factory.hh

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// factory.hh: this file is part of the Vaucanson project.
//
// Vaucanson, a generic library for finite state machines.
//
// Copyright (C) 2005 The Vaucanson Group.
//
// 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.
//
// The complete GNU General Public Licence Notice can be found as the
// `COPYING' file in the root directory.
//
// The Vaucanson Group consists of people listed in the `AUTHORS' file.
//
#ifndef VCSN_DESIGN_PATTERN_FACTORY_HH
# define VCSN_DESIGN_PATTERN_FACTORY_HH

# include <exception>
# include <map>

namespace vcsn
{

  /*--------------.
  | Error control |
  `--------------*/

  template <class IdentifierType, class ProductType>
  class DefaultFactoryError
  {
  public:
    class Exception : public std::exception
    {
    public:
      Exception(const IdentifierType& unknown_id) : unknown_id_(unknown_id) {}
      ~Exception() throw() {};
      virtual const char*       what()
      {
        return "Unknown object type passed to Factory.";
      }

      const IdentifierType      GetId()
      {
        return unknown_id_;
      }
    private:
      IdentifierType            unknown_id_;
    };

  protected:
    ProductType*                OnUnknownType(const IdentifierType& id)
    {
      throw Exception(id);
    }
  };


  /*----------------.
  | Generic Factory |
  `----------------*/

  template <
    class AbstractProduct,
    class IdentifierType,
    class ProductCreator = AbstractProduct* (*)(),
    template <typename, class> class FactoryErrorPolicy = DefaultFactoryError
  >
  class Factory : public FactoryErrorPolicy<IdentifierType, AbstractProduct>
  {
  public:
    bool                        reg(const IdentifierType& id,
                                    ProductCreator creator)
    {
      typedef typename assoc_map_t::value_type value_type;

      return associations_.insert(value_type(id, creator)).second;
    }


    bool                        unreg(const IdentifierType& id)
    {
      return associations_.erase(id) == 1;
    }


    AbstractProduct*            create_object(const IdentifierType& id)
    {
      typename assoc_map_t::const_iterator i = associations_.find(id);

      if (i != associations_.end())
        return (i->second)();
      return OnUnknownType(id);
    }

  private:
    typedef std::map<IdentifierType, ProductCreator> assoc_map_t;
    assoc_map_t associations_;
  };

} // !vcsn


#define factory_reg(factory, typeId, creationFunction) \
        factory.reg(typeId, creationFunction)

#define factory_create(factory, typeId) \
        factory.create_object(typeId)


#endif // ! VCSN_DESIGN_PATTERN_FACTORY_HH

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