// -*- mode:C++ -*-

#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