/*
  VISITOR-POLICIES.hpp  -  Acyclic Visitor library

  Copyright (C)         Lumiera.org
    2008,               Hermann Vosseler <Ichthyostega@web.de>

  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., 675 Mass Ave, Cambridge, MA 02139, USA.

*/


/** @file visitor-policies.hpp
 ** Policies usable for configuring the lib::visitor::Tool for different kinds of error handling. 
 ** @see buildertool.hpp for another flavour (calling an catch-all-function there)
 **
 */



#ifndef LUMIERA_VISITOR_POLICIES_H
#define LUMIERA_VISITOR_POLICIES_H

#include "lib/error.hpp"


namespace lib {
namespace visitor {
  
  /** 
   * Policy returning just the default return value in case
   * of encountering an unknown Visitor (typically caused by
   * adding a new class to the visitable hierarchy)
   */
  template<class RET>
  struct UseDefault
    {
      template<class TAR>
      RET 
      onUnknown (TAR&)
        {
          return RET();
        }
    };
  
  /** 
   * Policy to throw when encountering an unknown visiting tool
   */
  template<class RET>
  struct ThrowException
    {
      template<class TAR>
      RET 
      onUnknown (TAR&)
        {
          throw lumiera::error::Config("unable to decide what tool operation to call");
        }
    };
  
  
  
}} // namespace lib::visitor
#endif
