auto_ptr.h

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// auto_ptr implementation -*- C++ -*-
 
// Copyright (C) 2007-2020 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
 
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
 
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
/** @file backward/auto_ptr.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{memory}
 */
 
#ifndef _BACKWARD_AUTO_PTR_H
#define _BACKWARD_AUTO_PTR_H 1
 
#include <bits/c++config.h>
#include <debug/debug.h>
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
  /**
   *  A wrapper class to provide auto_ptr with reference semantics.
   *  For example, an auto_ptr can be assigned (or constructed from)
   *  the result of a function which returns an auto_ptr by value.
   *
   *  All the auto_ptr_ref stuff should happen behind the scenes.
   */
  template<typename _Tp1>
    struct auto_ptr_ref
    {
      _Tp1* _M_ptr;
      
      explicit
      auto_ptr_ref(_Tp1* __p): _M_ptr(__p) { }
    } _GLIBCXX_DEPRECATED;
 
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 
  /**
   *  @brief  A simple smart pointer providing strict ownership semantics.
   *
   *  The Standard says:
   *  <pre>
   *  An @c auto_ptr owns the object it holds a pointer to.  Copying
   *  an @c auto_ptr copies the pointer and transfers ownership to the
   *  destination.  If more than one @c auto_ptr owns the same object
   *  at the same time the behavior of the program is undefined.
   *
   *  The uses of @c auto_ptr include providing temporary
   *  exception-safety for dynamically allocated memory, passing
   *  ownership of dynamically allocated memory to a function, and
   *  returning dynamically allocated memory from a function.  @c
   *  auto_ptr does not meet the CopyConstructible and Assignable
   *  requirements for Standard Library <a
   *  href="tables.html#65">container</a> elements and thus
   *  instantiating a Standard Library container with an @c auto_ptr
   *  results in undefined behavior.
   *  </pre>
   *  Quoted from [20.4.5]/3.
   *
   *  Good examples of what can and cannot be done with auto_ptr can
   *  be found in the libstdc++ testsuite.
   *
   *  _GLIBCXX_RESOLVE_LIB_DEFECTS
   *  127.  auto_ptr<> conversion issues
   *  These resolutions have all been incorporated.
   */
  template<typename _Tp>
    class auto_ptr
    {
    private:
      _Tp* _M_ptr;
      
    public:
      /// The pointed-to type.
      typedef _Tp element_type;
      
      /**
       *  @brief  An %auto_ptr is usually constructed from a raw pointer.
       *  @param  __p  A pointer (defaults to NULL).
       *
       *  This object now @e owns the object pointed to by @a __p.
       */
      explicit
      auto_ptr(element_type* __p = 0) throw() : _M_ptr(__p) { }
 
      /**
       *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
       *  @param  __a  Another %auto_ptr of the same type.
       *
       *  This object now @e owns the object previously owned by @a __a,
       *  which has given up ownership.
       */
      auto_ptr(auto_ptr& __a) throw() : _M_ptr(__a.release()) { }
 
      /**
       *  @brief  An %auto_ptr can be constructed from another %auto_ptr.
       *  @param  __a  Another %auto_ptr of a different but related type.
       *
       *  A pointer-to-Tp1 must be convertible to a
       *  pointer-to-Tp/element_type.
       *
       *  This object now @e owns the object previously owned by @a __a,
       *  which has given up ownership.
       */
      template<typename _Tp1>
        auto_ptr(auto_ptr<_Tp1>& __a) throw() : _M_ptr(__a.release()) { }
 
      /**
       *  @brief  %auto_ptr assignment operator.
       *  @param  __a  Another %auto_ptr of the same type.
       *
       *  This object now @e owns the object previously owned by @a __a,
       *  which has given up ownership.  The object that this one @e
       *  used to own and track has been deleted.
       */
      auto_ptr&
      operator=(auto_ptr& __a) throw()
      {
        reset(__a.release());
        return *this;
      }
 
      /**
       *  @brief  %auto_ptr assignment operator.
       *  @param  __a  Another %auto_ptr of a different but related type.
       *
       *  A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.
       *
       *  This object now @e owns the object previously owned by @a __a,
       *  which has given up ownership.  The object that this one @e
       *  used to own and track has been deleted.
       */
      template<typename _Tp1>
        auto_ptr&
        operator=(auto_ptr<_Tp1>& __a) throw()
        {
          reset(__a.release());
          return *this;
        }
 
      /**
       *  When the %auto_ptr goes out of scope, the object it owns is
       *  deleted.  If it no longer owns anything (i.e., @c get() is
       *  @c NULL), then this has no effect.
       *
       *  The C++ standard says there is supposed to be an empty throw
       *  specification here, but omitting it is standard conforming.  Its
       *  presence can be detected only if _Tp::~_Tp() throws, but this is
       *  prohibited.  [17.4.3.6]/2
       */
      ~auto_ptr() { delete _M_ptr; }
      
      /**
       *  @brief  Smart pointer dereferencing.
       *
       *  If this %auto_ptr no longer owns anything, then this
       *  operation will crash.  (For a smart pointer, <em>no longer owns
       *  anything</em> is the same as being a null pointer, and you know
       *  what happens when you dereference one of those...)
       */
      element_type&
      operator*() const throw() 
      {
        __glibcxx_assert(_M_ptr != 0);
        return *_M_ptr; 
      }
      
      /**
       *  @brief  Smart pointer dereferencing.
       *
       *  This returns the pointer itself, which the language then will
       *  automatically cause to be dereferenced.
       */
      element_type*
      operator->() const throw() 
      {
        __glibcxx_assert(_M_ptr != 0);
        return _M_ptr; 
      }
      
      /**
       *  @brief  Bypassing the smart pointer.
       *  @return  The raw pointer being managed.
       *
       *  You can get a copy of the pointer that this object owns, for
       *  situations such as passing to a function which only accepts
       *  a raw pointer.
       *
       *  @note  This %auto_ptr still owns the memory.
       */
      element_type*
      get() const throw() { return _M_ptr; }
      
      /**
       *  @brief  Bypassing the smart pointer.
       *  @return  The raw pointer being managed.
       *
       *  You can get a copy of the pointer that this object owns, for
       *  situations such as passing to a function which only accepts
       *  a raw pointer.
       *
       *  @note  This %auto_ptr no longer owns the memory.  When this object
       *  goes out of scope, nothing will happen.
       */
      element_type*
      release() throw()
      {
        element_type* __tmp = _M_ptr;
        _M_ptr = 0;
        return __tmp;
      }
      
      /**
       *  @brief  Forcibly deletes the managed object.
       *  @param  __p  A pointer (defaults to NULL).
       *
       *  This object now @e owns the object pointed to by @a __p.  The
       *  previous object has been deleted.
       */
      void
      reset(element_type* __p = 0) throw()
      {
        if (__p != _M_ptr)
          {
            delete _M_ptr;
            _M_ptr = __p;
          }
      }
      
      /** 
       *  @brief  Automatic conversions
       *
       *  These operations are supposed to convert an %auto_ptr into and from
       *  an auto_ptr_ref automatically as needed.  This would allow
       *  constructs such as
       *  @code
       *    auto_ptr<Derived>  func_returning_auto_ptr(.....);
       *    ...
       *    auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
       *  @endcode
       *
       *  But it doesn't work, and won't be fixed. For further details see
       *  http://cplusplus.github.io/LWG/lwg-closed.html#463
       */
      auto_ptr(auto_ptr_ref<element_type> __ref) throw()
      : _M_ptr(__ref._M_ptr) { }
      
      auto_ptr&
      operator=(auto_ptr_ref<element_type> __ref) throw()
      {
        if (__ref._M_ptr != this->get())
          {
            delete _M_ptr;
            _M_ptr = __ref._M_ptr;
          }
        return *this;
      }
      
      template<typename _Tp1>
        operator auto_ptr_ref<_Tp1>() throw()
        { return auto_ptr_ref<_Tp1>(this->release()); }
 
      template<typename _Tp1>
        operator auto_ptr<_Tp1>() throw()
        { return auto_ptr<_Tp1>(this->release()); }
    } _GLIBCXX_DEPRECATED;
 
  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 541. shared_ptr template assignment and void
  template<>
    class auto_ptr<void>
    {
    public:
      typedef void element_type;
    } _GLIBCXX_DEPRECATED;
 
#if __cplusplus >= 201103L
  template<_Lock_policy _Lp>
  template<typename _Tp>
    inline
    __shared_count<_Lp>::__shared_count(std::auto_ptr<_Tp>&& __r)
    : _M_pi(new _Sp_counted_ptr<_Tp*, _Lp>(__r.get()))
    { __r.release(); }
 
  template<typename _Tp, _Lock_policy _Lp>
  template<typename _Tp1, typename>
    inline
    __shared_ptr<_Tp, _Lp>::__shared_ptr(std::auto_ptr<_Tp1>&& __r)
    : _M_ptr(__r.get()), _M_refcount()
    {
      __glibcxx_function_requires(_ConvertibleConcept<_Tp1*, _Tp*>)
      static_assert( sizeof(_Tp1) > 0, "incomplete type" );
      _Tp1* __tmp = __r.get();
      _M_refcount = __shared_count<_Lp>(std::move(__r));
      _M_enable_shared_from_this_with(__tmp);
    }
 
  template<typename _Tp>
  template<typename _Tp1, typename>
    inline
    shared_ptr<_Tp>::shared_ptr(std::auto_ptr<_Tp1>&& __r)
    : __shared_ptr<_Tp>(std::move(__r)) { }
 
  template<typename _Tp, typename _Dp>
  template<typename _Up, typename>
    inline
    unique_ptr<_Tp, _Dp>::unique_ptr(auto_ptr<_Up>&& __u) noexcept
    : _M_t(__u.release(), deleter_type()) { }
#endif
 
#pragma GCC diagnostic pop
 
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
 
#endif /* _BACKWARD_AUTO_PTR_H */