gcc/libstdc++-v3/include/bits/stl_auto_ptr.h

// auto_ptr implementation -*- C++ -*-

// Copyright (C) 2007 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 2, 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.

// You should have received a copy of the GNU General Public License
// along with this library; see the file COPYING.  If not, write to
// the Free Software Foundation, 51 Franklin Street, Fifth Floor,
// Boston, MA 02110-1301, USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

/** @file stl_auto_ptr.h
 *  This is an internal header file, included by other library headers.
 *  You should not attempt to use it directly.
 */

#ifndef _STL_AUTO_PTR_H
#define _STL_AUTO_PTR_H 1

#include <bits/c++config.h>
#include <debug/debug.h>

_GLIBCXX_BEGIN_NAMESPACE(std)

  /**
   *  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) { }
    };


  /**
   *  @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.
   *
   *  @if maint
   *  _GLIBCXX_RESOLVE_LIB_DEFECTS
   *  127.  auto_ptr<> conversion issues
   *  These resolutions have all been incorporated.
   *  @endif
   */
  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 ownsership.
       */
      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 ownsership.
       */
      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 ownsership.  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 ownsership.  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.
       *
       *  @if maint
       *  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
       *  @endif
       */
      ~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, "no longer owns
       *  anything" 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_DEBUG_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_DEBUG_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 convert an %auto_ptr into and from an auto_ptr_ref
       *  automatically as needed.  This allows constructs such as
       *  @code
       *    auto_ptr<Derived>  func_returning_auto_ptr(.....);
       *    ...
       *    auto_ptr<Base> ptr = func_returning_auto_ptr(.....);
       *  @endcode
       */
      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_RESOLVE_LIB_DEFECTS
  // 541. shared_ptr template assignment and void
  template<>
    class auto_ptr<void>
    {
    public:
      typedef void element_type;
    };

_GLIBCXX_END_NAMESPACE

#endif /* _STL_AUTO_PTR_H */