1// auto_ptr implementation -*- C++ -*-
2
3// Copyright (C) 2007-2020 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 backward/auto_ptr.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 _BACKWARD_AUTO_PTR_H
31#define _BACKWARD_AUTO_PTR_H 1
32
33#include <bits/c++config.h>
34#include <debug/debug.h>
35
36namespace std _GLIBCXX_VISIBILITY(default)
37{
38_GLIBCXX_BEGIN_NAMESPACE_VERSION
39
40  /**
41   *  A wrapper class to provide auto_ptr with reference semantics.
42   *  For example, an auto_ptr can be assigned (or constructed from)
43   *  the result of a function which returns an auto_ptr by value.
44   *
45   *  All the auto_ptr_ref stuff should happen behind the scenes.
46   */
47  template<typename _Tp1>
48    struct auto_ptr_ref
49    {
50      _Tp1* _M_ptr;
51
52      explicit
53      auto_ptr_ref(_Tp1* __p): _M_ptr(__p) { }
54    } _GLIBCXX_DEPRECATED;
55
56#pragma GCC diagnostic push
57#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
58
59  /**
60   *  @brief  A simple smart pointer providing strict ownership semantics.
61   *
62   *  The Standard says:
63   *  <pre>
64   *  An @c auto_ptr owns the object it holds a pointer to.  Copying
65   *  an @c auto_ptr copies the pointer and transfers ownership to the
66   *  destination.  If more than one @c auto_ptr owns the same object
67   *  at the same time the behavior of the program is undefined.
68   *
69   *  The uses of @c auto_ptr include providing temporary
70   *  exception-safety for dynamically allocated memory, passing
71   *  ownership of dynamically allocated memory to a function, and
72   *  returning dynamically allocated memory from a function.  @c
73   *  auto_ptr does not meet the CopyConstructible and Assignable
74   *  requirements for Standard Library <a
75   *  href="tables.html#65">container</a> elements and thus
76   *  instantiating a Standard Library container with an @c auto_ptr
77   *  results in undefined behavior.
78   *  </pre>
79   *  Quoted from [20.4.5]/3.
80   *
81   *  Good examples of what can and cannot be done with auto_ptr can
82   *  be found in the libstdc++ testsuite.
83   *
84   *  _GLIBCXX_RESOLVE_LIB_DEFECTS
85   *  127.  auto_ptr<> conversion issues
86   *  These resolutions have all been incorporated.
87   */
88  template<typename _Tp>
89    class auto_ptr
90    {
91    private:
92      _Tp* _M_ptr;
93
94    public:
95      /// The pointed-to type.
96      typedef _Tp element_type;
97
98      /**
99       *  @brief  An %auto_ptr is usually constructed from a raw pointer.
100       *  @param  __p  A pointer (defaults to NULL).
101       *
102       *  This object now @e owns the object pointed to by @a __p.
103       */
104      explicit
105      auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
106
107      /**
108       *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
109       *  @param  __a  Another %auto_ptr of the same type.
110       *
111       *  This object now @e owns the object previously owned by @a __a,
112       *  which has given up ownership.
113       */
114      auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
115
116      /**
117       *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
118       *  @param  __a  Another %auto_ptr of a different but related type.
119       *
120       *  A pointer-to-Tp1 must be convertible to a
121       *  pointer-to-Tp/element_type.
122       *
123       *  This object now @e owns the object previously owned by @a __a,
124       *  which has given up ownership.
125       */
126      template<typename _Tp1>
127        auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
128
129      /**
130       *  @brief  %auto_ptr assignment operator.
131       *  @param  __a  Another %auto_ptr of the same type.
132       *
133       *  This object now @e owns the object previously owned by @a __a,
134       *  which has given up ownership.  The object that this one @e
135       *  used to own and track has been deleted.
136       */
137      auto_ptr&
138      operator=(auto_ptr& __a) throw()
139      {
140	reset(__a.release());
141	return *this;
142      }
143
144      /**
145       *  @brief  %auto_ptr assignment operator.
146       *  @param  __a  Another %auto_ptr of a different but related type.
147       *
148       *  A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
149       *
150       *  This object now @e owns the object previously owned by @a __a,
151       *  which has given up ownership.  The object that this one @e
152       *  used to own and track has been deleted.
153       */
154      template<typename _Tp1>
155        auto_ptr&
156        operator=(auto_ptr<_Tp1>& __a) throw()
157        {
158	  reset(__a.release());
159	  return *this;
160	}
161
162      /**
163       *  When the %auto_ptr goes out of scope, the object it owns is
164       *  deleted.  If it no longer owns anything (i.e., @c get() is
165       *  @c NULL), then this has no effect.
166       *
167       *  The C++ standard says there is supposed to be an empty throw
168       *  specification here, but omitting it is standard conforming.  Its
169       *  presence can be detected only if _Tp::~_Tp() throws, but this is
170       *  prohibited.  [17.4.3.6]/2
171       */
172      ~auto_ptr() { delete _M_ptr; }
173
174      /**
175       *  @brief  Smart pointer dereferencing.
176       *
177       *  If this %auto_ptr no longer owns anything, then this
178       *  operation will crash.  (For a smart pointer, <em>no longer owns
179       *  anything</em> is the same as being a null pointer, and you know
180       *  what happens when you dereference one of those...)
181       */
182      element_type&
183      operator*() const throw()
184      {
185	__glibcxx_assert(_M_ptr != 0);
186	return *_M_ptr;
187      }
188
189      /**
190       *  @brief  Smart pointer dereferencing.
191       *
192       *  This returns the pointer itself, which the language then will
193       *  automatically cause to be dereferenced.
194       */
195      element_type*
196      operator->() const throw()
197      {
198	__glibcxx_assert(_M_ptr != 0);
199	return _M_ptr;
200      }
201
202      /**
203       *  @brief  Bypassing the smart pointer.
204       *  @return  The raw pointer being managed.
205       *
206       *  You can get a copy of the pointer that this object owns, for
207       *  situations such as passing to a function which only accepts
208       *  a raw pointer.
209       *
210       *  @note  This %auto_ptr still owns the memory.
211       */
212      element_type*
213      get() const throw() { return _M_ptr; }
214
215      /**
216       *  @brief  Bypassing the smart pointer.
217       *  @return  The raw pointer being managed.
218       *
219       *  You can get a copy of the pointer that this object owns, for
220       *  situations such as passing to a function which only accepts
221       *  a raw pointer.
222       *
223       *  @note  This %auto_ptr no longer owns the memory.  When this object
224       *  goes out of scope, nothing will happen.
225       */
226      element_type*
227      release() throw()
228      {
229	element_type* __tmp = _M_ptr;
230	_M_ptr = 0;
231	return __tmp;
232      }
233
234      /**
235       *  @brief  Forcibly deletes the managed object.
236       *  @param  __p  A pointer (defaults to NULL).
237       *
238       *  This object now @e owns the object pointed to by @a __p.  The
239       *  previous object has been deleted.
240       */
241      void
242      reset(element_type* __p = 0) throw()
243      {
244	if (__p != _M_ptr)
245	  {
246	    delete _M_ptr;
247	    _M_ptr = __p;
248	  }
249      }
250
251      /**
252       *  @brief  Automatic conversions
253       *
254       *  These operations are supposed to convert an %auto_ptr into and from
255       *  an auto_ptr_ref automatically as needed.  This would allow
256       *  constructs such as
257       *  @code
258       *    auto_ptr<Derived>  func_returning_auto_ptr(.....);
259       *    ...
260       *    auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
261       *  @endcode
262       *
263       *  But it doesn't work, and won't be fixed. For further details see
264       *  http://cplusplus.github.io/LWG/lwg-closed.html#463
265       */
266      auto_ptr(auto_ptr_ref<element_type> __ref) throw()
267      : _M_ptr(__ref._M_ptr) { }
268
269      auto_ptr&
270      operator=(auto_ptr_ref<element_type> __ref) throw()
271      {
272	if (__ref._M_ptr != this->get())
273	  {
274	    delete _M_ptr;
275	    _M_ptr = __ref._M_ptr;
276	  }
277	return *this;
278      }
279
280      template<typename _Tp1>
281        operator auto_ptr_ref<_Tp1>() throw()
282        { return auto_ptr_ref<_Tp1>(this->release()); }
283
284      template<typename _Tp1>
285        operator auto_ptr<_Tp1>() throw()
286        { return auto_ptr<_Tp1>(this->release()); }
287    } _GLIBCXX_DEPRECATED;
288
289  // _GLIBCXX_RESOLVE_LIB_DEFECTS
290  // 541. shared_ptr template assignment and void
291  template<>
292    class auto_ptr<void>
293    {
294    public:
295      typedef void element_type;
296    } _GLIBCXX_DEPRECATED;
297
298#if __cplusplus >= 201103L
299  template<_Lock_policy _Lp>
300  template<typename _Tp>
301    inline
302    __shared_count<_Lp>::__shared_count(std::auto_ptr<_Tp>&& __r)
303    : _M_pi(new _Sp_counted_ptr<_Tp*, _Lp>(__r.get()))
304    { __r.release(); }
305
306  template<typename _Tp, _Lock_policy _Lp>
307  template<typename _Tp1, typename>
308    inline
309    __shared_ptr<_Tp, _Lp>::__shared_ptr(std::auto_ptr<_Tp1>&& __r)
310    : _M_ptr(__r.get()), _M_refcount()
311    {
312      __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
313      static_assert( sizeof(_Tp1) > 0, "incomplete type" );
314      _Tp1* __tmp = __r.get();
315      _M_refcount = __shared_count<_Lp>(std::move(__r));
316      _M_enable_shared_from_this_with(__tmp);
317    }
318
319  template<typename _Tp>
320  template<typename _Tp1, typename>
321    inline
322    shared_ptr<_Tp>::shared_ptr(std::auto_ptr<_Tp1>&& __r)
323    : __shared_ptr<_Tp>(std::move(__r)) { }
324
325  template<typename _Tp, typename _Dp>
326  template<typename _Up, typename>
327    inline
328    unique_ptr<_Tp, _Dp>::unique_ptr(auto_ptr<_Up>&& __u) noexcept
329    : _M_t(__u.release(), deleter_type()) { }
330#endif
331
332#pragma GCC diagnostic pop
333
334_GLIBCXX_END_NAMESPACE_VERSION
335} // namespace
336
337#endif /* _BACKWARD_AUTO_PTR_H */
338