libstdc++: move.h Source File

libstdc++

move.h
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1// Move, forward and identity for C++11 + swap -*- C++ -*-
2
3// Copyright (C) 2007-2026 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 __attribute__((__always_inline__))
51 inline _GLIBCXX_CONSTEXPR _Tp*
52 __addressof(_Tp& __r) _GLIBCXX_NOEXCEPT
53 { return __builtin_addressof(__r); }
54
55#if __cplusplus >= 201103L
56
57 /**
58 * @addtogroup utilities
59 * @{
60 */
61
62 /**
63 * @brief Forward an lvalue.
64 * @return The parameter cast to the specified type.
65 *
66 * This function is used to implement "perfect forwarding".
67 * @since C++11
68 */
69 template<typename _Tp>
70 [[__nodiscard__,__gnu__::__always_inline__]]
71 constexpr _Tp&&
72 forward(typename std::remove_reference<_Tp>::type& __t) noexcept
73 { return static_cast<_Tp&&>(__t); }
74
75 /**
76 * @brief Forward an rvalue.
77 * @return The parameter cast to the specified type.
78 *
79 * This function is used to implement "perfect forwarding".
80 * @since C++11
81 */
82 template<typename _Tp>
83 [[__nodiscard__,__gnu__::__always_inline__]]
84 constexpr _Tp&&
85 forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
86 {
87 static_assert(!std::is_lvalue_reference<_Tp>::value,
88 "std::forward must not be used to convert an rvalue to an lvalue");
89 return static_cast<_Tp&&>(__t);
90 }
91
92 template<typename _Tp, typename _Up>
93 struct __like_impl; // _Tp must be a reference and _Up an lvalue reference
94
95 template<typename _Tp, typename _Up>
96 struct __like_impl<_Tp&, _Up&>
97 { using type = _Up&; };
98
99 template<typename _Tp, typename _Up>
100 struct __like_impl<const _Tp&, _Up&>
101 { using type = const _Up&; };
102
103 template<typename _Tp, typename _Up>
104 struct __like_impl<_Tp&&, _Up&>
105 { using type = _Up&&; };
106
107 template<typename _Tp, typename _Up>
108 struct __like_impl<const _Tp&&, _Up&>
109 { using type = const _Up&&; };
110
111 template<typename _Tp, typename _Up>
112 using __like_t = typename __like_impl<_Tp&&, _Up&>::type;
113
114#if __glibcxx_forward_like // C++ >= 23
115 /** @brief Forward with the cv-qualifiers and value category of another type.
116 * @tparam _Tp An lvalue reference or rvalue reference.
117 * @tparam _Up An lvalue reference type deduced from the function argument.
118 * @param __x An lvalue.
119 * @return `__x` converted to match the qualifiers of `_Tp`.
120 * @since C++23
121 */
122 template<typename _Tp, typename _Up>
123 [[nodiscard,__gnu__::__always_inline__]]
124 constexpr __like_t<_Tp, _Up>
125 forward_like(_Up&& __x) noexcept
126 { return static_cast<__like_t<_Tp, _Up>>(__x); }
127#endif
128
129 /**
130 * @brief Convert a value to an rvalue.
131 * @param __t A thing of arbitrary type.
132 * @return The parameter cast to an rvalue-reference to allow moving it.
133 * @since C++11
134 */
135 template<typename _Tp>
136 [[__nodiscard__,__gnu__::__always_inline__]]
137 constexpr typename std::remove_reference<_Tp>::type&&
138 move(_Tp&& __t) noexcept
139 { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
140
141
142 template<typename _Tp>
143 struct __move_if_noexcept_cond
144 : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
145 is_copy_constructible<_Tp>>::type { };
146
147 /**
148 * @brief Conditionally convert a value to an rvalue.
149 * @param __x A thing of arbitrary type.
150 * @return The parameter, possibly cast to an rvalue-reference.
151 *
152 * Same as std::move unless the type's move constructor could throw and the
153 * type is copyable, in which case an lvalue-reference is returned instead.
154 * @since C++11
155 */
156 template<typename _Tp>
157 [[__nodiscard__,__gnu__::__always_inline__]]
158 constexpr
159 __conditional_t<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>
160 move_if_noexcept(_Tp& __x) noexcept
161 { return std::move(__x); }
162
163 // declval, from type_traits.
164
165 /**
166 * @brief Returns the actual address of the object or function
167 * referenced by r, even in the presence of an overloaded
168 * operator&.
169 * @param __r Reference to an object or function.
170 * @return The actual address.
171 * @since C++11
172 */
173 template<typename _Tp>
174 [[__nodiscard__,__gnu__::__always_inline__]]
175 inline _GLIBCXX17_CONSTEXPR _Tp*
176 addressof(_Tp& __r) noexcept
177 { return __builtin_addressof(__r); }
178
179 // _GLIBCXX_RESOLVE_LIB_DEFECTS
180 // 2598. addressof works on temporaries
181 template<typename _Tp>
182 const _Tp* addressof(const _Tp&&) = delete;
183
184 // C++11 version of std::exchange for internal use.
185 template <typename _Tp, typename _Up = _Tp>
186 _GLIBCXX20_CONSTEXPR
187 inline _Tp
188 __exchange(_Tp& __obj, _Up&& __new_val)
189 {
190 _Tp __old_val = std::move(__obj);
191 __obj = std::forward<_Up>(__new_val);
192 return __old_val;
193 }
194
195 /// @} group utilities
196
197#define _GLIBCXX_FWDREF(_Tp) _Tp&&
198#define _GLIBCXX_MOVE(__val) std::move(__val)
199#define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
200#else
201#define _GLIBCXX_FWDREF(_Tp) const _Tp&
202#define _GLIBCXX_MOVE(__val) (__val)
203#define _GLIBCXX_FORWARD(_Tp, __val) (__val)
204#endif
205
206 /**
207 * @addtogroup utilities
208 * @{
209 */
210
211 /**
212 * @brief Swaps two values.
213 * @param __a A thing of arbitrary type.
214 * @param __b Another thing of arbitrary type.
215 */
216 template<typename _Tp>
217#if __glibcxx_concepts // >= C++20
218 requires (! __is_tuple_like<_Tp>::value)
219 && is_move_constructible_v<_Tp>
220 && is_move_assignable_v<_Tp>
221 constexpr void
222#elif __cplusplus >= 201103L
223 _GLIBCXX20_CONSTEXPR inline
224 __enable_if_t<__and_<__not_<__is_tuple_like<_Tp>>,
225 is_move_constructible<_Tp>,
226 is_move_assignable<_Tp>>::value>
227#else
228 inline void
229#endif
230 swap(_Tp& __a, _Tp& __b)
231 _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
232 is_nothrow_move_assignable<_Tp>>::value)
233 {
234#if __cplusplus < 201103L
235 // concept requirements
236 __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
237#endif
238 _Tp __tmp = _GLIBCXX_MOVE(__a);
239 __a = _GLIBCXX_MOVE(__b);
240 __b = _GLIBCXX_MOVE(__tmp);
241 }
242
243 // _GLIBCXX_RESOLVE_LIB_DEFECTS
244 // DR 809. std::swap should be overloaded for array types.
245 /// Swap the contents of two arrays.
246 template<typename _Tp, size_t _Nm>
247#if __glibcxx_concepts // >= C++20
248 requires is_swappable_v<_Tp>
249 constexpr void
250#elif __cplusplus >= 201103L
251 _GLIBCXX20_CONSTEXPR inline
252 __enable_if_t<__is_swappable<_Tp>::value>
253#else
254 inline void
255#endif
256 swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
257 _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
258 {
259 for (size_t __n = 0; __n < _Nm; ++__n)
260 swap(__a[__n], __b[__n]);
261 }
262
263 /// @} group utilities
264_GLIBCXX_END_NAMESPACE_VERSION
265} // namespace
266
267#endif /* _MOVE_H */
type_traits
concept_check.h
c++config.h
std::move_if_noexcept
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:160
std::forward_like
constexpr __like_t< _Tp, _Up > forward_like(_Up &&__x) noexcept
Forward with the cv-qualifiers and value category of another type.
Definition move.h:125
std::addressof
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:176
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition move.h:52
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:72
std
ISO C++ entities toplevel namespace is std.
std::is_lvalue_reference
is_lvalue_reference
Definition type_traits:677
std::is_move_constructible
is_move_constructible
Definition type_traits:1328
std::is_nothrow_move_constructible
is_nothrow_move_constructible
Definition type_traits:1370
std::is_move_assignable
is_move_assignable
Definition type_traits:1403
std::is_nothrow_move_assignable
is_nothrow_move_assignable
Definition type_traits:1438