libstdc++
move.h
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1 // Move, forward and identity for C++11 + swap -*- C++ -*-
2 
3 // Copyright (C) 2007-2021 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 #endif
37 
38 namespace std _GLIBCXX_VISIBILITY(default)
39 {
40 _GLIBCXX_BEGIN_NAMESPACE_VERSION
41 
42  // Used, in C++03 mode too, by allocators, etc.
43  /**
44  * @brief Same as C++11 std::addressof
45  * @ingroup utilities
46  */
47  template<typename _Tp>
48  inline _GLIBCXX_CONSTEXPR _Tp*
49  __addressof(_Tp& __r) _GLIBCXX_NOEXCEPT
50  { return __builtin_addressof(__r); }
51 
52 #if __cplusplus >= 201103L
53 
54 _GLIBCXX_END_NAMESPACE_VERSION
55 } // namespace
56 
57 #include <type_traits> // Brings in std::declval too.
58 
59 namespace std _GLIBCXX_VISIBILITY(default)
60 {
61 _GLIBCXX_BEGIN_NAMESPACE_VERSION
62 
63  /**
64  * @addtogroup utilities
65  * @{
66  */
67 
68  /**
69  * @brief Forward an lvalue.
70  * @return The parameter cast to the specified type.
71  *
72  * This function is used to implement "perfect forwarding".
73  */
74  template<typename _Tp>
75  _GLIBCXX_NODISCARD
76  constexpr _Tp&&
77  forward(typename std::remove_reference<_Tp>::type& __t) noexcept
78  { return static_cast<_Tp&&>(__t); }
79 
80  /**
81  * @brief Forward an rvalue.
82  * @return The parameter cast to the specified type.
83  *
84  * This function is used to implement "perfect forwarding".
85  */
86  template<typename _Tp>
87  _GLIBCXX_NODISCARD
88  constexpr _Tp&&
89  forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
90  {
91  static_assert(!std::is_lvalue_reference<_Tp>::value, "template argument"
92  " substituting _Tp must not be an lvalue reference type");
93  return static_cast<_Tp&&>(__t);
94  }
95 
96  /**
97  * @brief Convert a value to an rvalue.
98  * @param __t A thing of arbitrary type.
99  * @return The parameter cast to an rvalue-reference to allow moving it.
100  */
101  template<typename _Tp>
102  _GLIBCXX_NODISCARD
103  constexpr typename std::remove_reference<_Tp>::type&&
104  move(_Tp&& __t) noexcept
105  { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
106 
107 
108  template<typename _Tp>
109  struct __move_if_noexcept_cond
110  : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
111  is_copy_constructible<_Tp>>::type { };
112 
113  /**
114  * @brief Conditionally convert a value to an rvalue.
115  * @param __x A thing of arbitrary type.
116  * @return The parameter, possibly cast to an rvalue-reference.
117  *
118  * Same as std::move unless the type's move constructor could throw and the
119  * type is copyable, in which case an lvalue-reference is returned instead.
120  */
121  template<typename _Tp>
122  _GLIBCXX_NODISCARD
123  constexpr typename
124  conditional<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>::type
125  move_if_noexcept(_Tp& __x) noexcept
126  { return std::move(__x); }
127 
128  // declval, from type_traits.
129 
130 #if __cplusplus > 201402L
131  // _GLIBCXX_RESOLVE_LIB_DEFECTS
132  // 2296. std::addressof should be constexpr
133 # define __cpp_lib_addressof_constexpr 201603
134 #endif
135  /**
136  * @brief Returns the actual address of the object or function
137  * referenced by r, even in the presence of an overloaded
138  * operator&.
139  * @param __r Reference to an object or function.
140  * @return The actual address.
141  */
142  template<typename _Tp>
143  _GLIBCXX_NODISCARD
144  inline _GLIBCXX17_CONSTEXPR _Tp*
145  addressof(_Tp& __r) noexcept
146  { return std::__addressof(__r); }
147 
148  // _GLIBCXX_RESOLVE_LIB_DEFECTS
149  // 2598. addressof works on temporaries
150  template<typename _Tp>
151  const _Tp* addressof(const _Tp&&) = delete;
152 
153  // C++11 version of std::exchange for internal use.
154  template <typename _Tp, typename _Up = _Tp>
155  _GLIBCXX20_CONSTEXPR
156  inline _Tp
157  __exchange(_Tp& __obj, _Up&& __new_val)
158  {
159  _Tp __old_val = std::move(__obj);
160  __obj = std::forward<_Up>(__new_val);
161  return __old_val;
162  }
163 
164  /// @} group utilities
165 
166 #define _GLIBCXX_FWDREF(_Tp) _Tp&&
167 #define _GLIBCXX_MOVE(__val) std::move(__val)
168 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
169 #else
170 #define _GLIBCXX_FWDREF(_Tp) const _Tp&
171 #define _GLIBCXX_MOVE(__val) (__val)
172 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
173 #endif
174 
175  /**
176  * @addtogroup utilities
177  * @{
178  */
179 
180  /**
181  * @brief Swaps two values.
182  * @param __a A thing of arbitrary type.
183  * @param __b Another thing of arbitrary type.
184  * @return Nothing.
185  */
186  template<typename _Tp>
187  _GLIBCXX20_CONSTEXPR
188  inline
189 #if __cplusplus >= 201103L
190  typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
191  is_move_constructible<_Tp>,
192  is_move_assignable<_Tp>>::value>::type
193 #else
194  void
195 #endif
196  swap(_Tp& __a, _Tp& __b)
197  _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
199  {
200 #if __cplusplus < 201103L
201  // concept requirements
202  __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
203 #endif
204  _Tp __tmp = _GLIBCXX_MOVE(__a);
205  __a = _GLIBCXX_MOVE(__b);
206  __b = _GLIBCXX_MOVE(__tmp);
207  }
208 
209  // _GLIBCXX_RESOLVE_LIB_DEFECTS
210  // DR 809. std::swap should be overloaded for array types.
211  /// Swap the contents of two arrays.
212  template<typename _Tp, size_t _Nm>
213  _GLIBCXX20_CONSTEXPR
214  inline
215 #if __cplusplus >= 201103L
216  typename enable_if<__is_swappable<_Tp>::value>::type
217 #else
218  void
219 #endif
220  swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
221  _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
222  {
223  for (size_t __n = 0; __n < _Nm; ++__n)
224  swap(__a[__n], __b[__n]);
225  }
226 
227  /// @} group utilities
228 _GLIBCXX_END_NAMESPACE_VERSION
229 } // namespace
230 
231 #endif /* _MOVE_H */
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:49
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:104
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:77
constexpr conditional< __move_if_noexcept_cond< _Tp >::value, const _Tp &, _Tp && >::type move_if_noexcept(_Tp &__x) noexcept
Conditionally convert a value to an rvalue.
Definition: move.h:125
void swap(any &__x, any &__y) noexcept
Exchange the states of two any objects.
Definition: any:422
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:145
ISO C++ entities toplevel namespace is std.
is_lvalue_reference
Definition: type_traits:456
is_nothrow_move_constructible
Definition: type_traits:1079
is_nothrow_move_assignable
Definition: type_traits:1185