1// nonstandard construct and destroy functions -*- C++ -*-
2
3// Copyright (C) 2001-2021 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/*
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 __cplusplus >= 201703L
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 __cplusplus >= 202002L
92 template<typename _Tp, typename... _Args>
93 constexpr auto
94 construct_at(_Tp* __location, _Args&&... __args)
95 noexcept(noexcept(::new((void*)0) _Tp(std::declval<_Args>()...)))
96 -> decltype(::new((void*)0) _Tp(std::declval<_Args>()...))
97 { return ::new((void*)__location) _Tp(std::forward<_Args>(__args)...); }
98#endif // C++20
99#endif// C++17
100
101 /**
102 * Constructs an object in existing memory by invoking an allocated
103 * object's constructor with an initializer.
104 */
105#if __cplusplus >= 201103L
106 template<typename _Tp, typename... _Args>
107 _GLIBCXX20_CONSTEXPR
108 inline void
109 _Construct(_Tp* __p, _Args&&... __args)
110 {
111#if __cplusplus >= 202002L && __has_builtin(__builtin_is_constant_evaluated)
112 if (__builtin_is_constant_evaluated())
113 {
114 // Allow std::_Construct to be used in constant expressions.
115 std::construct_at(__p, std::forward<_Args>(__args)...);
116 return;
117 }
118#endif
119 ::new((void*)__p) _Tp(std::forward<_Args>(__args)...);
120 }
121#else
122 template<typename _T1, typename _T2>
123 inline void
124 _Construct(_T1* __p, const _T2& __value)
125 {
126 // _GLIBCXX_RESOLVE_LIB_DEFECTS
127 // 402. wrong new expression in [some_]allocator::construct
128 ::new(static_cast<void*>(__p)) _T1(__value);
129 }
130#endif
131
132 template<typename _T1>
133 inline void
134 _Construct_novalue(_T1* __p)
135 { ::new((void*)__p) _T1; }
136
137 template<typename _ForwardIterator>
138 _GLIBCXX20_CONSTEXPR void
139 _Destroy(_ForwardIterator __first, _ForwardIterator __last);
140
141 /**
142 * Destroy the object pointed to by a pointer type.
143 */
144 template<typename _Tp>
145 _GLIBCXX14_CONSTEXPR inline void
146 _Destroy(_Tp* __pointer)
147 {
148#if __cplusplus > 201703L
149 std::destroy_at(__pointer);
150#else
151 __pointer->~_Tp();
152#endif
153 }
154
155 template<bool>
156 struct _Destroy_aux
157 {
158 template<typename _ForwardIterator>
159 static _GLIBCXX20_CONSTEXPR void
160 __destroy(_ForwardIterator __first, _ForwardIterator __last)
161 {
162 for (; __first != __last; ++__first)
163 std::_Destroy(std::__addressof(*__first));
164 }
165 };
166
167 template<>
168 struct _Destroy_aux<true>
169 {
170 template<typename _ForwardIterator>
171 static void
172 __destroy(_ForwardIterator, _ForwardIterator) { }
173 };
174
175 /**
176 * Destroy a range of objects. If the value_type of the object has
177 * a trivial destructor, the compiler should optimize all of this
178 * away, otherwise the objects' destructors must be invoked.
179 */
180 template<typename _ForwardIterator>
181 _GLIBCXX20_CONSTEXPR inline void
182 _Destroy(_ForwardIterator __first, _ForwardIterator __last)
183 {
184 typedef typename iterator_traits<_ForwardIterator>::value_type
185 _Value_type;
186#if __cplusplus >= 201103L
187 // A deleted destructor is trivial, this ensures we reject such types:
188 static_assert(is_destructible<_Value_type>::value,
189 "value type is destructible");
190#endif
191#if __cplusplus > 201703L && defined __cpp_lib_is_constant_evaluated
192 if (std::is_constant_evaluated())
193 return _Destroy_aux<false>::__destroy(__first, __last);
194#endif
195 std::_Destroy_aux<__has_trivial_destructor(_Value_type)>::
196 __destroy(__first, __last);
197 }
198
199 template<bool>
200 struct _Destroy_n_aux
201 {
202 template<typename _ForwardIterator, typename _Size>
203 static _GLIBCXX20_CONSTEXPR _ForwardIterator
204 __destroy_n(_ForwardIterator __first, _Size __count)
205 {
206 for (; __count > 0; (void)++__first, --__count)
207 std::_Destroy(std::__addressof(*__first));
208 return __first;
209 }
210 };
211
212 template<>
213 struct _Destroy_n_aux<true>
214 {
215 template<typename _ForwardIterator, typename _Size>
216 static _ForwardIterator
217 __destroy_n(_ForwardIterator __first, _Size __count)
218 {
219 std::advance(__first, __count);
220 return __first;
221 }
222 };
223
224 /**
225 * Destroy a range of objects. If the value_type of the object has
226 * a trivial destructor, the compiler should optimize all of this
227 * away, otherwise the objects' destructors must be invoked.
228 */
229 template<typename _ForwardIterator, typename _Size>
230 _GLIBCXX20_CONSTEXPR inline _ForwardIterator
231 _Destroy_n(_ForwardIterator __first, _Size __count)
232 {
233 typedef typename iterator_traits<_ForwardIterator>::value_type
234 _Value_type;
235#if __cplusplus >= 201103L
236 // A deleted destructor is trivial, this ensures we reject such types:
237 static_assert(is_destructible<_Value_type>::value,
238 "value type is destructible");
239#endif
240#if __cplusplus > 201703L && defined __cpp_lib_is_constant_evaluated
241 if (std::is_constant_evaluated())
242 return _Destroy_n_aux<false>::__destroy_n(__first, __count);
243#endif
244 return std::_Destroy_n_aux<__has_trivial_destructor(_Value_type)>::
245 __destroy_n(__first, __count);
246 }
247
248#if __cplusplus >= 201703L
249 template <typename _ForwardIterator>
250 _GLIBCXX20_CONSTEXPR inline void
251 destroy(_ForwardIterator __first, _ForwardIterator __last)
252 {
253 std::_Destroy(__first, __last);
254 }
255
256 template <typename _ForwardIterator, typename _Size>
257 _GLIBCXX20_CONSTEXPR inline _ForwardIterator
258 destroy_n(_ForwardIterator __first, _Size __count)
259 {
260 return std::_Destroy_n(__first, __count);
261 }
262#endif // C++17
263
264_GLIBCXX_END_NAMESPACE_VERSION
265} // namespace std
266
267#endif /* _STL_CONSTRUCT_H */
268

source code of include/c++/11/bits/stl_construct.h