factory.h

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#ifndef FACTORY_INCLUDED
#define FACTORY_INCLUDED


#include <string>
#include <map>

typedef std::string   IdentifierType;

template<class AbstractProduct, typename ProductCreator>
class FactoryTemplate
{
 private:
  typedef std::map<IdentifierType, ProductCreator>   Map;


 public:
  static ProductCreator Find(const IdentifierType& subtype)
  {
    return Instance().find(subtype);
  }

  static bool Register(const IdentifierType& subtype, ProductCreator creator)
  {
    return Instance().append(subtype, creator);
  }

  ProductCreator find(const IdentifierType& subtype)
  {
    typename Map::const_iterator i = m_map.find(subtype);
    if (i != m_map.end()) {
      return i->second;
    } else {
      fprintf(stderr, "Factory::find: unknown type \"%s\"\n", subtype.c_str());

#ifdef DEBUG
      exit(EXIT_FAILURE);
#endif

      return 0;
    }
  }

  bool append(const IdentifierType& subtype, ProductCreator creator)
  {
    if ((m_map.find(subtype) == m_map.end()) &&
        m_map.insert(typename Map::value_type(subtype, creator)).second) {
      return true;
    } else {
      fprintf(stderr, "Factory::append: duplicate key \"%s\"\n", subtype.c_str());
      return false;
    }
  }

  static FactoryTemplate& Instance()
  {
    if (!s_instance) {
      // lock
      if (!s_instance) {
        create_instance();
      }
      // unlock
    }
    return *s_instance;
  }

 private:
  Map m_map;

  // singleton
  FactoryTemplate() {}
  FactoryTemplate(const FactoryTemplate&) {}
  FactoryTemplate& operator=(const FactoryTemplate&);

  virtual ~FactoryTemplate() {}

  static inline void create_instance()
  {
    static FactoryTemplate instance;

    s_instance = &instance;
  }

  static FactoryTemplate *s_instance;
};

template<class AbstractProduct, typename ProductCreator>
FactoryTemplate<AbstractProduct, ProductCreator> *FactoryTemplate<AbstractProduct, ProductCreator>::s_instance = 0;
#endif