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MetaObject.h
//
// MetaObject.h
//
// $Id: //poco/1.3/Foundation/include/Poco/MetaObject.h#1 $
//
// Library: Foundation
// Package: SharedLibrary
// Module:  ClassLoader
//
// Definition of the MetaObject class.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_MetaObject_INCLUDED
#define Foundation_MetaObject_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/Exception.h"
#include "Poco/SingletonHolder.h"
#include <set>


namespace Poco {


template <class B>
00053 class AbstractMetaObject
      /// A MetaObject stores some information
      /// about a C++ class. The MetaObject class
      /// is used by the Manifest class.
      /// AbstractMetaObject is a common base class
      /// for all MetaObject in a rooted class hierarchy.
      /// A MetaObject can also be used as an object
      /// factory for its class.
{
public:
      AbstractMetaObject(const char* name): _name(name)
      {
      }

      virtual ~AbstractMetaObject()
      {
            for (typename ObjectSet::iterator it = _deleteSet.begin(); it != _deleteSet.end(); ++it)
            {
                  delete *it;
            }
      }

      const char* name() const
      {
            return _name;
      }

      virtual B* create() const = 0;
            /// Create a new instance of a class.
            /// Cannot be used for singletons.
            
      virtual B& instance() const = 0;
            /// Returns a reference to the only instance
            /// of the class. Used for singletons only.

      virtual bool canCreate() const = 0;
            /// Returns true iff the create method can be used
            /// to create instances of the class.
            /// Returns false if the class is a singleton.

00093       virtual void destroy(B* pObject) const
            /// If pObject was owned by meta object, the
            /// ownership of the deleted object is removed
            /// and the object is deleted.
      {
            typename ObjectSet::iterator it = _deleteSet.find(pObject);
            
            if (it != _deleteSet.end())
            {
                  _deleteSet.erase(pObject);
                  delete pObject;
            }
      }

00107       B* autoDelete(B* pObject) const
            /// Give ownership of pObject to the meta object.
            /// The meta object will delete all objects it owns
            /// when it is destroyed.
            ///
            /// Returns pObject.
      {
            if (this->canCreate()) // guard against singleton
            {
                  poco_check_ptr (pObject);
                  _deleteSet.insert(pObject);
            }
            else throw InvalidAccessException("Cannot take ownership of", this->name());

            return pObject;
      }

00124       virtual bool isAutoDelete(B* pObject) const
            /// Returns true if the object is owned
            /// by meta object.
            ///
            /// Overloaded in MetaSingleton - returns true
            /// if the class is a singleton.
      {
            return _deleteSet.find(pObject) != _deleteSet.end();
      }

private:
      AbstractMetaObject();
      AbstractMetaObject(const AbstractMetaObject&);
      AbstractMetaObject& operator = (const AbstractMetaObject&);

      typedef std::set<B*> ObjectSet;
      
      const char* _name;
      mutable ObjectSet _deleteSet;
};


template <class C, class B>
00147 class MetaObject: public AbstractMetaObject<B>
      /// A MetaObject stores some information
      /// about a C++ class. The MetaObject class
      /// is used by the Manifest class.
      /// A MetaObject can also be used as an object
      /// factory for its class.
{
public:
      MetaObject(const char* name): AbstractMetaObject<B>(name)
      {
      }

      ~MetaObject()
      {
      }

      B* create() const
      {
            return new C;
      }
      
00168       B& instance() const
      {
            throw InvalidAccessException("Not a singleton. Use create() to create instances of", this->name());
      }
      
00173       bool canCreate() const
      {
            return true;
      }
};


template <class C, class B> 
00181 class MetaSingleton: public AbstractMetaObject<B> 
      /// A SingletonMetaObject disables the create() method
      /// and instead offers an instance() method to access
      /// the single instance of its class. 
{ 
public: 
      MetaSingleton(const char* name): AbstractMetaObject<B>(name) 
      {
      }
      
      ~MetaSingleton() 
      {
      }
      
      B* create() const
      {
            throw InvalidAccessException("Cannot create instances of a singleton class. Use instance() to obtain a", this->name());
      }
      
00200       bool canCreate() const
      {
            return false;
      }

00205       B& instance() const
      {
            return *_object.get();
      }
      
00210       bool isAutoDelete(B* pObject) const
      {
            return true;
      }

private: 
      mutable SingletonHolder<C> _object; 
}; 


} // namespace Poco


#endif // Foundation_MetaObject_INCLUDED

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