1 // Move, forward and identity for C++11 + swap -*- C++ -*-
2
3 // Copyright (C) 2007-2023 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 {
84 static_assert(!std::is_lvalue_reference<_Tp>::value,
85 "std::forward must not be used to convert an rvalue to an lvalue");
86 return static_cast<_Tp&&>(__t);
87 }
88
89 /**
90 * @brief Convert a value to an rvalue.
91 * @param __t A thing of arbitrary type.
92 * @return The parameter cast to an rvalue-reference to allow moving it.
93 */
94 template<typename _Tp>
95 _GLIBCXX_NODISCARD
96 constexpr typename std::remove_reference<_Tp>::type&&
97 move(_Tp&& __t) noexcept
98 { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
99
100
101 template<typename _Tp>
102 struct __move_if_noexcept_cond
103 : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
104 is_copy_constructible<_Tp>>::type { };
105
106 /**
107 * @brief Conditionally convert a value to an rvalue.
108 * @param __x A thing of arbitrary type.
109 * @return The parameter, possibly cast to an rvalue-reference.
110 *
111 * Same as std::move unless the type's move constructor could throw and the
112 * type is copyable, in which case an lvalue-reference is returned instead.
113 */
114 template<typename _Tp>
115 _GLIBCXX_NODISCARD
116 constexpr
117 __conditional_t<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>
118 move_if_noexcept(_Tp& __x) noexcept
119 { return std::move(__x); }
120
121 // declval, from type_traits.
122
123 #if __cplusplus > 201402L
124 // _GLIBCXX_RESOLVE_LIB_DEFECTS
125 // 2296. std::addressof should be constexpr
126 # define __cpp_lib_addressof_constexpr 201603L
127 #endif
128 /**
129 * @brief Returns the actual address of the object or function
130 * referenced by r, even in the presence of an overloaded
131 * operator&.
132 * @param __r Reference to an object or function.
133 * @return The actual address.
134 */
135 template<typename _Tp>
136 _GLIBCXX_NODISCARD
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 _GLIBCXX20_CONSTEXPR
149 inline _Tp
150 __exchange(_Tp& __obj, _Up&& __new_val)
151 {
152 _Tp __old_val = std::move(__obj);
153 __obj = std::forward<_Up>(__new_val);
154 return __old_val;
155 }
156
157 /// @} group utilities
158
159 #define _GLIBCXX_FWDREF(_Tp) _Tp&&
160 #define _GLIBCXX_MOVE(__val) std::move(__val)
161 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
162 #else
163 #define _GLIBCXX_FWDREF(_Tp) const _Tp&
164 #define _GLIBCXX_MOVE(__val) (__val)
165 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
166 #endif
167
168 /**
169 * @addtogroup utilities
170 * @{
171 */
172
173 /**
174 * @brief Swaps two values.
175 * @param __a A thing of arbitrary type.
176 * @param __b Another thing of arbitrary type.
177 * @return Nothing.
178 */
179 template<typename _Tp>
180 _GLIBCXX20_CONSTEXPR
181 inline
182 #if __cplusplus >= 201103L
183 typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
184 is_move_constructible<_Tp>,
185 is_move_assignable<_Tp>>::value>::type
186 #else
187 void
188 #endif
189 swap(_Tp& __a, _Tp& __b)
190 _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
191 is_nothrow_move_assignable<_Tp>>::value)
192 {
193 #if __cplusplus < 201103L
194 // concept requirements
195 __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
196 #endif
197 _Tp __tmp = _GLIBCXX_MOVE(__a);
198 __a = _GLIBCXX_MOVE(__b);
199 __b = _GLIBCXX_MOVE(__tmp);
200 }
201
202 // _GLIBCXX_RESOLVE_LIB_DEFECTS
203 // DR 809. std::swap should be overloaded for array types.
204 /// Swap the contents of two arrays.
205 template<typename _Tp, size_t _Nm>
206 _GLIBCXX20_CONSTEXPR
207 inline
208 #if __cplusplus >= 201103L
209 typename enable_if<__is_swappable<_Tp>::value>::type
210 #else
211 void
212 #endif
213 swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
214 _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
215 {
216 for (size_t __n = 0; __n < _Nm; ++__n)
217 swap(__a[__n], __b[__n]);
218 }
219
220 /// @} group utilities
221 _GLIBCXX_END_NAMESPACE_VERSION
222 } // namespace
223
224 #endif /* _MOVE_H */