/* -*- C++ -*-

  * lemon/invalid.h - Part of LEMON, a generic C++ optimization library

  *

  * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

  * (Egervary Research Group on Combinatorial Optimization, EGRES).

  *

  * Permission to use, modify and distribute this software is granted

  * provided that this copyright notice appears in all copies. For

  * precise terms see the accompanying LICENSE file.

  *

  * This software is provided "AS IS" with no warranty of any kind,

  * express or implied, and with no claim as to its suitability for any

  * purpose.

  *

  */

 #ifndef LEMON_INVALID_H

 #define LEMON_INVALID_H

 ///\file

 ///\brief Definition of INVALID.

 namespace lemon {

   /// Dummy type to make it easier to make invalid iterators.

   /// See \ref INVALID, how to use it.

   struct Invalid {

   public:

     bool operator==(Invalid) { return true;  }

     bool operator!=(Invalid) { return false; }

     bool operator< (Invalid) { return false; }

   };

   /// Invalid iterators.

   /// \ref Invalid is a global type that converts to each iterator

   /// in such a way that the value of the target iterator will be invalid.

   // It is also used to convert the \c INVALID constant to the

   // node iterator that makes is possible to write 

   //extern Invalid INVALID;

   //const Invalid &INVALID = *(Invalid *)0;

   const Invalid INVALID = Invalid();

 } //namespace lemon

 #endif