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4f5f9962 1// Move, forward and identity for C++11 + swap -*- C++ -*-
1476e59c 2
6441eb6d 3// Copyright (C) 2007-2025 Free Software Foundation, Inc.
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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
748086b7 8// Free Software Foundation; either version 3, or (at your option)
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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
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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/>.
1476e59c 24
f910786b 25/** @file bits/move.h
1476e59c 26 * This is an internal header file, included by other library headers.
f910786b 27 * Do not attempt to use it directly. @headername{utility}
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28 */
29
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30#ifndef _MOVE_H
31#define _MOVE_H 1
1476e59c 32
e14e932b 33#include <bits/c++config.h>
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34#if __cplusplus < 201103L
35# include <bits/concept_check.h>
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36#else
37# include <type_traits> // Brings in std::declval too.
6d0dff49 38#endif
e14e932b 39
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40namespace std _GLIBCXX_VISIBILITY(default)
41{
42_GLIBCXX_BEGIN_NAMESPACE_VERSION
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43
44 // Used, in C++03 mode too, by allocators, etc.
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45 /**
46 * @brief Same as C++11 std::addressof
47 * @ingroup utilities
48 */
882b3d5c 49 template<typename _Tp>
96c32a59 50 __attribute__((__always_inline__))
9e023e33 51 inline _GLIBCXX_CONSTEXPR _Tp*
5d861bf2 52 __addressof(_Tp& __r) _GLIBCXX_NOEXCEPT
9e023e33 53 { return __builtin_addressof(__r); }
882b3d5c 54
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55#if __cplusplus >= 201103L
56
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57 /**
58 * @addtogroup utilities
59 * @{
60 */
61
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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".
4a4e5394 67 * @since C++11
13901e4b 68 */
4c7aaebf 69 template<typename _Tp>
96c32a59 70 [[__nodiscard__,__gnu__::__always_inline__]]
a4eeb822 71 constexpr _Tp&&
5d861bf2 72 forward(typename std::remove_reference<_Tp>::type& __t) noexcept
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73 { return static_cast<_Tp&&>(__t); }
74
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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".
4a4e5394 80 * @since C++11
13901e4b 81 */
4c7aaebf 82 template<typename _Tp>
96c32a59 83 [[__nodiscard__,__gnu__::__always_inline__]]
a4eeb822 84 constexpr _Tp&&
5d861bf2 85 forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
ad269884 86 {
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87 static_assert(!std::is_lvalue_reference<_Tp>::value,
88 "std::forward must not be used to convert an rvalue to an lvalue");
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89 return static_cast<_Tp&&>(__t);
90 }
e7f1930f 91
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92#if __glibcxx_forward_like // C++ >= 23
93 template<typename _Tp, typename _Up>
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94 struct __like_impl; // _Tp must be a reference and _Up an lvalue reference
95
96 template<typename _Tp, typename _Up>
97 struct __like_impl<_Tp&, _Up&>
98 { using type = _Up&; };
99
100 template<typename _Tp, typename _Up>
101 struct __like_impl<const _Tp&, _Up&>
102 { using type = const _Up&; };
103
104 template<typename _Tp, typename _Up>
105 struct __like_impl<_Tp&&, _Up&>
106 { using type = _Up&&; };
107
108 template<typename _Tp, typename _Up>
109 struct __like_impl<const _Tp&&, _Up&>
110 { using type = const _Up&&; };
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111
112 template<typename _Tp, typename _Up>
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113 using __like_t = typename __like_impl<_Tp&&, _Up&>::type;
114
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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 */
8256d5c0 122 template<typename _Tp, typename _Up>
96c32a59 123 [[nodiscard,__gnu__::__always_inline__]]
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124 constexpr __like_t<_Tp, _Up>
125 forward_like(_Up&& __x) noexcept
126 { return static_cast<__like_t<_Tp, _Up>>(__x); }
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127#endif
128
fd9380a6 129 /**
13901e4b 130 * @brief Convert a value to an rvalue.
fd9380a6 131 * @param __t A thing of arbitrary type.
13901e4b 132 * @return The parameter cast to an rvalue-reference to allow moving it.
4a4e5394 133 * @since C++11
fd9380a6 134 */
1476e59c 135 template<typename _Tp>
96c32a59 136 [[__nodiscard__,__gnu__::__always_inline__]]
a4eeb822 137 constexpr typename std::remove_reference<_Tp>::type&&
5d861bf2 138 move(_Tp&& __t) noexcept
e7f1930f 139 { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
1476e59c 140
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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
1f428429 147 /**
13901e4b 148 * @brief Conditionally convert a value to an rvalue.
1f428429 149 * @param __x A thing of arbitrary type.
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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.
4a4e5394 154 * @since C++11
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155 */
156 template<typename _Tp>
96c32a59 157 [[__nodiscard__,__gnu__::__always_inline__]]
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158 constexpr
159 __conditional_t<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>
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160 move_if_noexcept(_Tp& __x) noexcept
161 { return std::move(__x); }
162
13901e4b 163 // declval, from type_traits.
7274deff 164
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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.
4a4e5394 171 * @since C++11
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172 */
173 template<typename _Tp>
96c32a59 174 [[__nodiscard__,__gnu__::__always_inline__]]
9e023e33 175 inline _GLIBCXX17_CONSTEXPR _Tp*
5d861bf2 176 addressof(_Tp& __r) noexcept
c91eb5a5 177 { return __builtin_addressof(__r); }
882b3d5c 178
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179 // _GLIBCXX_RESOLVE_LIB_DEFECTS
180 // 2598. addressof works on temporaries
181 template<typename _Tp>
182 const _Tp* addressof(const _Tp&&) = delete;
183
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184 // C++11 version of std::exchange for internal use.
185 template <typename _Tp, typename _Up = _Tp>
3a66e68a 186 _GLIBCXX20_CONSTEXPR
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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
13901e4b 195 /// @} group utilities
1476e59c 196
90bf60c3 197#define _GLIBCXX_FWDREF(_Tp) _Tp&&
5f1fd346 198#define _GLIBCXX_MOVE(__val) std::move(__val)
55dd8445 199#define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
d98f312c 200#else
90bf60c3 201#define _GLIBCXX_FWDREF(_Tp) const _Tp&
5f1fd346 202#define _GLIBCXX_MOVE(__val) (__val)
55dd8445 203#define _GLIBCXX_FORWARD(_Tp, __val) (__val)
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204#endif
205
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206 /**
207 * @addtogroup utilities
208 * @{
209 */
210
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211 /**
212 * @brief Swaps two values.
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213 * @param __a A thing of arbitrary type.
214 * @param __b Another thing of arbitrary type.
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215 * @return Nothing.
216 */
217 template<typename _Tp>
7a91c710 218 _GLIBCXX20_CONSTEXPR
ddb63209 219 inline
734f5023 220#if __cplusplus >= 201103L
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221 typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
222 is_move_constructible<_Tp>,
ddb63209 223 is_move_assignable<_Tp>>::value>::type
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224#else
225 void
173f26ae 226#endif
81912fb3 227 swap(_Tp& __a, _Tp& __b)
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228 _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
229 is_nothrow_move_assignable<_Tp>>::value)
e14e932b 230 {
6d0dff49 231#if __cplusplus < 201103L
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232 // concept requirements
233 __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
6d0dff49 234#endif
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235 _Tp __tmp = _GLIBCXX_MOVE(__a);
236 __a = _GLIBCXX_MOVE(__b);
237 __b = _GLIBCXX_MOVE(__tmp);
238 }
239
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240 // _GLIBCXX_RESOLVE_LIB_DEFECTS
241 // DR 809. std::swap should be overloaded for array types.
13901e4b 242 /// Swap the contents of two arrays.
caa8b3c6 243 template<typename _Tp, size_t _Nm>
7a91c710 244 _GLIBCXX20_CONSTEXPR
ddb63209 245 inline
734f5023 246#if __cplusplus >= 201103L
26b5ace7 247 typename enable_if<__is_swappable<_Tp>::value>::type
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248#else
249 void
ccb4f5a7 250#endif
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251 swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
252 _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
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253 {
254 for (size_t __n = 0; __n < _Nm; ++__n)
255 swap(__a[__n], __b[__n]);
256 }
257
13901e4b 258 /// @} group utilities
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259_GLIBCXX_END_NAMESPACE_VERSION
260} // namespace
e14e932b 261
caa8b3c6 262#endif /* _MOVE_H */