 template <class _Tp>
99 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
100 reference_wrapper<const _Tp>
101 cref(reference_wrapper<_Tp> __t) _NOEXCEPT
102 {
103     return __t;
104 }
105 
106 template <class _Tp> void ref(const _Tp&&) = delete;
107 template <class _Tp> void cref(const _Tp&&) = delete;
108 
109 _LIBCPP_END_NAMESPACE_STD
110 
111 #endif // _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H
112