libstdc++
move.h
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1 // Move, forward and identity for C++11 + swap -*- C++ -*-
2 
3 // Copyright (C) 2007-2019 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 #include <bits/concept_check.h>
35 
36 namespace std _GLIBCXX_VISIBILITY(default)
37 {
38 _GLIBCXX_BEGIN_NAMESPACE_VERSION
39 
40  // Used, in C++03 mode too, by allocators, etc.
41  /**
42  * @brief Same as C++11 std::addressof
43  * @ingroup utilities
44  */
45  template<typename _Tp>
46  inline _GLIBCXX_CONSTEXPR _Tp*
47  __addressof(_Tp& __r) _GLIBCXX_NOEXCEPT
48  { return __builtin_addressof(__r); }
49 
50 #if __cplusplus >= 201103L
51 
52 _GLIBCXX_END_NAMESPACE_VERSION
53 } // namespace
54 
55 #include <type_traits> // Brings in std::declval too.
56 
57 namespace std _GLIBCXX_VISIBILITY(default)
58 {
59 _GLIBCXX_BEGIN_NAMESPACE_VERSION
60 
61  /**
62  * @addtogroup utilities
63  * @{
64  */
65 
66  /**
67  * @brief Forward an lvalue.
68  * @return The parameter cast to the specified type.
69  *
70  * This function is used to implement "perfect forwarding".
71  */
72  template<typename _Tp>
73  constexpr _Tp&&
74  forward(typename std::remove_reference<_Tp>::type& __t) noexcept
75  { return static_cast<_Tp&&>(__t); }
76 
77  /**
78  * @brief Forward an rvalue.
79  * @return The parameter cast to the specified type.
80  *
81  * This function is used to implement "perfect forwarding".
82  */
83  template<typename _Tp>
84  constexpr _Tp&&
85  forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
86  {
87  static_assert(!std::is_lvalue_reference<_Tp>::value, "template argument"
88  " substituting _Tp is an lvalue reference type");
89  return static_cast<_Tp&&>(__t);
90  }
91 
92  /**
93  * @brief Convert a value to an rvalue.
94  * @param __t A thing of arbitrary type.
95  * @return The parameter cast to an rvalue-reference to allow moving it.
96  */
97  template<typename _Tp>
98  constexpr typename std::remove_reference<_Tp>::type&&
99  move(_Tp&& __t) noexcept
100  { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
101 
102 
103  template<typename _Tp>
104  struct __move_if_noexcept_cond
105  : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
106  is_copy_constructible<_Tp>>::type { };
107 
108  /**
109  * @brief Conditionally convert a value to an rvalue.
110  * @param __x A thing of arbitrary type.
111  * @return The parameter, possibly cast to an rvalue-reference.
112  *
113  * Same as std::move unless the type's move constructor could throw and the
114  * type is copyable, in which case an lvalue-reference is returned instead.
115  */
116  template<typename _Tp>
117  constexpr typename
118  conditional<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>::type
119  move_if_noexcept(_Tp& __x) noexcept
120  { return std::move(__x); }
121 
122  // declval, from type_traits.
123 
124 #if __cplusplus > 201402L
125  // _GLIBCXX_RESOLVE_LIB_DEFECTS
126  // 2296. std::addressof should be constexpr
127 # define __cpp_lib_addressof_constexpr 201603
128 #endif
129  /**
130  * @brief Returns the actual address of the object or function
131  * referenced by r, even in the presence of an overloaded
132  * operator&.
133  * @param __r Reference to an object or function.
134  * @return The actual address.
135  */
136  template<typename _Tp>
137  inline _GLIBCXX17_CONSTEXPR _Tp*
138  addressof(_Tp& __r) noexcept
139  { return std::__addressof(__r); }
140 
141  // _GLIBCXX_RESOLVE_LIB_DEFECTS
142  // 2598. addressof works on temporaries
143  template<typename _Tp>
144  const _Tp* addressof(const _Tp&&) = delete;
145 
146  // C++11 version of std::exchange for internal use.
147  template <typename _Tp, typename _Up = _Tp>
148  inline _Tp
149  __exchange(_Tp& __obj, _Up&& __new_val)
150  {
151  _Tp __old_val = std::move(__obj);
152  __obj = std::forward<_Up>(__new_val);
153  return __old_val;
154  }
155 
156  /// @} group utilities
157 
158 #define _GLIBCXX_MOVE(__val) std::move(__val)
159 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
160 #else
161 #define _GLIBCXX_MOVE(__val) (__val)
162 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
163 #endif
164 
165  /**
166  * @addtogroup utilities
167  * @{
168  */
169 
170  /**
171  * @brief Swaps two values.
172  * @param __a A thing of arbitrary type.
173  * @param __b Another thing of arbitrary type.
174  * @return Nothing.
175  */
176  template<typename _Tp>
177  inline
178 #if __cplusplus >= 201103L
179  typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
180  is_move_constructible<_Tp>,
181  is_move_assignable<_Tp>>::value>::type
182  swap(_Tp& __a, _Tp& __b)
183  noexcept(__and_<is_nothrow_move_constructible<_Tp>,
185 #else
186  void
187  swap(_Tp& __a, _Tp& __b)
188 #endif
189  {
190  // concept requirements
191  __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
192 
193  _Tp __tmp = _GLIBCXX_MOVE(__a);
194  __a = _GLIBCXX_MOVE(__b);
195  __b = _GLIBCXX_MOVE(__tmp);
196  }
197 
198  // _GLIBCXX_RESOLVE_LIB_DEFECTS
199  // DR 809. std::swap should be overloaded for array types.
200  /// Swap the contents of two arrays.
201  template<typename _Tp, size_t _Nm>
202  inline
203 #if __cplusplus >= 201103L
204  typename enable_if<__is_swappable<_Tp>::value>::type
205  swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
206  noexcept(__is_nothrow_swappable<_Tp>::value)
207 #else
208  void
209  swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
210 #endif
211  {
212  for (size_t __n = 0; __n < _Nm; ++__n)
213  swap(__a[__n], __b[__n]);
214  }
215 
216  /// @} group utilities
217 _GLIBCXX_END_NAMESPACE_VERSION
218 } // namespace
219 
220 #endif /* _MOVE_H */
ISO C++ entities toplevel namespace is std.
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:119
is_nothrow_move_constructible
Definition: type_traits:1011
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition: move.h:74
is_nothrow_move_assignable
Definition: type_traits:1101
is_lvalue_reference
Definition: type_traits:385
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:47
_GLIBCXX17_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:138