1 // nonstandard construct and destroy functions -*- C++ -*-
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39 * Copyright (c) 1996,1997
40 * Silicon Graphics Computer Systems, Inc.
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43 * and its documentation for any purpose is hereby granted without fee,
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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}
56 #ifndef _STL_CONSTRUCT_H
57 #define _STL_CONSTRUCT_H 1
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
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.
73 namespace std
_GLIBCXX_VISIBILITY(default)
75 _GLIBCXX_BEGIN_NAMESPACE_VERSION
77 #if __glibcxx_raw_memory_algorithms // >= C++17
78 template <typename _Tp
>
79 _GLIBCXX20_CONSTEXPR
inline void
80 destroy_at(_Tp
* __location
)
82 if constexpr (__cplusplus
> 201703L && is_array_v
<_Tp
>)
84 for (auto& __x
: *__location
)
85 std::destroy_at(std::__addressof(__x
));
91 #if __cpp_constexpr_dynamic_alloc // >= C++20
92 template<typename _Tp
, typename
... _Args
>
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
)...); }
102 * Constructs an object in existing memory by invoking an allocated
103 * object's constructor with an initializer.
105 #if __cplusplus >= 201103L
106 template<typename _Tp
, typename
... _Args
>
109 _Construct(_Tp
* __p
, _Args
&&... __args
)
111 #if __cpp_constexpr_dynamic_alloc // >= C++20
112 if (std::__is_constant_evaluated())
114 // Allow std::_Construct to be used in constant expressions.
115 std::construct_at(__p
, std::forward
<_Args
>(__args
)...);
119 ::new((void*)__p
) _Tp(std::forward
<_Args
>(__args
)...);
122 template<typename _T1
, typename _T2
>
124 _Construct(_T1
* __p
, const _T2
& __value
)
126 // _GLIBCXX_RESOLVE_LIB_DEFECTS
127 // 402. wrong new expression in [some_]allocator::construct
128 ::new(static_cast<void*>(__p
)) _T1(__value
);
132 template<typename _T1
>
134 _Construct_novalue(_T1
* __p
)
135 { ::new((void*)__p
) _T1
; }
137 template<typename _ForwardIterator
>
138 _GLIBCXX20_CONSTEXPR
void
139 _Destroy(_ForwardIterator __first
, _ForwardIterator __last
);
142 * Destroy the object pointed to by a pointer type.
144 template<typename _Tp
>
145 _GLIBCXX14_CONSTEXPR
inline void
146 _Destroy(_Tp
* __pointer
)
148 #if __cpp_constexpr_dynamic_alloc // >= C++20
149 std::destroy_at(__pointer
);
158 template<typename _ForwardIterator
>
159 static _GLIBCXX20_CONSTEXPR
void
160 __destroy(_ForwardIterator __first
, _ForwardIterator __last
)
162 for (; __first
!= __last
; ++__first
)
163 std::_Destroy(std::__addressof(*__first
));
168 struct _Destroy_aux
<true>
170 template<typename _ForwardIterator
>
172 __destroy(_ForwardIterator
, _ForwardIterator
) { }
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.
180 template<typename _ForwardIterator
>
181 _GLIBCXX20_CONSTEXPR
inline void
182 _Destroy(_ForwardIterator __first
, _ForwardIterator __last
)
184 typedef typename iterator_traits
<_ForwardIterator
>::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");
191 #if __cpp_constexpr_dynamic_alloc // >= C++20
192 if (std::__is_constant_evaluated())
193 return std::_Destroy_aux
<false>::__destroy(__first
, __last
);
195 std::_Destroy_aux
<__has_trivial_destructor(_Value_type
)>::
196 __destroy(__first
, __last
);
200 struct _Destroy_n_aux
202 template<typename _ForwardIterator
, typename _Size
>
203 static _GLIBCXX20_CONSTEXPR _ForwardIterator
204 __destroy_n(_ForwardIterator __first
, _Size __count
)
206 for (; __count
> 0; (void)++__first
, --__count
)
207 std::_Destroy(std::__addressof(*__first
));
213 struct _Destroy_n_aux
<true>
215 template<typename _ForwardIterator
, typename _Size
>
216 static _ForwardIterator
217 __destroy_n(_ForwardIterator __first
, _Size __count
)
219 std::advance(__first
, __count
);
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.
229 template<typename _ForwardIterator
, typename _Size
>
230 _GLIBCXX20_CONSTEXPR
inline _ForwardIterator
231 _Destroy_n(_ForwardIterator __first
, _Size __count
)
233 typedef typename iterator_traits
<_ForwardIterator
>::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");
240 #if __cpp_constexpr_dynamic_alloc // >= C++20
241 if (std::__is_constant_evaluated())
242 return std::_Destroy_n_aux
<false>::__destroy_n(__first
, __count
);
244 return std::_Destroy_n_aux
<__has_trivial_destructor(_Value_type
)>::
245 __destroy_n(__first
, __count
);
248 #if __glibcxx_raw_memory_algorithms // >= C++17
249 template <typename _ForwardIterator
>
250 _GLIBCXX20_CONSTEXPR
inline void
251 destroy(_ForwardIterator __first
, _ForwardIterator __last
)
253 std::_Destroy(__first
, __last
);
256 template <typename _ForwardIterator
, typename _Size
>
257 _GLIBCXX20_CONSTEXPR
inline _ForwardIterator
258 destroy_n(_ForwardIterator __first
, _Size __count
)
260 return std::_Destroy_n(__first
, __count
);
264 _GLIBCXX_END_NAMESPACE_VERSION
267 #endif /* _STL_CONSTRUCT_H */