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  */
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  [[nodiscard]]
92  constexpr decltype(auto)
93  forward_like(_Up&& __x) noexcept
94  {
95  constexpr bool __as_rval = is_rvalue_reference_v<_Tp&&>;
96 
97  if constexpr (is_const_v<remove_reference_t<_Tp>>)
98  {
99  using _Up2 = remove_reference_t<_Up>;
100  if constexpr (__as_rval)
101  return static_cast<const _Up2&&>(__x);
102  else
103  return static_cast<const _Up2&>(__x);
104  }
105  else
106  {
107  if constexpr (__as_rval)
108  return static_cast<remove_reference_t<_Up>&&>(__x);
109  else
110  return static_cast<_Up&>(__x);
111  }
112  }
113 
114  template<typename _Tp, typename _Up>
115  using __like_t = decltype(std::forward_like<_Tp>(std::declval<_Up>()));
116 #endif
117 
118  /**
119  * @brief Convert a value to an rvalue.
120  * @param __t A thing of arbitrary type.
121  * @return The parameter cast to an rvalue-reference to allow moving it.
122  */
123  template<typename _Tp>
124  _GLIBCXX_NODISCARD
125  constexpr typename std::remove_reference<_Tp>::type&&
126  move(_Tp&& __t) noexcept
127  { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
128 
129 
130  template<typename _Tp>
131  struct __move_if_noexcept_cond
132  : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
133  is_copy_constructible<_Tp>>::type { };
134 
135  /**
136  * @brief Conditionally convert a value to an rvalue.
137  * @param __x A thing of arbitrary type.
138  * @return The parameter, possibly cast to an rvalue-reference.
139  *
140  * Same as std::move unless the type's move constructor could throw and the
141  * type is copyable, in which case an lvalue-reference is returned instead.
142  */
143  template<typename _Tp>
144  _GLIBCXX_NODISCARD
145  constexpr
146  __conditional_t<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>
147  move_if_noexcept(_Tp& __x) noexcept
148  { return std::move(__x); }
149 
150  // declval, from type_traits.
151 
152  /**
153  * @brief Returns the actual address of the object or function
154  * referenced by r, even in the presence of an overloaded
155  * operator&.
156  * @param __r Reference to an object or function.
157  * @return The actual address.
158  */
159  template<typename _Tp>
160  _GLIBCXX_NODISCARD
161  inline _GLIBCXX17_CONSTEXPR _Tp*
162  addressof(_Tp& __r) noexcept
163  { return std::__addressof(__r); }
164 
165  // _GLIBCXX_RESOLVE_LIB_DEFECTS
166  // 2598. addressof works on temporaries
167  template<typename _Tp>
168  const _Tp* addressof(const _Tp&&) = delete;
169 
170  // C++11 version of std::exchange for internal use.
171  template <typename _Tp, typename _Up = _Tp>
172  _GLIBCXX20_CONSTEXPR
173  inline _Tp
174  __exchange(_Tp& __obj, _Up&& __new_val)
175  {
176  _Tp __old_val = std::move(__obj);
177  __obj = std::forward<_Up>(__new_val);
178  return __old_val;
179  }
180 
181  /// @} group utilities
182 
183 #define _GLIBCXX_FWDREF(_Tp) _Tp&&
184 #define _GLIBCXX_MOVE(__val) std::move(__val)
185 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
186 #else
187 #define _GLIBCXX_FWDREF(_Tp) const _Tp&
188 #define _GLIBCXX_MOVE(__val) (__val)
189 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
190 #endif
191 
192  /**
193  * @addtogroup utilities
194  * @{
195  */
196 
197  /**
198  * @brief Swaps two values.
199  * @param __a A thing of arbitrary type.
200  * @param __b Another thing of arbitrary type.
201  * @return Nothing.
202  */
203  template<typename _Tp>
204  _GLIBCXX20_CONSTEXPR
205  inline
206 #if __cplusplus >= 201103L
207  typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
208  is_move_constructible<_Tp>,
209  is_move_assignable<_Tp>>::value>::type
210 #else
211  void
212 #endif
213  swap(_Tp& __a, _Tp& __b)
214  _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
216  {
217 #if __cplusplus < 201103L
218  // concept requirements
219  __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
220 #endif
221  _Tp __tmp = _GLIBCXX_MOVE(__a);
222  __a = _GLIBCXX_MOVE(__b);
223  __b = _GLIBCXX_MOVE(__tmp);
224  }
225 
226  // _GLIBCXX_RESOLVE_LIB_DEFECTS
227  // DR 809. std::swap should be overloaded for array types.
228  /// Swap the contents of two arrays.
229  template<typename _Tp, size_t _Nm>
230  _GLIBCXX20_CONSTEXPR
231  inline
232 #if __cplusplus >= 201103L
233  typename enable_if<__is_swappable<_Tp>::value>::type
234 #else
235  void
236 #endif
237  swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
238  _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
239  {
240  for (size_t __n = 0; __n < _Nm; ++__n)
241  swap(__a[__n], __b[__n]);
242  }
243 
244  /// @} group utilities
245 _GLIBCXX_END_NAMESPACE_VERSION
246 } // namespace
247 
248 #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:147
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:51
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:126
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:70
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:162
ISO C++ entities toplevel namespace is std.
is_lvalue_reference
Definition: type_traits:562
is_nothrow_move_constructible
Definition: type_traits:1212
is_nothrow_move_assignable
Definition: type_traits:1280