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singleton.h

/* ScummVM - Scumm Interpreter
 * Copyright (C) 2001  Ludvig Strigeus
 * Copyright (C) 2001-2005 The ScummVM project
 *
 * 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.
 *
 * $Header: /cvsroot/scummvm/scummvm/common/singleton.h,v 1.16.2.1 2005/10/18 02:11:18 sev Exp $
 *
 */

#ifndef COMMON_SINGLETON_H
#define COMMON_SINGLETON_H

namespace Common {

/**
 * Generic template base class for implementing the singleton design pattern.
 */
template <class T>
00032 class Singleton
{
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
00052       static T* makeInstance() {
            return new T();
      }


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;
      }
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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