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 
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  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  * @since C++11
67  */
68  template<typename _Tp>
69  _GLIBCXX_NODISCARD
70  constexpr _Tp&&
71  forward(typename std::remove_reference<_Tp>::type& __t) noexcept
72  { return static_cast<_Tp&&>(__t); }
73 
74  /**
75  * @brief Forward an rvalue.
76  * @return The parameter cast to the specified type.
77  *
78  * This function is used to implement "perfect forwarding".
79  * @since C++11
80  */
81  template<typename _Tp>
82  _GLIBCXX_NODISCARD
83  constexpr _Tp&&
84  forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
85  {
87  "std::forward must not be used to convert an rvalue to an lvalue");
88  return static_cast<_Tp&&>(__t);
89  }
90 
91 #if __glibcxx_forward_like // C++ >= 23
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  /** @brief Forward with the cv-qualifiers and value category of another type.
115  * @tparam _Tp An lvalue reference or rvalue reference.
116  * @tparam _Up An lvalue reference type deduced from the function argument.
117  * @param __x An lvalue.
118  * @return `__x` converted to match the qualifiers of `_Tp`.
119  * @since C++23
120  */
121  template<typename _Tp, typename _Up>
122  [[nodiscard]]
123  constexpr __like_t<_Tp, _Up>
124  forward_like(_Up&& __x) noexcept
125  { return static_cast<__like_t<_Tp, _Up>>(__x); }
126 #endif
127 
128  /**
129  * @brief Convert a value to an rvalue.
130  * @param __t A thing of arbitrary type.
131  * @return The parameter cast to an rvalue-reference to allow moving it.
132  * @since C++11
133  */
134  template<typename _Tp>
135  _GLIBCXX_NODISCARD
136  constexpr typename std::remove_reference<_Tp>::type&&
137  move(_Tp&& __t) noexcept
138  { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
139 
140 
141  template<typename _Tp>
142  struct __move_if_noexcept_cond
143  : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
144  is_copy_constructible<_Tp>>::type { };
145 
146  /**
147  * @brief Conditionally convert a value to an rvalue.
148  * @param __x A thing of arbitrary type.
149  * @return The parameter, possibly cast to an rvalue-reference.
150  *
151  * Same as std::move unless the type's move constructor could throw and the
152  * type is copyable, in which case an lvalue-reference is returned instead.
153  * @since C++11
154  */
155  template<typename _Tp>
156  _GLIBCXX_NODISCARD
157  constexpr
158  __conditional_t<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>
159  move_if_noexcept(_Tp& __x) noexcept
160  { return std::move(__x); }
161 
162  // declval, from type_traits.
163 
164  /**
165  * @brief Returns the actual address of the object or function
166  * referenced by r, even in the presence of an overloaded
167  * operator&.
168  * @param __r Reference to an object or function.
169  * @return The actual address.
170  * @since C++11
171  */
172  template<typename _Tp>
173  _GLIBCXX_NODISCARD
174  inline _GLIBCXX17_CONSTEXPR _Tp*
175  addressof(_Tp& __r) noexcept
176  { return std::__addressof(__r); }
177 
178  // _GLIBCXX_RESOLVE_LIB_DEFECTS
179  // 2598. addressof works on temporaries
180  template<typename _Tp>
181  const _Tp* addressof(const _Tp&&) = delete;
182 
183  // C++11 version of std::exchange for internal use.
184  template <typename _Tp, typename _Up = _Tp>
185  _GLIBCXX20_CONSTEXPR
186  inline _Tp
187  __exchange(_Tp& __obj, _Up&& __new_val)
188  {
189  _Tp __old_val = std::move(__obj);
190  __obj = std::forward<_Up>(__new_val);
191  return __old_val;
192  }
193 
194  /// @} group utilities
195 
196 #define _GLIBCXX_FWDREF(_Tp) _Tp&&
197 #define _GLIBCXX_MOVE(__val) std::move(__val)
198 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
199 #else
200 #define _GLIBCXX_FWDREF(_Tp) const _Tp&
201 #define _GLIBCXX_MOVE(__val) (__val)
202 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
203 #endif
204 
205  /**
206  * @addtogroup utilities
207  * @{
208  */
209 
210  /**
211  * @brief Swaps two values.
212  * @param __a A thing of arbitrary type.
213  * @param __b Another thing of arbitrary type.
214  * @return Nothing.
215  */
216  template<typename _Tp>
217  _GLIBCXX20_CONSTEXPR
218  inline
219 #if __cplusplus >= 201103L
220  typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
221  is_move_constructible<_Tp>,
222  is_move_assignable<_Tp>>::value>::type
223 #else
224  void
225 #endif
226  swap(_Tp& __a, _Tp& __b)
227  _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
229  {
230 #if __cplusplus < 201103L
231  // concept requirements
232  __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
233 #endif
234  _Tp __tmp = _GLIBCXX_MOVE(__a);
235  __a = _GLIBCXX_MOVE(__b);
236  __b = _GLIBCXX_MOVE(__tmp);
237  }
238 
239  // _GLIBCXX_RESOLVE_LIB_DEFECTS
240  // DR 809. std::swap should be overloaded for array types.
241  /// Swap the contents of two arrays.
242  template<typename _Tp, size_t _Nm>
243  _GLIBCXX20_CONSTEXPR
244  inline
245 #if __cplusplus >= 201103L
246  typename enable_if<__is_swappable<_Tp>::value>::type
247 #else
248  void
249 #endif
250  swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
251  _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
252  {
253  for (size_t __n = 0; __n < _Nm; ++__n)
254  swap(__a[__n], __b[__n]);
255  }
256 
257  /// @} group utilities
258 _GLIBCXX_END_NAMESPACE_VERSION
259 } // namespace
260 
261 #endif /* _MOVE_H */
ISO C++ entities toplevel namespace is std.
is_nothrow_move_assignable
Definition: type_traits:1277
is_lvalue_reference
Definition: type_traits:561
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:71
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:175
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:137
is_nothrow_move_constructible
Definition: type_traits:1210
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:159
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:51