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singleton.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/singleton.h $
 * $Id: singleton.h 31852 2008-05-03 23:02:05Z lordhoto $
 *
 */

#ifndef COMMON_SINGLETON_H
#define COMMON_SINGLETON_H

#include "common/noncopyable.h"

namespace Common {

/**
 * Generic template base class for implementing the singleton design pattern.
 */
template<class T>
00037 class Singleton : NonCopyable {
private:
      Singleton<T>(const Singleton<T> &);
      Singleton<T> &operator=(const Singleton<T> &);

      static T *_singleton;

      /**
       * The default object factory used by the template class Singleton.
       * By specialising this template function, one can make a singleton use a
       * custom object factory. For example, to support encapsulation, your
       * singleton class might be pure virtual (or "abstract" in Java terminology),
       * and you specialise makeInstance to return an instance of a subclass.
       */
      //template <class T>
#if defined (_WIN32_WCE) || defined (_MSC_VER) || defined (__WINS__)
//FIXME evc4 and msvc7 doesn't like it as private member
public:
#endif
00056       static T *makeInstance() {
            return new T();
      }

      static void destroyInstance() {
            delete _singleton;
            _singleton = 0;
      }


public:
      static T& instance() {
            // TODO: We aren't thread safe. For now we ignore it since the
            // only thing using this singleton template is the config manager,
            // and that is first instantiated long before any threads.
            // TODO: We don't leak, but the destruction order is nevertheless
            // semi-random. If we use multiple singletons, the destruction
            // order might become an issue. There are various approaches
            // to solve that problem, but for now this is sufficient
            if (!_singleton)
                  _singleton = T::makeInstance();
            return *_singleton;
      }

      static void destroy() {
            T::destroyInstance();
      }
protected:
      Singleton<T>()          { }
#ifdef __SYMBIAN32__
      virtual ~Singleton()    { }
#else
      virtual ~Singleton<T>() { }
#endif

      typedef T   SingletonBaseType;
};

#define DECLARE_SINGLETON(T) template<> T *Common::Singleton<T>::_singleton = 0

}     // End of namespace Common

#endif

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