class ShapeFactory
{
protected:
   typedef Shape *(*CreateObjectFunc)();

public:
   bool Register(int shape, CreateObjectFunc create_object)
   {
      if (m_object_creator.find(shape) != m_object_creator.end())
         return false;

      m_object_creator[shape] = create_object;

      return true;
   }

   bool Unregister(int shape)
   {
      return (m_object_creator.erase(shape) == 1);
   }

   Shape *Create(int shape)
   {
      std::map<int, CreateObjectFunc>::iterator iter = m_object_creator.find(shape);

      if (iter == m_object_creator.end())
         return NULL;

      return ((*iter).second)();
   }

protected:
   std::map<int, CreateObjectFunc> m_object_creator;
};