// -*- c++ -*-

 #ifndef LEMON_EXTENDABLE_GRAPH_EXTENDER_H

 #define LEMON_EXTENDABLE_GRAPH_EXTENDER_H

 namespace lemon {

   template <typename _Base> 

   class ExtendableGraphExtender : public _Base {

   public:

     typedef ExtendableGraphExtender Graph;

     typedef _Base Parent;

     typedef typename Parent::Node Node;

     typedef typename Parent::Edge Edge;

     Node addNode() {

       Node node = Parent::addNode();

       Parent::getObserverRegistry(Node()).add(node);

       return node;

     }

     Edge addEdge(const Node& from, const Node& to) {

       Edge edge = Parent::addEdge(from, to);

       Parent::getObserverRegistry(Edge()).add(edge);

       return edge;

     }

   };

 }

 #endif