libstdc++-v3/include/bits/alloc_traits.h

   1 // Allocator traits -*- C++ -*-
   2
   3 // Copyright (C) 2011-2022 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 /** @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 #endif
  42
  43 namespace std _GLIBCXX_VISIBILITY(default)
  44 {
  45 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  46
  47 #if __cplusplus >= 201103L
  48 #define __cpp_lib_allocator_traits_is_always_equal 201411L
  49
  50   /// @cond undocumented
  51   struct __allocator_traits_base
  52   {
  53     template<typename _Tp, typename _Up, typename = void>
  54       struct __rebind : __replace_first_arg<_Tp, _Up> { };
  55
  56     template<typename _Tp, typename _Up>
  57       struct __rebind<_Tp, _Up,
  58                       __void_t<typename _Tp::template rebind<_Up>::other>>
  59       { using type = typename _Tp::template rebind<_Up>::other; };
  60
  61   protected:
  62     template<typename _Tp>
  63       using __pointer = typename _Tp::pointer;
  64     template<typename _Tp>
  65       using __c_pointer = typename _Tp::const_pointer;
  66     template<typename _Tp>
  67       using __v_pointer = typename _Tp::void_pointer;
  68     template<typename _Tp>
  69       using __cv_pointer = typename _Tp::const_void_pointer;
  70     template<typename _Tp>
  71       using __pocca = typename _Tp::propagate_on_container_copy_assignment;
  72     template<typename _Tp>
  73       using __pocma = typename _Tp::propagate_on_container_move_assignment;
  74     template<typename _Tp>
  75       using __pocs = typename _Tp::propagate_on_container_swap;
  76     template<typename _Tp>
  77       using __equal = __type_identity<typename _Tp::is_always_equal>;
  78   };
  79
  80   template<typename _Alloc, typename _Up>
  81     using __alloc_rebind
  82       = typename __allocator_traits_base::template __rebind<_Alloc, _Up>::type;
  83   /// @endcond
  84
  85   /**
  86    * @brief  Uniform interface to all allocator types.
  87    * @headerfile memory
  88    * @ingroup allocators
  89    * @since C++11
  90   */
  91   template<typename _Alloc>
  92     struct allocator_traits : __allocator_traits_base
  93     {
  94       /// The allocator type
  95       typedef _Alloc allocator_type;
  96       /// The allocated type
  97       typedef typename _Alloc::value_type value_type;
  98
  99       /**
 100        * @brief   The allocator's pointer type.
 101        *
 102        * @c Alloc::pointer if that type exists, otherwise @c value_type*
 103       */
 104       using pointer = __detected_or_t<value_type*, __pointer, _Alloc>;
 105
 106     private:
 107       // Select _Func<_Alloc> or pointer_traits<pointer>::rebind<_Tp>
 108       template<template<typename> class _Func, typename _Tp, typename = void>
 109         struct _Ptr
 110         {
 111           using type = typename pointer_traits<pointer>::template rebind<_Tp>;
 112         };
 113
 114       template<template<typename> class _Func, typename _Tp>
 115         struct _Ptr<_Func, _Tp, __void_t<_Func<_Alloc>>>
 116         {
 117           using type = _Func<_Alloc>;
 118         };
 119
 120       // Select _A2::difference_type or pointer_traits<_Ptr>::difference_type
 121       template<typename _A2, typename _PtrT, typename = void>
 122         struct _Diff
 123         { using type = typename pointer_traits<_PtrT>::difference_type; };
 124
 125       template<typename _A2, typename _PtrT>
 126         struct _Diff<_A2, _PtrT, __void_t<typename _A2::difference_type>>
 127         { using type = typename _A2::difference_type; };
 128
 129       // Select _A2::size_type or make_unsigned<_DiffT>::type
 130       template<typename _A2, typename _DiffT, typename = void>
 131         struct _Size : make_unsigned<_DiffT> { };
 132
 133       template<typename _A2, typename _DiffT>
 134         struct _Size<_A2, _DiffT, __void_t<typename _A2::size_type>>
 135         { using type = typename _A2::size_type; };
 136
 137     public:
 138       /**
 139        * @brief   The allocator's const pointer type.
 140        *
 141        * @c Alloc::const_pointer if that type exists, otherwise
 142        * <tt> pointer_traits<pointer>::rebind<const value_type> </tt>
 143       */
 144       using const_pointer = typename _Ptr<__c_pointer, const value_type>::type;
 145
 146       /**
 147        * @brief   The allocator's void pointer type.
 148        *
 149        * @c Alloc::void_pointer if that type exists, otherwise
 150        * <tt> pointer_traits<pointer>::rebind<void> </tt>
 151       */
 152       using void_pointer = typename _Ptr<__v_pointer, void>::type;
 153
 154       /**
 155        * @brief   The allocator's const void pointer type.
 156        *
 157        * @c Alloc::const_void_pointer if that type exists, otherwise
 158        * <tt> pointer_traits<pointer>::rebind<const void> </tt>
 159       */
 160       using const_void_pointer = typename _Ptr<__cv_pointer, const void>::type;
 161
 162       /**
 163        * @brief   The allocator's difference type
 164        *
 165        * @c Alloc::difference_type if that type exists, otherwise
 166        * <tt> pointer_traits<pointer>::difference_type </tt>
 167       */
 168       using difference_type = typename _Diff<_Alloc, pointer>::type;
 169
 170       /**
 171        * @brief   The allocator's size type
 172        *
 173        * @c Alloc::size_type if that type exists, otherwise
 174        * <tt> make_unsigned<difference_type>::type </tt>
 175       */
 176       using size_type = typename _Size<_Alloc, difference_type>::type;
 177
 178       /**
 179        * @brief   How the allocator is propagated on copy assignment
 180        *
 181        * @c Alloc::propagate_on_container_copy_assignment if that type exists,
 182        * otherwise @c false_type
 183       */
 184       using propagate_on_container_copy_assignment
 185         = __detected_or_t<false_type, __pocca, _Alloc>;
 186
 187       /**
 188        * @brief   How the allocator is propagated on move assignment
 189        *
 190        * @c Alloc::propagate_on_container_move_assignment if that type exists,
 191        * otherwise @c false_type
 192       */
 193       using propagate_on_container_move_assignment
 194         = __detected_or_t<false_type, __pocma, _Alloc>;
 195
 196       /**
 197        * @brief   How the allocator is propagated on swap
 198        *
 199        * @c Alloc::propagate_on_container_swap if that type exists,
 200        * otherwise @c false_type
 201       */
 202       using propagate_on_container_swap
 203         = __detected_or_t<false_type, __pocs, _Alloc>;
 204
 205       /**
 206        * @brief   Whether all instances of the allocator type compare equal.
 207        *
 208        * @c Alloc::is_always_equal if that type exists,
 209        * otherwise @c is_empty<Alloc>::type
 210       */
 211       using is_always_equal
 212         = typename __detected_or_t<is_empty<_Alloc>, __equal, _Alloc>::type;
 213
 214       template<typename _Tp>
 215         using rebind_alloc = __alloc_rebind<_Alloc, _Tp>;
 216       template<typename _Tp>
 217         using rebind_traits = allocator_traits<rebind_alloc<_Tp>>;
 218
 219     private:
 220       template<typename _Alloc2>
 221         static constexpr auto
 222         _S_allocate(_Alloc2& __a, size_type __n, const_void_pointer __hint, int)
 223         -> decltype(__a.allocate(__n, __hint))
 224         { return __a.allocate(__n, __hint); }
 225
 226       template<typename _Alloc2>
 227         static constexpr pointer
 228         _S_allocate(_Alloc2& __a, size_type __n, const_void_pointer, ...)
 229         { return __a.allocate(__n); }
 230
 231       template<typename _Tp, typename... _Args>
 232         struct __construct_helper
 233         {
 234           template<typename _Alloc2,
 235             typename = decltype(std::declval<_Alloc2*>()->construct(
 236                   std::declval<_Tp*>(), std::declval<_Args>()...))>
 237             static true_type __test(int);
 238
 239           template<typename>
 240             static false_type __test(...);
 241
 242           using type = decltype(__test<_Alloc>(0));
 243         };
 244
 245       template<typename _Tp, typename... _Args>
 246         using __has_construct
 247           = typename __construct_helper<_Tp, _Args...>::type;
 248
 249       template<typename _Tp, typename... _Args>
 250         static _GLIBCXX14_CONSTEXPR _Require<__has_construct<_Tp, _Args...>>
 251         _S_construct(_Alloc& __a, _Tp* __p, _Args&&... __args)
 252         noexcept(noexcept(__a.construct(__p, std::forward<_Args>(__args)...)))
 253         { __a.construct(__p, std::forward<_Args>(__args)...); }
 254
 255       template<typename _Tp, typename... _Args>
 256         static _GLIBCXX14_CONSTEXPR
 257         _Require<__and_<__not_<__has_construct<_Tp, _Args...>>,
 258                                is_constructible<_Tp, _Args...>>>
 259         _S_construct(_Alloc&, _Tp* __p, _Args&&... __args)
 260         noexcept(std::is_nothrow_constructible<_Tp, _Args...>::value)
 261         {
 262 #if __cplusplus <= 201703L
 263           ::new((void*)__p) _Tp(std::forward<_Args>(__args)...);
 264 #else
 265           std::construct_at(__p, std::forward<_Args>(__args)...);
 266 #endif
 267         }
 268
 269       template<typename _Alloc2, typename _Tp>
 270         static _GLIBCXX14_CONSTEXPR auto
 271         _S_destroy(_Alloc2& __a, _Tp* __p, int)
 272         noexcept(noexcept(__a.destroy(__p)))
 273         -> decltype(__a.destroy(__p))
 274         { __a.destroy(__p); }
 275
 276       template<typename _Alloc2, typename _Tp>
 277         static _GLIBCXX14_CONSTEXPR void
 278         _S_destroy(_Alloc2&, _Tp* __p, ...)
 279         noexcept(std::is_nothrow_destructible<_Tp>::value)
 280         { std::_Destroy(__p); }
 281
 282       template<typename _Alloc2>
 283         static constexpr auto
 284         _S_max_size(_Alloc2& __a, int)
 285         -> decltype(__a.max_size())
 286         { return __a.max_size(); }
 287
 288       template<typename _Alloc2>
 289         static constexpr size_type
 290         _S_max_size(_Alloc2&, ...)
 291         {
 292           // _GLIBCXX_RESOLVE_LIB_DEFECTS
 293           // 2466. allocator_traits::max_size() default behavior is incorrect
 294           return __gnu_cxx::__numeric_traits<size_type>::__max
 295             / sizeof(value_type);
 296         }
 297
 298       template<typename _Alloc2>
 299         static constexpr auto
 300         _S_select(_Alloc2& __a, int)
 301         -> decltype(__a.select_on_container_copy_construction())
 302         { return __a.select_on_container_copy_construction(); }
 303
 304       template<typename _Alloc2>
 305         static constexpr _Alloc2
 306         _S_select(_Alloc2& __a, ...)
 307         { return __a; }
 308
 309     public:
 310
 311       /**
 312        *  @brief  Allocate memory.
 313        *  @param  __a  An allocator.
 314        *  @param  __n  The number of objects to allocate space for.
 315        *
 316        *  Calls @c a.allocate(n)
 317       */
 318       _GLIBCXX_NODISCARD static _GLIBCXX20_CONSTEXPR pointer
 319       allocate(_Alloc& __a, size_type __n)
 320       { return __a.allocate(__n); }
 321
 322       /**
 323        *  @brief  Allocate memory.
 324        *  @param  __a  An allocator.
 325        *  @param  __n  The number of objects to allocate space for.
 326        *  @param  __hint Aid to locality.
 327        *  @return Memory of suitable size and alignment for @a n objects
 328        *          of type @c value_type
 329        *
 330        *  Returns <tt> a.allocate(n, hint) </tt> if that expression is
 331        *  well-formed, otherwise returns @c a.allocate(n)
 332       */
 333       _GLIBCXX_NODISCARD static _GLIBCXX20_CONSTEXPR pointer
 334       allocate(_Alloc& __a, size_type __n, const_void_pointer __hint)
 335       { return _S_allocate(__a, __n, __hint, 0); }
 336
 337       /**
 338        *  @brief  Deallocate memory.
 339        *  @param  __a  An allocator.
 340        *  @param  __p  Pointer to the memory to deallocate.
 341        *  @param  __n  The number of objects space was allocated for.
 342        *
 343        *  Calls <tt> a.deallocate(p, n) </tt>
 344       */
 345       static _GLIBCXX20_CONSTEXPR void
 346       deallocate(_Alloc& __a, pointer __p, size_type __n)
 347       { __a.deallocate(__p, __n); }
 348
 349       /**
 350        *  @brief  Construct an object of type `_Tp`
 351        *  @param  __a  An allocator.
 352        *  @param  __p  Pointer to memory of suitable size and alignment for Tp
 353        *  @param  __args Constructor arguments.
 354        *
 355        *  Calls <tt> __a.construct(__p, std::forward<Args>(__args)...) </tt>
 356        *  if that expression is well-formed, otherwise uses placement-new
 357        *  to construct an object of type @a _Tp at location @a __p from the
 358        *  arguments @a __args...
 359       */
 360       template<typename _Tp, typename... _Args>
 361         static _GLIBCXX20_CONSTEXPR auto
 362         construct(_Alloc& __a, _Tp* __p, _Args&&... __args)
 363         noexcept(noexcept(_S_construct(__a, __p,
 364                                        std::forward<_Args>(__args)...)))
 365         -> decltype(_S_construct(__a, __p, std::forward<_Args>(__args)...))
 366         { _S_construct(__a, __p, std::forward<_Args>(__args)...); }
 367
 368       /**
 369        *  @brief  Destroy an object of type @a _Tp
 370        *  @param  __a  An allocator.
 371        *  @param  __p  Pointer to the object to destroy
 372        *
 373        *  Calls @c __a.destroy(__p) if that expression is well-formed,
 374        *  otherwise calls @c __p->~_Tp()
 375       */
 376       template<typename _Tp>
 377         static _GLIBCXX20_CONSTEXPR void
 378         destroy(_Alloc& __a, _Tp* __p)
 379         noexcept(noexcept(_S_destroy(__a, __p, 0)))
 380         { _S_destroy(__a, __p, 0); }
 381
 382       /**
 383        *  @brief  The maximum supported allocation size
 384        *  @param  __a  An allocator.
 385        *  @return @c __a.max_size() or @c numeric_limits<size_type>::max()
 386        *
 387        *  Returns @c __a.max_size() if that expression is well-formed,
 388        *  otherwise returns @c numeric_limits<size_type>::max()
 389       */
 390       static _GLIBCXX20_CONSTEXPR size_type
 391       max_size(const _Alloc& __a) noexcept
 392       { return _S_max_size(__a, 0); }
 393
 394       /**
 395        *  @brief  Obtain an allocator to use when copying a container.
 396        *  @param  __rhs  An allocator.
 397        *  @return @c __rhs.select_on_container_copy_construction() or @a __rhs
 398        *
 399        *  Returns @c __rhs.select_on_container_copy_construction() if that
 400        *  expression is well-formed, otherwise returns @a __rhs
 401       */
 402       static _GLIBCXX20_CONSTEXPR _Alloc
 403       select_on_container_copy_construction(const _Alloc& __rhs)
 404       { return _S_select(__rhs, 0); }
 405     };
 406
 407 #if _GLIBCXX_HOSTED
 408
 409 #if __cplusplus > 201703L
 410 # define __cpp_lib_constexpr_dynamic_alloc 201907L
 411 #endif
 412
 413   /// Partial specialization for std::allocator.
 414   template<typename _Tp>
 415     struct allocator_traits<allocator<_Tp>>
 416     {
 417       /// The allocator type
 418       using allocator_type = allocator<_Tp>;
 419
 420       /// The allocated type
 421       using value_type = _Tp;
 422
 423       /// The allocator's pointer type.
 424       using pointer = _Tp*;
 425
 426       /// The allocator's const pointer type.
 427       using const_pointer = const _Tp*;
 428
 429       /// The allocator's void pointer type.
 430       using void_pointer = void*;
 431
 432       /// The allocator's const void pointer type.
 433       using const_void_pointer = const void*;
 434
 435       /// The allocator's difference type
 436       using difference_type = std::ptrdiff_t;
 437
 438       /// The allocator's size type
 439       using size_type = std::size_t;
 440
 441       /// How the allocator is propagated on copy assignment
 442       using propagate_on_container_copy_assignment = false_type;
 443
 444       /// How the allocator is propagated on move assignment
 445       using propagate_on_container_move_assignment = true_type;
 446
 447       /// How the allocator is propagated on swap
 448       using propagate_on_container_swap = false_type;
 449
 450       /// Whether all instances of the allocator type compare equal.
 451       using is_always_equal = true_type;
 452
 453       template<typename _Up>
 454         using rebind_alloc = allocator<_Up>;
 455
 456       template<typename _Up>
 457         using rebind_traits = allocator_traits<allocator<_Up>>;
 458
 459       /**
 460        *  @brief  Allocate memory.
 461        *  @param  __a  An allocator.
 462        *  @param  __n  The number of objects to allocate space for.
 463        *
 464        *  Calls @c a.allocate(n)
 465       */
 466       [[__nodiscard__,__gnu__::__always_inline__]]
 467       static _GLIBCXX20_CONSTEXPR pointer
 468       allocate(allocator_type& __a, size_type __n)
 469       { return __a.allocate(__n); }
 470
 471       /**
 472        *  @brief  Allocate memory.
 473        *  @param  __a  An allocator.
 474        *  @param  __n  The number of objects to allocate space for.
 475        *  @param  __hint Aid to locality.
 476        *  @return Memory of suitable size and alignment for @a n objects
 477        *          of type @c value_type
 478        *
 479        *  Returns <tt> a.allocate(n, hint) </tt>
 480       */
 481       [[__nodiscard__,__gnu__::__always_inline__]]
 482       static _GLIBCXX20_CONSTEXPR pointer
 483       allocate(allocator_type& __a, size_type __n, const_void_pointer __hint)
 484       {
 485 #if __cplusplus <= 201703L
 486         return __a.allocate(__n, __hint);
 487 #else
 488         return __a.allocate(__n);
 489 #endif
 490       }
 491
 492       /**
 493        *  @brief  Deallocate memory.
 494        *  @param  __a  An allocator.
 495        *  @param  __p  Pointer to the memory to deallocate.
 496        *  @param  __n  The number of objects space was allocated for.
 497        *
 498        *  Calls <tt> a.deallocate(p, n) </tt>
 499       */
 500       [[__gnu__::__always_inline__]]
 501       static _GLIBCXX20_CONSTEXPR void
 502       deallocate(allocator_type& __a, pointer __p, size_type __n)
 503       { __a.deallocate(__p, __n); }
 504
 505       /**
 506        *  @brief  Construct an object of type `_Up`
 507        *  @param  __a  An allocator.
 508        *  @param  __p  Pointer to memory of suitable size and alignment for
 509        *               an object of type `_Up`.
 510        *  @param  __args Constructor arguments.
 511        *
 512        *  Calls `__a.construct(__p, std::forward<_Args>(__args)...)`
 513        *  in C++11, C++14 and C++17. Changed in C++20 to call
 514        *  `std::construct_at(__p, std::forward<_Args>(__args)...)` instead.
 515       */
 516       template<typename _Up, typename... _Args>
 517         [[__gnu__::__always_inline__]]
 518         static _GLIBCXX20_CONSTEXPR void
 519         construct(allocator_type& __a __attribute__((__unused__)), _Up* __p,
 520                   _Args&&... __args)
 521         noexcept(std::is_nothrow_constructible<_Up, _Args...>::value)
 522         {
 523 #if __cplusplus <= 201703L
 524           __a.construct(__p, std::forward<_Args>(__args)...);
 525 #else
 526           std::construct_at(__p, std::forward<_Args>(__args)...);
 527 #endif
 528         }
 529
 530       /**
 531        *  @brief  Destroy an object of type @a _Up
 532        *  @param  __a  An allocator.
 533        *  @param  __p  Pointer to the object to destroy
 534        *
 535        *  Calls @c __a.destroy(__p).
 536       */
 537       template<typename _Up>
 538         [[__gnu__::__always_inline__]]
 539         static _GLIBCXX20_CONSTEXPR void
 540         destroy(allocator_type& __a __attribute__((__unused__)), _Up* __p)
 541         noexcept(is_nothrow_destructible<_Up>::value)
 542         {
 543 #if __cplusplus <= 201703L
 544           __a.destroy(__p);
 545 #else
 546           std::destroy_at(__p);
 547 #endif
 548         }
 549
 550       /**
 551        *  @brief  The maximum supported allocation size
 552        *  @param  __a  An allocator.
 553        *  @return @c __a.max_size()
 554       */
 555       [[__gnu__::__always_inline__]]
 556       static _GLIBCXX20_CONSTEXPR size_type
 557       max_size(const allocator_type& __a __attribute__((__unused__))) noexcept
 558       {
 559 #if __cplusplus <= 201703L
 560         return __a.max_size();
 561 #else
 562         return size_t(-1) / sizeof(value_type);
 563 #endif
 564       }
 565
 566       /**
 567        *  @brief  Obtain an allocator to use when copying a container.
 568        *  @param  __rhs  An allocator.
 569        *  @return @c __rhs
 570       */
 571       [[__gnu__::__always_inline__]]
 572       static _GLIBCXX20_CONSTEXPR allocator_type
 573       select_on_container_copy_construction(const allocator_type& __rhs)
 574       { return __rhs; }
 575     };
 576
 577   /// Explicit specialization for std::allocator<void>.
 578   template<>
 579     struct allocator_traits<allocator<void>>
 580     {
 581       /// The allocator type
 582       using allocator_type = allocator<void>;
 583
 584       /// The allocated type
 585       using value_type = void;
 586
 587       /// The allocator's pointer type.
 588       using pointer = void*;
 589
 590       /// The allocator's const pointer type.
 591       using const_pointer = const void*;
 592
 593       /// The allocator's void pointer type.
 594       using void_pointer = void*;
 595
 596       /// The allocator's const void pointer type.
 597       using const_void_pointer = const void*;
 598
 599       /// The allocator's difference type
 600       using difference_type = std::ptrdiff_t;
 601
 602       /// The allocator's size type
 603       using size_type = std::size_t;
 604
 605       /// How the allocator is propagated on copy assignment
 606       using propagate_on_container_copy_assignment = false_type;
 607
 608       /// How the allocator is propagated on move assignment
 609       using propagate_on_container_move_assignment = true_type;
 610
 611       /// How the allocator is propagated on swap
 612       using propagate_on_container_swap = false_type;
 613
 614       /// Whether all instances of the allocator type compare equal.
 615       using is_always_equal = true_type;
 616
 617       template<typename _Up>
 618         using rebind_alloc = allocator<_Up>;
 619
 620       template<typename _Up>
 621         using rebind_traits = allocator_traits<allocator<_Up>>;
 622
 623       /// allocate is ill-formed for allocator<void>
 624       static void*
 625       allocate(allocator_type&, size_type, const void* = nullptr) = delete;
 626
 627       /// deallocate is ill-formed for allocator<void>
 628       static void
 629       deallocate(allocator_type&, void*, size_type) = delete;
 630
 631       /**
 632        *  @brief  Construct an object of type `_Up`
 633        *  @param  __a  An allocator.
 634        *  @param  __p  Pointer to memory of suitable size and alignment for
 635        *               an object of type `_Up`.
 636        *  @param  __args Constructor arguments.
 637        *
 638        *  Calls `__a.construct(__p, std::forward<_Args>(__args)...)`
 639        *  in C++11, C++14 and C++17. Changed in C++20 to call
 640        *  `std::construct_at(__p, std::forward<_Args>(__args)...)` instead.
 641       */
 642       template<typename _Up, typename... _Args>
 643         [[__gnu__::__always_inline__]]
 644         static _GLIBCXX20_CONSTEXPR void
 645         construct(allocator_type&, _Up* __p, _Args&&... __args)
 646         noexcept(std::is_nothrow_constructible<_Up, _Args...>::value)
 647         { std::_Construct(__p, std::forward<_Args>(__args)...); }
 648
 649       /**
 650        *  @brief  Destroy an object of type `_Up`
 651        *  @param  __a  An allocator.
 652        *  @param  __p  Pointer to the object to destroy
 653        *
 654        *  Invokes the destructor for `*__p`.
 655       */
 656       template<typename _Up>
 657         [[__gnu__::__always_inline__]]
 658         static _GLIBCXX20_CONSTEXPR void
 659         destroy(allocator_type&, _Up* __p)
 660         noexcept(is_nothrow_destructible<_Up>::value)
 661         { std::_Destroy(__p); }
 662
 663       /// max_size is ill-formed for allocator<void>
 664       static size_type
 665       max_size(const allocator_type&) = delete;
 666
 667       /**
 668        *  @brief  Obtain an allocator to use when copying a container.
 669        *  @param  __rhs  An allocator.
 670        *  @return `__rhs`
 671       */
 672       [[__gnu__::__always_inline__]]
 673       static _GLIBCXX20_CONSTEXPR allocator_type
 674       select_on_container_copy_construction(const allocator_type& __rhs)
 675       { return __rhs; }
 676     };
 677 #endif
 678
 679   /// @cond undocumented
 680 #if __cplusplus < 201703L
 681   template<typename _Alloc>
 682     [[__gnu__::__always_inline__]]
 683     inline void
 684     __do_alloc_on_copy(_Alloc& __one, const _Alloc& __two, true_type)
 685     { __one = __two; }
 686
 687   template<typename _Alloc>
 688     [[__gnu__::__always_inline__]]
 689     inline void
 690     __do_alloc_on_copy(_Alloc&, const _Alloc&, false_type)
 691     { }
 692 #endif
 693
 694   template<typename _Alloc>
 695     [[__gnu__::__always_inline__]]
 696     _GLIBCXX14_CONSTEXPR inline void
 697     __alloc_on_copy(_Alloc& __one, const _Alloc& __two)
 698     {
 699       using __traits = allocator_traits<_Alloc>;
 700       using __pocca =
 701         typename __traits::propagate_on_container_copy_assignment::type;
 702 #if __cplusplus >= 201703L
 703       if constexpr (__pocca::value)
 704         __one = __two;
 705 #else
 706       __do_alloc_on_copy(__one, __two, __pocca());
 707 #endif
 708     }
 709
 710   template<typename _Alloc>
 711     [[__gnu__::__always_inline__]]
 712     constexpr _Alloc
 713     __alloc_on_copy(const _Alloc& __a)
 714     {
 715       typedef allocator_traits<_Alloc> __traits;
 716       return __traits::select_on_container_copy_construction(__a);
 717     }
 718
 719 #if __cplusplus < 201703L
 720   template<typename _Alloc>
 721     [[__gnu__::__always_inline__]]
 722     inline void __do_alloc_on_move(_Alloc& __one, _Alloc& __two, true_type)
 723     { __one = std::move(__two); }
 724
 725   template<typename _Alloc>
 726     [[__gnu__::__always_inline__]]
 727     inline void __do_alloc_on_move(_Alloc&, _Alloc&, false_type)
 728     { }
 729 #endif
 730
 731   template<typename _Alloc>
 732     [[__gnu__::__always_inline__]]
 733     _GLIBCXX14_CONSTEXPR inline void
 734     __alloc_on_move(_Alloc& __one, _Alloc& __two)
 735     {
 736       using __traits = allocator_traits<_Alloc>;
 737       using __pocma
 738         = typename __traits::propagate_on_container_move_assignment::type;
 739 #if __cplusplus >= 201703L
 740       if constexpr (__pocma::value)
 741         __one = std::move(__two);
 742 #else
 743       __do_alloc_on_move(__one, __two, __pocma());
 744 #endif
 745     }
 746
 747 #if __cplusplus < 201703L
 748   template<typename _Alloc>
 749     [[__gnu__::__always_inline__]]
 750     inline void __do_alloc_on_swap(_Alloc& __one, _Alloc& __two, true_type)
 751     {
 752       using std::swap;
 753       swap(__one, __two);
 754     }
 755
 756   template<typename _Alloc>
 757     [[__gnu__::__always_inline__]]
 758     inline void __do_alloc_on_swap(_Alloc&, _Alloc&, false_type)
 759     { }
 760 #endif
 761
 762   template<typename _Alloc>
 763     [[__gnu__::__always_inline__]]
 764     _GLIBCXX14_CONSTEXPR inline void
 765     __alloc_on_swap(_Alloc& __one, _Alloc& __two)
 766     {
 767       using __traits = allocator_traits<_Alloc>;
 768       using __pocs = typename __traits::propagate_on_container_swap::type;
 769 #if __cplusplus >= 201703L
 770       if constexpr (__pocs::value)
 771         {
 772           using std::swap;
 773           swap(__one, __two);
 774         }
 775 #else
 776       __do_alloc_on_swap(__one, __two, __pocs());
 777 #endif
 778     }
 779
 780   template<typename _Alloc, typename _Tp,
 781            typename _ValueT = __remove_cvref_t<typename _Alloc::value_type>,
 782            typename = void>
 783     struct __is_alloc_insertable_impl
 784     : false_type
 785     { };
 786
 787   template<typename _Alloc, typename _Tp, typename _ValueT>
 788     struct __is_alloc_insertable_impl<_Alloc, _Tp, _ValueT,
 789       __void_t<decltype(allocator_traits<_Alloc>::construct(
 790                    std::declval<_Alloc&>(), std::declval<_ValueT*>(),
 791                    std::declval<_Tp>()))>>
 792     : true_type
 793     { };
 794
 795   // true if _Alloc::value_type is CopyInsertable into containers using _Alloc
 796   // (might be wrong if _Alloc::construct exists but is not constrained,
 797   // i.e. actually trying to use it would still be invalid. Use with caution.)
 798   template<typename _Alloc>
 799     struct __is_copy_insertable
 800     : __is_alloc_insertable_impl<_Alloc,
 801                                  typename _Alloc::value_type const&>::type
 802     { };
 803
 804 #if _GLIBCXX_HOSTED
 805   // std::allocator<_Tp> just requires CopyConstructible
 806   template<typename _Tp>
 807     struct __is_copy_insertable<allocator<_Tp>>
 808     : is_copy_constructible<_Tp>
 809     { };
 810 #endif
 811
 812   // true if _Alloc::value_type is MoveInsertable into containers using _Alloc
 813   // (might be wrong if _Alloc::construct exists but is not constrained,
 814   // i.e. actually trying to use it would still be invalid. Use with caution.)
 815   template<typename _Alloc>
 816     struct __is_move_insertable
 817     : __is_alloc_insertable_impl<_Alloc, typename _Alloc::value_type>::type
 818     { };
 819
 820 #if _GLIBCXX_HOSTED
 821   // std::allocator<_Tp> just requires MoveConstructible
 822   template<typename _Tp>
 823     struct __is_move_insertable<allocator<_Tp>>
 824     : is_move_constructible<_Tp>
 825     { };
 826 #endif
 827
 828   // Trait to detect Allocator-like types.
 829   template<typename _Alloc, typename = void>
 830     struct __is_allocator : false_type { };
 831
 832   template<typename _Alloc>
 833     struct __is_allocator<_Alloc,
 834       __void_t<typename _Alloc::value_type,
 835                decltype(std::declval<_Alloc&>().allocate(size_t{}))>>
 836     : true_type { };
 837
 838   template<typename _Alloc>
 839     using _RequireAllocator
 840       = typename enable_if<__is_allocator<_Alloc>::value, _Alloc>::type;
 841
 842   template<typename _Alloc>
 843     using _RequireNotAllocator
 844       = typename enable_if<!__is_allocator<_Alloc>::value, _Alloc>::type;
 845
 846 #if __cpp_concepts >= 201907L
 847   template<typename _Alloc>
 848     concept __allocator_like = requires (_Alloc& __a) {
 849       typename _Alloc::value_type;
 850       __a.deallocate(__a.allocate(1u), 1u);
 851     };
 852 #endif
 853   /// @endcond
 854 #endif // C++11
 855
 856   /// @cond undocumented
 857
 858   // To implement Option 3 of DR 431.
 859   template<typename _Alloc, bool = __is_empty(_Alloc)>
 860     struct __alloc_swap
 861     { static void _S_do_it(_Alloc&, _Alloc&) _GLIBCXX_NOEXCEPT { } };
 862
 863   template<typename _Alloc>
 864     struct __alloc_swap<_Alloc, false>
 865     {
 866       static void
 867       _S_do_it(_Alloc& __one, _Alloc& __two) _GLIBCXX_NOEXCEPT
 868       {
 869         // Precondition: swappable allocators.
 870         if (__one != __two)
 871           swap(__one, __two);
 872       }
 873     };
 874
 875 #if __cplusplus >= 201103L
 876   template<typename _Tp, bool
 877     = __or_<is_copy_constructible<typename _Tp::value_type>,
 878             is_nothrow_move_constructible<typename _Tp::value_type>>::value>
 879     struct __shrink_to_fit_aux
 880     { static bool _S_do_it(_Tp&) noexcept { return false; } };
 881
 882   template<typename _Tp>
 883     struct __shrink_to_fit_aux<_Tp, true>
 884     {
 885       _GLIBCXX20_CONSTEXPR
 886       static bool
 887       _S_do_it(_Tp& __c) noexcept
 888       {
 889 #if __cpp_exceptions
 890         try
 891           {
 892             _Tp(__make_move_if_noexcept_iterator(__c.begin()),
 893                 __make_move_if_noexcept_iterator(__c.end()),
 894                 __c.get_allocator()).swap(__c);
 895             return true;
 896           }
 897         catch(...)
 898           { return false; }
 899 #else
 900         return false;
 901 #endif
 902       }
 903     };
 904 #endif
 905
 906   /**
 907    * Destroy a range of objects using the supplied allocator.  For
 908    * non-default allocators we do not optimize away invocation of
 909    * destroy() even if _Tp has a trivial destructor.
 910    */
 911
 912   template<typename _ForwardIterator, typename _Allocator>
 913     _GLIBCXX20_CONSTEXPR
 914     void
 915     _Destroy(_ForwardIterator __first, _ForwardIterator __last,
 916              _Allocator& __alloc)
 917     {
 918       for (; __first != __last; ++__first)
 919 #if __cplusplus < 201103L
 920         __alloc.destroy(std::__addressof(*__first));
 921 #else
 922         allocator_traits<_Allocator>::destroy(__alloc,
 923                                               std::__addressof(*__first));
 924 #endif
 925     }
 926
 927 #if _GLIBCXX_HOSTED
 928   template<typename _ForwardIterator, typename _Tp>
 929     __attribute__((__always_inline__)) _GLIBCXX20_CONSTEXPR
 930     inline void
 931     _Destroy(_ForwardIterator __first, _ForwardIterator __last,
 932              allocator<_Tp>&)
 933     {
 934       _Destroy(__first, __last);
 935     }
 936 #endif
 937   /// @endcond
 938
 939 _GLIBCXX_END_NAMESPACE_VERSION
 940 } // namespace std
 941 #endif // _ALLOC_TRAITS_H