Re: Problem implementing an object factory

Here is my attempt at implementing a object factory. The purpose of this
is to replace a large switch statement in a factory class with the
functors. I get an error at line 88, marked, "expected primary-expression
before ')' token". I am using Modern C++ Design chapter 8 as a guide.

Stephen

---------------------

#include <map>
#include <iostream>

namespace tool
{
  namespace component
  {
    class Component;
  }

  namespace infrastructure
  {

    class Component_Factory
    {
    public:
      typedef component::Component* (*CreateComponentCallback)();
      
      bool RegisterComponent ( int component_id,
                   CreateComponentCallback call_func )
      {
    return m_callbacks.insert ( CallbackMap::value_type ( component_id,
    call_func ) ).second;
      }
      
      bool UnregisterComponent ( int component_id ) {
    return m_callbacks.erase ( component_id ) == 1;
      }

      component::Component* CreateComponent ( int component_id ) {
    CallbackMap::const_iterator pos = m_callbacks.find ( component_id );

    if ( pos == m_callbacks.end() )
      {
        std::cerr << "Unknown Component ID" << std::endl; abort();
      }

    return (pos->second)();
      }
      
    private:
      typedef std::map<int, CreateComponentCallback> CallbackMap;
      
      CallbackMap m_callbacks;
    };

  }

  namespace component
  {
    class Component
    {};

    class Apple : public Component
    {
    public:

      static const int ID = 1;

      Component* operator()()
      {
    return new Apple;
      }
    };

    class Blueberry : public Component
    {
    public:

      static const int ID = 5;

      Component* operator()()
      {
    return new Blueberry;
      }
    };
  }
}

int main (int, char**)
{
  tool::infrastructure::Component_Factory fact_ref;

  /* LINE 88 */
  fact_ref.RegisterComponent ( tool::component::Apple::ID,
  tool::component::Apple );

  fact_ref.UnregisterComponent ( tool::component::Apple::ID );

  return 0;
}