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ptr.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program 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
 * of the License, or (at your option) any later version.
 *
 * This program 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 program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * $URL: https://scummvm.svn.sourceforge.net/svnroot/scummvm/scummvm/tags/release-0-13-0/common/ptr.h $
 * $Id: ptr.h 35481 2008-12-22 11:22:15Z jvprat $
 */

#ifndef COMMON_PTR_H
#define COMMON_PTR_H

#include "common/scummsys.h"

namespace Common {

class SharedPtrDeletionInternal {
public:
      virtual ~SharedPtrDeletionInternal() {}
};

template<class T>
class SharedPtrDeletionImpl : public SharedPtrDeletionInternal {
public:
      SharedPtrDeletionImpl(T *ptr) : _ptr(ptr) {}
      ~SharedPtrDeletionImpl() {
            // Checks if the supplied type is not just a plain
            // forward definition, taken from boost::checked_delete
            // This makes the user really aware what he tries to do
            // when using this with an incomplete type.
            typedef char completeCheck[sizeof(T) ? 1 : -1];
            (void)sizeof(completeCheck);
            delete _ptr;
      }
private:
      T *_ptr;
};

template<class T, class D>
class SharedPtrDeletionDeleterImpl : public SharedPtrDeletionInternal {
public:
      SharedPtrDeletionDeleterImpl(T *ptr, D d) : _ptr(ptr), _deleter(d) {}
      ~SharedPtrDeletionDeleterImpl() { _deleter(_ptr); }
private:
      T *_ptr;
      D _deleter;
};

/**
 * A simple shared pointer implementation modelled after boost.
 *
 * This object keeps track of the assigned pointer and automatically
 * frees it when no more SharedPtr references to it exist.
 *
 * To achieve that the object implements an internal reference counting.
 * Thus you should try to avoid using the plain pointer after assigning
 * it to a SharedPtr object for the first time. If you still use the
 * plain pointer be sure you do not delete it on your own. You may also
 * not use the plain pointer to create a new SharedPtr object, since that
 * would result in a double deletion of the pointer sooner or later.
 *
 * Example creation:
 * Common::SharedPtr<int> pointer(new int(1));
 * would create a pointer to int. Later on usage via *pointer is the same
 * as for a normal pointer. If you need to access the plain pointer value
 * itself later on use the get method. The class also supplies a operator
 * ->, which does the same as the -> operator on a normal pointer.
 *
 * Be sure you are using new to initialize the pointer you want to manage.
 * If you do not use new for allocating, you have to supply a deleter as
 * second parameter when creating a SharedPtr object. The deleter has to
 * implement operator() which takes the pointer it should free as argument.
 *
 * Note that you have to specify the type itself not the pointer type as
 * template parameter.
 *
 * When creating a SharedPtr object from a normal pointer you need a real
 * definition of the type you want SharedPtr to manage, a simple forward
 * definition is not enough.
 *
 * The class has implicit upcast support, so if you got a class B derived
 * from class A, you can assign a pointer to B without any problems to a
 * SharedPtr object with template parameter A. The very same applies to
 * assignment of a SharedPtr<B> object to a SharedPtr<A> object.
 *
 * There are also operators != and == to compare two SharedPtr objects
 * with compatible pointers. Comparison between a SharedPtr object and
 * a plain pointer is only possible via SharedPtr::get.
 */
template<class T>
00106 class SharedPtr {
#if !((__GNUC__ == 2) && (__GNUC_MINOR__ >= 95))
      template<class T2> friend class SharedPtr;
#endif
public:
      typedef int RefValue;
      typedef T ValueType;
      typedef T *Pointer;

      SharedPtr() : _refCount(0), _deletion(0), _pointer(0) {}
      template<class T2> explicit SharedPtr(T2 *p) : _refCount(new RefValue(1)), _deletion(new SharedPtrDeletionImpl<T2>(p)), _pointer(p) {}
      template<class T2, class D> SharedPtr(T2 *p, D d) : _refCount(new RefValue(1)), _deletion(new SharedPtrDeletionDeleterImpl<T2, D>(p, d)), _pointer(p) {}

      SharedPtr(const SharedPtr &r) : _refCount(r._refCount), _deletion(r._deletion), _pointer(r._pointer) { if (_refCount) ++(*_refCount); }
      template<class T2> SharedPtr(const SharedPtr<T2> &r) : _refCount(r._refCount), _deletion(r._deletion), _pointer(r._pointer) { if (_refCount) ++(*_refCount); }

      ~SharedPtr() { decRef(); }

      SharedPtr &operator=(const SharedPtr &r) {
            if (r._refCount)
                  ++(*r._refCount);
            decRef();

            _refCount = r._refCount;
            _deletion = r._deletion;
            _pointer = r._pointer;

            return *this;
      }

      template<class T2>
      SharedPtr &operator=(const SharedPtr<T2> &r) {
            if (r._refCount)
                  ++(*r._refCount);
            decRef();

            _refCount = r._refCount;
            _deletion = r._deletion;
            _pointer = r._pointer;

            return *this;
      }

      ValueType &operator*() const { assert(_pointer); return *_pointer; }
      Pointer operator->() const { assert(_pointer); return _pointer; }

      /**
       * Returns the plain pointer value. Be sure you know what you
       * do if you are continuing to use that pointer.
       *
       * @return the pointer the SharedPtr object manages
       */
00158       Pointer get() const { return _pointer; }

      /**
       * Implicit conversion operator to bool for convenience, to make
       * checks like "if (sharedPtr) ..." possible.
       */
00164       operator bool() const { return _pointer != 0; }

      /**
       * Checks if the SharedPtr object is the only object refering
       * to the assigned pointer. This should just be used for
       * debugging purposes.
       */
00171       bool unique() const { return refCount() == 1; }

      /**
       * Resets the SharedPtr object to a NULL pointer.
       */
00176       void reset() {
            decRef();
            _deletion = 0;
            _refCount = 0;
            _pointer = 0;
      }

      /**
       * Returns the number of references to the assigned pointer.
       * This should just be used for debugging purposes.
       */
00187       RefValue refCount() const { return _refCount ? *_refCount : 0; }
#if !((__GNUC__ == 2) && (__GNUC_MINOR__ >= 95))
private:
#endif
      void decRef() {
            if (_refCount) {
                  --(*_refCount);
                  if (!*_refCount) {
                        delete _refCount;
                        delete _deletion;
                        _deletion = 0;
                        _refCount = 0;
                        _pointer = 0;
                  }
            }
      }

      RefValue *_refCount;
      SharedPtrDeletionInternal *_deletion;
      T *_pointer;
};

} // end of namespace Common

template<class T1, class T2>
bool operator==(const Common::SharedPtr<T1> &l, const Common::SharedPtr<T2> &r) {
      return l.get() == r.get();
}

template<class T1, class T2>
bool operator!=(const Common::SharedPtr<T1> &l, const Common::SharedPtr<T2> &r) {
      return l.get() != r.get();
}

#endif

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