object_factory.h

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/*
 * This file is part of Vlasiator.
 * Copyright 2010-2016 Finnish Meteorological Institute
 *
 * For details of usage, see the COPYING file and read the "Rules of the Road"
 * at http://www.physics.helsinki.fi/vlasiator/
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
#ifndef OBJECT_FACTORY_H
#define OBJECT_FACTORY_H
 
#include <iostream>
#include <map>
 
#include "definitions.h"

template<typename PRODUCT>
class ObjectFactory {
 public:
   
   PRODUCT* create(const std::string& name) const;
   bool add(const std::string& name,PRODUCT* (*maker)());
   size_t size() const;
 
 private:
 
   // Here the mysterious "PRODUCT* (*)()" is just a function pointer.
   // If it had a name 'maker', it could be expanded as
   // PRODUCT* (*maker)()
   // In other words, it is a pointer to a function that takes no arguments, 
   // and that returns a pointer to PRODUCT.
   std::map<std::string,PRODUCT* (*)() > manufacturers; 
};

template<typename PRODUCT> inline
PRODUCT* ObjectFactory<PRODUCT>::create(const std::string& name) const {
   typename std::map<std::string,PRODUCT* (*)()>::const_iterator it = manufacturers.find(name);
   if (it == manufacturers.end()) {
      return NULL;
   }
   return (*it->second)();
}

template<typename PRODUCT> inline
bool ObjectFactory<PRODUCT>::add(const std::string& name,PRODUCT* (*maker)()) {
   // The insert returns a pair<iterator,bool>, where the boolean value is 'true' 
   // if the maker function was inserted to the map. Skip the pair creation 
   // and just return the boolean.
   return manufacturers.insert(make_pair(name,maker)).second;
}
 
template<typename PRODUCT> inline
size_t ObjectFactory<PRODUCT>::size() const {
   return this->manufacturers.size();
}
 
#endif