libstdc++
stl_construct.h
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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 
73 namespace 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 > 201703L
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  inline void
108  _Construct(_Tp* __p, _Args&&... __args)
109  { ::new(static_cast<void*>(__p)) _Tp(std::forward<_Args>(__args)...); }
110 #else
111  template<typename _T1, typename _T2>
112  inline void
113  _Construct(_T1* __p, const _T2& __value)
114  {
115  // _GLIBCXX_RESOLVE_LIB_DEFECTS
116  // 402. wrong new expression in [some_]allocator::construct
117  ::new(static_cast<void*>(__p)) _T1(__value);
118  }
119 #endif
120 
121  template<typename _T1>
122  inline void
123  _Construct_novalue(_T1* __p)
124  { ::new(static_cast<void*>(__p)) _T1; }
125 
126  template<typename _ForwardIterator>
127  _GLIBCXX20_CONSTEXPR void
128  _Destroy(_ForwardIterator __first, _ForwardIterator __last);
129 
130  /**
131  * Destroy the object pointed to by a pointer type.
132  */
133  template<typename _Tp>
134  _GLIBCXX14_CONSTEXPR inline void
135  _Destroy(_Tp* __pointer)
136  {
137 #if __cplusplus > 201703L
138  std::destroy_at(__pointer);
139 #else
140  __pointer->~_Tp();
141 #endif
142  }
143 
144  template<bool>
145  struct _Destroy_aux
146  {
147  template<typename _ForwardIterator>
148  static _GLIBCXX20_CONSTEXPR void
149  __destroy(_ForwardIterator __first, _ForwardIterator __last)
150  {
151  for (; __first != __last; ++__first)
152  std::_Destroy(std::__addressof(*__first));
153  }
154  };
155 
156  template<>
157  struct _Destroy_aux<true>
158  {
159  template<typename _ForwardIterator>
160  static void
161  __destroy(_ForwardIterator, _ForwardIterator) { }
162  };
163 
164  /**
165  * Destroy a range of objects. If the value_type of the object has
166  * a trivial destructor, the compiler should optimize all of this
167  * away, otherwise the objects' destructors must be invoked.
168  */
169  template<typename _ForwardIterator>
170  _GLIBCXX20_CONSTEXPR inline void
171  _Destroy(_ForwardIterator __first, _ForwardIterator __last)
172  {
174  _Value_type;
175 #if __cplusplus >= 201103L
176  // A deleted destructor is trivial, this ensures we reject such types:
178  "value type is destructible");
179 #endif
180 #if __cplusplus > 201703L && defined __cpp_lib_is_constant_evaluated
181  if (std::is_constant_evaluated())
182  return _Destroy_aux<false>::__destroy(__first, __last);
183 #endif
184  std::_Destroy_aux<__has_trivial_destructor(_Value_type)>::
185  __destroy(__first, __last);
186  }
187 
188  template<bool>
189  struct _Destroy_n_aux
190  {
191  template<typename _ForwardIterator, typename _Size>
192  static _GLIBCXX20_CONSTEXPR _ForwardIterator
193  __destroy_n(_ForwardIterator __first, _Size __count)
194  {
195  for (; __count > 0; (void)++__first, --__count)
196  std::_Destroy(std::__addressof(*__first));
197  return __first;
198  }
199  };
200 
201  template<>
202  struct _Destroy_n_aux<true>
203  {
204  template<typename _ForwardIterator, typename _Size>
205  static _ForwardIterator
206  __destroy_n(_ForwardIterator __first, _Size __count)
207  {
208  std::advance(__first, __count);
209  return __first;
210  }
211  };
212 
213  /**
214  * Destroy a range of objects. If the value_type of the object has
215  * a trivial destructor, the compiler should optimize all of this
216  * away, otherwise the objects' destructors must be invoked.
217  */
218  template<typename _ForwardIterator, typename _Size>
219  _GLIBCXX20_CONSTEXPR inline _ForwardIterator
220  _Destroy_n(_ForwardIterator __first, _Size __count)
221  {
223  _Value_type;
224 #if __cplusplus >= 201103L
225  // A deleted destructor is trivial, this ensures we reject such types:
227  "value type is destructible");
228 #endif
229 #if __cplusplus > 201703L && defined __cpp_lib_is_constant_evaluated
230  if (std::is_constant_evaluated())
231  return _Destroy_n_aux<false>::__destroy_n(__first, __count);
232 #endif
233  return std::_Destroy_n_aux<__has_trivial_destructor(_Value_type)>::
234  __destroy_n(__first, __count);
235  }
236 
237 #if __cplusplus >= 201703L
238  template <typename _ForwardIterator>
239  _GLIBCXX20_CONSTEXPR inline void
240  destroy(_ForwardIterator __first, _ForwardIterator __last)
241  {
242  std::_Destroy(__first, __last);
243  }
244 
245  template <typename _ForwardIterator, typename _Size>
246  _GLIBCXX20_CONSTEXPR inline _ForwardIterator
247  destroy_n(_ForwardIterator __first, _Size __count)
248  {
249  return std::_Destroy_n(__first, __count);
250  }
251 #endif // C++17
252 
253 _GLIBCXX_END_NAMESPACE_VERSION
254 } // namespace std
255 
256 #endif /* _STL_CONSTRUCT_H */
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:49
ISO C++ entities toplevel namespace is std.
void _Construct(_Tp *__p, _Args &&... __args)
constexpr _ForwardIterator _Destroy_n(_ForwardIterator __first, _Size __count)
void _Destroy(_ForwardIterator __first, _ForwardIterator __last, _Allocator &__alloc)
is_destructible
Definition: type_traits:884
Traits class for iterators.