libstdc++
move.h
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1// Move, forward and identity for C++11 + swap -*- C++ -*-
2
3// Copyright (C) 2007-2024 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 bits/move.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{utility}
28 */
29
30#ifndef _MOVE_H
31#define _MOVE_H 1
32
33#include <bits/c++config.h>
34#if __cplusplus < 201103L
35# include <bits/concept_check.h>
36#else
37# include <type_traits> // Brings in std::declval too.
38#endif
39
40namespace std _GLIBCXX_VISIBILITY(default)
41{
42_GLIBCXX_BEGIN_NAMESPACE_VERSION
43
44 // Used, in C++03 mode too, by allocators, etc.
45 /**
46 * @brief Same as C++11 std::addressof
47 * @ingroup utilities
48 */
49 template<typename _Tp>
50 inline _GLIBCXX_CONSTEXPR _Tp*
51 __addressof(_Tp& __r) _GLIBCXX_NOEXCEPT
52 { return __builtin_addressof(__r); }
53
54#if __cplusplus >= 201103L
55
56 /**
57 * @addtogroup utilities
58 * @{
59 */
60
61 /**
62 * @brief Forward an lvalue.
63 * @return The parameter cast to the specified type.
64 *
65 * This function is used to implement "perfect forwarding".
66 */
67 template<typename _Tp>
68 _GLIBCXX_NODISCARD
69 constexpr _Tp&&
70 forward(typename std::remove_reference<_Tp>::type& __t) noexcept
71 { return static_cast<_Tp&&>(__t); }
72
73 /**
74 * @brief Forward an rvalue.
75 * @return The parameter cast to the specified type.
76 *
77 * This function is used to implement "perfect forwarding".
78 */
79 template<typename _Tp>
80 _GLIBCXX_NODISCARD
81 constexpr _Tp&&
82 forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
83 {
85 "std::forward must not be used to convert an rvalue to an lvalue");
86 return static_cast<_Tp&&>(__t);
87 }
88
89#if __glibcxx_forward_like // C++ >= 23
90 template<typename _Tp, typename _Up>
91 struct __like_impl; // _Tp must be a reference and _Up an lvalue reference
92
93 template<typename _Tp, typename _Up>
94 struct __like_impl<_Tp&, _Up&>
95 { using type = _Up&; };
96
97 template<typename _Tp, typename _Up>
98 struct __like_impl<const _Tp&, _Up&>
99 { using type = const _Up&; };
100
101 template<typename _Tp, typename _Up>
102 struct __like_impl<_Tp&&, _Up&>
103 { using type = _Up&&; };
104
105 template<typename _Tp, typename _Up>
106 struct __like_impl<const _Tp&&, _Up&>
107 { using type = const _Up&&; };
108
109 template<typename _Tp, typename _Up>
110 using __like_t = typename __like_impl<_Tp&&, _Up&>::type;
111
112 template<typename _Tp, typename _Up>
113 [[nodiscard]]
114 constexpr __like_t<_Tp, _Up>
115 forward_like(_Up&& __x) noexcept
116 { return static_cast<__like_t<_Tp, _Up>>(__x); }
117#endif
118
119 /**
120 * @brief Convert a value to an rvalue.
121 * @param __t A thing of arbitrary type.
122 * @return The parameter cast to an rvalue-reference to allow moving it.
123 */
124 template<typename _Tp>
125 _GLIBCXX_NODISCARD
126 constexpr typename std::remove_reference<_Tp>::type&&
127 move(_Tp&& __t) noexcept
128 { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
129
130
131 template<typename _Tp>
132 struct __move_if_noexcept_cond
133 : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
134 is_copy_constructible<_Tp>>::type { };
135
136 /**
137 * @brief Conditionally convert a value to an rvalue.
138 * @param __x A thing of arbitrary type.
139 * @return The parameter, possibly cast to an rvalue-reference.
140 *
141 * Same as std::move unless the type's move constructor could throw and the
142 * type is copyable, in which case an lvalue-reference is returned instead.
143 */
144 template<typename _Tp>
145 _GLIBCXX_NODISCARD
146 constexpr
147 __conditional_t<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>
148 move_if_noexcept(_Tp& __x) noexcept
149 { return std::move(__x); }
150
151 // declval, from type_traits.
152
153 /**
154 * @brief Returns the actual address of the object or function
155 * referenced by r, even in the presence of an overloaded
156 * operator&.
157 * @param __r Reference to an object or function.
158 * @return The actual address.
159 */
160 template<typename _Tp>
161 _GLIBCXX_NODISCARD
162 inline _GLIBCXX17_CONSTEXPR _Tp*
163 addressof(_Tp& __r) noexcept
164 { return std::__addressof(__r); }
165
166 // _GLIBCXX_RESOLVE_LIB_DEFECTS
167 // 2598. addressof works on temporaries
168 template<typename _Tp>
169 const _Tp* addressof(const _Tp&&) = delete;
170
171 // C++11 version of std::exchange for internal use.
172 template <typename _Tp, typename _Up = _Tp>
173 _GLIBCXX20_CONSTEXPR
174 inline _Tp
175 __exchange(_Tp& __obj, _Up&& __new_val)
176 {
177 _Tp __old_val = std::move(__obj);
178 __obj = std::forward<_Up>(__new_val);
179 return __old_val;
180 }
181
182 /// @} group utilities
183
184#define _GLIBCXX_FWDREF(_Tp) _Tp&&
185#define _GLIBCXX_MOVE(__val) std::move(__val)
186#define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
187#else
188#define _GLIBCXX_FWDREF(_Tp) const _Tp&
189#define _GLIBCXX_MOVE(__val) (__val)
190#define _GLIBCXX_FORWARD(_Tp, __val) (__val)
191#endif
192
193 /**
194 * @addtogroup utilities
195 * @{
196 */
197
198 /**
199 * @brief Swaps two values.
200 * @param __a A thing of arbitrary type.
201 * @param __b Another thing of arbitrary type.
202 * @return Nothing.
203 */
204 template<typename _Tp>
205 _GLIBCXX20_CONSTEXPR
206 inline
207#if __cplusplus >= 201103L
208 typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
209 is_move_constructible<_Tp>,
210 is_move_assignable<_Tp>>::value>::type
211#else
212 void
213#endif
214 swap(_Tp& __a, _Tp& __b)
215 _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
217 {
218#if __cplusplus < 201103L
219 // concept requirements
220 __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
221#endif
222 _Tp __tmp = _GLIBCXX_MOVE(__a);
223 __a = _GLIBCXX_MOVE(__b);
224 __b = _GLIBCXX_MOVE(__tmp);
225 }
226
227 // _GLIBCXX_RESOLVE_LIB_DEFECTS
228 // DR 809. std::swap should be overloaded for array types.
229 /// Swap the contents of two arrays.
230 template<typename _Tp, size_t _Nm>
231 _GLIBCXX20_CONSTEXPR
232 inline
233#if __cplusplus >= 201103L
234 typename enable_if<__is_swappable<_Tp>::value>::type
235#else
236 void
237#endif
238 swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
239 _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
240 {
241 for (size_t __n = 0; __n < _Nm; ++__n)
242 swap(__a[__n], __b[__n]);
243 }
244
245 /// @} group utilities
246_GLIBCXX_END_NAMESPACE_VERSION
247} // namespace
248
249#endif /* _MOVE_H */
constexpr __conditional_t< __move_if_noexcept_cond< _Tp >::value, const _Tp &, _Tp && > move_if_noexcept(_Tp &__x) noexcept
Conditionally convert a value to an rvalue.
Definition move.h:148
constexpr _Tp * addressof(_Tp &__r) noexcept
Returns the actual address of the object or function referenced by r, even in the presence of an over...
Definition move.h:163
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:127
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition move.h:51
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:70
ISO C++ entities toplevel namespace is std.
is_lvalue_reference
Definition type_traits:578
is_nothrow_move_constructible
Definition type_traits:1252
is_nothrow_move_assignable
Definition type_traits:1320