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1// Experimental shared_ptr with array support -*- C++ -*-
2
3// Copyright (C) 2015-2025 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
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 experimental/bits/shared_ptr.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{experimental/memory}
28 */
29
30#ifndef _GLIBCXX_EXPERIMENTAL_SHARED_PTR_H
31#define _GLIBCXX_EXPERIMENTAL_SHARED_PTR_H 1
32
33#ifdef _GLIBCXX_SYSHDR
34#pragma GCC system_header
35#endif
36
37#if __cplusplus >= 201402L
38
39#include <memory>
40#include <experimental/type_traits>
41
42namespace std _GLIBCXX_VISIBILITY(default)
43{
44_GLIBCXX_BEGIN_NAMESPACE_VERSION
45
46namespace experimental
47{
48inline namespace fundamentals_v2
49{
50 // 8.2.1
51
52 template<typename _Tp> class shared_ptr;
53 template<typename _Tp> class weak_ptr;
54 template<typename _Tp> class enable_shared_from_this;
55
56 template<typename _Yp, typename _Tp>
57 constexpr bool __sp_compatible_v
58 = std::__sp_compatible_with<_Yp*, _Tp*>::value;
59
60 template<typename _Tp, typename _Yp>
61 constexpr bool __sp_is_constructible_v
62 = std::__sp_is_constructible<_Tp, _Yp>::value;
63
64 template<typename _Tp>
65 class shared_ptr : public __shared_ptr<_Tp>
66 {
67 using _Base_type = __shared_ptr<_Tp>;
68
69 public:
70 using element_type = typename _Base_type::element_type;
71
72 private:
73 // Constraint for construction from a pointer of type _Yp*:
74 template<typename _Yp>
75 using _SafeConv = enable_if_t<__sp_is_constructible_v<_Tp, _Yp>>;
76
77 template<typename _Tp1, typename _Res = void>
78 using _Compatible
79 = enable_if_t<__sp_compatible_v<_Tp1, _Tp>, _Res>;
80
81 template<typename _Tp1, typename _Del,
82 typename _Ptr = typename unique_ptr<_Tp1, _Del>::pointer,
83 typename _Res = void>
84 using _UniqCompatible = enable_if_t<
85 __sp_compatible_v<_Tp1, _Tp>
86 && experimental::is_convertible_v<_Ptr, element_type*>,
87 _Res>;
88
89 public:
90
91 // 8.2.1.1, shared_ptr constructors
92 constexpr shared_ptr() noexcept = default;
93
94 template<typename _Tp1, typename = _SafeConv<_Tp1>>
95 explicit
96 shared_ptr(_Tp1* __p) : _Base_type(__p)
97 { _M_enable_shared_from_this_with(__p); }
98
99 template<typename _Tp1, typename _Deleter, typename = _SafeConv<_Tp1>>
100 shared_ptr(_Tp1* __p, _Deleter __d)
101 : _Base_type(__p, __d)
102 { _M_enable_shared_from_this_with(__p); }
103
104 template<typename _Tp1, typename _Deleter, typename _Alloc,
105 typename = _SafeConv<_Tp1>>
106 shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
107 : _Base_type(__p, __d, __a)
108 { _M_enable_shared_from_this_with(__p); }
109
110 template<typename _Deleter>
111 shared_ptr(nullptr_t __p, _Deleter __d)
112 : _Base_type(__p, __d) { }
113
114 template<typename _Deleter, typename _Alloc>
115 shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
116 : _Base_type(__p, __d, __a) { }
117
118 template<typename _Tp1>
119 shared_ptr(const shared_ptr<_Tp1>& __r, element_type* __p) noexcept
120 : _Base_type(__r, __p) { }
121
122 shared_ptr(const shared_ptr& __r) noexcept
123 : _Base_type(__r) { }
124
125 template<typename _Tp1, typename = _Compatible<_Tp1>>
126 shared_ptr(const shared_ptr<_Tp1>& __r) noexcept
127 : _Base_type(__r) { }
128
129 shared_ptr(shared_ptr&& __r) noexcept
130 : _Base_type(std::move(__r)) { }
131
132 template<typename _Tp1, typename = _Compatible<_Tp1>>
133 shared_ptr(shared_ptr<_Tp1>&& __r) noexcept
134 : _Base_type(std::move(__r)) { }
135
136 template<typename _Tp1, typename = _Compatible<_Tp1>>
137 explicit
138 shared_ptr(const weak_ptr<_Tp1>& __r)
139 : _Base_type(__r) { }
140
141#if _GLIBCXX_USE_DEPRECATED
142#pragma GCC diagnostic push
143#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
144 template<typename _Tp1, typename = _Compatible<_Tp1>>
145 shared_ptr(std::auto_ptr<_Tp1>&& __r)
146 : _Base_type(std::move(__r))
147 { _M_enable_shared_from_this_with(static_cast<_Tp1*>(this->get())); }
148#pragma GCC diagnostic pop
149#endif
150
151 template<typename _Tp1, typename _Del,
152 typename = _UniqCompatible<_Tp1, _Del>>
153 shared_ptr(unique_ptr<_Tp1, _Del>&& __r)
154 : _Base_type(std::move(__r))
155 {
156 // XXX assume conversion from __r.get() to this->get() to __elem_t*
157 // is a round trip, which might not be true in all cases.
158 using __elem_t = typename unique_ptr<_Tp1, _Del>::element_type;
159 _M_enable_shared_from_this_with(static_cast<__elem_t*>(this->get()));
160 }
161
162 constexpr shared_ptr(nullptr_t __p)
163 : _Base_type(__p) { }
164
165 // C++14 20.8.2.2
166 ~shared_ptr() = default;
167
168 // C++14 20.8.2.3
169 shared_ptr& operator=(const shared_ptr&) noexcept = default;
170
171 template <typename _Tp1>
172 _Compatible<_Tp1, shared_ptr&>
173 operator=(const shared_ptr<_Tp1>& __r) noexcept
174 {
175 _Base_type::operator=(__r);
176 return *this;
177 }
178
179 shared_ptr&
180 operator=(shared_ptr&& __r) noexcept
181 {
182 _Base_type::operator=(std::move(__r));
183 return *this;
184 }
185
186 template <typename _Tp1>
187 _Compatible<_Tp1, shared_ptr&>
188 operator=(shared_ptr<_Tp1>&& __r) noexcept
189 {
190 _Base_type::operator=(std::move(__r));
191 return *this;
192 }
193
194#if _GLIBCXX_USE_DEPRECATED
195#pragma GCC diagnostic push
196#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
197 template<typename _Tp1>
198 _Compatible<_Tp1, shared_ptr&>
199 operator=(std::auto_ptr<_Tp1>&& __r)
200 {
201 __shared_ptr<_Tp>::operator=(std::move(__r));
202 return *this;
203 }
204#pragma GCC diagnostic pop
205#endif
206
207 template <typename _Tp1, typename _Del>
208 _UniqCompatible<_Tp1, _Del, shared_ptr&>
209 operator=(unique_ptr<_Tp1, _Del>&& __r)
210 {
211 _Base_type::operator=(std::move(__r));
212 return *this;
213 }
214
215 // C++14 20.8.2.2.4
216 // swap & reset
217 // 8.2.1.2 shared_ptr observers
218 // in __shared_ptr
219
220 private:
221 template<typename _Alloc, typename... _Args>
222 shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
223 _Args&&... __args)
224 : _Base_type(__tag, __a, std::forward<_Args>(__args)...)
225 { _M_enable_shared_from_this_with(this->get()); }
226
227 template<typename _Tp1, typename _Alloc, typename... _Args>
228 friend shared_ptr<_Tp1>
229 allocate_shared(const _Alloc& __a, _Args&&... __args);
230
231 shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t)
232 : _Base_type(__r, std::nothrow) { }
233
234 friend class weak_ptr<_Tp>;
235
236 template<typename _Yp>
237 using __esft_base_t =
238 decltype(__expt_enable_shared_from_this_base(std::declval<_Yp*>()));
239
240 // Detect an accessible and unambiguous enable_shared_from_this base.
241 template<typename _Yp, typename = void>
242 struct __has_esft_base
243 : false_type { };
244
245 template<typename _Yp>
246 struct __has_esft_base<_Yp, __void_t<__esft_base_t<_Yp>>>
247 : __bool_constant<!is_array_v<_Tp>> { }; // ignore base for arrays
248
249 template<typename _Yp>
250 typename enable_if<__has_esft_base<_Yp>::value>::type
251 _M_enable_shared_from_this_with(const _Yp* __p) noexcept
252 {
253 if (auto __base = __expt_enable_shared_from_this_base(__p))
254 {
255 __base->_M_weak_this
256 = shared_ptr<_Yp>(*this, const_cast<_Yp*>(__p));
257 }
258 }
259
260 template<typename _Yp>
261 typename enable_if<!__has_esft_base<_Yp>::value>::type
262 _M_enable_shared_from_this_with(const _Yp*) noexcept
263 { }
264 };
265
266 // C++14 20.8.2.2.7
267 template<typename _Tp1, typename _Tp2>
268 bool operator==(const shared_ptr<_Tp1>& __a,
269 const shared_ptr<_Tp2>& __b) noexcept
270 { return __a.get() == __b.get(); }
271
272 template<typename _Tp>
273 inline bool
274 operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
275 { return !__a; }
276
277 template<typename _Tp>
278 inline bool
279 operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
280 { return !__a; }
281
282 template<typename _Tp1, typename _Tp2>
283 inline bool
284 operator!=(const shared_ptr<_Tp1>& __a,
285 const shared_ptr<_Tp2>& __b) noexcept
286 { return __a.get() != __b.get(); }
287
288 template<typename _Tp>
289 inline bool
290 operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
291 { return (bool)__a; }
292
293 template<typename _Tp>
294 inline bool
295 operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
296 { return (bool)__a; }
297
298 template<typename _Tp1, typename _Tp2>
299 inline bool
300 operator<(const shared_ptr<_Tp1>& __a,
301 const shared_ptr<_Tp2>& __b) noexcept
302 {
303 using __elem_t1 = typename shared_ptr<_Tp1>::element_type;
304 using __elem_t2 = typename shared_ptr<_Tp2>::element_type;
305 using _CT = common_type_t<__elem_t1*, __elem_t2*>;
306 return std::less<_CT>()(__a.get(), __b.get());
307 }
308
309 template<typename _Tp>
310 inline bool
311 operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
312 {
313 using __elem_t = typename shared_ptr<_Tp>::element_type;
314 return std::less<__elem_t*>()(__a.get(), nullptr);
315 }
316
317 template<typename _Tp>
318 inline bool
319 operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
320 {
321 using __elem_t = typename shared_ptr<_Tp>::element_type;
322 return std::less<__elem_t*>()(nullptr, __a.get());
323 }
324
325 template<typename _Tp1, typename _Tp2>
326 inline bool
327 operator<=(const shared_ptr<_Tp1>& __a,
328 const shared_ptr<_Tp2>& __b) noexcept
329 { return !(__b < __a); }
330
331 template<typename _Tp>
332 inline bool
333 operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
334 { return !(nullptr < __a); }
335
336 template<typename _Tp>
337 inline bool
338 operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
339 { return !(__a < nullptr); }
340
341 template<typename _Tp1, typename _Tp2>
342 inline bool
343 operator>(const shared_ptr<_Tp1>& __a,
344 const shared_ptr<_Tp2>& __b) noexcept
345 { return (__b < __a); }
346
347 template<typename _Tp>
348 inline bool
349 operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
350 {
351 using __elem_t = typename shared_ptr<_Tp>::element_type;
352 return std::less<__elem_t*>()(nullptr, __a.get());
353 }
354
355 template<typename _Tp>
356 inline bool
357 operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
358 {
359 using __elem_t = typename shared_ptr<_Tp>::element_type;
360 return std::less<__elem_t*>()(__a.get(), nullptr);
361 }
362
363 template<typename _Tp1, typename _Tp2>
364 inline bool
365 operator>=(const shared_ptr<_Tp1>& __a,
366 const shared_ptr<_Tp2>& __b) noexcept
367 { return !(__a < __b); }
368
369 template<typename _Tp>
370 inline bool
371 operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
372 { return !(__a < nullptr); }
373
374 template<typename _Tp>
375 inline bool
376 operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
377 { return !(nullptr < __a); }
378
379 // C++14 20.8.2.2.8
380 template<typename _Tp>
381 inline void
382 swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept
383 { __a.swap(__b); }
384
385 // 8.2.1.3, shared_ptr casts
386 template<typename _Tp, typename _Tp1>
387 inline shared_ptr<_Tp>
388 static_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
389 {
390 using __elem_t = typename shared_ptr<_Tp>::element_type;
391 return shared_ptr<_Tp>(__r, static_cast<__elem_t*>(__r.get()));
392 }
393
394 template<typename _Tp, typename _Tp1>
395 inline shared_ptr<_Tp>
396 dynamic_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
397 {
398 using __elem_t = typename shared_ptr<_Tp>::element_type;
399 if (_Tp* __p = dynamic_cast<__elem_t*>(__r.get()))
400 return shared_ptr<_Tp>(__r, __p);
401 return shared_ptr<_Tp>();
402 }
403
404 template<typename _Tp, typename _Tp1>
405 inline shared_ptr<_Tp>
406 const_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
407 {
408 using __elem_t = typename shared_ptr<_Tp>::element_type;
409 return shared_ptr<_Tp>(__r, const_cast<__elem_t*>(__r.get()));
410 }
411
412 template<typename _Tp, typename _Tp1>
413 inline shared_ptr<_Tp>
414 reinterpret_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
415 {
416 using __elem_t = typename shared_ptr<_Tp>::element_type;
417 return shared_ptr<_Tp>(__r, reinterpret_cast<__elem_t*>(__r.get()));
418 }
419
420 // C++14 20.8.2.3
421 template<typename _Tp>
422 class weak_ptr : public __weak_ptr<_Tp>
423 {
424 template<typename _Tp1, typename _Res = void>
425 using _Compatible = enable_if_t<__sp_compatible_v<_Tp1, _Tp>, _Res>;
426
427 using _Base_type = __weak_ptr<_Tp>;
428
429 public:
430 constexpr weak_ptr() noexcept = default;
431
432 template<typename _Tp1, typename = _Compatible<_Tp1>>
433 weak_ptr(const shared_ptr<_Tp1>& __r) noexcept
434 : _Base_type(__r) { }
435
436 weak_ptr(const weak_ptr&) noexcept = default;
437
438 template<typename _Tp1, typename = _Compatible<_Tp1>>
439 weak_ptr(const weak_ptr<_Tp1>& __r) noexcept
440 : _Base_type(__r) { }
441
442 weak_ptr(weak_ptr&&) noexcept = default;
443
444 template<typename _Tp1, typename = _Compatible<_Tp1>>
445 weak_ptr(weak_ptr<_Tp1>&& __r) noexcept
446 : _Base_type(std::move(__r)) { }
447
448 weak_ptr&
449 operator=(const weak_ptr& __r) noexcept = default;
450
451 template<typename _Tp1>
452 _Compatible<_Tp1, weak_ptr&>
453 operator=(const weak_ptr<_Tp1>& __r) noexcept
454 {
455 this->_Base_type::operator=(__r);
456 return *this;
457 }
458
459 template<typename _Tp1>
460 _Compatible<_Tp1, weak_ptr&>
461 operator=(const shared_ptr<_Tp1>& __r) noexcept
462 {
463 this->_Base_type::operator=(__r);
464 return *this;
465 }
466
467 weak_ptr&
468 operator=(weak_ptr&& __r) noexcept = default;
469
470 template<typename _Tp1>
471 _Compatible<_Tp1, weak_ptr&>
472 operator=(weak_ptr<_Tp1>&& __r) noexcept
473 {
474 this->_Base_type::operator=(std::move(__r));
475 return *this;
476 }
477
478 shared_ptr<_Tp>
479 lock() const noexcept
480 { return shared_ptr<_Tp>(*this, std::nothrow); }
481
482 friend class enable_shared_from_this<_Tp>;
483 };
484
485 // C++14 20.8.2.3.6
486 template<typename _Tp>
487 inline void
488 swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept
489 { __a.swap(__b); }
490
491 /// C++14 20.8.2.2.10
492 template<typename _Del, typename _Tp>
493 inline _Del*
494 get_deleter(const shared_ptr<_Tp>& __p) noexcept
495 { return std::get_deleter<_Del>(__p); }
496
497 // C++14 20.8.2.2.11
498 template<typename _Ch, typename _Tr, typename _Tp>
499 inline std::basic_ostream<_Ch, _Tr>&
500 operator<<(std::basic_ostream<_Ch, _Tr>& __os, const shared_ptr<_Tp>& __p)
501 {
502 __os << __p.get();
503 return __os;
504 }
505
506 // C++14 20.8.2.4
507 template<typename _Tp = void> class owner_less;
508
509 /// Partial specialization of owner_less for shared_ptr.
510 template<typename _Tp>
511 struct owner_less<shared_ptr<_Tp>>
512 : public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>>
513 { };
514
515 /// Partial specialization of owner_less for weak_ptr.
516 template<typename _Tp>
517 struct owner_less<weak_ptr<_Tp>>
518 : public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>>
519 { };
520
521 template<>
522 class owner_less<void>
523 {
524 template<typename _Tp, typename _Up>
525 bool
526 operator()(shared_ptr<_Tp> const& __lhs,
527 shared_ptr<_Up> const& __rhs) const
528 { return __lhs.owner_before(__rhs); }
529
530 template<typename _Tp, typename _Up>
531 bool
532 operator()(shared_ptr<_Tp> const& __lhs,
533 weak_ptr<_Up> const& __rhs) const
534 { return __lhs.owner_before(__rhs); }
535
536 template<typename _Tp, typename _Up>
537 bool
538 operator()(weak_ptr<_Tp> const& __lhs,
539 shared_ptr<_Up> const& __rhs) const
540 { return __lhs.owner_before(__rhs); }
541
542 template<typename _Tp, typename _Up>
543 bool
544 operator()(weak_ptr<_Tp> const& __lhs,
545 weak_ptr<_Up> const& __rhs) const
546 { return __lhs.owner_before(__rhs); }
547
548 typedef void is_transparent;
549 };
550
551 // C++14 20.8.2.6
552 template<typename _Tp>
553 inline bool
554 atomic_is_lock_free(const shared_ptr<_Tp>* __p)
555 { return std::atomic_is_lock_free<_Tp, __default_lock_policy>(__p); }
556
557 template<typename _Tp>
558 shared_ptr<_Tp> atomic_load(const shared_ptr<_Tp>* __p)
559 { return std::atomic_load<_Tp>(__p); }
560
561 template<typename _Tp>
562 shared_ptr<_Tp>
563 atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order __mo)
564 { return std::atomic_load_explicit<_Tp>(__p, __mo); }
565
566 template<typename _Tp>
567 void atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
568 { return std::atomic_store<_Tp>(__p, __r); }
569
570 template<typename _Tp>
571 shared_ptr<_Tp>
572 atomic_store_explicit(const shared_ptr<_Tp>* __p,
573 shared_ptr<_Tp> __r,
574 memory_order __mo)
575 { return std::atomic_store_explicit<_Tp>(__p, __r, __mo); }
576
577 template<typename _Tp>
578 void atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
579 { return std::atomic_exchange<_Tp>(__p, __r); }
580
581 template<typename _Tp>
582 shared_ptr<_Tp>
583 atomic_exchange_explicit(const shared_ptr<_Tp>* __p,
584 shared_ptr<_Tp> __r,
585 memory_order __mo)
586 { return std::atomic_exchange_explicit<_Tp>(__p, __r, __mo); }
587
588 template<typename _Tp>
589 bool atomic_compare_exchange_weak(shared_ptr<_Tp>* __p,
590 shared_ptr<_Tp>* __v,
591 shared_ptr<_Tp> __w)
592 { return std::atomic_compare_exchange_weak<_Tp>(__p, __v, __w); }
593
594 template<typename _Tp>
595 bool atomic_compare_exchange_strong(shared_ptr<_Tp>* __p,
596 shared_ptr<_Tp>* __v,
597 shared_ptr<_Tp> __w)
598 { return std::atomic_compare_exchange_strong<_Tp>(__p, __v, __w); }
599
600 template<typename _Tp>
601 bool atomic_compare_exchange_weak_explicit(shared_ptr<_Tp>* __p,
602 shared_ptr<_Tp>* __v,
603 shared_ptr<_Tp> __w,
604 memory_order __success,
605 memory_order __failure)
606 { return std::atomic_compare_exchange_weak_explicit<_Tp>(__p, __v, __w,
607 __success,
608 __failure); }
609
610 template<typename _Tp>
611 bool atomic_compare_exchange_strong_explicit(shared_ptr<_Tp>* __p,
612 shared_ptr<_Tp>* __v,
613 shared_ptr<_Tp> __w,
614 memory_order __success,
615 memory_order __failure)
616 { return std::atomic_compare_exchange_strong_explicit<_Tp>(__p, __v, __w,
617 __success,
618 __failure); }
619
620 //enable_shared_from_this
621 template<typename _Tp>
622 class enable_shared_from_this
623 {
624 protected:
625 constexpr enable_shared_from_this() noexcept { }
626
627 enable_shared_from_this(const enable_shared_from_this&) noexcept { }
628
629 enable_shared_from_this&
630 operator=(const enable_shared_from_this&) noexcept
631 { return *this; }
632
633 ~enable_shared_from_this() { }
634
635 public:
636 shared_ptr<_Tp>
637 shared_from_this()
638 { return shared_ptr<_Tp>(this->_M_weak_this); }
639
640 shared_ptr<const _Tp>
641 shared_from_this() const
642 { return shared_ptr<const _Tp>(this->_M_weak_this); }
643
644 weak_ptr<_Tp>
645 weak_from_this() noexcept
646 { return _M_weak_this; }
647
648 weak_ptr<const _Tp>
649 weak_from_this() const noexcept
650 { return _M_weak_this; }
651
652 private:
653 template<typename _Tp1>
654 void
655 _M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
656 { _M_weak_this._M_assign(__p, __n); }
657
658 // Found by ADL when this is an associated class.
659 friend const enable_shared_from_this*
660 __expt_enable_shared_from_this_base(const enable_shared_from_this* __p)
661 { return __p; }
662
663 template<typename>
664 friend class shared_ptr;
665
666 mutable weak_ptr<_Tp> _M_weak_this;
667 };
668} // namespace fundamentals_v2
669} // namespace experimental
670
671 /// std::hash specialization for shared_ptr.
672 template<typename _Tp>
673 struct hash<experimental::shared_ptr<_Tp>>
674 : public __hash_base<size_t, experimental::shared_ptr<_Tp>>
675 {
676 size_t
677 operator()(const experimental::shared_ptr<_Tp>& __s) const noexcept
678 { return std::hash<_Tp*>()(__s.get()); }
679 };
680
681_GLIBCXX_END_NAMESPACE_VERSION
682} // namespace std
683
684#endif // __cplusplus <= 201103L
685
686#endif // _GLIBCXX_EXPERIMENTAL_SHARED_PTR_H
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