1 // Experimental shared_ptr with array support -*- C++ -*-
2
3 // Copyright (C) 2015-2023 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 #pragma GCC system_header
34
35 #if __cplusplus >= 201402L
36
37 #include <memory>
38 #include <experimental/type_traits>
39
40 namespace std _GLIBCXX_VISIBILITY(default)
41 {
42 _GLIBCXX_BEGIN_NAMESPACE_VERSION
43
44 namespace experimental
45 {
46 inline namespace fundamentals_v2
47 {
48 // 8.2.1
49
50 template<typename _Tp> class shared_ptr;
51 template<typename _Tp> class weak_ptr;
52 template<typename _Tp> class enable_shared_from_this;
53
54 template<typename _Yp, typename _Tp>
55 constexpr bool __sp_compatible_v
56 = std::__sp_compatible_with<_Yp*, _Tp*>::value;
57
58 template<typename _Tp, typename _Yp>
59 constexpr bool __sp_is_constructible_v
60 = std::__sp_is_constructible<_Tp, _Yp>::value;
61
62 template<typename _Tp>
63 class shared_ptr : public __shared_ptr<_Tp>
64 {
65 using _Base_type = __shared_ptr<_Tp>;
66
67 public:
68 using element_type = typename _Base_type::element_type;
69
70 private:
71 // Constraint for construction from a pointer of type _Yp*:
72 template<typename _Yp>
73 using _SafeConv = enable_if_t<__sp_is_constructible_v<_Tp, _Yp>>;
74
75 template<typename _Tp1, typename _Res = void>
76 using _Compatible
77 = enable_if_t<__sp_compatible_v<_Tp1, _Tp>, _Res>;
78
79 template<typename _Tp1, typename _Del,
80 typename _Ptr = typename unique_ptr<_Tp1, _Del>::pointer,
81 typename _Res = void>
82 using _UniqCompatible = enable_if_t<
83 __sp_compatible_v<_Tp1, _Tp>
84 && experimental::is_convertible_v<_Ptr, element_type*>,
85 _Res>;
86
87 public:
88
89 // 8.2.1.1, shared_ptr constructors
90 constexpr shared_ptr() noexcept = default;
91
92 template<typename _Tp1, typename = _SafeConv<_Tp1>>
93 explicit
94 shared_ptr(_Tp1* __p) : _Base_type(__p)
95 { _M_enable_shared_from_this_with(__p); }
96
97 template<typename _Tp1, typename _Deleter, typename = _SafeConv<_Tp1>>
98 shared_ptr(_Tp1* __p, _Deleter __d)
99 : _Base_type(__p, __d)
100 { _M_enable_shared_from_this_with(__p); }
101
102 template<typename _Tp1, typename _Deleter, typename _Alloc,
103 typename = _SafeConv<_Tp1>>
104 shared_ptr(_Tp1* __p, _Deleter __d, _Alloc __a)
105 : _Base_type(__p, __d, __a)
106 { _M_enable_shared_from_this_with(__p); }
107
108 template<typename _Deleter>
109 shared_ptr(nullptr_t __p, _Deleter __d)
110 : _Base_type(__p, __d) { }
111
112 template<typename _Deleter, typename _Alloc>
113 shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
114 : _Base_type(__p, __d, __a) { }
115
116 template<typename _Tp1>
117 shared_ptr(const shared_ptr<_Tp1>& __r, element_type* __p) noexcept
118 : _Base_type(__r, __p) { }
119
120 shared_ptr(const shared_ptr& __r) noexcept
121 : _Base_type(__r) { }
122
123 template<typename _Tp1, typename = _Compatible<_Tp1>>
124 shared_ptr(const shared_ptr<_Tp1>& __r) noexcept
125 : _Base_type(__r) { }
126
127 shared_ptr(shared_ptr&& __r) noexcept
128 : _Base_type(std::move(__r)) { }
129
130 template<typename _Tp1, typename = _Compatible<_Tp1>>
131 shared_ptr(shared_ptr<_Tp1>&& __r) noexcept
132 : _Base_type(std::move(__r)) { }
133
134 template<typename _Tp1, typename = _Compatible<_Tp1>>
135 explicit
136 shared_ptr(const weak_ptr<_Tp1>& __r)
137 : _Base_type(__r) { }
138
139 #if _GLIBCXX_USE_DEPRECATED
140 #pragma GCC diagnostic push
141 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
142 template<typename _Tp1, typename = _Compatible<_Tp1>>
143 shared_ptr(std::auto_ptr<_Tp1>&& __r)
144 : _Base_type(std::move(__r))
145 { _M_enable_shared_from_this_with(static_cast<_Tp1*>(this->get())); }
146 #pragma GCC diagnostic pop
147 #endif
148
149 template<typename _Tp1, typename _Del,
150 typename = _UniqCompatible<_Tp1, _Del>>
151 shared_ptr(unique_ptr<_Tp1, _Del>&& __r)
152 : _Base_type(std::move(__r))
153 {
154 // XXX assume conversion from __r.get() to this->get() to __elem_t*
155 // is a round trip, which might not be true in all cases.
156 using __elem_t = typename unique_ptr<_Tp1, _Del>::element_type;
157 _M_enable_shared_from_this_with(static_cast<__elem_t*>(this->get()));
158 }
159
160 constexpr shared_ptr(nullptr_t __p)
161 : _Base_type(__p) { }
162
163 // C++14 20.8.2.2
164 ~shared_ptr() = default;
165
166 // C++14 20.8.2.3
167 shared_ptr& operator=(const shared_ptr&) noexcept = default;
168
169 template <typename _Tp1>
170 _Compatible<_Tp1, shared_ptr&>
171 operator=(const shared_ptr<_Tp1>& __r) noexcept
172 {
173 _Base_type::operator=(__r);
174 return *this;
175 }
176
177 shared_ptr&
178 operator=(shared_ptr&& __r) noexcept
179 {
180 _Base_type::operator=(std::move(__r));
181 return *this;
182 }
183
184 template <typename _Tp1>
185 _Compatible<_Tp1, shared_ptr&>
186 operator=(shared_ptr<_Tp1>&& __r) noexcept
187 {
188 _Base_type::operator=(std::move(__r));
189 return *this;
190 }
191
192 #if _GLIBCXX_USE_DEPRECATED
193 #pragma GCC diagnostic push
194 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
195 template<typename _Tp1>
196 _Compatible<_Tp1, shared_ptr&>
197 operator=(std::auto_ptr<_Tp1>&& __r)
198 {
199 __shared_ptr<_Tp>::operator=(std::move(__r));
200 return *this;
201 }
202 #pragma GCC diagnostic pop
203 #endif
204
205 template <typename _Tp1, typename _Del>
206 _UniqCompatible<_Tp1, _Del, shared_ptr&>
207 operator=(unique_ptr<_Tp1, _Del>&& __r)
208 {
209 _Base_type::operator=(std::move(__r));
210 return *this;
211 }
212
213 // C++14 20.8.2.2.4
214 // swap & reset
215 // 8.2.1.2 shared_ptr observers
216 // in __shared_ptr
217
218 private:
219 template<typename _Alloc, typename... _Args>
220 shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
221 _Args&&... __args)
222 : _Base_type(__tag, __a, std::forward<_Args>(__args)...)
223 { _M_enable_shared_from_this_with(this->get()); }
224
225 template<typename _Tp1, typename _Alloc, typename... _Args>
226 friend shared_ptr<_Tp1>
227 allocate_shared(const _Alloc& __a, _Args&&... __args);
228
229 shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t)
230 : _Base_type(__r, std::nothrow) { }
231
232 friend class weak_ptr<_Tp>;
233
234 template<typename _Yp>
235 using __esft_base_t =
236 decltype(__expt_enable_shared_from_this_base(std::declval<_Yp*>()));
237
238 // Detect an accessible and unambiguous enable_shared_from_this base.
239 template<typename _Yp, typename = void>
240 struct __has_esft_base
241 : false_type { };
242
243 template<typename _Yp>
244 struct __has_esft_base<_Yp, __void_t<__esft_base_t<_Yp>>>
245 : __bool_constant<!is_array_v<_Tp>> { }; // ignore base for arrays
246
247 template<typename _Yp>
248 typename enable_if<__has_esft_base<_Yp>::value>::type
249 _M_enable_shared_from_this_with(const _Yp* __p) noexcept
250 {
251 if (auto __base = __expt_enable_shared_from_this_base(__p))
252 {
253 __base->_M_weak_this
254 = shared_ptr<_Yp>(*this, const_cast<_Yp*>(__p));
255 }
256 }
257
258 template<typename _Yp>
259 typename enable_if<!__has_esft_base<_Yp>::value>::type
260 _M_enable_shared_from_this_with(const _Yp*) noexcept
261 { }
262 };
263
264 // C++14 20.8.2.2.7
265 template<typename _Tp1, typename _Tp2>
266 bool operator==(const shared_ptr<_Tp1>& __a,
267 const shared_ptr<_Tp2>& __b) noexcept
268 { return __a.get() == __b.get(); }
269
270 template<typename _Tp>
271 inline bool
272 operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
273 { return !__a; }
274
275 template<typename _Tp>
276 inline bool
277 operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
278 { return !__a; }
279
280 template<typename _Tp1, typename _Tp2>
281 inline bool
282 operator!=(const shared_ptr<_Tp1>& __a,
283 const shared_ptr<_Tp2>& __b) noexcept
284 { return __a.get() != __b.get(); }
285
286 template<typename _Tp>
287 inline bool
288 operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
289 { return (bool)__a; }
290
291 template<typename _Tp>
292 inline bool
293 operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
294 { return (bool)__a; }
295
296 template<typename _Tp1, typename _Tp2>
297 inline bool
298 operator<(const shared_ptr<_Tp1>& __a,
299 const shared_ptr<_Tp2>& __b) noexcept
300 {
301 using __elem_t1 = typename shared_ptr<_Tp1>::element_type;
302 using __elem_t2 = typename shared_ptr<_Tp2>::element_type;
303 using _CT = common_type_t<__elem_t1*, __elem_t2*>;
304 return std::less<_CT>()(__a.get(), __b.get());
305 }
306
307 template<typename _Tp>
308 inline bool
309 operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
310 {
311 using __elem_t = typename shared_ptr<_Tp>::element_type;
312 return std::less<__elem_t*>()(__a.get(), nullptr);
313 }
314
315 template<typename _Tp>
316 inline bool
317 operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
318 {
319 using __elem_t = typename shared_ptr<_Tp>::element_type;
320 return std::less<__elem_t*>()(nullptr, __a.get());
321 }
322
323 template<typename _Tp1, typename _Tp2>
324 inline bool
325 operator<=(const shared_ptr<_Tp1>& __a,
326 const shared_ptr<_Tp2>& __b) noexcept
327 { return !(__b < __a); }
328
329 template<typename _Tp>
330 inline bool
331 operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
332 { return !(nullptr < __a); }
333
334 template<typename _Tp>
335 inline bool
336 operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
337 { return !(__a < nullptr); }
338
339 template<typename _Tp1, typename _Tp2>
340 inline bool
341 operator>(const shared_ptr<_Tp1>& __a,
342 const shared_ptr<_Tp2>& __b) noexcept
343 { return (__b < __a); }
344
345 template<typename _Tp>
346 inline bool
347 operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
348 {
349 using __elem_t = typename shared_ptr<_Tp>::element_type;
350 return std::less<__elem_t*>()(nullptr, __a.get());
351 }
352
353 template<typename _Tp>
354 inline bool
355 operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
356 {
357 using __elem_t = typename shared_ptr<_Tp>::element_type;
358 return std::less<__elem_t*>()(__a.get(), nullptr);
359 }
360
361 template<typename _Tp1, typename _Tp2>
362 inline bool
363 operator>=(const shared_ptr<_Tp1>& __a,
364 const shared_ptr<_Tp2>& __b) noexcept
365 { return !(__a < __b); }
366
367 template<typename _Tp>
368 inline bool
369 operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
370 { return !(__a < nullptr); }
371
372 template<typename _Tp>
373 inline bool
374 operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
375 { return !(nullptr < __a); }
376
377 // C++14 20.8.2.2.8
378 template<typename _Tp>
379 inline void
380 swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept
381 { __a.swap(__b); }
382
383 // 8.2.1.3, shared_ptr casts
384 template<typename _Tp, typename _Tp1>
385 inline shared_ptr<_Tp>
386 static_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
387 {
388 using __elem_t = typename shared_ptr<_Tp>::element_type;
389 return shared_ptr<_Tp>(__r, static_cast<__elem_t*>(__r.get()));
390 }
391
392 template<typename _Tp, typename _Tp1>
393 inline shared_ptr<_Tp>
394 dynamic_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
395 {
396 using __elem_t = typename shared_ptr<_Tp>::element_type;
397 if (_Tp* __p = dynamic_cast<__elem_t*>(__r.get()))
398 return shared_ptr<_Tp>(__r, __p);
399 return shared_ptr<_Tp>();
400 }
401
402 template<typename _Tp, typename _Tp1>
403 inline shared_ptr<_Tp>
404 const_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
405 {
406 using __elem_t = typename shared_ptr<_Tp>::element_type;
407 return shared_ptr<_Tp>(__r, const_cast<__elem_t*>(__r.get()));
408 }
409
410 template<typename _Tp, typename _Tp1>
411 inline shared_ptr<_Tp>
412 reinterpret_pointer_cast(const shared_ptr<_Tp1>& __r) noexcept
413 {
414 using __elem_t = typename shared_ptr<_Tp>::element_type;
415 return shared_ptr<_Tp>(__r, reinterpret_cast<__elem_t*>(__r.get()));
416 }
417
418 // C++14 20.8.2.3
419 template<typename _Tp>
420 class weak_ptr : public __weak_ptr<_Tp>
421 {
422 template<typename _Tp1, typename _Res = void>
423 using _Compatible = enable_if_t<__sp_compatible_v<_Tp1, _Tp>, _Res>;
424
425 using _Base_type = __weak_ptr<_Tp>;
426
427 public:
428 constexpr weak_ptr() noexcept = default;
429
430 template<typename _Tp1, typename = _Compatible<_Tp1>>
431 weak_ptr(const shared_ptr<_Tp1>& __r) noexcept
432 : _Base_type(__r) { }
433
434 weak_ptr(const weak_ptr&) noexcept = default;
435
436 template<typename _Tp1, typename = _Compatible<_Tp1>>
437 weak_ptr(const weak_ptr<_Tp1>& __r) noexcept
438 : _Base_type(__r) { }
439
440 weak_ptr(weak_ptr&&) noexcept = default;
441
442 template<typename _Tp1, typename = _Compatible<_Tp1>>
443 weak_ptr(weak_ptr<_Tp1>&& __r) noexcept
444 : _Base_type(std::move(__r)) { }
445
446 weak_ptr&
447 operator=(const weak_ptr& __r) noexcept = default;
448
449 template<typename _Tp1>
450 _Compatible<_Tp1, weak_ptr&>
451 operator=(const weak_ptr<_Tp1>& __r) noexcept
452 {
453 this->_Base_type::operator=(__r);
454 return *this;
455 }
456
457 template<typename _Tp1>
458 _Compatible<_Tp1, weak_ptr&>
459 operator=(const shared_ptr<_Tp1>& __r) noexcept
460 {
461 this->_Base_type::operator=(__r);
462 return *this;
463 }
464
465 weak_ptr&
466 operator=(weak_ptr&& __r) noexcept = default;
467
468 template<typename _Tp1>
469 _Compatible<_Tp1, weak_ptr&>
470 operator=(weak_ptr<_Tp1>&& __r) noexcept
471 {
472 this->_Base_type::operator=(std::move(__r));
473 return *this;
474 }
475
476 shared_ptr<_Tp>
477 lock() const noexcept
478 { return shared_ptr<_Tp>(*this, std::nothrow); }
479
480 friend class enable_shared_from_this<_Tp>;
481 };
482
483 // C++14 20.8.2.3.6
484 template<typename _Tp>
485 inline void
486 swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept
487 { __a.swap(__b); }
488
489 /// C++14 20.8.2.2.10
490 template<typename _Del, typename _Tp>
491 inline _Del*
492 get_deleter(const shared_ptr<_Tp>& __p) noexcept
493 { return std::get_deleter<_Del>(__p); }
494
495 // C++14 20.8.2.2.11
496 template<typename _Ch, typename _Tr, typename _Tp>
497 inline std::basic_ostream<_Ch, _Tr>&
498 operator<<(std::basic_ostream<_Ch, _Tr>& __os, const shared_ptr<_Tp>& __p)
499 {
500 __os << __p.get();
501 return __os;
502 }
503
504 // C++14 20.8.2.4
505 template<typename _Tp = void> class owner_less;
506
507 /// Partial specialization of owner_less for shared_ptr.
508 template<typename _Tp>
509 struct owner_less<shared_ptr<_Tp>>
510 : public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>>
511 { };
512
513 /// Partial specialization of owner_less for weak_ptr.
514 template<typename _Tp>
515 struct owner_less<weak_ptr<_Tp>>
516 : public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>>
517 { };
518
519 template<>
520 class owner_less<void>
521 {
522 template<typename _Tp, typename _Up>
523 bool
524 operator()(shared_ptr<_Tp> const& __lhs,
525 shared_ptr<_Up> const& __rhs) const
526 { return __lhs.owner_before(__rhs); }
527
528 template<typename _Tp, typename _Up>
529 bool
530 operator()(shared_ptr<_Tp> const& __lhs,
531 weak_ptr<_Up> const& __rhs) const
532 { return __lhs.owner_before(__rhs); }
533
534 template<typename _Tp, typename _Up>
535 bool
536 operator()(weak_ptr<_Tp> const& __lhs,
537 shared_ptr<_Up> const& __rhs) const
538 { return __lhs.owner_before(__rhs); }
539
540 template<typename _Tp, typename _Up>
541 bool
542 operator()(weak_ptr<_Tp> const& __lhs,
543 weak_ptr<_Up> const& __rhs) const
544 { return __lhs.owner_before(__rhs); }
545
546 typedef void is_transparent;
547 };
548
549 // C++14 20.8.2.6
550 template<typename _Tp>
551 inline bool
552 atomic_is_lock_free(const shared_ptr<_Tp>* __p)
553 { return std::atomic_is_lock_free<_Tp, __default_lock_policy>(__p); }
554
555 template<typename _Tp>
556 shared_ptr<_Tp> atomic_load(const shared_ptr<_Tp>* __p)
557 { return std::atomic_load<_Tp>(__p); }
558
559 template<typename _Tp>
560 shared_ptr<_Tp>
561 atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order __mo)
562 { return std::atomic_load_explicit<_Tp>(__p, __mo); }
563
564 template<typename _Tp>
565 void atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
566 { return std::atomic_store<_Tp>(__p, __r); }
567
568 template<typename _Tp>
569 shared_ptr<_Tp>
570 atomic_store_explicit(const shared_ptr<_Tp>* __p,
571 shared_ptr<_Tp> __r,
572 memory_order __mo)
573 { return std::atomic_store_explicit<_Tp>(__p, __r, __mo); }
574
575 template<typename _Tp>
576 void atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r)
577 { return std::atomic_exchange<_Tp>(__p, __r); }
578
579 template<typename _Tp>
580 shared_ptr<_Tp>
581 atomic_exchange_explicit(const shared_ptr<_Tp>* __p,
582 shared_ptr<_Tp> __r,
583 memory_order __mo)
584 { return std::atomic_exchange_explicit<_Tp>(__p, __r, __mo); }
585
586 template<typename _Tp>
587 bool atomic_compare_exchange_weak(shared_ptr<_Tp>* __p,
588 shared_ptr<_Tp>* __v,
589 shared_ptr<_Tp> __w)
590 { return std::atomic_compare_exchange_weak<_Tp>(__p, __v, __w); }
591
592 template<typename _Tp>
593 bool atomic_compare_exchange_strong(shared_ptr<_Tp>* __p,
594 shared_ptr<_Tp>* __v,
595 shared_ptr<_Tp> __w)
596 { return std::atomic_compare_exchange_strong<_Tp>(__p, __v, __w); }
597
598 template<typename _Tp>
599 bool atomic_compare_exchange_weak_explicit(shared_ptr<_Tp>* __p,
600 shared_ptr<_Tp>* __v,
601 shared_ptr<_Tp> __w,
602 memory_order __success,
603 memory_order __failure)
604 { return std::atomic_compare_exchange_weak_explicit<_Tp>(__p, __v, __w,
605 __success,
606 __failure); }
607
608 template<typename _Tp>
609 bool atomic_compare_exchange_strong_explicit(shared_ptr<_Tp>* __p,
610 shared_ptr<_Tp>* __v,
611 shared_ptr<_Tp> __w,
612 memory_order __success,
613 memory_order __failure)
614 { return std::atomic_compare_exchange_strong_explicit<_Tp>(__p, __v, __w,
615 __success,
616 __failure); }
617
618 //enable_shared_from_this
619 template<typename _Tp>
620 class enable_shared_from_this
621 {
622 protected:
623 constexpr enable_shared_from_this() noexcept { }
624
625 enable_shared_from_this(const enable_shared_from_this&) noexcept { }
626
627 enable_shared_from_this&
628 operator=(const enable_shared_from_this&) noexcept
629 { return *this; }
630
631 ~enable_shared_from_this() { }
632
633 public:
634 shared_ptr<_Tp>
635 shared_from_this()
636 { return shared_ptr<_Tp>(this->_M_weak_this); }
637
638 shared_ptr<const _Tp>
639 shared_from_this() const
640 { return shared_ptr<const _Tp>(this->_M_weak_this); }
641
642 weak_ptr<_Tp>
643 weak_from_this() noexcept
644 { return _M_weak_this; }
645
646 weak_ptr<const _Tp>
647 weak_from_this() const noexcept
648 { return _M_weak_this; }
649
650 private:
651 template<typename _Tp1>
652 void
653 _M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
654 { _M_weak_this._M_assign(__p, __n); }
655
656 // Found by ADL when this is an associated class.
657 friend const enable_shared_from_this*
658 __expt_enable_shared_from_this_base(const enable_shared_from_this* __p)
659 { return __p; }
660
661 template<typename>
662 friend class shared_ptr;
663
664 mutable weak_ptr<_Tp> _M_weak_this;
665 };
666 } // namespace fundamentals_v2
667 } // namespace experimental
668
669 /// std::hash specialization for shared_ptr.
670 template<typename _Tp>
671 struct hash<experimental::shared_ptr<_Tp>>
672 : public __hash_base<size_t, experimental::shared_ptr<_Tp>>
673 {
674 size_t
675 operator()(const experimental::shared_ptr<_Tp>& __s) const noexcept
676 { return std::hash<_Tp*>()(__s.get()); }
677 };
678
679 _GLIBCXX_END_NAMESPACE_VERSION
680 } // namespace std
681
682 #endif // __cplusplus <= 201103L
683
684 #endif // _GLIBCXX_EXPERIMENTAL_SHARED_PTR_H