libstdc++
invoke.h
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1 // Implementation of INVOKE -*- C++ -*-
2 
3 // Copyright (C) 2016-2025 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file include/bits/invoke.h
26  * This is an internal header file, included by other library headers.
27  * Do not attempt to use it directly. @headername{functional}
28  */
29 
30 #ifndef _GLIBCXX_INVOKE_H
31 #define _GLIBCXX_INVOKE_H 1
32 
33 #ifdef _GLIBCXX_SYSHDR
34 #pragma GCC system_header
35 #endif
36 
37 #if __cplusplus < 201103L
38 # include <bits/c++0x_warning.h>
39 #else
40 
41 #include <type_traits>
42 #include <bits/move.h> // forward
43 
44 namespace std _GLIBCXX_VISIBILITY(default)
45 {
46 _GLIBCXX_BEGIN_NAMESPACE_VERSION
47 
48  /**
49  * @addtogroup utilities
50  * @{
51  */
52 
53  // Used by __invoke_impl instead of std::forward<_Tp> so that a
54  // reference_wrapper is converted to an lvalue-reference.
55  template<typename _Tp, typename _Up = typename __inv_unwrap<_Tp>::type>
56  constexpr _Up&&
57  __invfwd(typename remove_reference<_Tp>::type& __t) noexcept
58  { return static_cast<_Up&&>(__t); }
59 
60  template<typename _Res, typename _Fn, typename... _Args>
61  constexpr _Res
62  __invoke_impl(__invoke_other, _Fn&& __f, _Args&&... __args)
63  { return std::forward<_Fn>(__f)(std::forward<_Args>(__args)...); }
64 
65  template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
66  constexpr _Res
67  __invoke_impl(__invoke_memfun_ref, _MemFun&& __f, _Tp&& __t,
68  _Args&&... __args)
69  { return (__invfwd<_Tp>(__t).*__f)(std::forward<_Args>(__args)...); }
70 
71  template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
72  constexpr _Res
73  __invoke_impl(__invoke_memfun_deref, _MemFun&& __f, _Tp&& __t,
74  _Args&&... __args)
75  {
76  return ((*std::forward<_Tp>(__t)).*__f)(std::forward<_Args>(__args)...);
77  }
78 
79  template<typename _Res, typename _MemPtr, typename _Tp>
80  constexpr _Res
81  __invoke_impl(__invoke_memobj_ref, _MemPtr&& __f, _Tp&& __t)
82  { return __invfwd<_Tp>(__t).*__f; }
83 
84  template<typename _Res, typename _MemPtr, typename _Tp>
85  constexpr _Res
86  __invoke_impl(__invoke_memobj_deref, _MemPtr&& __f, _Tp&& __t)
87  { return (*std::forward<_Tp>(__t)).*__f; }
88 
89  /// Invoke a callable object.
90  template<typename _Callable, typename... _Args>
91  constexpr typename __invoke_result<_Callable, _Args...>::type
92  __invoke(_Callable&& __fn, _Args&&... __args)
93  noexcept(__is_nothrow_invocable<_Callable, _Args...>::value)
94  {
95  using __result = __invoke_result<_Callable, _Args...>;
96  using __type = typename __result::type;
97  using __tag = typename __result::__invoke_type;
98  return std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
99  std::forward<_Args>(__args)...);
100  }
101 
102 #if __cplusplus >= 201703L
103  // INVOKE<R>: Invoke a callable object and convert the result to R.
104  template<typename _Res, typename _Callable, typename... _Args>
105  constexpr enable_if_t<is_invocable_r_v<_Res, _Callable, _Args...>, _Res>
106  __invoke_r(_Callable&& __fn, _Args&&... __args)
107  noexcept(is_nothrow_invocable_r_v<_Res, _Callable, _Args...>)
108  {
109  using __result = __invoke_result<_Callable, _Args...>;
110  using __type = typename __result::type;
111  using __tag = typename __result::__invoke_type;
112  if constexpr (is_void_v<_Res>)
113  std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
114  std::forward<_Args>(__args)...);
115  else
116  return std::__invoke_impl<__type>(__tag{},
117  std::forward<_Callable>(__fn),
118  std::forward<_Args>(__args)...);
119  }
120 #else // C++11 or C++14
121  // This is a non-SFINAE-friendly std::invoke_r<R>(fn, args...) for C++11/14.
122  // It's used in std::function, std::bind, and std::packaged_task. Only
123  // std::function is constrained on is_invocable_r, but that is checked on
124  // construction so doesn't need to be checked again when calling __invoke_r.
125  // Consequently, these __invoke_r overloads do not check for invocable
126  // arguments, nor check that the invoke result is convertible to R.
127 
128  // INVOKE<R>: Invoke a callable object and convert the result to R.
129  template<typename _Res, typename _Callable, typename... _Args>
130  constexpr __enable_if_t<!is_void<_Res>::value, _Res>
131  __invoke_r(_Callable&& __fn, _Args&&... __args)
132  {
133  using __result = __invoke_result<_Callable, _Args...>;
134  using __type = typename __result::type;
135 #if __has_builtin(__reference_converts_from_temporary)
136  static_assert(!__reference_converts_from_temporary(_Res, __type),
137  "INVOKE<R> must not create a dangling reference");
138 #endif
139  using __tag = typename __result::__invoke_type;
140  return std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
141  std::forward<_Args>(__args)...);
142  }
143 
144  // INVOKE<R> when R is cv void
145  template<typename _Res, typename _Callable, typename... _Args>
146  _GLIBCXX14_CONSTEXPR __enable_if_t<is_void<_Res>::value, _Res>
147  __invoke_r(_Callable&& __fn, _Args&&... __args)
148  {
149  using __result = __invoke_result<_Callable, _Args...>;
150  using __type = typename __result::type;
151  using __tag = typename __result::__invoke_type;
152  std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
153  std::forward<_Args>(__args)...);
154  }
155 #endif // C++11 or C++14
156 
157 _GLIBCXX_END_NAMESPACE_VERSION
158 } // namespace std
159 
160 #endif // C++11
161 
162 #endif // _GLIBCXX_INVOKE_H
typename enable_if< _Cond, _Tp >::type enable_if_t
Alias template for enable_if.
Definition: type_traits:2837
constexpr __invoke_result< _Callable, _Args... >::type __invoke(_Callable &&__fn, _Args &&... __args) noexcept(__is_nothrow_invocable< _Callable, _Args... >::value)
Invoke a callable object.
Definition: invoke.h:92
ISO C++ entities toplevel namespace is std.