text: // Copyright 2007-2009 Google Inc.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //      http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  // ========================================================================
  
  #ifndef OMAHA_BASE_OBJECT_FACTORY_H_
  #define OMAHA_BASE_OBJECT_FACTORY_H_
  
  #include <map>
  
  namespace omaha {
  
  // Factory creates instances of objects based on a unique type id.
  //
  // AbstractProduct - base class of the product hierarchy.
  // TypeId - type id for each type in the hierarchy.
  // ProductCreator - callable entity to create objects.
  
  template <class AbstractProduct,
            typename TypeId,
            typename ProductCreator = AbstractProduct* (*)()>
  class Factory {
   public:
    Factory() {}
  
    // Registers a creator for the type id. Returns true if the creator has
    // been registered succesfully.
    bool Register(const TypeId& id, ProductCreator creator) {
      return id_to_creators_.insert(Map::value_type(id, creator)).second;
    }
  
    // Unregisters a type id.
    bool Unregister(const TypeId& id) {
      return id_to_creators_.erase(id) == 1;
    }
  
    // Creates an instance of the abstract product.
    AbstractProduct* CreateObject(const TypeId& id) const {
      typename Map::const_iterator it = id_to_creators_.find(id);
      if (it != id_to_creators_.end()) {
        return (it->second)();
      } else {
        return NULL;
      }
    }
  
   private:
    typedef std::map<TypeId, ProductCreator> Map;
    Map id_to_creators_;
  
    DISALLOW_EVIL_CONSTRUCTORS(Factory);
  };
  
  }  // namespace omaha
  
  #endif  // OMAHA_BASE_OBJECT_FACTORY_H_
  
  