libstdc++
move.h
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1 // Move, forward and identity for C++11 + swap -*- C++ -*-
2 
3 // Copyright (C) 2007-2025 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 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 
40 namespace 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  {
88  "std::forward must not be used to convert an rvalue to an lvalue");
89  return static_cast<_Tp&&>(__t);
90  }
91 
92 #if __glibcxx_forward_like // C++ >= 23
93  template<typename _Tp, typename _Up>
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&&; };
111 
112  template<typename _Tp, typename _Up>
113  using __like_t = typename __like_impl<_Tp&&, _Up&>::type;
114 
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 std::__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  * @return Nothing.
216  */
217  template<typename _Tp>
218  _GLIBCXX20_CONSTEXPR
219  inline
220 #if __cplusplus >= 201103L
221  typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
222  is_move_constructible<_Tp>,
223  is_move_assignable<_Tp>>::value>::type
224 #else
225  void
226 #endif
227  swap(_Tp& __a, _Tp& __b)
228  _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
230  {
231 #if __cplusplus < 201103L
232  // concept requirements
233  __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
234 #endif
235  _Tp __tmp = _GLIBCXX_MOVE(__a);
236  __a = _GLIBCXX_MOVE(__b);
237  __b = _GLIBCXX_MOVE(__tmp);
238  }
239 
240  // _GLIBCXX_RESOLVE_LIB_DEFECTS
241  // DR 809. std::swap should be overloaded for array types.
242  /// Swap the contents of two arrays.
243  template<typename _Tp, size_t _Nm>
244  _GLIBCXX20_CONSTEXPR
245  inline
246 #if __cplusplus >= 201103L
247  typename enable_if<__is_swappable<_Tp>::value>::type
248 #else
249  void
250 #endif
251  swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
252  _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
253  {
254  for (size_t __n = 0; __n < _Nm; ++__n)
255  swap(__a[__n], __b[__n]);
256  }
257 
258  /// @} group utilities
259 _GLIBCXX_END_NAMESPACE_VERSION
260 } // namespace
261 
262 #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:160
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:52
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:138
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:72
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
ISO C++ entities toplevel namespace is std.
is_lvalue_reference
Definition: type_traits:581
is_nothrow_move_constructible
Definition: type_traits:1263
is_nothrow_move_assignable
Definition: type_traits:1331