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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 : #if __cplusplus >= 201103L
34 :
35 : #include <bits/memoryfwd.h>
36 : #include <bits/ptr_traits.h>
37 : #include <ext/numeric_traits.h>
38 :
39 : #define __cpp_lib_allocator_traits_is_always_equal 201411
40 :
41 : namespace std _GLIBCXX_VISIBILITY(default)
42 : {
43 : _GLIBCXX_BEGIN_NAMESPACE_VERSION
44 :
45 : struct __allocator_traits_base
46 : {
47 : template<typename _Tp, typename _Up, typename = void>
48 : struct __rebind : __replace_first_arg<_Tp, _Up> { };
49 :
50 : template<typename _Tp, typename _Up>
51 : struct __rebind<_Tp, _Up,
52 : __void_t<typename _Tp::template rebind<_Up>::other>>
53 : { using type = typename _Tp::template rebind<_Up>::other; };
54 :
55 : protected:
56 : template<typename _Tp>
57 : using __pointer = typename _Tp::pointer;
58 : template<typename _Tp>
59 : using __c_pointer = typename _Tp::const_pointer;
60 : template<typename _Tp>
61 : using __v_pointer = typename _Tp::void_pointer;
62 : template<typename _Tp>
63 : using __cv_pointer = typename _Tp::const_void_pointer;
64 : template<typename _Tp>
65 : using __pocca = typename _Tp::propagate_on_container_copy_assignment;
66 : template<typename _Tp>
67 : using __pocma = typename _Tp::propagate_on_container_move_assignment;
68 : template<typename _Tp>
69 : using __pocs = typename _Tp::propagate_on_container_swap;
70 : template<typename _Tp>
71 : using __equal = typename _Tp::is_always_equal;
72 : };
73 :
74 : template<typename _Alloc, typename _Up>
75 : using __alloc_rebind
76 : = typename __allocator_traits_base::template __rebind<_Alloc, _Up>::type;
77 :
78 : /**
79 : * @brief Uniform interface to all allocator types.
80 : * @ingroup allocators
81 : */
82 : template<typename _Alloc>
83 : struct allocator_traits : __allocator_traits_base
84 : {
85 : /// The allocator type
86 : typedef _Alloc allocator_type;
87 : /// The allocated type
88 : typedef typename _Alloc::value_type value_type;
89 :
90 : /**
91 : * @brief The allocator's pointer type.
92 : *
93 : * @c Alloc::pointer if that type exists, otherwise @c value_type*
94 : */
95 : using pointer = __detected_or_t<value_type*, __pointer, _Alloc>;
96 :
97 : private:
98 : // Select _Func<_Alloc> or pointer_traits<pointer>::rebind<_Tp>
99 : template<template<typename> class _Func, typename _Tp, typename = void>
100 : struct _Ptr
101 : {
102 : using type = typename pointer_traits<pointer>::template rebind<_Tp>;
103 : };
104 :
105 : template<template<typename> class _Func, typename _Tp>
106 : struct _Ptr<_Func, _Tp, __void_t<_Func<_Alloc>>>
107 : {
108 : using type = _Func<_Alloc>;
109 : };
110 :
111 : // Select _A2::difference_type or pointer_traits<_Ptr>::difference_type
112 : template<typename _A2, typename _PtrT, typename = void>
113 : struct _Diff
114 : { using type = typename pointer_traits<_PtrT>::difference_type; };
115 :
116 : template<typename _A2, typename _PtrT>
117 : struct _Diff<_A2, _PtrT, __void_t<typename _A2::difference_type>>
118 : { using type = typename _A2::difference_type; };
119 :
120 : // Select _A2::size_type or make_unsigned<_DiffT>::type
121 : template<typename _A2, typename _DiffT, typename = void>
122 : struct _Size : make_unsigned<_DiffT> { };
123 :
124 : template<typename _A2, typename _DiffT>
125 : struct _Size<_A2, _DiffT, __void_t<typename _A2::size_type>>
126 : { using type = typename _A2::size_type; };
127 :
128 : public:
129 : /**
130 : * @brief The allocator's const pointer type.
131 : *
132 : * @c Alloc::const_pointer if that type exists, otherwise
133 : * <tt> pointer_traits<pointer>::rebind<const value_type> </tt>
134 : */
135 : using const_pointer = typename _Ptr<__c_pointer, const value_type>::type;
136 :
137 : /**
138 : * @brief The allocator's void pointer type.
139 : *
140 : * @c Alloc::void_pointer if that type exists, otherwise
141 : * <tt> pointer_traits<pointer>::rebind<void> </tt>
142 : */
143 : using void_pointer = typename _Ptr<__v_pointer, void>::type;
144 :
145 : /**
146 : * @brief The allocator's const void pointer type.
147 : *
148 : * @c Alloc::const_void_pointer if that type exists, otherwise
149 : * <tt> pointer_traits<pointer>::rebind<const void> </tt>
150 : */
151 : using const_void_pointer = typename _Ptr<__cv_pointer, const void>::type;
152 :
153 : /**
154 : * @brief The allocator's difference type
155 : *
156 : * @c Alloc::difference_type if that type exists, otherwise
157 : * <tt> pointer_traits<pointer>::difference_type </tt>
158 : */
159 : using difference_type = typename _Diff<_Alloc, pointer>::type;
160 :
161 : /**
162 : * @brief The allocator's size type
163 : *
164 : * @c Alloc::size_type if that type exists, otherwise
165 : * <tt> make_unsigned<difference_type>::type </tt>
166 : */
167 : using size_type = typename _Size<_Alloc, difference_type>::type;
168 :
169 : /**
170 : * @brief How the allocator is propagated on copy assignment
171 : *
172 : * @c Alloc::propagate_on_container_copy_assignment if that type exists,
173 : * otherwise @c false_type
174 : */
175 : using propagate_on_container_copy_assignment
176 : = __detected_or_t<false_type, __pocca, _Alloc>;
177 :
178 : /**
179 : * @brief How the allocator is propagated on move assignment
180 : *
181 : * @c Alloc::propagate_on_container_move_assignment if that type exists,
182 : * otherwise @c false_type
183 : */
184 : using propagate_on_container_move_assignment
185 : = __detected_or_t<false_type, __pocma, _Alloc>;
186 :
187 : /**
188 : * @brief How the allocator is propagated on swap
189 : *
190 : * @c Alloc::propagate_on_container_swap if that type exists,
191 : * otherwise @c false_type
192 : */
193 : using propagate_on_container_swap
194 : = __detected_or_t<false_type, __pocs, _Alloc>;
195 :
196 : /**
197 : * @brief Whether all instances of the allocator type compare equal.
198 : *
199 : * @c Alloc::is_always_equal if that type exists,
200 : * otherwise @c is_empty<Alloc>::type
201 : */
202 : using is_always_equal
203 : = __detected_or_t<typename is_empty<_Alloc>::type, __equal, _Alloc>;
204 :
205 : template<typename _Tp>
206 : using rebind_alloc = __alloc_rebind<_Alloc, _Tp>;
207 : template<typename _Tp>
208 : using rebind_traits = allocator_traits<rebind_alloc<_Tp>>;
209 :
210 : private:
211 : template<typename _Alloc2>
212 : static auto
213 : _S_allocate(_Alloc2& __a, size_type __n, const_void_pointer __hint, int)
214 : -> decltype(__a.allocate(__n, __hint))
215 : { return __a.allocate(__n, __hint); }
216 :
217 : template<typename _Alloc2>
218 : static pointer
219 : _S_allocate(_Alloc2& __a, size_type __n, const_void_pointer, ...)
220 : { return __a.allocate(__n); }
221 :
222 : template<typename _Tp, typename... _Args>
223 : struct __construct_helper
224 : {
225 : template<typename _Alloc2,
226 : typename = decltype(std::declval<_Alloc2*>()->construct(
227 : std::declval<_Tp*>(), std::declval<_Args>()...))>
228 : static true_type __test(int);
229 :
230 : template<typename>
231 : static false_type __test(...);
232 :
233 : using type = decltype(__test<_Alloc>(0));
234 : };
235 :
236 : template<typename _Tp, typename... _Args>
237 : using __has_construct
238 : = typename __construct_helper<_Tp, _Args...>::type;
239 :
240 : template<typename _Tp, typename... _Args>
241 : static _Require<__has_construct<_Tp, _Args...>>
242 : _S_construct(_Alloc& __a, _Tp* __p, _Args&&... __args)
243 : noexcept(noexcept(__a.construct(__p, std::forward<_Args>(__args)...)))
244 : { __a.construct(__p, std::forward<_Args>(__args)...); }
245 :
246 : template<typename _Tp, typename... _Args>
247 : static
248 : _Require<__and_<__not_<__has_construct<_Tp, _Args...>>,
249 : is_constructible<_Tp, _Args...>>>
250 : _S_construct(_Alloc&, _Tp* __p, _Args&&... __args)
251 : noexcept(std::is_nothrow_constructible<_Tp, _Args...>::value)
252 : { ::new((void*)__p) _Tp(std::forward<_Args>(__args)...); }
253 :
254 : template<typename _Alloc2, typename _Tp>
255 : static auto
256 : _S_destroy(_Alloc2& __a, _Tp* __p, int)
257 : noexcept(noexcept(__a.destroy(__p)))
258 : -> decltype(__a.destroy(__p))
259 : { __a.destroy(__p); }
260 :
261 : template<typename _Alloc2, typename _Tp>
262 : static void
263 0 : _S_destroy(_Alloc2&, _Tp* __p, ...)
264 : noexcept(std::is_nothrow_destructible<_Tp>::value)
265 0 : { __p->~_Tp(); }
266 :
267 : template<typename _Alloc2>
268 : static auto
269 : _S_max_size(_Alloc2& __a, int)
270 : -> decltype(__a.max_size())
271 : { return __a.max_size(); }
272 :
273 : template<typename _Alloc2>
274 : static size_type
275 : _S_max_size(_Alloc2&, ...)
276 : {
277 : // _GLIBCXX_RESOLVE_LIB_DEFECTS
278 : // 2466. allocator_traits::max_size() default behavior is incorrect
279 : return __gnu_cxx::__numeric_traits<size_type>::__max
280 : / sizeof(value_type);
281 : }
282 :
283 : template<typename _Alloc2>
284 : static auto
285 : _S_select(_Alloc2& __a, int)
286 : -> decltype(__a.select_on_container_copy_construction())
287 : { return __a.select_on_container_copy_construction(); }
288 :
289 : template<typename _Alloc2>
290 : static _Alloc2
291 0 : _S_select(_Alloc2& __a, ...)
292 : { return __a; }
293 :
294 : public:
295 :
296 : /**
297 : * @brief Allocate memory.
298 : * @param __a An allocator.
299 : * @param __n The number of objects to allocate space for.
300 : *
301 : * Calls @c a.allocate(n)
302 : */
303 : _GLIBCXX_NODISCARD static pointer
304 : allocate(_Alloc& __a, size_type __n)
305 : { return __a.allocate(__n); }
306 :
307 : /**
308 : * @brief Allocate memory.
309 : * @param __a An allocator.
310 : * @param __n The number of objects to allocate space for.
311 : * @param __hint Aid to locality.
312 : * @return Memory of suitable size and alignment for @a n objects
313 : * of type @c value_type
314 : *
315 : * Returns <tt> a.allocate(n, hint) </tt> if that expression is
316 : * well-formed, otherwise returns @c a.allocate(n)
317 : */
318 : _GLIBCXX_NODISCARD static pointer
319 : allocate(_Alloc& __a, size_type __n, const_void_pointer __hint)
320 : { return _S_allocate(__a, __n, __hint, 0); }
321 :
322 : /**
323 : * @brief Deallocate memory.
324 : * @param __a An allocator.
325 : * @param __p Pointer to the memory to deallocate.
326 : * @param __n The number of objects space was allocated for.
327 : *
328 : * Calls <tt> a.deallocate(p, n) </tt>
329 : */
330 : static void
331 0 : deallocate(_Alloc& __a, pointer __p, size_type __n)
332 0 : { __a.deallocate(__p, __n); }
333 :
334 : /**
335 : * @brief Construct an object of type `_Tp`
336 : * @param __a An allocator.
337 : * @param __p Pointer to memory of suitable size and alignment for Tp
338 : * @param __args Constructor arguments.
339 : *
340 : * Calls <tt> __a.construct(__p, std::forward<Args>(__args)...) </tt>
341 : * if that expression is well-formed, otherwise uses placement-new
342 : * to construct an object of type @a _Tp at location @a __p from the
343 : * arguments @a __args...
344 : */
345 : template<typename _Tp, typename... _Args>
346 : static auto construct(_Alloc& __a, _Tp* __p, _Args&&... __args)
347 : noexcept(noexcept(_S_construct(__a, __p,
348 : std::forward<_Args>(__args)...)))
349 : -> decltype(_S_construct(__a, __p, std::forward<_Args>(__args)...))
350 : { _S_construct(__a, __p, std::forward<_Args>(__args)...); }
351 :
352 : /**
353 : * @brief Destroy an object of type @a _Tp
354 : * @param __a An allocator.
355 : * @param __p Pointer to the object to destroy
356 : *
357 : * Calls @c __a.destroy(__p) if that expression is well-formed,
358 : * otherwise calls @c __p->~_Tp()
359 : */
360 : template<typename _Tp>
361 0 : static void destroy(_Alloc& __a, _Tp* __p)
362 : noexcept(noexcept(_S_destroy(__a, __p, 0)))
363 0 : { _S_destroy(__a, __p, 0); }
364 :
365 : /**
366 : * @brief The maximum supported allocation size
367 : * @param __a An allocator.
368 : * @return @c __a.max_size() or @c numeric_limits<size_type>::max()
369 : *
370 : * Returns @c __a.max_size() if that expression is well-formed,
371 : * otherwise returns @c numeric_limits<size_type>::max()
372 : */
373 : static size_type max_size(const _Alloc& __a) noexcept
374 : { return _S_max_size(__a, 0); }
375 :
376 : /**
377 : * @brief Obtain an allocator to use when copying a container.
378 : * @param __rhs An allocator.
379 : * @return @c __rhs.select_on_container_copy_construction() or @a __rhs
380 : *
381 : * Returns @c __rhs.select_on_container_copy_construction() if that
382 : * expression is well-formed, otherwise returns @a __rhs
383 : */
384 : static _Alloc
385 0 : select_on_container_copy_construction(const _Alloc& __rhs)
386 0 : { return _S_select(__rhs, 0); }
387 : };
388 :
389 : /// Partial specialization for std::allocator.
390 : template<typename _Tp>
391 : struct allocator_traits<allocator<_Tp>>
392 : {
393 : /// The allocator type
394 : using allocator_type = allocator<_Tp>;
395 : /// The allocated type
396 : using value_type = _Tp;
397 :
398 : /// The allocator's pointer type.
399 : using pointer = _Tp*;
400 :
401 : /// The allocator's const pointer type.
402 : using const_pointer = const _Tp*;
403 :
404 : /// The allocator's void pointer type.
405 : using void_pointer = void*;
406 :
407 : /// The allocator's const void pointer type.
408 : using const_void_pointer = const void*;
409 :
410 : /// The allocator's difference type
411 : using difference_type = std::ptrdiff_t;
412 :
413 : /// The allocator's size type
414 : using size_type = std::size_t;
415 :
416 : /// How the allocator is propagated on copy assignment
417 : using propagate_on_container_copy_assignment = false_type;
418 :
419 : /// How the allocator is propagated on move assignment
420 : using propagate_on_container_move_assignment = true_type;
421 :
422 : /// How the allocator is propagated on swap
423 : using propagate_on_container_swap = false_type;
424 :
425 : /// Whether all instances of the allocator type compare equal.
426 : using is_always_equal = true_type;
427 :
428 : template<typename _Up>
429 : using rebind_alloc = allocator<_Up>;
430 :
431 : template<typename _Up>
432 : using rebind_traits = allocator_traits<allocator<_Up>>;
433 :
434 : /**
435 : * @brief Allocate memory.
436 : * @param __a An allocator.
437 : * @param __n The number of objects to allocate space for.
438 : *
439 : * Calls @c a.allocate(n)
440 : */
441 : _GLIBCXX_NODISCARD static pointer
442 88218015 : allocate(allocator_type& __a, size_type __n)
443 88303491 : { return __a.allocate(__n); }
444 :
445 : /**
446 : * @brief Allocate memory.
447 : * @param __a An allocator.
448 : * @param __n The number of objects to allocate space for.
449 : * @param __hint Aid to locality.
450 : * @return Memory of suitable size and alignment for @a n objects
451 : * of type @c value_type
452 : *
453 : * Returns <tt> a.allocate(n, hint) </tt>
454 : */
455 : _GLIBCXX_NODISCARD static pointer
456 : allocate(allocator_type& __a, size_type __n, const_void_pointer __hint)
457 : { return __a.allocate(__n, __hint); }
458 :
459 : /**
460 : * @brief Deallocate memory.
461 : * @param __a An allocator.
462 : * @param __p Pointer to the memory to deallocate.
463 : * @param __n The number of objects space was allocated for.
464 : *
465 : * Calls <tt> a.deallocate(p, n) </tt>
466 : */
467 : static void
468 1362438898 : deallocate(allocator_type& __a, pointer __p, size_type __n)
469 1362438898 : { __a.deallocate(__p, __n); }
470 :
471 : /**
472 : * @brief Construct an object of type @a _Up
473 : * @param __a An allocator.
474 : * @param __p Pointer to memory of suitable size and alignment for Tp
475 : * @param __args Constructor arguments.
476 : *
477 : * Calls <tt> __a.construct(__p, std::forward<Args>(__args)...) </tt>
478 : */
479 : template<typename _Up, typename... _Args>
480 : static void
481 817550419 : construct(allocator_type& __a, _Up* __p, _Args&&... __args)
482 : noexcept(std::is_nothrow_constructible<_Up, _Args...>::value)
483 5500017824 : { __a.construct(__p, std::forward<_Args>(__args)...); }
484 :
485 : /**
486 : * @brief Destroy an object of type @a _Up
487 : * @param __a An allocator.
488 : * @param __p Pointer to the object to destroy
489 : *
490 : * Calls @c __a.destroy(__p).
491 : */
492 : template<typename _Up>
493 : static void
494 926905280 : destroy(allocator_type& __a, _Up* __p)
495 : noexcept(noexcept(__a.destroy(__p)))
496 921574296 : { __a.destroy(__p); }
497 :
498 : /**
499 : * @brief The maximum supported allocation size
500 : * @param __a An allocator.
501 : * @return @c __a.max_size()
502 : */
503 : static size_type
504 1085614365 : max_size(const allocator_type& __a) noexcept
505 1085613410 : { return __a.max_size(); }
506 :
507 : /**
508 : * @brief Obtain an allocator to use when copying a container.
509 : * @param __rhs An allocator.
510 : * @return @c __rhs
511 : */
512 : static allocator_type
513 129320051 : select_on_container_copy_construction(const allocator_type& __rhs)
514 433953395 : { return __rhs; }
515 : };
516 :
517 :
518 : template<typename _Alloc>
519 : inline void
520 : __do_alloc_on_copy(_Alloc& __one, const _Alloc& __two, true_type)
521 : { __one = __two; }
522 :
523 : template<typename _Alloc>
524 : inline void
525 : __do_alloc_on_copy(_Alloc&, const _Alloc&, false_type)
526 : { }
527 :
528 : template<typename _Alloc>
529 : inline void __alloc_on_copy(_Alloc& __one, const _Alloc& __two)
530 : {
531 : typedef allocator_traits<_Alloc> __traits;
532 : typedef typename __traits::propagate_on_container_copy_assignment __pocca;
533 : __do_alloc_on_copy(__one, __two, __pocca());
534 : }
535 :
536 : template<typename _Alloc>
537 : inline _Alloc __alloc_on_copy(const _Alloc& __a)
538 : {
539 : typedef allocator_traits<_Alloc> __traits;
540 : return __traits::select_on_container_copy_construction(__a);
541 : }
542 :
543 : template<typename _Alloc>
544 31733640 : inline void __do_alloc_on_move(_Alloc& __one, _Alloc& __two, true_type)
545 31733640 : { __one = std::move(__two); }
546 :
547 : template<typename _Alloc>
548 : inline void __do_alloc_on_move(_Alloc&, _Alloc&, false_type)
549 : { }
550 :
551 : template<typename _Alloc>
552 31733640 : inline void __alloc_on_move(_Alloc& __one, _Alloc& __two)
553 : {
554 : typedef allocator_traits<_Alloc> __traits;
555 : typedef typename __traits::propagate_on_container_move_assignment __pocma;
556 31647995 : __do_alloc_on_move(__one, __two, __pocma());
557 : }
558 :
559 : template<typename _Alloc>
560 : inline void __do_alloc_on_swap(_Alloc& __one, _Alloc& __two, true_type)
561 : {
562 : using std::swap;
563 : swap(__one, __two);
564 : }
565 :
566 : template<typename _Alloc>
567 355 : inline void __do_alloc_on_swap(_Alloc&, _Alloc&, false_type)
568 : { }
569 :
570 : template<typename _Alloc>
571 355 : inline void __alloc_on_swap(_Alloc& __one, _Alloc& __two)
572 : {
573 : typedef allocator_traits<_Alloc> __traits;
574 : typedef typename __traits::propagate_on_container_swap __pocs;
575 355 : __do_alloc_on_swap(__one, __two, __pocs());
576 : }
577 :
578 : template<typename _Alloc, typename _Tp,
579 : typename _ValueT = __remove_cvref_t<typename _Alloc::value_type>,
580 : typename = void>
581 : struct __is_alloc_insertable_impl
582 : : false_type
583 : { };
584 :
585 : template<typename _Alloc, typename _Tp, typename _ValueT>
586 : struct __is_alloc_insertable_impl<_Alloc, _Tp, _ValueT,
587 : __void_t<decltype(allocator_traits<_Alloc>::construct(
588 : std::declval<_Alloc&>(), std::declval<_ValueT*>(),
589 : std::declval<_Tp>()))>>
590 : : true_type
591 : { };
592 :
593 : // true if _Alloc::value_type is CopyInsertable into containers using _Alloc
594 : // (might be wrong if _Alloc::construct exists but is not constrained,
595 : // i.e. actually trying to use it would still be invalid. Use with caution.)
596 : template<typename _Alloc>
597 : struct __is_copy_insertable
598 : : __is_alloc_insertable_impl<_Alloc,
599 : typename _Alloc::value_type const&>::type
600 : { };
601 :
602 : // std::allocator<_Tp> just requires CopyConstructible
603 : template<typename _Tp>
604 : struct __is_copy_insertable<allocator<_Tp>>
605 : : is_copy_constructible<_Tp>
606 : { };
607 :
608 : // true if _Alloc::value_type is MoveInsertable into containers using _Alloc
609 : // (might be wrong if _Alloc::construct exists but is not constrained,
610 : // i.e. actually trying to use it would still be invalid. Use with caution.)
611 : template<typename _Alloc>
612 : struct __is_move_insertable
613 : : __is_alloc_insertable_impl<_Alloc, typename _Alloc::value_type>::type
614 : { };
615 :
616 : // std::allocator<_Tp> just requires MoveConstructible
617 : template<typename _Tp>
618 : struct __is_move_insertable<allocator<_Tp>>
619 : : is_move_constructible<_Tp>
620 : { };
621 :
622 : // Trait to detect Allocator-like types.
623 : template<typename _Alloc, typename = void>
624 : struct __is_allocator : false_type { };
625 :
626 : template<typename _Alloc>
627 : struct __is_allocator<_Alloc,
628 : __void_t<typename _Alloc::value_type,
629 : decltype(std::declval<_Alloc&>().allocate(size_t{}))>>
630 : : true_type { };
631 :
632 : template<typename _Alloc>
633 : using _RequireAllocator
634 : = typename enable_if<__is_allocator<_Alloc>::value, _Alloc>::type;
635 :
636 : template<typename _Alloc>
637 : using _RequireNotAllocator
638 : = typename enable_if<!__is_allocator<_Alloc>::value, _Alloc>::type;
639 :
640 : _GLIBCXX_END_NAMESPACE_VERSION
641 : } // namespace std
642 : #endif // C++11
643 : #endif // _ALLOC_TRAITS_H
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