libstdc++
stl_construct.h
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1 // nonstandard construct and destroy functions -*- C++ -*-
2 
3 // Copyright (C) 2001-2020 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 _Construct and _Destroy functions will dispatch to construct_at and
69  * destroy_at during constant evaluation, because calls to those functions are
70  * intercepted by the compiler 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  constexpr _Tp*
108  _Construct(_Tp* __p, _Args&&... __args)
109  {
110 #if __cplusplus > 201703L
111  return std::construct_at(__p, std::forward<_Args>(__args)...);
112 #else
113  return ::new(static_cast<void*>(__p)) _Tp(std::forward<_Args>(__args)...);
114 #endif
115  }
116 #else
117  template<typename _T1, typename _T2>
118  inline _T1*
119  _Construct(_T1* __p, const _T2& __value)
120  {
121  // _GLIBCXX_RESOLVE_LIB_DEFECTS
122  // 402. wrong new expression in [some_]allocator::construct
123  return ::new(static_cast<void*>(__p)) _T1(__value);
124  }
125 #endif
126 
127  template<typename _T1>
128  inline void
129  _Construct_novalue(_T1* __p)
130  { ::new(static_cast<void*>(__p)) _T1; }
131 
132  template<typename _ForwardIterator>
133  _GLIBCXX20_CONSTEXPR void
134  _Destroy(_ForwardIterator __first, _ForwardIterator __last);
135 
136  /**
137  * Destroy the object pointed to by a pointer type.
138  */
139  template<typename _Tp>
140  _GLIBCXX14_CONSTEXPR inline void
141  _Destroy(_Tp* __pointer)
142  {
143 #if __cplusplus > 201703L
144  std::destroy_at(__pointer);
145 #else
146  __pointer->~_Tp();
147 #endif
148  }
149 
150  template<bool>
151  struct _Destroy_aux
152  {
153  template<typename _ForwardIterator>
154  static _GLIBCXX20_CONSTEXPR void
155  __destroy(_ForwardIterator __first, _ForwardIterator __last)
156  {
157  for (; __first != __last; ++__first)
158  std::_Destroy(std::__addressof(*__first));
159  }
160  };
161 
162  template<>
163  struct _Destroy_aux<true>
164  {
165  template<typename _ForwardIterator>
166  static void
167  __destroy(_ForwardIterator, _ForwardIterator) { }
168  };
169 
170  /**
171  * Destroy a range of objects. If the value_type of the object has
172  * a trivial destructor, the compiler should optimize all of this
173  * away, otherwise the objects' destructors must be invoked.
174  */
175  template<typename _ForwardIterator>
176  _GLIBCXX20_CONSTEXPR inline void
177  _Destroy(_ForwardIterator __first, _ForwardIterator __last)
178  {
180  _Value_type;
181 #if __cplusplus >= 201103L
182  // A deleted destructor is trivial, this ensures we reject such types:
184  "value type is destructible");
185 #endif
186 #if __cplusplus > 201703L && defined __cpp_lib_is_constant_evaluated
187  if (std::is_constant_evaluated())
188  return _Destroy_aux<false>::__destroy(__first, __last);
189 #endif
190  std::_Destroy_aux<__has_trivial_destructor(_Value_type)>::
191  __destroy(__first, __last);
192  }
193 
194  template<bool>
195  struct _Destroy_n_aux
196  {
197  template<typename _ForwardIterator, typename _Size>
198  static _GLIBCXX20_CONSTEXPR _ForwardIterator
199  __destroy_n(_ForwardIterator __first, _Size __count)
200  {
201  for (; __count > 0; (void)++__first, --__count)
202  std::_Destroy(std::__addressof(*__first));
203  return __first;
204  }
205  };
206 
207  template<>
208  struct _Destroy_n_aux<true>
209  {
210  template<typename _ForwardIterator, typename _Size>
211  static _ForwardIterator
212  __destroy_n(_ForwardIterator __first, _Size __count)
213  {
214  std::advance(__first, __count);
215  return __first;
216  }
217  };
218 
219  /**
220  * Destroy a range of objects. If the value_type of the object has
221  * a trivial destructor, the compiler should optimize all of this
222  * away, otherwise the objects' destructors must be invoked.
223  */
224  template<typename _ForwardIterator, typename _Size>
225  _GLIBCXX20_CONSTEXPR inline _ForwardIterator
226  _Destroy_n(_ForwardIterator __first, _Size __count)
227  {
229  _Value_type;
230 #if __cplusplus >= 201103L
231  // A deleted destructor is trivial, this ensures we reject such types:
233  "value type is destructible");
234 #endif
235 #if __cplusplus > 201703L && defined __cpp_lib_is_constant_evaluated
236  if (std::is_constant_evaluated())
237  return _Destroy_n_aux<false>::__destroy_n(__first, __count);
238 #endif
239  return std::_Destroy_n_aux<__has_trivial_destructor(_Value_type)>::
240  __destroy_n(__first, __count);
241  }
242 
243 #if __cplusplus >= 201703L
244  template <typename _ForwardIterator>
245  _GLIBCXX20_CONSTEXPR inline void
246  destroy(_ForwardIterator __first, _ForwardIterator __last)
247  {
248  std::_Destroy(__first, __last);
249  }
250 
251  template <typename _ForwardIterator, typename _Size>
252  _GLIBCXX20_CONSTEXPR inline _ForwardIterator
253  destroy_n(_ForwardIterator __first, _Size __count)
254  {
255  return std::_Destroy_n(__first, __count);
256  }
257 #endif // C++17
258 
259 _GLIBCXX_END_NAMESPACE_VERSION
260 } // namespace std
261 
262 #endif /* _STL_CONSTRUCT_H */
std::_Destroy_n
constexpr _ForwardIterator _Destroy_n(_ForwardIterator __first, _Size __count)
Definition: stl_construct.h:226
stl_iterator_base_funcs.h
std
ISO C++ entities toplevel namespace is std.
std::advance
constexpr void advance(_InputIterator &__i, _Distance __n)
A generalization of pointer arithmetic.
Definition: stl_iterator_base_funcs.h:202
move.h
std::__addressof
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:49
new
stl_iterator_base_types.h
std::_Construct
constexpr _Tp * _Construct(_Tp *__p, _Args &&... __args)
Definition: stl_construct.h:108
std::is_destructible
is_destructible
Definition: type_traits:841
std::iterator_traits
Traits class for iterators.
Definition: cpp_type_traits.h:423
std::_Destroy
void _Destroy(_ForwardIterator __first, _ForwardIterator __last, _Allocator &__alloc)
Definition: bits/alloc_traits.h:716