1    	// shared_ptr and weak_ptr implementation -*- C++ -*-
2    	
3    	// Copyright (C) 2007-2017 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   	// GCC Note: Based on files from version 1.32.0 of the Boost library.
26   	
27   	//  shared_count.hpp
28   	//  Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
29   	
30   	//  shared_ptr.hpp
31   	//  Copyright (C) 1998, 1999 Greg Colvin and Beman Dawes.
32   	//  Copyright (C) 2001, 2002, 2003 Peter Dimov
33   	
34   	//  weak_ptr.hpp
35   	//  Copyright (C) 2001, 2002, 2003 Peter Dimov
36   	
37   	//  enable_shared_from_this.hpp
38   	//  Copyright (C) 2002 Peter Dimov
39   	
40   	// Distributed under the Boost Software License, Version 1.0. (See
41   	// accompanying file LICENSE_1_0.txt or copy at
42   	// http://www.boost.org/LICENSE_1_0.txt)
43   	
44   	/** @file
45   	 *  This is an internal header file, included by other library headers.
46   	 *  Do not attempt to use it directly. @headername{memory}
47   	 */
48   	
49   	#ifndef _SHARED_PTR_H
50   	#define _SHARED_PTR_H 1
51   	
52   	#include <bits/shared_ptr_base.h>
53   	
54   	namespace std _GLIBCXX_VISIBILITY(default)
55   	{
56   	_GLIBCXX_BEGIN_NAMESPACE_VERSION
57   	
58   	  /**
59   	   * @addtogroup pointer_abstractions
60   	   * @{
61   	   */
62   	
63   	  /// 20.7.2.2.11 shared_ptr I/O
64   	  template<typename _Ch, typename _Tr, typename _Tp, _Lock_policy _Lp>
65   	    inline std::basic_ostream<_Ch, _Tr>&
66   	    operator<<(std::basic_ostream<_Ch, _Tr>& __os,
67   		       const __shared_ptr<_Tp, _Lp>& __p)
68   	    {
69   	      __os << __p.get();
70   	      return __os;
71   	    }
72   	
73   	  /// 20.7.2.2.10 shared_ptr get_deleter
74   	  template<typename _Del, typename _Tp, _Lock_policy _Lp>
75   	    inline _Del*
76   	    get_deleter(const __shared_ptr<_Tp, _Lp>& __p) noexcept
77   	    {
78   	#if __cpp_rtti
79   	      return static_cast<_Del*>(__p._M_get_deleter(typeid(_Del)));
80   	#else
81   	      return 0;
82   	#endif
83   	    }
84   	
85   	
86   	  /**
87   	   *  @brief  A smart pointer with reference-counted copy semantics.
88   	   *
89   	   *  The object pointed to is deleted when the last shared_ptr pointing to
90   	   *  it is destroyed or reset.
91   	  */
92   	  template<typename _Tp>
93   	    class shared_ptr : public __shared_ptr<_Tp>
94   	    {
95   	      template<typename... _Args>
96   		using _Constructible = typename enable_if<
97   		  is_constructible<__shared_ptr<_Tp>, _Args...>::value
98   		>::type;
99   	
100  	      template<typename _Arg>
101  		using _Assignable = typename enable_if<
102  		  is_assignable<__shared_ptr<_Tp>&, _Arg>::value, shared_ptr&
103  		>::type;
104  	
105  	    public:
106  	
107  	      using element_type = typename __shared_ptr<_Tp>::element_type;
108  	
109  	#if __cplusplus > 201402L
110  	# define __cpp_lib_shared_ptr_weak_type 201606
111  	      using weak_type = weak_ptr<_Tp>;
112  	#endif
113  	      /**
114  	       *  @brief  Construct an empty %shared_ptr.
115  	       *  @post   use_count()==0 && get()==0
116  	       */
117  	      constexpr shared_ptr() noexcept : __shared_ptr<_Tp>() { }
118  	
119  	      shared_ptr(const shared_ptr&) noexcept = default;
120  	
121  	      /**
122  	       *  @brief  Construct a %shared_ptr that owns the pointer @a __p.
123  	       *  @param  __p  A pointer that is convertible to element_type*.
124  	       *  @post   use_count() == 1 && get() == __p
125  	       *  @throw  std::bad_alloc, in which case @c delete @a __p is called.
126  	       */
127  	      template<typename _Yp, typename = _Constructible<_Yp*>>
128  		explicit
129  		shared_ptr(_Yp* __p) : __shared_ptr<_Tp>(__p) { }
130  	
131  	      /**
132  	       *  @brief  Construct a %shared_ptr that owns the pointer @a __p
133  	       *          and the deleter @a __d.
134  	       *  @param  __p  A pointer.
135  	       *  @param  __d  A deleter.
136  	       *  @post   use_count() == 1 && get() == __p
137  	       *  @throw  std::bad_alloc, in which case @a __d(__p) is called.
138  	       *
139  	       *  Requirements: _Deleter's copy constructor and destructor must
140  	       *  not throw
141  	       *
142  	       *  __shared_ptr will release __p by calling __d(__p)
143  	       */
144  	      template<typename _Yp, typename _Deleter,
145  		       typename = _Constructible<_Yp*, _Deleter>>
146  		shared_ptr(_Yp* __p, _Deleter __d)
147  	        : __shared_ptr<_Tp>(__p, std::move(__d)) { }
148  	
149  	      /**
150  	       *  @brief  Construct a %shared_ptr that owns a null pointer
151  	       *          and the deleter @a __d.
152  	       *  @param  __p  A null pointer constant.
153  	       *  @param  __d  A deleter.
154  	       *  @post   use_count() == 1 && get() == __p
155  	       *  @throw  std::bad_alloc, in which case @a __d(__p) is called.
156  	       *
157  	       *  Requirements: _Deleter's copy constructor and destructor must
158  	       *  not throw
159  	       *
160  	       *  The last owner will call __d(__p)
161  	       */
162  	      template<typename _Deleter>
163  		shared_ptr(nullptr_t __p, _Deleter __d)
164  	        : __shared_ptr<_Tp>(__p, std::move(__d)) { }
165  	
166  	      /**
167  	       *  @brief  Construct a %shared_ptr that owns the pointer @a __p
168  	       *          and the deleter @a __d.
169  	       *  @param  __p  A pointer.
170  	       *  @param  __d  A deleter.
171  	       *  @param  __a  An allocator.
172  	       *  @post   use_count() == 1 && get() == __p
173  	       *  @throw  std::bad_alloc, in which case @a __d(__p) is called.
174  	       *
175  	       *  Requirements: _Deleter's copy constructor and destructor must
176  	       *  not throw _Alloc's copy constructor and destructor must not
177  	       *  throw.
178  	       *
179  	       *  __shared_ptr will release __p by calling __d(__p)
180  	       */
181  	      template<typename _Yp, typename _Deleter, typename _Alloc,
182  		       typename = _Constructible<_Yp*, _Deleter, _Alloc>>
183  		shared_ptr(_Yp* __p, _Deleter __d, _Alloc __a)
184  		: __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
185  	
186  	      /**
187  	       *  @brief  Construct a %shared_ptr that owns a null pointer
188  	       *          and the deleter @a __d.
189  	       *  @param  __p  A null pointer constant.
190  	       *  @param  __d  A deleter.
191  	       *  @param  __a  An allocator.
192  	       *  @post   use_count() == 1 && get() == __p
193  	       *  @throw  std::bad_alloc, in which case @a __d(__p) is called.
194  	       *
195  	       *  Requirements: _Deleter's copy constructor and destructor must
196  	       *  not throw _Alloc's copy constructor and destructor must not
197  	       *  throw.
198  	       *
199  	       *  The last owner will call __d(__p)
200  	       */
201  	      template<typename _Deleter, typename _Alloc>
202  		shared_ptr(nullptr_t __p, _Deleter __d, _Alloc __a)
203  		: __shared_ptr<_Tp>(__p, std::move(__d), std::move(__a)) { }
204  	
205  	      // Aliasing constructor
206  	
207  	      /**
208  	       *  @brief  Constructs a %shared_ptr instance that stores @a __p
209  	       *          and shares ownership with @a __r.
210  	       *  @param  __r  A %shared_ptr.
211  	       *  @param  __p  A pointer that will remain valid while @a *__r is valid.
212  	       *  @post   get() == __p && use_count() == __r.use_count()
213  	       *
214  	       *  This can be used to construct a @c shared_ptr to a sub-object
215  	       *  of an object managed by an existing @c shared_ptr.
216  	       *
217  	       * @code
218  	       * shared_ptr< pair<int,int> > pii(new pair<int,int>());
219  	       * shared_ptr<int> pi(pii, &pii->first);
220  	       * assert(pii.use_count() == 2);
221  	       * @endcode
222  	       */
223  	      template<typename _Yp>
224  		shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) noexcept
225  		: __shared_ptr<_Tp>(__r, __p) { }
226  	
227  	      /**
228  	       *  @brief  If @a __r is empty, constructs an empty %shared_ptr;
229  	       *          otherwise construct a %shared_ptr that shares ownership
230  	       *          with @a __r.
231  	       *  @param  __r  A %shared_ptr.
232  	       *  @post   get() == __r.get() && use_count() == __r.use_count()
233  	       */
234  	      template<typename _Yp,
235  		       typename = _Constructible<const shared_ptr<_Yp>&>>
236  		shared_ptr(const shared_ptr<_Yp>& __r) noexcept
237  	        : __shared_ptr<_Tp>(__r) { }
238  	
239  	      /**
240  	       *  @brief  Move-constructs a %shared_ptr instance from @a __r.
241  	       *  @param  __r  A %shared_ptr rvalue.
242  	       *  @post   *this contains the old value of @a __r, @a __r is empty.
243  	       */
244  	      shared_ptr(shared_ptr&& __r) noexcept
245  	      : __shared_ptr<_Tp>(std::move(__r)) { }
246  	
247  	      /**
248  	       *  @brief  Move-constructs a %shared_ptr instance from @a __r.
249  	       *  @param  __r  A %shared_ptr rvalue.
250  	       *  @post   *this contains the old value of @a __r, @a __r is empty.
251  	       */
252  	      template<typename _Yp, typename = _Constructible<shared_ptr<_Yp>>>
253  		shared_ptr(shared_ptr<_Yp>&& __r) noexcept
254  		: __shared_ptr<_Tp>(std::move(__r)) { }
255  	
256  	      /**
257  	       *  @brief  Constructs a %shared_ptr that shares ownership with @a __r
258  	       *          and stores a copy of the pointer stored in @a __r.
259  	       *  @param  __r  A weak_ptr.
260  	       *  @post   use_count() == __r.use_count()
261  	       *  @throw  bad_weak_ptr when __r.expired(),
262  	       *          in which case the constructor has no effect.
263  	       */
264  	      template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
265  		explicit shared_ptr(const weak_ptr<_Yp>& __r)
266  		: __shared_ptr<_Tp>(__r) { }
267  	
268  	#if _GLIBCXX_USE_DEPRECATED
269  	      template<typename _Yp, typename = _Constructible<auto_ptr<_Yp>>>
270  		shared_ptr(auto_ptr<_Yp>&& __r);
271  	#endif
272  	
273  	      // _GLIBCXX_RESOLVE_LIB_DEFECTS
274  	      // 2399. shared_ptr's constructor from unique_ptr should be constrained
275  	      template<typename _Yp, typename _Del,
276  		       typename = _Constructible<unique_ptr<_Yp, _Del>>>
277  		shared_ptr(unique_ptr<_Yp, _Del>&& __r)
278  		: __shared_ptr<_Tp>(std::move(__r)) { }
279  	
280  	#if __cplusplus <= 201402L && _GLIBCXX_USE_DEPRECATED
281  	      // This non-standard constructor exists to support conversions that
282  	      // were possible in C++11 and C++14 but are ill-formed in C++17.
283  	      // If an exception is thrown this constructor has no effect.
284  	      template<typename _Yp, typename _Del,
285  			_Constructible<unique_ptr<_Yp, _Del>, __sp_array_delete>* = 0>
286  		shared_ptr(unique_ptr<_Yp, _Del>&& __r)
287  		: __shared_ptr<_Tp>(std::move(__r), __sp_array_delete()) { }
288  	#endif
289  	
290  	      /**
291  	       *  @brief  Construct an empty %shared_ptr.
292  	       *  @post   use_count() == 0 && get() == nullptr
293  	       */
294  	      constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
295  	
296  	      shared_ptr& operator=(const shared_ptr&) noexcept = default;
297  	
298  	      template<typename _Yp>
299  		_Assignable<const shared_ptr<_Yp>&>
300  		operator=(const shared_ptr<_Yp>& __r) noexcept
301  		{
302  		  this->__shared_ptr<_Tp>::operator=(__r);
303  		  return *this;
304  		}
305  	
306  	#if _GLIBCXX_USE_DEPRECATED
307  	      template<typename _Yp>
308  		_Assignable<auto_ptr<_Yp>>
309  		operator=(auto_ptr<_Yp>&& __r)
310  		{
311  		  this->__shared_ptr<_Tp>::operator=(std::move(__r));
312  		  return *this;
313  		}
314  	#endif
315  	
316  	      shared_ptr&
317  	      operator=(shared_ptr&& __r) noexcept
318  	      {
319  		this->__shared_ptr<_Tp>::operator=(std::move(__r));
320  		return *this;
321  	      }
322  	
323  	      template<class _Yp>
324  		_Assignable<shared_ptr<_Yp>>
325  		operator=(shared_ptr<_Yp>&& __r) noexcept
326  		{
327  		  this->__shared_ptr<_Tp>::operator=(std::move(__r));
328  		  return *this;
329  		}
330  	
331  	      template<typename _Yp, typename _Del>
332  		_Assignable<unique_ptr<_Yp, _Del>>
333  		operator=(unique_ptr<_Yp, _Del>&& __r)
334  		{
335  		  this->__shared_ptr<_Tp>::operator=(std::move(__r));
336  		  return *this;
337  		}
338  	
339  	    private:
340  	      // This constructor is non-standard, it is used by allocate_shared.
341  	      template<typename _Alloc, typename... _Args>
342  		shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
343  			   _Args&&... __args)
344  		: __shared_ptr<_Tp>(__tag, __a, std::forward<_Args>(__args)...)
345  		{ }
346  	
347  	      template<typename _Yp, typename _Alloc, typename... _Args>
348  		friend shared_ptr<_Yp>
349  		allocate_shared(const _Alloc& __a, _Args&&... __args);
350  	
351  	      // This constructor is non-standard, it is used by weak_ptr::lock().
352  	      shared_ptr(const weak_ptr<_Tp>& __r, std::nothrow_t)
353  	      : __shared_ptr<_Tp>(__r, std::nothrow) { }
354  	
355  	      friend class weak_ptr<_Tp>;
356  	    };
357  	
358  	#if __cpp_deduction_guides >= 201606
359  	  template<typename _Tp>
360  	    shared_ptr(weak_ptr<_Tp>) ->  shared_ptr<_Tp>;
361  	  template<typename _Tp, typename _Del>
362  	    shared_ptr(unique_ptr<_Tp, _Del>) ->  shared_ptr<_Tp>;
363  	#endif
364  	
365  	  // 20.7.2.2.7 shared_ptr comparisons
366  	  template<typename _Tp, typename _Up>
367  	    inline bool
368  	    operator==(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
369  	    { return __a.get() == __b.get(); }
370  	
371  	  template<typename _Tp>
372  	    inline bool
373  	    operator==(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
374  	    { return !__a; }
375  	
376  	  template<typename _Tp>
377  	    inline bool
378  	    operator==(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
379  	    { return !__a; }
380  	
381  	  template<typename _Tp, typename _Up>
382  	    inline bool
383  	    operator!=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
384  	    { return __a.get() != __b.get(); }
385  	
386  	  template<typename _Tp>
387  	    inline bool
388  	    operator!=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
389  	    { return (bool)__a; }
390  	
391  	  template<typename _Tp>
392  	    inline bool
393  	    operator!=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
394  	    { return (bool)__a; }
395  	
396  	  template<typename _Tp, typename _Up>
397  	    inline bool
398  	    operator<(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
399  	    {
400  	      using _Tp_elt = typename shared_ptr<_Tp>::element_type;
401  	      using _Up_elt = typename shared_ptr<_Up>::element_type;
402  	      using _Vp = typename common_type<_Tp_elt*, _Up_elt*>::type;
403  	      return less<_Vp>()(__a.get(), __b.get());
404  	    }
405  	
406  	  template<typename _Tp>
407  	    inline bool
408  	    operator<(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
409  	    {
410  	      using _Tp_elt = typename shared_ptr<_Tp>::element_type;
411  	      return less<_Tp_elt*>()(__a.get(), nullptr);
412  	    }
413  	
414  	  template<typename _Tp>
415  	    inline bool
416  	    operator<(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
417  	    {
418  	      using _Tp_elt = typename shared_ptr<_Tp>::element_type;
419  	      return less<_Tp_elt*>()(nullptr, __a.get());
420  	    }
421  	
422  	  template<typename _Tp, typename _Up>
423  	    inline bool
424  	    operator<=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
425  	    { return !(__b < __a); }
426  	
427  	  template<typename _Tp>
428  	    inline bool
429  	    operator<=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
430  	    { return !(nullptr < __a); }
431  	
432  	  template<typename _Tp>
433  	    inline bool
434  	    operator<=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
435  	    { return !(__a < nullptr); }
436  	
437  	  template<typename _Tp, typename _Up>
438  	    inline bool
439  	    operator>(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
440  	    { return (__b < __a); }
441  	
442  	  template<typename _Tp>
443  	    inline bool
444  	    operator>(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
445  	    { return nullptr < __a; }
446  	
447  	  template<typename _Tp>
448  	    inline bool
449  	    operator>(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
450  	    { return __a < nullptr; }
451  	
452  	  template<typename _Tp, typename _Up>
453  	    inline bool
454  	    operator>=(const shared_ptr<_Tp>& __a, const shared_ptr<_Up>& __b) noexcept
455  	    { return !(__a < __b); }
456  	
457  	  template<typename _Tp>
458  	    inline bool
459  	    operator>=(const shared_ptr<_Tp>& __a, nullptr_t) noexcept
460  	    { return !(__a < nullptr); }
461  	
462  	  template<typename _Tp>
463  	    inline bool
464  	    operator>=(nullptr_t, const shared_ptr<_Tp>& __a) noexcept
465  	    { return !(nullptr < __a); }
466  	
467  	  template<typename _Tp>
468  	    struct less<shared_ptr<_Tp>> : public _Sp_less<shared_ptr<_Tp>>
469  	    { };
470  	
471  	  // 20.7.2.2.8 shared_ptr specialized algorithms.
472  	  template<typename _Tp>
473  	    inline void
474  	    swap(shared_ptr<_Tp>& __a, shared_ptr<_Tp>& __b) noexcept
475  	    { __a.swap(__b); }
476  	
477  	  // 20.7.2.2.9 shared_ptr casts.
478  	  template<typename _Tp, typename _Up>
479  	    inline shared_ptr<_Tp>
480  	    static_pointer_cast(const shared_ptr<_Up>& __r) noexcept
481  	    {
482  	      using _Sp = shared_ptr<_Tp>;
483  	      return _Sp(__r, static_cast<typename _Sp::element_type*>(__r.get()));
484  	    }
485  	
486  	  template<typename _Tp, typename _Up>
487  	    inline shared_ptr<_Tp>
488  	    const_pointer_cast(const shared_ptr<_Up>& __r) noexcept
489  	    {
490  	      using _Sp = shared_ptr<_Tp>;
491  	      return _Sp(__r, const_cast<typename _Sp::element_type*>(__r.get()));
492  	    }
493  	
494  	  template<typename _Tp, typename _Up>
495  	    inline shared_ptr<_Tp>
496  	    dynamic_pointer_cast(const shared_ptr<_Up>& __r) noexcept
497  	    {
498  	      using _Sp = shared_ptr<_Tp>;
499  	      if (auto* __p = dynamic_cast<typename _Sp::element_type*>(__r.get()))
500  		return _Sp(__r, __p);
501  	      return _Sp();
502  	    }
503  	
504  	#if __cplusplus > 201402L
505  	  template<typename _Tp, typename _Up>
506  	    inline shared_ptr<_Tp>
507  	    reinterpret_pointer_cast(const shared_ptr<_Up>& __r) noexcept
508  	    {
509  	      using _Sp = shared_ptr<_Tp>;
510  	      return _Sp(__r, reinterpret_cast<typename _Sp::element_type*>(__r.get()));
511  	    }
512  	#endif
513  	
514  	  /**
515  	   *  @brief  A smart pointer with weak semantics.
516  	   *
517  	   *  With forwarding constructors and assignment operators.
518  	   */
519  	  template<typename _Tp>
520  	    class weak_ptr : public __weak_ptr<_Tp>
521  	    {
522  	      template<typename _Arg>
523  		using _Constructible = typename enable_if<
524  		  is_constructible<__weak_ptr<_Tp>, _Arg>::value
525  		>::type;
526  	
527  	      template<typename _Arg>
528  		using _Assignable = typename enable_if<
529  		  is_assignable<__weak_ptr<_Tp>&, _Arg>::value, weak_ptr&
530  		>::type;
531  	
532  	    public:
533  	      constexpr weak_ptr() noexcept = default;
534  	
535  	      template<typename _Yp,
536  		       typename = _Constructible<const shared_ptr<_Yp>&>>
537  		weak_ptr(const shared_ptr<_Yp>& __r) noexcept
538  		: __weak_ptr<_Tp>(__r) { }
539  	
540  	      weak_ptr(const weak_ptr&) noexcept = default;
541  	
542  	      template<typename _Yp, typename = _Constructible<const weak_ptr<_Yp>&>>
543  		weak_ptr(const weak_ptr<_Yp>& __r) noexcept
544  		: __weak_ptr<_Tp>(__r) { }
545  	
546  	      weak_ptr(weak_ptr&&) noexcept = default;
547  	
548  	      template<typename _Yp, typename = _Constructible<weak_ptr<_Yp>>>
549  		weak_ptr(weak_ptr<_Yp>&& __r) noexcept
550  		: __weak_ptr<_Tp>(std::move(__r)) { }
551  	
552  	      weak_ptr&
553  	      operator=(const weak_ptr& __r) noexcept = default;
554  	
555  	      template<typename _Yp>
556  		_Assignable<const weak_ptr<_Yp>&>
557  		operator=(const weak_ptr<_Yp>& __r) noexcept
558  		{
559  		  this->__weak_ptr<_Tp>::operator=(__r);
560  		  return *this;
561  		}
562  	
563  	      template<typename _Yp>
564  		_Assignable<const shared_ptr<_Yp>&>
565  		operator=(const shared_ptr<_Yp>& __r) noexcept
566  		{
567  		  this->__weak_ptr<_Tp>::operator=(__r);
568  		  return *this;
569  		}
570  	
571  	      weak_ptr&
572  	      operator=(weak_ptr&& __r) noexcept = default;
573  	
574  	      template<typename _Yp>
575  		_Assignable<weak_ptr<_Yp>>
576  		operator=(weak_ptr<_Yp>&& __r) noexcept
577  		{
578  		  this->__weak_ptr<_Tp>::operator=(std::move(__r));
579  		  return *this;
580  		}
581  	
582  	      shared_ptr<_Tp>
583  	      lock() const noexcept
584  	      { return shared_ptr<_Tp>(*this, std::nothrow); }
585  	    };
586  	
587  	#if __cpp_deduction_guides >= 201606
588  	  template<typename _Tp>
589  	    weak_ptr(shared_ptr<_Tp>) ->  weak_ptr<_Tp>;
590  	#endif
591  	
592  	  // 20.7.2.3.6 weak_ptr specialized algorithms.
593  	  template<typename _Tp>
594  	    inline void
595  	    swap(weak_ptr<_Tp>& __a, weak_ptr<_Tp>& __b) noexcept
596  	    { __a.swap(__b); }
597  	
598  	
599  	  /// Primary template owner_less
600  	  template<typename _Tp = void>
601  	    struct owner_less;
602  	
603  	  /// Void specialization of owner_less
604  	  template<>
605  	    struct owner_less<void> : _Sp_owner_less<void, void>
606  	    { };
607  	
608  	  /// Partial specialization of owner_less for shared_ptr.
609  	  template<typename _Tp>
610  	    struct owner_less<shared_ptr<_Tp>>
611  	    : public _Sp_owner_less<shared_ptr<_Tp>, weak_ptr<_Tp>>
612  	    { };
613  	
614  	  /// Partial specialization of owner_less for weak_ptr.
615  	  template<typename _Tp>
616  	    struct owner_less<weak_ptr<_Tp>>
617  	    : public _Sp_owner_less<weak_ptr<_Tp>, shared_ptr<_Tp>>
618  	    { };
619  	
620  	  /**
621  	   *  @brief Base class allowing use of member function shared_from_this.
622  	   */
623  	  template<typename _Tp>
624  	    class enable_shared_from_this
625  	    {
626  	    protected:
627  	      constexpr enable_shared_from_this() noexcept { }
628  	
629  	      enable_shared_from_this(const enable_shared_from_this&) noexcept { }
630  	
631  	      enable_shared_from_this&
632  	      operator=(const enable_shared_from_this&) noexcept
633  	      { return *this; }
634  	
635  	      ~enable_shared_from_this() { }
636  	
637  	    public:
638  	      shared_ptr<_Tp>
639  	      shared_from_this()
640  	      { return shared_ptr<_Tp>(this->_M_weak_this); }
641  	
642  	      shared_ptr<const _Tp>
643  	      shared_from_this() const
644  	      { return shared_ptr<const _Tp>(this->_M_weak_this); }
645  	
646  	#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
647  	#define __cpp_lib_enable_shared_from_this 201603
648  	      weak_ptr<_Tp>
649  	      weak_from_this() noexcept
650  	      { return this->_M_weak_this; }
651  	
652  	      weak_ptr<const _Tp>
653  	      weak_from_this() const noexcept
654  	      { return this->_M_weak_this; }
655  	#endif
656  	
657  	    private:
658  	      template<typename _Tp1>
659  		void
660  		_M_weak_assign(_Tp1* __p, const __shared_count<>& __n) const noexcept
661  		{ _M_weak_this._M_assign(__p, __n); }
662  	
663  	      // Found by ADL when this is an associated class.
664  	      friend const enable_shared_from_this*
665  	      __enable_shared_from_this_base(const __shared_count<>&,
666  					     const enable_shared_from_this* __p)
667  	      { return __p; }
668  	
669  	      template<typename, _Lock_policy>
670  		friend class __shared_ptr;
671  	
672  	      mutable weak_ptr<_Tp>  _M_weak_this;
673  	    };
674  	
675  	  /**
676  	   *  @brief  Create an object that is owned by a shared_ptr.
677  	   *  @param  __a     An allocator.
678  	   *  @param  __args  Arguments for the @a _Tp object's constructor.
679  	   *  @return A shared_ptr that owns the newly created object.
680  	   *  @throw  An exception thrown from @a _Alloc::allocate or from the
681  	   *          constructor of @a _Tp.
682  	   *
683  	   *  A copy of @a __a will be used to allocate memory for the shared_ptr
684  	   *  and the new object.
685  	   */
686  	  template<typename _Tp, typename _Alloc, typename... _Args>
687  	    inline shared_ptr<_Tp>
688  	    allocate_shared(const _Alloc& __a, _Args&&... __args)
689  	    {
690  	      return shared_ptr<_Tp>(_Sp_make_shared_tag(), __a,
691  				     std::forward<_Args>(__args)...);
692  	    }
693  	
694  	  /**
695  	   *  @brief  Create an object that is owned by a shared_ptr.
696  	   *  @param  __args  Arguments for the @a _Tp object's constructor.
697  	   *  @return A shared_ptr that owns the newly created object.
698  	   *  @throw  std::bad_alloc, or an exception thrown from the
699  	   *          constructor of @a _Tp.
700  	   */
701  	  template<typename _Tp, typename... _Args>
702  	    inline shared_ptr<_Tp>
703  	    make_shared(_Args&&... __args)
704  	    {
705  	      typedef typename std::remove_const<_Tp>::type _Tp_nc;
706  	      return std::allocate_shared<_Tp>(std::allocator<_Tp_nc>(),
707  					       std::forward<_Args>(__args)...);
708  	    }
709  	
710  	  /// std::hash specialization for shared_ptr.
711  	  template<typename _Tp>
712  	    struct hash<shared_ptr<_Tp>>
713  	    : public __hash_base<size_t, shared_ptr<_Tp>>
714  	    {
715  	      size_t
716  	      operator()(const shared_ptr<_Tp>& __s) const noexcept
717  	      {
718  		return std::hash<typename shared_ptr<_Tp>::element_type*>()(__s.get());
719  	      }
720  	    };
721  	
722  	  // @} group pointer_abstractions
723  	
724  	_GLIBCXX_END_NAMESPACE_VERSION
725  	} // namespace
726  	
727  	#endif // _SHARED_PTR_H
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