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

   1 // Allocator traits -*- C++ -*-
   2
   3 // Copyright (C) 2011-2019 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/allocator.h>
  37 # include <bits/ptr_traits.h>
  38 # include <ext/numeric_traits.h>
  39 #endif
  40
  41 namespace std _GLIBCXX_VISIBILITY(default)
  42 {
  43 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  44
  45 #if __cplusplus >= 201103L
  46 #define __cpp_lib_allocator_traits_is_always_equal 201411
  47
  48   struct __allocator_traits_base
  49   {
  50     template<typename _Tp, typename _Up, typename = void>
  51       struct __rebind : __replace_first_arg<_Tp, _Up> { };
  52
  53     template<typename _Tp, typename _Up>
  54       struct __rebind<_Tp, _Up,
  55                       __void_t<typename _Tp::template rebind<_Up>::other>>
  56       { using type = typename _Tp::template rebind<_Up>::other; };
  57
  58   protected:
  59     template<typename _Tp>
  60       using __pointer = typename _Tp::pointer;
  61     template<typename _Tp>
  62       using __c_pointer = typename _Tp::const_pointer;
  63     template<typename _Tp>
  64       using __v_pointer = typename _Tp::void_pointer;
  65     template<typename _Tp>
  66       using __cv_pointer = typename _Tp::const_void_pointer;
  67     template<typename _Tp>
  68       using __pocca = typename _Tp::propagate_on_container_copy_assignment;
  69     template<typename _Tp>
  70       using __pocma = typename _Tp::propagate_on_container_move_assignment;
  71     template<typename _Tp>
  72       using __pocs = typename _Tp::propagate_on_container_swap;
  73     template<typename _Tp>
  74       using __equal = typename _Tp::is_always_equal;
  75   };
  76
  77   template<typename _Alloc, typename _Up>
  78     using __alloc_rebind
  79       = typename __allocator_traits_base::template __rebind<_Alloc, _Up>::type;
  80
  81   /**
  82    * @brief  Uniform interface to all allocator types.
  83    * @ingroup allocators
  84   */
  85   template<typename _Alloc>
  86     struct allocator_traits : __allocator_traits_base
  87     {
  88       /// The allocator type
  89       typedef _Alloc allocator_type;
  90       /// The allocated type
  91       typedef typename _Alloc::value_type value_type;
  92
  93       /**
  94        * @brief   The allocator's pointer type.
  95        *
  96        * @c Alloc::pointer if that type exists, otherwise @c value_type*
  97       */
  98       using pointer = __detected_or_t<value_type*, __pointer, _Alloc>;
  99
 100     private:
 101       // Select _Func<_Alloc> or pointer_traits<pointer>::rebind<_Tp>
 102       template<template<typename> class _Func, typename _Tp, typename = void>
 103         struct _Ptr
 104         {
 105           using type = typename pointer_traits<pointer>::template rebind<_Tp>;
 106         };
 107
 108       template<template<typename> class _Func, typename _Tp>
 109         struct _Ptr<_Func, _Tp, __void_t<_Func<_Alloc>>>
 110         {
 111           using type = _Func<_Alloc>;
 112         };
 113
 114       // Select _A2::difference_type or pointer_traits<_Ptr>::difference_type
 115       template<typename _A2, typename _PtrT, typename = void>
 116         struct _Diff
 117         { using type = typename pointer_traits<_PtrT>::difference_type; };
 118
 119       template<typename _A2, typename _PtrT>
 120         struct _Diff<_A2, _PtrT, __void_t<typename _A2::difference_type>>
 121         { using type = typename _A2::difference_type; };
 122
 123       // Select _A2::size_type or make_unsigned<_DiffT>::type
 124       template<typename _A2, typename _DiffT, typename = void>
 125         struct _Size : make_unsigned<_DiffT> { };
 126
 127       template<typename _A2, typename _DiffT>
 128         struct _Size<_A2, _DiffT, __void_t<typename _A2::size_type>>
 129         { using type = typename _A2::size_type; };
 130
 131     public:
 132       /**
 133        * @brief   The allocator's const pointer type.
 134        *
 135        * @c Alloc::const_pointer if that type exists, otherwise
 136        * <tt> pointer_traits<pointer>::rebind<const value_type> </tt>
 137       */
 138       using const_pointer = typename _Ptr<__c_pointer, const value_type>::type;
 139
 140       /**
 141        * @brief   The allocator's void pointer type.
 142        *
 143        * @c Alloc::void_pointer if that type exists, otherwise
 144        * <tt> pointer_traits<pointer>::rebind<void> </tt>
 145       */
 146       using void_pointer = typename _Ptr<__v_pointer, void>::type;
 147
 148       /**
 149        * @brief   The allocator's const void pointer type.
 150        *
 151        * @c Alloc::const_void_pointer if that type exists, otherwise
 152        * <tt> pointer_traits<pointer>::rebind<const void> </tt>
 153       */
 154       using const_void_pointer = typename _Ptr<__cv_pointer, const void>::type;
 155
 156       /**
 157        * @brief   The allocator's difference type
 158        *
 159        * @c Alloc::difference_type if that type exists, otherwise
 160        * <tt> pointer_traits<pointer>::difference_type </tt>
 161       */
 162       using difference_type = typename _Diff<_Alloc, pointer>::type;
 163
 164       /**
 165        * @brief   The allocator's size type
 166        *
 167        * @c Alloc::size_type if that type exists, otherwise
 168        * <tt> make_unsigned<difference_type>::type </tt>
 169       */
 170       using size_type = typename _Size<_Alloc, difference_type>::type;
 171
 172       /**
 173        * @brief   How the allocator is propagated on copy assignment
 174        *
 175        * @c Alloc::propagate_on_container_copy_assignment if that type exists,
 176        * otherwise @c false_type
 177       */
 178       using propagate_on_container_copy_assignment
 179         = __detected_or_t<false_type, __pocca, _Alloc>;
 180
 181       /**
 182        * @brief   How the allocator is propagated on move assignment
 183        *
 184        * @c Alloc::propagate_on_container_move_assignment if that type exists,
 185        * otherwise @c false_type
 186       */
 187       using propagate_on_container_move_assignment
 188         = __detected_or_t<false_type, __pocma, _Alloc>;
 189
 190       /**
 191        * @brief   How the allocator is propagated on swap
 192        *
 193        * @c Alloc::propagate_on_container_swap if that type exists,
 194        * otherwise @c false_type
 195       */
 196       using propagate_on_container_swap
 197         = __detected_or_t<false_type, __pocs, _Alloc>;
 198
 199       /**
 200        * @brief   Whether all instances of the allocator type compare equal.
 201        *
 202        * @c Alloc::is_always_equal if that type exists,
 203        * otherwise @c is_empty<Alloc>::type
 204       */
 205       using is_always_equal
 206         = __detected_or_t<typename is_empty<_Alloc>::type, __equal, _Alloc>;
 207
 208       template<typename _Tp>
 209         using rebind_alloc = __alloc_rebind<_Alloc, _Tp>;
 210       template<typename _Tp>
 211         using rebind_traits = allocator_traits<rebind_alloc<_Tp>>;
 212
 213     private:
 214       template<typename _Alloc2>
 215         static constexpr auto
 216         _S_allocate(_Alloc2& __a, size_type __n, const_void_pointer __hint, int)
 217         -> decltype(__a.allocate(__n, __hint))
 218         { return __a.allocate(__n, __hint); }
 219
 220       template<typename _Alloc2>
 221         static constexpr pointer
 222         _S_allocate(_Alloc2& __a, size_type __n, const_void_pointer, ...)
 223         { return __a.allocate(__n); }
 224
 225       template<typename _Tp, typename... _Args>
 226         struct __construct_helper
 227         {
 228           template<typename _Alloc2,
 229             typename = decltype(std::declval<_Alloc2*>()->construct(
 230                   std::declval<_Tp*>(), std::declval<_Args>()...))>
 231             static true_type __test(int);
 232
 233           template<typename>
 234             static false_type __test(...);
 235
 236           using type = decltype(__test<_Alloc>(0));
 237         };
 238
 239       template<typename _Tp, typename... _Args>
 240         using __has_construct
 241           = typename __construct_helper<_Tp, _Args...>::type;
 242
 243       template<typename _Tp, typename... _Args>
 244         static _GLIBCXX14_CONSTEXPR _Require<__has_construct<_Tp, _Args...>>
 245         _S_construct(_Alloc& __a, _Tp* __p, _Args&&... __args)
 246         noexcept(noexcept(__a.construct(__p, std::forward<_Args>(__args)...)))
 247         { __a.construct(__p, std::forward<_Args>(__args)...); }
 248
 249       template<typename _Tp, typename... _Args>
 250         static _GLIBCXX14_CONSTEXPR
 251         _Require<__and_<__not_<__has_construct<_Tp, _Args...>>,
 252                                is_constructible<_Tp, _Args...>>>
 253         _S_construct(_Alloc&, _Tp* __p, _Args&&... __args)
 254         noexcept(noexcept(::new((void*)__p)
 255                           _Tp(std::forward<_Args>(__args)...)))
 256         { std::_Construct(__p, std::forward<_Args>(__args)...); }
 257
 258       template<typename _Alloc2, typename _Tp>
 259         static _GLIBCXX14_CONSTEXPR auto
 260         _S_destroy(_Alloc2& __a, _Tp* __p, int)
 261         noexcept(noexcept(__a.destroy(__p)))
 262         -> decltype(__a.destroy(__p))
 263         { __a.destroy(__p); }
 264
 265       template<typename _Alloc2, typename _Tp>
 266         static _GLIBCXX14_CONSTEXPR void
 267         _S_destroy(_Alloc2&, _Tp* __p, ...)
 268         noexcept(noexcept(__p->~_Tp()))
 269         { std::_Destroy(__p); }
 270
 271       template<typename _Alloc2>
 272         static constexpr auto
 273         _S_max_size(_Alloc2& __a, int)
 274         -> decltype(__a.max_size())
 275         { return __a.max_size(); }
 276
 277       template<typename _Alloc2>
 278         static constexpr size_type
 279         _S_max_size(_Alloc2&, ...)
 280         {
 281           // _GLIBCXX_RESOLVE_LIB_DEFECTS
 282           // 2466. allocator_traits::max_size() default behavior is incorrect
 283           return __gnu_cxx::__numeric_traits<size_type>::__max
 284             / sizeof(value_type);
 285         }
 286
 287       template<typename _Alloc2>
 288         static constexpr auto
 289         _S_select(_Alloc2& __a, int)
 290         -> decltype(__a.select_on_container_copy_construction())
 291         { return __a.select_on_container_copy_construction(); }
 292
 293       template<typename _Alloc2>
 294         static constexpr _Alloc2
 295         _S_select(_Alloc2& __a, ...)
 296         { return __a; }
 297
 298     public:
 299
 300       /**
 301        *  @brief  Allocate memory.
 302        *  @param  __a  An allocator.
 303        *  @param  __n  The number of objects to allocate space for.
 304        *
 305        *  Calls @c a.allocate(n)
 306       */
 307       _GLIBCXX_NODISCARD static _GLIBCXX20_CONSTEXPR pointer
 308       allocate(_Alloc& __a, size_type __n)
 309       { return __a.allocate(__n); }
 310
 311       /**
 312        *  @brief  Allocate memory.
 313        *  @param  __a  An allocator.
 314        *  @param  __n  The number of objects to allocate space for.
 315        *  @param  __hint Aid to locality.
 316        *  @return Memory of suitable size and alignment for @a n objects
 317        *          of type @c value_type
 318        *
 319        *  Returns <tt> a.allocate(n, hint) </tt> if that expression is
 320        *  well-formed, otherwise returns @c a.allocate(n)
 321       */
 322       _GLIBCXX_NODISCARD static _GLIBCXX20_CONSTEXPR pointer
 323       allocate(_Alloc& __a, size_type __n, const_void_pointer __hint)
 324       { return _S_allocate(__a, __n, __hint, 0); }
 325
 326       /**
 327        *  @brief  Deallocate memory.
 328        *  @param  __a  An allocator.
 329        *  @param  __p  Pointer to the memory to deallocate.
 330        *  @param  __n  The number of objects space was allocated for.
 331        *
 332        *  Calls <tt> a.deallocate(p, n) </tt>
 333       */
 334       static _GLIBCXX20_CONSTEXPR void
 335       deallocate(_Alloc& __a, pointer __p, size_type __n)
 336       { __a.deallocate(__p, __n); }
 337
 338       /**
 339        *  @brief  Construct an object of type @a _Tp
 340        *  @param  __a  An allocator.
 341        *  @param  __p  Pointer to memory of suitable size and alignment for Tp
 342        *  @param  __args Constructor arguments.
 343        *
 344        *  Calls <tt> __a.construct(__p, std::forward<Args>(__args)...) </tt>
 345        *  if that expression is well-formed, otherwise uses placement-new
 346        *  to construct an object of type @a _Tp at location @a __p from the
 347        *  arguments @a __args...
 348       */
 349       template<typename _Tp, typename... _Args>
 350         static _GLIBCXX20_CONSTEXPR auto
 351         construct(_Alloc& __a, _Tp* __p, _Args&&... __args)
 352         noexcept(noexcept(_S_construct(__a, __p,
 353                                        std::forward<_Args>(__args)...)))
 354         -> decltype(_S_construct(__a, __p, std::forward<_Args>(__args)...))
 355         { _S_construct(__a, __p, std::forward<_Args>(__args)...); }
 356
 357       /**
 358        *  @brief  Destroy an object of type @a _Tp
 359        *  @param  __a  An allocator.
 360        *  @param  __p  Pointer to the object to destroy
 361        *
 362        *  Calls @c __a.destroy(__p) if that expression is well-formed,
 363        *  otherwise calls @c __p->~_Tp()
 364       */
 365       template<typename _Tp>
 366         static _GLIBCXX20_CONSTEXPR void
 367         destroy(_Alloc& __a, _Tp* __p)
 368         noexcept(noexcept(_S_destroy(__a, __p, 0)))
 369         { _S_destroy(__a, __p, 0); }
 370
 371       /**
 372        *  @brief  The maximum supported allocation size
 373        *  @param  __a  An allocator.
 374        *  @return @c __a.max_size() or @c numeric_limits<size_type>::max()
 375        *
 376        *  Returns @c __a.max_size() if that expression is well-formed,
 377        *  otherwise returns @c numeric_limits<size_type>::max()
 378       */
 379       static _GLIBCXX20_CONSTEXPR size_type
 380       max_size(const _Alloc& __a) noexcept
 381       { return _S_max_size(__a, 0); }
 382
 383       /**
 384        *  @brief  Obtain an allocator to use when copying a container.
 385        *  @param  __rhs  An allocator.
 386        *  @return @c __rhs.select_on_container_copy_construction() or @a __rhs
 387        *
 388        *  Returns @c __rhs.select_on_container_copy_construction() if that
 389        *  expression is well-formed, otherwise returns @a __rhs
 390       */
 391       static _GLIBCXX20_CONSTEXPR _Alloc
 392       select_on_container_copy_construction(const _Alloc& __rhs)
 393       { return _S_select(__rhs, 0); }
 394     };
 395
 396 #if __cplusplus > 201703L
 397 # define __cpp_lib_constexpr_dynamic_alloc 201907L
 398 #endif
 399
 400   /// Partial specialization for std::allocator.
 401   template<typename _Tp>
 402     struct allocator_traits<allocator<_Tp>>
 403     {
 404       /// The allocator type
 405       using allocator_type = allocator<_Tp>;
 406
 407       /// The allocated type
 408       using value_type = _Tp;
 409
 410       /// The allocator's pointer type.
 411       using pointer = _Tp*;
 412
 413       /// The allocator's const pointer type.
 414       using const_pointer = const _Tp*;
 415
 416       /// The allocator's void pointer type.
 417       using void_pointer = void*;
 418
 419       /// The allocator's const void pointer type.
 420       using const_void_pointer = const void*;
 421
 422       /// The allocator's difference type
 423       using difference_type = std::ptrdiff_t;
 424
 425       /// The allocator's size type
 426       using size_type = std::size_t;
 427
 428       /// How the allocator is propagated on copy assignment
 429       using propagate_on_container_copy_assignment = false_type;
 430
 431       /// How the allocator is propagated on move assignment
 432       using propagate_on_container_move_assignment = true_type;
 433
 434       /// How the allocator is propagated on swap
 435       using propagate_on_container_swap = false_type;
 436
 437       /// Whether all instances of the allocator type compare equal.
 438       using is_always_equal = true_type;
 439
 440       template<typename _Up>
 441         using rebind_alloc = allocator<_Up>;
 442
 443       template<typename _Up>
 444         using rebind_traits = allocator_traits<allocator<_Up>>;
 445
 446       /**
 447        *  @brief  Allocate memory.
 448        *  @param  __a  An allocator.
 449        *  @param  __n  The number of objects to allocate space for.
 450        *
 451        *  Calls @c a.allocate(n)
 452       */
 453       _GLIBCXX_NODISCARD static _GLIBCXX20_CONSTEXPR pointer
 454       allocate(allocator_type& __a, size_type __n)
 455       { return __a.allocate(__n); }
 456
 457       /**
 458        *  @brief  Allocate memory.
 459        *  @param  __a  An allocator.
 460        *  @param  __n  The number of objects to allocate space for.
 461        *  @param  __hint Aid to locality.
 462        *  @return Memory of suitable size and alignment for @a n objects
 463        *          of type @c value_type
 464        *
 465        *  Returns <tt> a.allocate(n, hint) </tt>
 466       */
 467       _GLIBCXX_NODISCARD static _GLIBCXX20_CONSTEXPR pointer
 468       allocate(allocator_type& __a, size_type __n, const_void_pointer __hint)
 469       {
 470 #if __cplusplus <= 201703L
 471         return __a.allocate(__n, __hint);
 472 #else
 473         return __a.allocate(__n);
 474 #endif
 475       }
 476
 477       /**
 478        *  @brief  Deallocate memory.
 479        *  @param  __a  An allocator.
 480        *  @param  __p  Pointer to the memory to deallocate.
 481        *  @param  __n  The number of objects space was allocated for.
 482        *
 483        *  Calls <tt> a.deallocate(p, n) </tt>
 484       */
 485       static _GLIBCXX20_CONSTEXPR void
 486       deallocate(allocator_type& __a, pointer __p, size_type __n)
 487       { __a.deallocate(__p, __n); }
 488
 489       /**
 490        *  @brief  Construct an object of type `_Up`
 491        *  @param  __a  An allocator.
 492        *  @param  __p  Pointer to memory of suitable size and alignment for
 493        *               an object of type `_Up`.
 494        *  @param  __args Constructor arguments.
 495        *
 496        *  Calls `__a.construct(__p, std::forward<_Args>(__args)...)`
 497        *  in C++11, C++14 and C++17. Changed in C++20 to call
 498        *  `std::construct_at(__p, std::forward<_Args>(__args)...)` instead.
 499       */
 500       template<typename _Up, typename... _Args>
 501         static _GLIBCXX20_CONSTEXPR void
 502         construct(allocator_type& __a __attribute__((__unused__)), _Up* __p,
 503                   _Args&&... __args)
 504         noexcept(noexcept(::new((void*)__p) _Up(std::declval<_Args>()...)))
 505         {
 506 #if __cplusplus <= 201703L
 507           __a.construct(__p, std::forward<_Args>(__args)...);
 508 #else
 509           std::construct_at(__p, std::forward<_Args>(__args)...);
 510 #endif
 511         }
 512
 513       /**
 514        *  @brief  Destroy an object of type @a _Up
 515        *  @param  __a  An allocator.
 516        *  @param  __p  Pointer to the object to destroy
 517        *
 518        *  Calls @c __a.destroy(__p).
 519       */
 520       template<typename _Up>
 521         static _GLIBCXX20_CONSTEXPR void
 522         destroy(allocator_type& __a __attribute__((__unused__)), _Up* __p)
 523         noexcept(is_nothrow_destructible<_Up>::value)
 524         {
 525 #if __cplusplus <= 201703L
 526           __a.destroy(__p);
 527 #else
 528           std::destroy_at(__p);
 529 #endif
 530         }
 531
 532       /**
 533        *  @brief  The maximum supported allocation size
 534        *  @param  __a  An allocator.
 535        *  @return @c __a.max_size()
 536       */
 537       static _GLIBCXX20_CONSTEXPR size_type
 538       max_size(const allocator_type& __a __attribute__((__unused__))) noexcept
 539       {
 540 #if __cplusplus <= 201703L
 541         return __a.max_size();
 542 #else
 543         return size_t(-1) / sizeof(value_type);
 544 #endif
 545       }
 546
 547       /**
 548        *  @brief  Obtain an allocator to use when copying a container.
 549        *  @param  __rhs  An allocator.
 550        *  @return @c __rhs
 551       */
 552       static _GLIBCXX20_CONSTEXPR allocator_type
 553       select_on_container_copy_construction(const allocator_type& __rhs)
 554       { return __rhs; }
 555     };
 556
 557 #if __cplusplus < 201703L
 558   template<typename _Alloc>
 559     inline void
 560     __do_alloc_on_copy(_Alloc& __one, const _Alloc& __two, true_type)
 561     { __one = __two; }
 562
 563   template<typename _Alloc>
 564     inline void
 565     __do_alloc_on_copy(_Alloc&, const _Alloc&, false_type)
 566     { }
 567 #endif
 568
 569   template<typename _Alloc>
 570     _GLIBCXX14_CONSTEXPR inline void
 571     __alloc_on_copy(_Alloc& __one, const _Alloc& __two)
 572     {
 573       typedef allocator_traits<_Alloc> __traits;
 574       typedef typename __traits::propagate_on_container_copy_assignment __pocca;
 575 #if __cplusplus >= 201703L
 576       if constexpr (__pocca::value)
 577         __one = __two;
 578 #else
 579       __do_alloc_on_copy(__one, __two, __pocca());
 580 #endif
 581     }
 582
 583   template<typename _Alloc>
 584     constexpr _Alloc
 585     __alloc_on_copy(const _Alloc& __a)
 586     {
 587       typedef allocator_traits<_Alloc> __traits;
 588       return __traits::select_on_container_copy_construction(__a);
 589     }
 590
 591 #if __cplusplus < 201703L
 592   template<typename _Alloc>
 593     inline void __do_alloc_on_move(_Alloc& __one, _Alloc& __two, true_type)
 594     { __one = std::move(__two); }
 595
 596   template<typename _Alloc>
 597     inline void __do_alloc_on_move(_Alloc&, _Alloc&, false_type)
 598     { }
 599 #endif
 600
 601   template<typename _Alloc>
 602     _GLIBCXX14_CONSTEXPR inline void
 603     __alloc_on_move(_Alloc& __one, _Alloc& __two)
 604     {
 605       typedef allocator_traits<_Alloc> __traits;
 606       typedef typename __traits::propagate_on_container_move_assignment __pocma;
 607 #if __cplusplus >= 201703L
 608       if constexpr (__pocma::value)
 609         __one = std::move(__two);
 610 #else
 611       __do_alloc_on_move(__one, __two, __pocma());
 612 #endif
 613     }
 614
 615 #if __cplusplus < 201703L
 616   template<typename _Alloc>
 617     inline void __do_alloc_on_swap(_Alloc& __one, _Alloc& __two, true_type)
 618     {
 619       using std::swap;
 620       swap(__one, __two);
 621     }
 622
 623   template<typename _Alloc>
 624     inline void __do_alloc_on_swap(_Alloc&, _Alloc&, false_type)
 625     { }
 626 #endif
 627
 628   template<typename _Alloc>
 629     _GLIBCXX14_CONSTEXPR inline void
 630     __alloc_on_swap(_Alloc& __one, _Alloc& __two)
 631     {
 632       typedef allocator_traits<_Alloc> __traits;
 633       typedef typename __traits::propagate_on_container_swap __pocs;
 634 #if __cplusplus >= 201703L
 635       if constexpr (__pocs::value)
 636         {
 637           using std::swap;
 638           swap(__one, __two);
 639         }
 640 #else
 641       __do_alloc_on_swap(__one, __two, __pocs());
 642 #endif
 643     }
 644
 645   template<typename _Alloc, typename _Tp,
 646            typename _ValueT = __remove_cvref_t<typename _Alloc::value_type>,
 647            typename = void>
 648     struct __is_alloc_insertable_impl
 649     : false_type
 650     { };
 651
 652   template<typename _Alloc, typename _Tp, typename _ValueT>
 653     struct __is_alloc_insertable_impl<_Alloc, _Tp, _ValueT,
 654       __void_t<decltype(allocator_traits<_Alloc>::construct(
 655                    std::declval<_Alloc&>(), std::declval<_ValueT*>(),
 656                    std::declval<_Tp>()))>>
 657     : true_type
 658     { };
 659
 660   // true if _Alloc::value_type is CopyInsertable into containers using _Alloc
 661   // (might be wrong if _Alloc::construct exists but is not constrained,
 662   // i.e. actually trying to use it would still be invalid. Use with caution.)
 663   template<typename _Alloc>
 664     struct __is_copy_insertable
 665     : __is_alloc_insertable_impl<_Alloc,
 666                                  typename _Alloc::value_type const&>::type
 667     { };
 668
 669   // std::allocator<_Tp> just requires CopyConstructible
 670   template<typename _Tp>
 671     struct __is_copy_insertable<allocator<_Tp>>
 672     : is_copy_constructible<_Tp>
 673     { };
 674
 675   // true if _Alloc::value_type is MoveInsertable into containers using _Alloc
 676   // (might be wrong if _Alloc::construct exists but is not constrained,
 677   // i.e. actually trying to use it would still be invalid. Use with caution.)
 678   template<typename _Alloc>
 679     struct __is_move_insertable
 680     : __is_alloc_insertable_impl<_Alloc, typename _Alloc::value_type>::type
 681     { };
 682
 683   // std::allocator<_Tp> just requires MoveConstructible
 684   template<typename _Tp>
 685     struct __is_move_insertable<allocator<_Tp>>
 686     : is_move_constructible<_Tp>
 687     { };
 688
 689   // Trait to detect Allocator-like types.
 690   template<typename _Alloc, typename = void>
 691     struct __is_allocator : false_type { };
 692
 693   template<typename _Alloc>
 694     struct __is_allocator<_Alloc,
 695       __void_t<typename _Alloc::value_type,
 696                decltype(std::declval<_Alloc&>().allocate(size_t{}))>>
 697     : true_type { };
 698
 699   template<typename _Alloc>
 700     using _RequireAllocator
 701       = typename enable_if<__is_allocator<_Alloc>::value, _Alloc>::type;
 702
 703   template<typename _Alloc>
 704     using _RequireNotAllocator
 705       = typename enable_if<!__is_allocator<_Alloc>::value, _Alloc>::type;
 706 #endif // C++11
 707
 708   /**
 709    * Destroy a range of objects using the supplied allocator.  For
 710    * non-default allocators we do not optimize away invocation of
 711    * destroy() even if _Tp has a trivial destructor.
 712    */
 713
 714   template<typename _ForwardIterator, typename _Allocator>
 715     void
 716     _Destroy(_ForwardIterator __first, _ForwardIterator __last,
 717              _Allocator& __alloc)
 718     {
 719       for (; __first != __last; ++__first)
 720 #if __cplusplus < 201103L
 721         __alloc.destroy(std::__addressof(*__first));
 722 #else
 723         allocator_traits<_Allocator>::destroy(__alloc,
 724                                               std::__addressof(*__first));
 725 #endif
 726     }
 727
 728   template<typename _ForwardIterator, typename _Tp>
 729     inline void
 730     _Destroy(_ForwardIterator __first, _ForwardIterator __last,
 731              allocator<_Tp>&)
 732     {
 733       _Destroy(__first, __last);
 734     }
 735
 736 _GLIBCXX_END_NAMESPACE_VERSION
 737 } // namespace std
 738 #endif // _ALLOC_TRAITS_H