RhodeCode

        ///@param g the digraph

        ArcIt(const Digraph& g) { ignore_unused_variable_warning(g); }

        /// Arc -> ArcIt conversion

        /// Sets the iterator to the value of the trivial iterator \c e.

        /// This feature necessitates that each time we 

        /// iterate the arc-set, the iteration order is the same.

        ArcIt(const Digraph&, const Arc&) { } 

        ///Next arc

        /// Assign the iterator to the next arc.

        ArcIt& operator++() { return *this; }

      };

      ///Gives back the target node of an arc.

      ///Gives back the target node of an arc.

      ///

      Node target(Arc) const { return INVALID; }

      ///Gives back the source node of an arc.

      ///Gives back the source node of an arc.

      ///

      Node source(Arc) const { return INVALID; }

      void first(Node&) const {}

      void next(Node&) const {}

      void first(Arc&) const {}

      void next(Arc&) const {}

      void firstIn(Arc&, const Node&) const {}

      void nextIn(Arc&) const {}

      void firstOut(Arc&, const Node&) const {}

      void nextOut(Arc&) const {}

      /// \brief The base node of the iterator.

      ///

      /// Gives back the base node of the iterator.

      /// It is always the target of the pointed arc.

      Node baseNode(const InArcIt&) const { return INVALID; }

      /// \brief The running node of the iterator.

      ///

      /// Gives back the running node of the iterator.

      /// It is always the source of the pointed arc.

      Node runningNode(const InArcIt&) const { return INVALID; }

      /// \brief The base node of the iterator.

      ///

      /// Gives back the base node of the iterator.

      /// It is always the source of the pointed arc.

      Node baseNode(const OutArcIt&) const { return INVALID; }

      /// \brief The running node of the iterator.

      ///

      /// Gives back the running node of the iterator.

      /// It is always the target of the pointed arc.

      Node runningNode(const OutArcIt&) const { return INVALID; }

      /// Reference map of the arcs to type \c T.

      /// \sa Reference

      template<class T> 

      class ArcMap : public ReadWriteMap<Arc,T> {

      public:

        ///\e

        ArcMap(const Digraph&) { }

        ///\e

        ArcMap(const Digraph&, T) { }

        ///Copy constructor

        ArcMap(const ArcMap& em) : ReadWriteMap<Arc,T>(em) { }

        ///Assignment operator

        template <typename CMap>

        ArcMap& operator=(const CMap&) { 

          checkConcept<ReadMap<Arc, T>, CMap>();

          return *this; 

        }

      };

      template <typename RDigraph>

      struct Constraints {

        void constraints() {

          checkConcept<IterableDigraphComponent<>, Digraph>();

          checkConcept<MappableDigraphComponent<>, Digraph>();

        }

      };

    };

  } //namespace concepts  

} //namespace lemon

#endif // LEMON_CONCEPT_DIGRAPH_H

      Node oppositeNode(Node, Edge) const { return INVALID; }

      /// \brief First node of the edge.

      ///

      /// \return the first node of the given Edge.

      ///

      /// Naturally edges don't have direction and thus

      /// don't have source and target node. But we use these two methods

      /// to query the two nodes of the arc. The direction of the arc

      /// which arises this way is called the inherent direction of the

      /// edge, and is used to define the "default" direction

      /// of the directed versions of the arcs.

      /// \sa direction

      Node u(Edge) const { return INVALID; }

      /// \brief Second node of the edge.

      Node v(Edge) const { return INVALID; }

      /// \brief Source node of the directed arc.

      Node source(Arc) const { return INVALID; }

      /// \brief Target node of the directed arc.

      Node target(Arc) const { return INVALID; }

      void first(Node&) const {}

      void next(Node&) const {}

      void first(Edge&) const {}

      void next(Edge&) const {}

      void first(Arc&) const {}

      void next(Arc&) const {}

      void firstOut(Arc&, Node) const {}

      void nextOut(Arc&) const {}

      void firstIn(Arc&, Node) const {}

      void nextIn(Arc&) const {}

      void firstInc(Edge &, bool &, const Node &) const {}

      void nextInc(Edge &, bool &) const {}

      /// \brief Base node of the iterator

      ///

      /// Returns the base node (the source in this case) of the iterator

      Node baseNode(OutArcIt e) const {

	return source(e);

      }

      /// \brief Running node of the iterator

      ///

      /// Returns the running node (the target in this case) of the

      /// iterator

      Node runningNode(OutArcIt e) const {

	return target(e);

      }

      /// \brief Base node of the iterator

      ///

      /// Returns the base node (the target in this case) of the iterator

      Node baseNode(InArcIt e) const {

	return target(e);

      }

      /// \brief Running node of the iterator

      ///

      /// Returns the running node (the source in this case) of the

      /// iterator

      Node runningNode(InArcIt e) const {

	return source(e);

      }

      /// \brief Base node of the iterator

      ///

      /// Returns the base node of the iterator

      Node baseNode(IncArcIt) const {

	return INVALID;

      }

      /// \brief Running node of the iterator

      ///

      /// Returns the running node of the iterator

      Node runningNode(IncArcIt) const {

	return INVALID;

      }

      template <typename Graph>

      struct Constraints {

	void constraints() {

	  checkConcept<IterableGraphComponent<>, Graph>();

	  checkConcept<MappableGraphComponent<>, Graph>();

	}

      };

    };

  }

}

#endif