libstdc++
stl_construct.h
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1// nonstandard construct and destroy functions -*- C++ -*-
2
3// Copyright (C) 2001-2025 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/*
26 *
27 * Copyright (c) 1994
28 * Hewlett-Packard Company
29 *
30 * Permission to use, copy, modify, distribute and sell this software
31 * and its documentation for any purpose is hereby granted without fee,
32 * provided that the above copyright notice appear in all copies and
33 * that both that copyright notice and this permission notice appear
34 * in supporting documentation. Hewlett-Packard Company makes no
35 * representations about the suitability of this software for any
36 * purpose. It is provided "as is" without express or implied warranty.
37 *
38 *
39 * Copyright (c) 1996,1997
40 * Silicon Graphics Computer Systems, Inc.
41 *
42 * Permission to use, copy, modify, distribute and sell this software
43 * and its documentation for any purpose is hereby granted without fee,
44 * provided that the above copyright notice appear in all copies and
45 * that both that copyright notice and this permission notice appear
46 * in supporting documentation. Silicon Graphics makes no
47 * representations about the suitability of this software for any
48 * purpose. It is provided "as is" without express or implied warranty.
49 */
50
51/** @file bits/stl_construct.h
52 * This is an internal header file, included by other library headers.
53 * Do not attempt to use it directly. @headername{memory}
54 */
55
56#ifndef _STL_CONSTRUCT_H
57#define _STL_CONSTRUCT_H 1
58
59#include <new>
60#include <bits/move.h>
61#include <bits/stl_iterator_base_types.h> // for iterator_traits
62#include <bits/stl_iterator_base_funcs.h> // for advance
63
64/* This file provides the C++17 functions std::destroy_at, std::destroy, and
65 * std::destroy_n, and the C++20 function std::construct_at.
66 * It also provides std::_Construct, std::_Destroy,and std::_Destroy_n functions
67 * which are defined in all standard modes and so can be used in C++98-14 code.
68 * The _Destroy functions will dispatch to destroy_at during constant
69 * evaluation, because calls to that function are intercepted by the compiler
70 * to allow use in constant expressions.
71 */
72
73namespace std _GLIBCXX_VISIBILITY(default)
74{
75_GLIBCXX_BEGIN_NAMESPACE_VERSION
76
77#if __glibcxx_raw_memory_algorithms // >= C++17
78 template <typename _Tp>
79 _GLIBCXX20_CONSTEXPR inline void
80 destroy_at(_Tp* __location)
81 {
82 if constexpr (__cplusplus > 201703L && is_array_v<_Tp>)
83 {
84 for (auto& __x : *__location)
85 std::destroy_at(std::__addressof(__x));
86 }
87 else
88 __location->~_Tp();
89 }
90
91#if __cpp_constexpr_dynamic_alloc // >= C++20
92 template<typename _Tp, typename... _Args>
93 requires (!is_unbounded_array_v<_Tp>)
94 && requires { ::new((void*)0) _Tp(std::declval<_Args>()...); }
95 constexpr _Tp*
96 construct_at(_Tp* __location, _Args&&... __args)
97 noexcept(noexcept(::new((void*)0) _Tp(std::declval<_Args>()...)))
98 {
99 void* __loc = __location;
100 // _GLIBCXX_RESOLVE_LIB_DEFECTS
101 // 3436. std::construct_at should support arrays
102 if constexpr (is_array_v<_Tp>)
103 {
104 static_assert(sizeof...(_Args) == 0, "std::construct_at for array "
105 "types must not use any arguments to initialize the "
106 "array");
107 return ::new(__loc) _Tp[1]();
108 }
109 else
110 return ::new(__loc) _Tp(std::forward<_Args>(__args)...);
111 }
112#endif // C++20
113#endif// C++17
114
115 /**
116 * Constructs an object in existing memory by invoking an allocated
117 * object's constructor with an initializer.
118 */
119#if __cplusplus >= 201103L
120 template<typename _Tp, typename... _Args>
121 _GLIBCXX20_CONSTEXPR
122 inline void
123 _Construct(_Tp* __p, _Args&&... __args)
124 {
125#if __cpp_constexpr_dynamic_alloc // >= C++20
126 if (std::__is_constant_evaluated())
127 {
128 // Allow std::_Construct to be used in constant expressions.
129 std::construct_at(__p, std::forward<_Args>(__args)...);
130 return;
131 }
132#endif
133 ::new(static_cast<void*>(__p)) _Tp(std::forward<_Args>(__args)...);
134 }
135#else
136 template<typename _T1, typename _T2>
137 inline void
138 _Construct(_T1* __p, const _T2& __value)
139 {
140 // _GLIBCXX_RESOLVE_LIB_DEFECTS
141 // 402. wrong new expression in [some_]allocator::construct
142 ::new(static_cast<void*>(__p)) _T1(__value);
143 }
144#endif
145
146 template<typename _T1>
147 _GLIBCXX26_CONSTEXPR
148 inline void
149 _Construct_novalue(_T1* __p)
150 { ::new(static_cast<void*>(__p)) _T1; }
151
152 template<typename _ForwardIterator>
153 _GLIBCXX20_CONSTEXPR void
154 _Destroy(_ForwardIterator __first, _ForwardIterator __last);
155
156 /**
157 * Destroy the object pointed to by a pointer type.
158 */
159 template<typename _Tp>
160 _GLIBCXX14_CONSTEXPR inline void
161 _Destroy(_Tp* __pointer)
162 {
163#if __cpp_constexpr_dynamic_alloc // >= C++20
164 std::destroy_at(__pointer);
165#else
166 __pointer->~_Tp();
167#endif
168 }
169
170#pragma GCC diagnostic push
171#pragma GCC diagnostic ignored "-Wc++17-extensions" // for if-constexpr
172
173#if __cplusplus < 201103L
174 template<bool>
175 struct _Destroy_aux
176 {
177 template<typename _ForwardIterator>
178 static _GLIBCXX20_CONSTEXPR void
179 __destroy(_ForwardIterator __first, _ForwardIterator __last)
180 {
181 for (; __first != __last; ++__first)
183 }
184 };
185
186 template<>
187 struct _Destroy_aux<true>
188 {
189 template<typename _ForwardIterator>
190 static void
191 __destroy(_ForwardIterator, _ForwardIterator) { }
192 };
193#endif
194
195 /**
196 * Destroy a range of objects. If the value_type of the object has
197 * a trivial destructor, the compiler should optimize all of this
198 * away, otherwise the objects' destructors must be invoked.
199 */
200 template<typename _ForwardIterator>
201 _GLIBCXX20_CONSTEXPR inline void
203 {
205 _Value_type;
206#if __cplusplus >= 201103L
207 // A deleted destructor is trivial, this ensures we reject such types:
209 "value type is destructible");
210 if constexpr (!__has_trivial_destructor(_Value_type))
211 for (; __first != __last; ++__first)
213#if __cpp_constexpr_dynamic_alloc // >= C++20
214 else if (std::__is_constant_evaluated())
215 for (; __first != __last; ++__first)
216 std::destroy_at(std::__addressof(*__first));
217#endif
218#else
220 __destroy(__first, __last);
221#endif
222 }
223
224#if __cplusplus < 201103L
225 template<bool>
226 struct _Destroy_n_aux
227 {
228 template<typename _ForwardIterator, typename _Size>
229 static _GLIBCXX20_CONSTEXPR _ForwardIterator
230 __destroy_n(_ForwardIterator __first, _Size __count)
231 {
232 for (; __count > 0; (void)++__first, --__count)
234 return __first;
235 }
236 };
237
238 template<>
239 struct _Destroy_n_aux<true>
240 {
241 template<typename _ForwardIterator, typename _Size>
242 static _ForwardIterator
243 __destroy_n(_ForwardIterator __first, _Size __count)
244 {
245 std::advance(__first, __count);
246 return __first;
247 }
248 };
249#endif
250
251 /**
252 * Destroy a range of objects. If the value_type of the object has
253 * a trivial destructor, the compiler should optimize all of this
254 * away, otherwise the objects' destructors must be invoked.
255 */
256 template<typename _ForwardIterator, typename _Size>
257 _GLIBCXX20_CONSTEXPR inline _ForwardIterator
258 _Destroy_n(_ForwardIterator __first, _Size __count)
259 {
261 _Value_type;
262#if __cplusplus >= 201103L
263 // A deleted destructor is trivial, this ensures we reject such types:
265 "value type is destructible");
266 if constexpr (!__has_trivial_destructor(_Value_type))
267 for (; __count > 0; (void)++__first, --__count)
269#if __cpp_constexpr_dynamic_alloc // >= C++20
270 else if (std::__is_constant_evaluated())
271 for (; __count > 0; (void)++__first, --__count)
272 std::destroy_at(std::__addressof(*__first));
273#endif
274 else
275 std::advance(__first, __count);
276 return __first;
277#else
278 return std::_Destroy_n_aux<__has_trivial_destructor(_Value_type)>::
279 __destroy_n(__first, __count);
280#endif
281 }
282#pragma GCC diagnostic pop
283
284#if __glibcxx_raw_memory_algorithms // >= C++17
285 template <typename _ForwardIterator>
286 _GLIBCXX20_CONSTEXPR inline void
287 destroy(_ForwardIterator __first, _ForwardIterator __last)
288 {
289 std::_Destroy(__first, __last);
290 }
291
292 template <typename _ForwardIterator, typename _Size>
293 _GLIBCXX20_CONSTEXPR inline _ForwardIterator
294 destroy_n(_ForwardIterator __first, _Size __count)
295 {
296 return std::_Destroy_n(__first, __count);
297 }
298#endif // C++17
299
300_GLIBCXX_END_NAMESPACE_VERSION
301} // namespace std
302
303#endif /* _STL_CONSTRUCT_H */
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition move.h:52
ISO C++ entities toplevel namespace is std.
constexpr _ForwardIterator _Destroy_n(_ForwardIterator __first, _Size __count)
constexpr void _Construct(_Tp *__p, _Args &&... __args)
constexpr void advance(_InputIterator &__i, _Distance __n)
A generalization of pointer arithmetic.
constexpr void _Destroy(_ForwardIterator __first, _ForwardIterator __last)
is_destructible
Definition type_traits:1089
Traits class for iterators.