libstdc++
bits/alloc_traits.h
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1 // Allocator traits -*- C++ -*-
2 
3 // Copyright (C) 2011-2025 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
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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
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22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file bits/alloc_traits.h
26  * This is an internal header file, included by other library headers.
27  * Do not attempt to use it directly. @headername{memory}
28  */
29 
30 #ifndef _ALLOC_TRAITS_H
31 #define _ALLOC_TRAITS_H 1
32 
33 #include <bits/stl_construct.h>
34 #include <bits/memoryfwd.h>
35 #if __cplusplus >= 201103L
36 # include <bits/ptr_traits.h>
37 # include <ext/numeric_traits.h>
38 # if _GLIBCXX_HOSTED
39 # include <bits/allocator.h>
40 # endif
41 # if __cpp_exceptions
42 # include <bits/stl_iterator.h> // __make_move_if_noexcept_iterator
43 # endif
44 #endif
45 
46 namespace std _GLIBCXX_VISIBILITY(default)
47 {
48 _GLIBCXX_BEGIN_NAMESPACE_VERSION
49 
50 #if __cplusplus >= 201103L
51 
52 #pragma GCC diagnostic push
53 #pragma GCC diagnostic ignored "-Wc++14-extensions" // for variable templates
54 #pragma GCC diagnostic ignored "-Wc++17-extensions" // for if-constexpr
55 
56  /// @cond undocumented
57  struct __allocator_traits_base
58  {
59 #if __cpp_concepts
60  template<typename _Tp, typename _Up>
61 #else
62  template<typename _Tp, typename _Up, typename = void>
63 #endif
64  struct __rebind : __replace_first_arg<_Tp, _Up>
65  {
66  static_assert(is_same<
67  typename __replace_first_arg<_Tp, typename _Tp::value_type>::type,
68  _Tp>::value,
69  "allocator_traits<A>::rebind_alloc<A::value_type> must be A");
70  };
71 
72  template<typename _Tp, typename _Up>
73 #if __cpp_concepts
74  requires requires { typename _Tp::template rebind<_Up>::other; }
75  struct __rebind<_Tp, _Up>
76 #else
77  struct __rebind<_Tp, _Up,
78  __void_t<typename _Tp::template rebind<_Up>::other>>
79 #endif
80  {
81  using type = typename _Tp::template rebind<_Up>::other;
82 
83  static_assert(is_same<
84  typename _Tp::template rebind<typename _Tp::value_type>::other,
85  _Tp>::value,
86  "allocator_traits<A>::rebind_alloc<A::value_type> must be A");
87  };
88 
89  protected:
90  template<typename _Tp>
91  using __pointer = typename _Tp::pointer;
92  template<typename _Tp>
93  using __c_pointer = typename _Tp::const_pointer;
94  template<typename _Tp>
95  using __v_pointer = typename _Tp::void_pointer;
96  template<typename _Tp>
97  using __cv_pointer = typename _Tp::const_void_pointer;
98  template<typename _Tp>
99  using __pocca = typename _Tp::propagate_on_container_copy_assignment;
100  template<typename _Tp>
101  using __pocma = typename _Tp::propagate_on_container_move_assignment;
102  template<typename _Tp>
103  using __pocs = typename _Tp::propagate_on_container_swap;
104  template<typename _Tp>
105  using __equal = __type_identity<typename _Tp::is_always_equal>;
106 
107  // __has_allocate_hint is true if a.allocate(n, hint) is well-formed.
108 #if __cpp_concepts
109  template<typename _Alloc, typename _Sz, typename _Vp>
110  static constexpr bool __has_allocate_hint
111  = requires (_Alloc& __a, _Sz __n, _Vp __hint) {
112  __a.allocate(__n, __hint);
113  };
114 #else
115  template<typename _Alloc, typename _Sz, typename _Vp>
116  using __allocate_hint_t
117  = decltype(std::declval<_Alloc&>()
118  .allocate(std::declval<_Sz>(), std::declval<_Vp>()));
119  template<typename _Alloc, typename _Sz, typename _Vp, typename = void>
120  static constexpr bool __has_allocate_hint = false;
121  template<typename _Alloc, typename _Sz, typename _Vp>
122  static constexpr bool
123  __has_allocate_hint<_Alloc, _Sz, _Vp,
124  __void_t<__allocate_hint_t<_Alloc, _Sz, _Vp>>>
125  = true;
126 #endif
127 
128  // __has_construct is true if a.construct(p, args...) is well-formed.
129  // __can_construct is true if either __has_construct is true, or if
130  // a placement new-expression for T(args...) is well-formed. We use this
131  // to constrain allocator_traits::construct, as a libstdc++ extension.
132 #if __cpp_concepts
133  template<typename _Alloc, typename _Tp, typename... _Args>
134  static constexpr bool __has_construct
135  = requires (_Alloc& __a, _Tp* __p, _Args&&... __args) {
136  __a.construct(__p, std::forward<_Args>(__args)...);
137  };
138  template<typename _Tp, typename... _Args>
139  static constexpr bool __can_construct_at
140  = requires (_Tp* __p, _Args&&... __args) {
141 #if __cpp_constexpr_dynamic_alloc
142  std::construct_at(__p, std::forward<_Args>(__args)...);
143 #else
144  ::new((void*)__p) _Tp(std::forward<_Args>(__args)...);
145 #endif
146  };
147  template<typename _Alloc, typename _Tp, typename... _Args>
148  static constexpr bool __can_construct
149  = __has_construct<_Alloc, _Tp, _Args...>
150  || __can_construct_at<_Tp, _Args...>;
151 #else
152  template<typename _Alloc, typename _Tp, typename... _Args>
153  using __construct_t
154  = decltype(std::declval<_Alloc&>().construct(std::declval<_Tp*>(),
155  std::declval<_Args>()...));
156  template<typename _Alloc, typename _Tp, typename, typename... _Args>
157  static constexpr bool __has_construct_impl = false;
158  template<typename _Alloc, typename _Tp, typename... _Args>
159  static constexpr bool
160  __has_construct_impl<_Alloc, _Tp,
161  __void_t<__construct_t<_Alloc, _Tp, _Args...>>,
162  _Args...>
163  = true;
164  template<typename _Alloc, typename _Tp, typename... _Args>
165  static constexpr bool __has_construct
166  = __has_construct_impl<_Alloc, _Tp, void, _Args...>;
167  template<typename _Tp, typename... _Args>
168  using __new_expr_t
169  = decltype(::new((void*)0) _Tp(std::declval<_Args>()...));
170  template<typename _Tp, typename, typename... _Args>
171  static constexpr bool __has_new_expr = false;
172  template<typename _Tp, typename... _Args>
173  static constexpr bool
174  __has_new_expr<_Tp, __void_t<__new_expr_t<_Tp, _Args...>>, _Args...>
175  = true;
176  template<typename _Alloc, typename _Tp, typename... _Args>
177  static constexpr bool __can_construct
178  = __has_construct<_Alloc, _Tp, _Args...>
179  || __has_new_expr<_Tp, void, _Args...>;
180 #endif
181 
182  // __has_destroy is true if a.destroy(p) is well-formed.
183 #if __cpp_concepts
184  template<typename _Alloc, typename _Tp>
185  static constexpr bool __has_destroy = requires (_Alloc& __a, _Tp* __p) {
186  __a.destroy(__p);
187  };
188 #else
189  template<typename _Alloc, typename _Tp>
190  using __destroy_t
191  = decltype(std::declval<_Alloc&>().destroy(std::declval<_Tp*>()));
192  template<typename _Alloc, typename _Tp, typename = void>
193  static constexpr bool __has_destroy = false;
194  template<typename _Alloc, typename _Tp>
195  static constexpr bool __has_destroy<_Alloc, _Tp,
196  __void_t<__destroy_t<_Alloc, _Tp>>>
197  = true;
198 #endif
199 
200  // __has_max_size is true if a.max_size() is well-formed.
201 #if __cpp_concepts
202  template<typename _Alloc>
203  static constexpr bool __has_max_size = requires (const _Alloc& __a) {
204  __a.max_size();
205  };
206 #else
207  template<typename _Alloc>
208  using __max_size_t = decltype(std::declval<const _Alloc&>().max_size());
209  template<typename _Alloc, typename = void>
210  static constexpr bool __has_max_size = false;
211  template<typename _Alloc>
212  static constexpr bool __has_max_size<_Alloc,
213  __void_t<__max_size_t<_Alloc>>>
214  = true;
215 #endif
216 
217  // __has_soccc is true if a.select_on_container_copy_construction()
218  // is well-formed.
219 #if __cpp_concepts
220  template<typename _Alloc>
221  static constexpr bool __has_soccc = requires (const _Alloc& __a) {
222  __a.select_on_container_copy_construction();
223  };
224 #else
225  template<typename _Alloc>
226  using __soccc_t
227  = decltype(std::declval<const _Alloc&>()
228  .select_on_container_copy_construction());
229  template<typename _Alloc, typename = void>
230  static constexpr bool __has_soccc = false;
231  template<typename _Alloc>
232  static constexpr bool __has_soccc<_Alloc, __void_t<__soccc_t<_Alloc>>>
233  = true;
234 #endif
235  };
236 
237  template<typename _Alloc, typename _Up>
238  using __alloc_rebind
239  = typename __allocator_traits_base::template __rebind<_Alloc, _Up>::type;
240  /// @endcond
241 
242  /**
243  * @brief Uniform interface to all allocator types.
244  * @headerfile memory
245  * @ingroup allocators
246  * @since C++11
247  */
248  template<typename _Alloc>
249  struct allocator_traits : __allocator_traits_base
250  {
251  /// The allocator type
252  typedef _Alloc allocator_type;
253  /// The allocated type
254  typedef typename _Alloc::value_type value_type;
255 
256  /**
257  * @brief The allocator's pointer type.
258  *
259  * @c Alloc::pointer if that type exists, otherwise @c value_type*
260  */
261  using pointer = __detected_or_t<value_type*, __pointer, _Alloc>;
262 
263  private:
264  // Select _Func<_Alloc> or pointer_traits<pointer>::rebind<_Tp>
265  template<template<typename> class _Func, typename _Tp, typename = void>
266  struct _Ptr
267  {
268  using type = typename pointer_traits<pointer>::template rebind<_Tp>;
269  };
270 
271  template<template<typename> class _Func, typename _Tp>
272  struct _Ptr<_Func, _Tp, __void_t<_Func<_Alloc>>>
273  {
274  using type = _Func<_Alloc>;
275  };
276 
277  // Select _A2::difference_type or pointer_traits<_Ptr>::difference_type
278  template<typename _A2, typename _PtrT, typename = void>
279  struct _Diff
280  { using type = typename pointer_traits<_PtrT>::difference_type; };
281 
282  template<typename _A2, typename _PtrT>
283  struct _Diff<_A2, _PtrT, __void_t<typename _A2::difference_type>>
284  { using type = typename _A2::difference_type; };
285 
286  // Select _A2::size_type or make_unsigned<_DiffT>::type
287  template<typename _A2, typename _DiffT, typename = void>
288  struct _Size : make_unsigned<_DiffT> { };
289 
290  template<typename _A2, typename _DiffT>
291  struct _Size<_A2, _DiffT, __void_t<typename _A2::size_type>>
292  { using type = typename _A2::size_type; };
293 
294  public:
295  /**
296  * @brief The allocator's const pointer type.
297  *
298  * @c Alloc::const_pointer if that type exists, otherwise
299  * <tt> pointer_traits<pointer>::rebind<const value_type> </tt>
300  */
301  using const_pointer = typename _Ptr<__c_pointer, const value_type>::type;
302 
303  /**
304  * @brief The allocator's void pointer type.
305  *
306  * @c Alloc::void_pointer if that type exists, otherwise
307  * <tt> pointer_traits<pointer>::rebind<void> </tt>
308  */
309  using void_pointer = typename _Ptr<__v_pointer, void>::type;
310 
311  /**
312  * @brief The allocator's const void pointer type.
313  *
314  * @c Alloc::const_void_pointer if that type exists, otherwise
315  * <tt> pointer_traits<pointer>::rebind<const void> </tt>
316  */
317  using const_void_pointer = typename _Ptr<__cv_pointer, const void>::type;
318 
319  /**
320  * @brief The allocator's difference type
321  *
322  * @c Alloc::difference_type if that type exists, otherwise
323  * <tt> pointer_traits<pointer>::difference_type </tt>
324  */
325  using difference_type = typename _Diff<_Alloc, pointer>::type;
326 
327  /**
328  * @brief The allocator's size type
329  *
330  * @c Alloc::size_type if that type exists, otherwise
331  * <tt> make_unsigned<difference_type>::type </tt>
332  */
333  using size_type = typename _Size<_Alloc, difference_type>::type;
334 
335  /**
336  * @brief How the allocator is propagated on copy assignment
337  *
338  * @c Alloc::propagate_on_container_copy_assignment if that type exists,
339  * otherwise @c false_type
340  */
342  = __detected_or_t<false_type, __pocca, _Alloc>;
343 
344  /**
345  * @brief How the allocator is propagated on move assignment
346  *
347  * @c Alloc::propagate_on_container_move_assignment if that type exists,
348  * otherwise @c false_type
349  */
351  = __detected_or_t<false_type, __pocma, _Alloc>;
352 
353  /**
354  * @brief How the allocator is propagated on swap
355  *
356  * @c Alloc::propagate_on_container_swap if that type exists,
357  * otherwise @c false_type
358  */
360  = __detected_or_t<false_type, __pocs, _Alloc>;
361 
362  /**
363  * @brief Whether all instances of the allocator type compare equal.
364  *
365  * @c Alloc::is_always_equal if that type exists,
366  * otherwise @c is_empty<Alloc>::type
367  */
369  = typename __detected_or_t<is_empty<_Alloc>, __equal, _Alloc>::type;
370 
371  template<typename _Tp>
372  using rebind_alloc = __alloc_rebind<_Alloc, _Tp>;
373  template<typename _Tp>
375 
376  /**
377  * @brief Allocate memory.
378  * @param __a An allocator.
379  * @param __n The number of objects to allocate space for.
380  *
381  * Calls @c a.allocate(n)
382  */
383  _GLIBCXX_NODISCARD static _GLIBCXX20_CONSTEXPR pointer
384  allocate(_Alloc& __a, size_type __n)
385  { return __a.allocate(__n); }
386 
387  /**
388  * @brief Allocate memory.
389  * @param __a An allocator.
390  * @param __n The number of objects to allocate space for.
391  * @param __hint Aid to locality.
392  * @return Memory of suitable size and alignment for @a n objects
393  * of type @c value_type
394  *
395  * Returns <tt> a.allocate(n, hint) </tt> if that expression is
396  * well-formed, otherwise returns @c a.allocate(n)
397  */
398  _GLIBCXX_NODISCARD static _GLIBCXX20_CONSTEXPR pointer
399  allocate(_Alloc& __a, size_type __n, const_void_pointer __hint)
400  {
401  if constexpr (__has_allocate_hint<_Alloc, size_type, const_void_pointer>)
402  return __a.allocate(__n, __hint);
403  else
404  return __a.allocate(__n);
405  }
406 
407  /**
408  * @brief Deallocate memory.
409  * @param __a An allocator.
410  * @param __p Pointer to the memory to deallocate.
411  * @param __n The number of objects space was allocated for.
412  *
413  * Calls <tt> a.deallocate(p, n) </tt>
414  */
415  static _GLIBCXX20_CONSTEXPR void
416  deallocate(_Alloc& __a, pointer __p, size_type __n)
417  { __a.deallocate(__p, __n); }
418 
419  /**
420  * @brief Construct an object of type `_Tp`
421  * @param __a An allocator.
422  * @param __p Pointer to memory of suitable size and alignment for Tp
423  * @param __args Constructor arguments.
424  *
425  * Calls <tt> __a.construct(__p, std::forward<Args>(__args)...) </tt>
426  * if that expression is well-formed, otherwise uses placement-new
427  * to construct an object of type @a _Tp at location @a __p from the
428  * arguments @a __args...
429  */
430  template<typename _Tp, typename... _Args>
431 #if __cpp_concepts && __cpp_constexpr_dynamic_alloc
432  requires __can_construct<_Alloc, _Tp, _Args...>
433  static constexpr void
434 #else
435  static __enable_if_t<__can_construct<_Alloc, _Tp, _Args...>>
436 #endif
437  construct(_Alloc& __a, _Tp* __p, _Args&&... __args)
438  noexcept(_S_nothrow_construct<_Tp, _Args...>())
439  {
440  if constexpr (__has_construct<_Alloc, _Tp, _Args...>)
441  __a.construct(__p, std::forward<_Args>(__args)...);
442  else
443  std::_Construct(__p, std::forward<_Args>(__args)...);
444  }
445 
446  /**
447  * @brief Destroy an object of type @a _Tp
448  * @param __a An allocator.
449  * @param __p Pointer to the object to destroy
450  *
451  * Calls @c __a.destroy(__p) if that expression is well-formed,
452  * otherwise calls @c __p->~_Tp()
453  */
454  template<typename _Tp>
455  static _GLIBCXX20_CONSTEXPR void
456  destroy(_Alloc& __a, _Tp* __p)
457  noexcept(_S_nothrow_destroy<_Tp>())
458  {
459  if constexpr (__has_destroy<_Alloc, _Tp>)
460  __a.destroy(__p);
461  else
462  std::_Destroy(__p);
463  }
464 
465  /**
466  * @brief The maximum supported allocation size
467  * @param __a An allocator.
468  * @return @c __a.max_size() or @c numeric_limits<size_type>::max()
469  *
470  * Returns @c __a.max_size() if that expression is well-formed,
471  * otherwise returns @c numeric_limits<size_type>::max()
472  */
473  static _GLIBCXX20_CONSTEXPR size_type
474  max_size(const _Alloc& __a) noexcept
475  {
476  if constexpr (__has_max_size<_Alloc>)
477  return __a.max_size();
478  else
479  // _GLIBCXX_RESOLVE_LIB_DEFECTS
480  // 2466. allocator_traits::max_size() default behavior is incorrect
481  return __gnu_cxx::__numeric_traits<size_type>::__max
482  / sizeof(value_type);
483  }
484 
485  /**
486  * @brief Obtain an allocator to use when copying a container.
487  * @param __rhs An allocator.
488  * @return @c __rhs.select_on_container_copy_construction() or @a __rhs
489  *
490  * Returns @c __rhs.select_on_container_copy_construction() if that
491  * expression is well-formed, otherwise returns @a __rhs
492  */
493  static _GLIBCXX20_CONSTEXPR _Alloc
495  {
496  if constexpr (__has_soccc<_Alloc>)
497  return __rhs.select_on_container_copy_construction();
498  else
499  return __rhs;
500  }
501 
502  private:
503 #if __cpp_constexpr >= 201304 // >= C++14
504  template<typename _Tp, typename... _Args>
505  static constexpr bool
506  _S_nothrow_construct(_Alloc* __a = nullptr, _Tp* __p = nullptr)
507  {
508  if constexpr (__has_construct<_Alloc, _Tp, _Args...>)
509  return noexcept(__a->construct(__p, std::declval<_Args>()...));
510  else
511  return __is_nothrow_new_constructible<_Tp, _Args...>;
512  }
513 
514  template<typename _Tp>
515  static constexpr bool
516  _S_nothrow_destroy(_Alloc* __a = nullptr, _Tp* __p = nullptr)
517  {
518  if constexpr (__has_destroy<_Alloc, _Tp>)
519  return noexcept(__a->destroy(__p));
520  else
521  return is_nothrow_destructible<_Tp>::value;
522  }
523 #else
524  template<typename _Tp, typename... _Args>
525  static constexpr
526  __enable_if_t<__has_construct<_Alloc, _Tp, _Args...>, bool>
527  _S_nothrow_construct(_Alloc* __a = nullptr, _Tp* __p = nullptr)
528  { return noexcept(__a->construct(__p, std::declval<_Args>()...)); }
529 
530  template<typename _Tp, typename... _Args>
531  static constexpr
532  __enable_if_t<!__has_construct<_Alloc, _Tp, _Args...>, bool>
533  _S_nothrow_construct(_Alloc* = nullptr, _Tp* __p = nullptr)
534  { return __is_nothrow_new_constructible<_Tp, _Args...>; }
535 
536  template<typename _Tp>
537  static constexpr
538  __enable_if_t<__has_destroy<_Alloc, _Tp>, bool>
539  _S_nothrow_destroy(_Alloc* __a = nullptr, _Tp* __p = nullptr)
540  { return noexcept(__a->destroy(__p)); }
541 
542  template<typename _Tp>
543  static constexpr
544  __enable_if_t<!__has_destroy<_Alloc, _Tp>, bool>
545  _S_nothrow_destroy(_Alloc* = nullptr, _Tp* __p = nullptr)
546  { return is_nothrow_destructible<_Tp>::value; }
547 #endif
548  };
549 #pragma GCC diagnostic pop
550 
551 #if _GLIBCXX_HOSTED
552  /**
553  * @brief Partial specialization for `std::allocator`
554  * @headerfile memory
555  * @ingroup allocators
556  * @since C++11
557  * @see std::allocator_traits
558  */
559  template<typename _Tp>
561  {
562  /// The allocator type
564 
565  /// The allocated type
566  using value_type = _Tp;
567 
568  /// The allocator's pointer type.
569  using pointer = _Tp*;
570 
571  /// The allocator's const pointer type.
572  using const_pointer = const _Tp*;
573 
574  /// The allocator's void pointer type.
575  using void_pointer = void*;
576 
577  /// The allocator's const void pointer type.
578  using const_void_pointer = const void*;
579 
580  /// The allocator's difference type
581  using difference_type = std::ptrdiff_t;
582 
583  /// The allocator's size type
584  using size_type = std::size_t;
585 
586  /// How the allocator is propagated on copy assignment
588 
589  /// How the allocator is propagated on move assignment
591 
592  /// How the allocator is propagated on swap
594 
595  /// Whether all instances of the allocator type compare equal.
597 
598  template<typename _Up>
600 
601  template<typename _Up>
603 
604  /**
605  * @brief Allocate memory.
606  * @param __a An allocator.
607  * @param __n The number of objects to allocate space for.
608  *
609  * Calls @c a.allocate(n)
610  */
611  [[__nodiscard__,__gnu__::__always_inline__]]
612  static _GLIBCXX20_CONSTEXPR pointer
614  { return __a.allocate(__n); }
615 
616  /**
617  * @brief Allocate memory.
618  * @param __a An allocator.
619  * @param __n The number of objects to allocate space for.
620  * @param __hint Aid to locality.
621  * @return Memory of suitable size and alignment for @a n objects
622  * of type @c value_type
623  *
624  * Returns <tt> a.allocate(n, hint) </tt>
625  */
626  [[__nodiscard__,__gnu__::__always_inline__]]
627  static _GLIBCXX20_CONSTEXPR pointer
629  [[maybe_unused]] const_void_pointer __hint)
630  {
631 #if __cplusplus <= 201703L
632  return __a.allocate(__n, __hint);
633 #else
634  return __a.allocate(__n);
635 #endif
636  }
637 
638  /**
639  * @brief Deallocate memory.
640  * @param __a An allocator.
641  * @param __p Pointer to the memory to deallocate.
642  * @param __n The number of objects space was allocated for.
643  *
644  * Calls <tt> a.deallocate(p, n) </tt>
645  */
646  [[__gnu__::__always_inline__]]
647  static _GLIBCXX20_CONSTEXPR void
649  { __a.deallocate(__p, __n); }
650 
651  /**
652  * @brief Construct an object of type `_Up`
653  * @param __a An allocator.
654  * @param __p Pointer to memory of suitable size and alignment for
655  * an object of type `_Up`.
656  * @param __args Constructor arguments.
657  *
658  * Calls `__a.construct(__p, std::forward<_Args>(__args)...)`
659  * in C++11, C++14 and C++17. Changed in C++20 to call
660  * `std::construct_at(__p, std::forward<_Args>(__args)...)` instead.
661  */
662  template<typename _Up, typename... _Args>
663  [[__gnu__::__always_inline__]]
664  static _GLIBCXX20_CONSTEXPR void
665  construct(allocator_type& __a __attribute__((__unused__)),
666  _Up* __p, _Args&&... __args)
667 #if __cplusplus <= 201703L
668  noexcept(noexcept(__a.construct(__p, std::forward<_Args>(__args)...)))
669 #else
670  noexcept(__is_nothrow_new_constructible<_Up, _Args...>)
671 #endif
672  {
673 #if __cplusplus <= 201703L
674  __a.construct(__p, std::forward<_Args>(__args)...);
675 #elif __cpp_constexpr_dynamic_alloc // >= C++20
676  std::construct_at(__p, std::forward<_Args>(__args)...);
677 #else
678  std::_Construct(__p, std::forward<_Args>(__args)...);
679 #endif
680  }
681 
682  /**
683  * @brief Destroy an object of type @a _Up
684  * @param __a An allocator.
685  * @param __p Pointer to the object to destroy
686  *
687  * Calls @c __a.destroy(__p).
688  */
689  template<typename _Up>
690  [[__gnu__::__always_inline__]]
691  static _GLIBCXX20_CONSTEXPR void
692  destroy(allocator_type& __a __attribute__((__unused__)), _Up* __p)
694  {
695 #if __cplusplus <= 201703L
696  __a.destroy(__p);
697 #else
698  std::destroy_at(__p);
699 #endif
700  }
701 
702  /**
703  * @brief The maximum supported allocation size
704  * @param __a An allocator.
705  * @return @c __a.max_size()
706  */
707  [[__gnu__::__always_inline__]]
708  static _GLIBCXX20_CONSTEXPR size_type
709  max_size(const allocator_type& __a __attribute__((__unused__))) noexcept
710  {
711 #if __cplusplus <= 201703L
712  return __a.max_size();
713 #else
714  return size_t(-1) / sizeof(value_type);
715 #endif
716  }
717 
718  /**
719  * @brief Obtain an allocator to use when copying a container.
720  * @param __rhs An allocator.
721  * @return @c __rhs
722  */
723  [[__gnu__::__always_inline__]]
724  static _GLIBCXX20_CONSTEXPR allocator_type
726  { return __rhs; }
727  };
728 
729  /**
730  * @brief Explicit specialization for `std::allocator<void>`
731  * @headerfile memory
732  * @ingroup allocators
733  * @since C++11
734  * @see std::allocator_traits
735  */
736  template<>
738  {
739  /// The allocator type
741 
742  /// The allocated type
743  using value_type = void;
744 
745  /// The allocator's pointer type.
746  using pointer = void*;
747 
748  /// The allocator's const pointer type.
749  using const_pointer = const void*;
750 
751  /// The allocator's void pointer type.
752  using void_pointer = void*;
753 
754  /// The allocator's const void pointer type.
755  using const_void_pointer = const void*;
756 
757  /// The allocator's difference type
758  using difference_type = std::ptrdiff_t;
759 
760  /// The allocator's size type
761  using size_type = std::size_t;
762 
763  /// How the allocator is propagated on copy assignment
765 
766  /// How the allocator is propagated on move assignment
768 
769  /// How the allocator is propagated on swap
771 
772  /// Whether all instances of the allocator type compare equal.
774 
775  template<typename _Up>
777 
778  template<typename _Up>
780 
781  /// allocate is ill-formed for allocator<void>
782  static void*
783  allocate(allocator_type&, size_type, const void* = nullptr) = delete;
784 
785  /// deallocate is ill-formed for allocator<void>
786  static void
787  deallocate(allocator_type&, void*, size_type) = delete;
788 
789  /**
790  * @brief Construct an object of type `_Up`
791  * @param __a An allocator.
792  * @param __p Pointer to memory of suitable size and alignment for
793  * an object of type `_Up`.
794  * @param __args Constructor arguments.
795  *
796  * Calls `__a.construct(__p, std::forward<_Args>(__args)...)`
797  * in C++11, C++14 and C++17. Changed in C++20 to call
798  * `std::construct_at(__p, std::forward<_Args>(__args)...)` instead.
799  */
800  template<typename _Up, typename... _Args>
801  [[__gnu__::__always_inline__]]
802  static _GLIBCXX20_CONSTEXPR void
803  construct(allocator_type&, _Up* __p, _Args&&... __args)
804  noexcept(__is_nothrow_new_constructible<_Up, _Args...>)
805  { std::_Construct(__p, std::forward<_Args>(__args)...); }
806 
807  /**
808  * @brief Destroy an object of type `_Up`
809  * @param __a An allocator.
810  * @param __p Pointer to the object to destroy
811  *
812  * Invokes the destructor for `*__p`.
813  */
814  template<typename _Up>
815  [[__gnu__::__always_inline__]]
816  static _GLIBCXX20_CONSTEXPR void
819  { std::_Destroy(__p); }
820 
821  /// max_size is ill-formed for allocator<void>
822  static size_type
823  max_size(const allocator_type&) = delete;
824 
825  /**
826  * @brief Obtain an allocator to use when copying a container.
827  * @param __rhs An allocator.
828  * @return `__rhs`
829  */
830  [[__gnu__::__always_inline__]]
831  static _GLIBCXX20_CONSTEXPR allocator_type
833  { return __rhs; }
834  };
835 #endif
836 
837  /// @cond undocumented
838 #pragma GCC diagnostic push
839 #pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr
840  template<typename _Alloc>
841  [[__gnu__::__always_inline__]]
842  _GLIBCXX14_CONSTEXPR inline void
843  __alloc_on_copy(_Alloc& __one, const _Alloc& __two)
844  {
845  using __traits = allocator_traits<_Alloc>;
846  using __pocca =
847  typename __traits::propagate_on_container_copy_assignment::type;
848  if constexpr (__pocca::value)
849  __one = __two;
850  }
851 
852  template<typename _Alloc>
853  [[__gnu__::__always_inline__]]
854  constexpr _Alloc
855  __alloc_on_copy(const _Alloc& __a)
856  {
857  typedef allocator_traits<_Alloc> __traits;
858  return __traits::select_on_container_copy_construction(__a);
859  }
860 
861  template<typename _Alloc>
862  [[__gnu__::__always_inline__]]
863  _GLIBCXX14_CONSTEXPR inline void
864  __alloc_on_move(_Alloc& __one, _Alloc& __two)
865  {
866  using __traits = allocator_traits<_Alloc>;
867  using __pocma
868  = typename __traits::propagate_on_container_move_assignment::type;
869  if constexpr (__pocma::value)
870  __one = std::move(__two);
871  }
872 
873  template<typename _Alloc>
874  [[__gnu__::__always_inline__]]
875  _GLIBCXX14_CONSTEXPR inline void
876  __alloc_on_swap(_Alloc& __one, _Alloc& __two)
877  {
878  using __traits = allocator_traits<_Alloc>;
879  using __pocs = typename __traits::propagate_on_container_swap::type;
880  if constexpr (__pocs::value)
881  {
882  using std::swap;
883  swap(__one, __two);
884  }
885  }
886 #pragma GCC diagnostic pop
887 
888  template<typename _Alloc, typename _Tp,
889  typename _ValueT = __remove_cvref_t<typename _Alloc::value_type>,
890  typename = void>
891  struct __is_alloc_insertable_impl
892  : false_type
893  { };
894 
895  template<typename _Alloc, typename _Tp, typename _ValueT>
896  struct __is_alloc_insertable_impl<_Alloc, _Tp, _ValueT,
897  __void_t<decltype(allocator_traits<_Alloc>::construct(
898  std::declval<_Alloc&>(), std::declval<_ValueT*>(),
899  std::declval<_Tp>()))>>
900  : true_type
901  { };
902 
903  // true if _Alloc::value_type is CopyInsertable into containers using _Alloc
904  // (might be wrong if _Alloc::construct exists but is not constrained,
905  // i.e. actually trying to use it would still be invalid. Use with caution.)
906  template<typename _Alloc>
907  struct __is_copy_insertable
908  : __is_alloc_insertable_impl<_Alloc,
909  typename _Alloc::value_type const&>::type
910  { };
911 
912 #if _GLIBCXX_HOSTED
913  // std::allocator<_Tp> just requires CopyConstructible
914  template<typename _Tp>
915  struct __is_copy_insertable<allocator<_Tp>>
916  : is_copy_constructible<_Tp>
917  { };
918 #endif
919 
920  // true if _Alloc::value_type is MoveInsertable into containers using _Alloc
921  // (might be wrong if _Alloc::construct exists but is not constrained,
922  // i.e. actually trying to use it would still be invalid. Use with caution.)
923  template<typename _Alloc>
924  struct __is_move_insertable
925  : __is_alloc_insertable_impl<_Alloc, typename _Alloc::value_type>::type
926  { };
927 
928 #if _GLIBCXX_HOSTED
929  // std::allocator<_Tp> just requires MoveConstructible
930  template<typename _Tp>
931  struct __is_move_insertable<allocator<_Tp>>
932  : is_move_constructible<_Tp>
933  { };
934 #endif
935 
936  // Trait to detect Allocator-like types.
937  template<typename _Alloc, typename = void>
938  struct __is_allocator : false_type { };
939 
940  template<typename _Alloc>
941  struct __is_allocator<_Alloc,
942  __void_t<typename _Alloc::value_type,
943  decltype(std::declval<_Alloc&>().allocate(size_t{}))>>
944  : true_type { };
945 
946  template<typename _Alloc>
947  using _RequireAllocator
948  = typename enable_if<__is_allocator<_Alloc>::value, _Alloc>::type;
949 
950  template<typename _Alloc>
951  using _RequireNotAllocator
952  = typename enable_if<!__is_allocator<_Alloc>::value, _Alloc>::type;
953 
954 #if __cpp_concepts >= 201907L
955  template<typename _Alloc>
956  concept __allocator_like = requires (_Alloc& __a) {
957  typename _Alloc::value_type;
958  __a.deallocate(__a.allocate(1u), 1u);
959  };
960 
961  template<typename _Alloc>
962  concept __not_allocator_like = !__allocator_like<_Alloc>;
963 #endif
964  /// @endcond
965 #endif // C++11
966 
967  /// @cond undocumented
968 
969  // To implement Option 3 of DR 431.
970  template<typename _Alloc, bool = __is_empty(_Alloc)>
971  struct __alloc_swap
972  { static void _S_do_it(_Alloc&, _Alloc&) _GLIBCXX_NOEXCEPT { } };
973 
974  template<typename _Alloc>
975  struct __alloc_swap<_Alloc, false>
976  {
977  static void
978  _S_do_it(_Alloc& __one, _Alloc& __two) _GLIBCXX_NOEXCEPT
979  {
980  // Precondition: swappable allocators.
981  if (__one != __two)
982  swap(__one, __two);
983  }
984  };
985 
986 #if __cplusplus >= 201103L
987  template<typename _Tp, bool
988  = __or_<is_copy_constructible<typename _Tp::value_type>,
989  is_nothrow_move_constructible<typename _Tp::value_type>>::value>
990  struct __shrink_to_fit_aux
991  { static bool _S_do_it(_Tp&) noexcept { return false; } };
992 
993  template<typename _Tp>
994  struct __shrink_to_fit_aux<_Tp, true>
995  {
996  _GLIBCXX20_CONSTEXPR
997  static bool
998  _S_do_it(_Tp& __c) noexcept
999  {
1000 #if __cpp_exceptions
1001  try
1002  {
1003  _Tp(__make_move_if_noexcept_iterator(__c.begin()),
1004  __make_move_if_noexcept_iterator(__c.end()),
1005  __c.get_allocator()).swap(__c);
1006  return true;
1007  }
1008  catch(...)
1009  { return false; }
1010 #else
1011  return false;
1012 #endif
1013  }
1014  };
1015 #endif
1016 
1017  /**
1018  * Destroy a range of objects using the supplied allocator. For
1019  * non-default allocators we do not optimize away invocation of
1020  * destroy() even if _Tp has a trivial destructor.
1021  */
1022 
1023  template<typename _ForwardIterator, typename _Allocator>
1024  _GLIBCXX20_CONSTEXPR
1025  void
1026  _Destroy(_ForwardIterator __first, _ForwardIterator __last,
1027  _Allocator& __alloc)
1028  {
1029  for (; __first != __last; ++__first)
1030 #if __cplusplus < 201103L
1031  __alloc.destroy(std::__addressof(*__first));
1032 #else
1034  std::__addressof(*__first));
1035 #endif
1036  }
1037 
1038 #if _GLIBCXX_HOSTED
1039  template<typename _ForwardIterator, typename _Tp>
1040  __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR
1041  inline void
1042  _Destroy(_ForwardIterator __first, _ForwardIterator __last,
1043  allocator<_Tp>&)
1044  {
1045  std::_Destroy(__first, __last);
1046  }
1047 #endif
1048 
1049  /// @endcond
1050 
1051 _GLIBCXX_END_NAMESPACE_VERSION
1052 } // namespace std
1053 #endif // _ALLOC_TRAITS_H
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition: type_traits:116
__bool_constant< false > false_type
The type used as a compile-time boolean with false value.
Definition: type_traits:119
constexpr _Tp * __addressof(_Tp &__r) noexcept
Same as C++11 std::addressof.
Definition: move.h:52
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:138
ISO C++ entities toplevel namespace is std.
constexpr void _Construct(_Tp *__p, _Args &&... __args)
constexpr void _Destroy(_ForwardIterator __first, _ForwardIterator __last)
is_nothrow_destructible
Definition: type_traits:1143
Uniform interface to all allocator types.
__detected_or_t< false_type, __pocma, _Alloc > propagate_on_container_move_assignment
How the allocator is propagated on move assignment.
typename _Ptr< __v_pointer, void >::type void_pointer
The allocator's void pointer type.
__detected_or_t< value_type *, __pointer, _Alloc > pointer
The allocator's pointer type.
static constexpr pointer allocate(_Alloc &__a, size_type __n)
Allocate memory.
static constexpr pointer allocate(_Alloc &__a, size_type __n, const_void_pointer __hint)
Allocate memory.
typename _Size< _Alloc, difference_type >::type size_type
The allocator's size type.
typename _Ptr< __cv_pointer, const void >::type const_void_pointer
The allocator's const void pointer type.
static constexpr void destroy(_Alloc &__a, _Tp *__p) noexcept(_S_nothrow_destroy< _Tp >())
Destroy an object of type _Tp.
typename _Diff< _Alloc, pointer >::type difference_type
The allocator's difference type.
typename _Ptr< __c_pointer, const value_type >::type const_pointer
The allocator's const pointer type.
requires static constexpr __can_construct< _Alloc, _Tp, _Args... > void construct(_Alloc &__a, _Tp *__p, _Args &&... __args) noexcept(_S_nothrow_construct< _Tp, _Args... >())
Construct an object of type _Tp
_Alloc::value_type value_type
The allocated type.
static constexpr void deallocate(_Alloc &__a, pointer __p, size_type __n)
Deallocate memory.
typename __detected_or_t< is_empty< _Alloc >, __equal, _Alloc >::type is_always_equal
Whether all instances of the allocator type compare equal.
static constexpr size_type max_size(const _Alloc &__a) noexcept
The maximum supported allocation size.
__detected_or_t< false_type, __pocca, _Alloc > propagate_on_container_copy_assignment
How the allocator is propagated on copy assignment.
static constexpr _Alloc select_on_container_copy_construction(const _Alloc &__rhs)
Obtain an allocator to use when copying a container.
__detected_or_t< false_type, __pocs, _Alloc > propagate_on_container_swap
How the allocator is propagated on swap.
_Alloc allocator_type
The allocator type.
static constexpr pointer allocate(allocator_type &__a, size_type __n, [[maybe_unused]] const_void_pointer __hint)
Allocate memory.
allocator< _Tp > allocator_type
The allocator type.
static constexpr void construct(allocator_type &__a, _Up *__p, _Args &&... __args) noexcept(__is_nothrow_new_constructible< _Up, _Args... >)
Construct an object of type _Up
void * void_pointer
The allocator's void pointer type.
_Tp * pointer
The allocator's pointer type.
false_type propagate_on_container_swap
How the allocator is propagated on swap.
static constexpr pointer allocate(allocator_type &__a, size_type __n)
Allocate memory.
std::ptrdiff_t difference_type
The allocator's difference type.
true_type is_always_equal
Whether all instances of the allocator type compare equal.
const _Tp * const_pointer
The allocator's const pointer type.
const void * const_void_pointer
The allocator's const void pointer type.
true_type propagate_on_container_move_assignment
How the allocator is propagated on move assignment.
static constexpr void deallocate(allocator_type &__a, pointer __p, size_type __n)
Deallocate memory.
static constexpr size_type max_size(const allocator_type &__a) noexcept
The maximum supported allocation size.
static constexpr allocator_type select_on_container_copy_construction(const allocator_type &__rhs)
Obtain an allocator to use when copying a container.
static constexpr void destroy(allocator_type &__a, _Up *__p) noexcept(is_nothrow_destructible< _Up >::value)
Destroy an object of type _Up.
false_type propagate_on_container_copy_assignment
How the allocator is propagated on copy assignment.
std::size_t size_type
The allocator's size type.
false_type propagate_on_container_copy_assignment
How the allocator is propagated on copy assignment.
void * pointer
The allocator's pointer type.
void * void_pointer
The allocator's void pointer type.
static void deallocate(allocator_type &, void *, size_type)=delete
deallocate is ill-formed for allocator<void>
true_type is_always_equal
Whether all instances of the allocator type compare equal.
static size_type max_size(const allocator_type &)=delete
max_size is ill-formed for allocator<void>
std::size_t size_type
The allocator's size type.
true_type propagate_on_container_move_assignment
How the allocator is propagated on move assignment.
const void * const_pointer
The allocator's const pointer type.
static void * allocate(allocator_type &, size_type, const void *=nullptr)=delete
allocate is ill-formed for allocator<void>
std::ptrdiff_t difference_type
The allocator's difference type.
static constexpr allocator_type select_on_container_copy_construction(const allocator_type &__rhs)
Obtain an allocator to use when copying a container.
static constexpr void construct(allocator_type &, _Up *__p, _Args &&... __args) noexcept(__is_nothrow_new_constructible< _Up, _Args... >)
Construct an object of type _Up
const void * const_void_pointer
The allocator's const void pointer type.
static constexpr void destroy(allocator_type &, _Up *__p) noexcept(is_nothrow_destructible< _Up >::value)
Destroy an object of type _Up
false_type propagate_on_container_swap
How the allocator is propagated on swap.
The standard allocator, as per C++03 [20.4.1].
Definition: allocator.h:134
Uniform interface to all pointer-like types.
Definition: ptr_traits.h:178