/// \brief Class to extend a graph with the functionality of alteration

   /// observing.

   ///

   /// AlterableGraphExtender extends the _Base graphs functionality with

   /// the possibility of alteration observing. It defines two observer

   /// registrys for the nodes and mapes.

   /// 

   /// \todo Document what "alteration observing" is. And probably find a

   /// better (shorter) name.

   ///

   /// \param _Base is the base class to extend.

   ///

   /// \pre _Base is conform to the BaseGraphComponent concept.

   ///

   /// \post AlterableGraphExtender<_Base> is conform to the

   /// AlterableGraphComponent concept.

   ///

   /// \author Balazs Dezso

   template <typename _Base> 

   class AlterableGraphExtender : public _Base {

   public:

     typedef AlterableGraphExtender Graph;

     typedef _Base Parent;

     typedef typename Parent::Node Node;

     typedef typename Parent::Edge Edge;

     /// The edge observer registry.

     typedef AlterationNotifier<Edge> EdgeNotifier;

     /// The node observer registry.

     typedef AlterationNotifier<Node> NodeNotifier;

   protected:

     mutable EdgeNotifier edge_notifier;

     mutable NodeNotifier node_notifier;

   public:

     /// \brief Gives back the edge alteration notifier.

     ///

     /// Gives back the edge alteration notifier.

     EdgeNotifier& getNotifier(Edge) const {

       return edge_notifier;

     }

     /// \brief Gives back the node alteration notifier.

     ///

     /// Gives back the node alteration notifier.

     NodeNotifier& getNotifier(Node) const {

       return node_notifier;

     }

     ~AlterableGraphExtender() {

       node_notifier.clear();

       edge_notifier.clear();

     }

   };

   template <typename _Base> 

   class AlterableEdgeSetExtender : public _Base {

   public:

     typedef AlterableEdgeSetExtender Graph;

     typedef _Base Parent;

     typedef typename Parent::Edge Edge;

     /// The edge observer registry.

     typedef AlterationNotifier<Edge> EdgeNotifier;

   protected:

     mutable EdgeNotifier edge_notifier;

   public:

     /// \brief Gives back the edge alteration notifier.

     ///

     /// Gives back the edge alteration notifier.

     EdgeNotifier& getNotifier(Edge) const {

       return edge_notifier;

     }

     ~AlterableEdgeSetExtender() {

       edge_notifier.clear();

     }

   };

   /// \brief Class to extend an undirected graph with the functionality of

   /// alteration observing.

   ///

   /// \todo Document.

   ///

   /// \sa AlterableGraphExtender

   ///

   /// \bug This should be done some other way. Possibilities: template

   /// specialization (not very easy, if at all possible); some kind of

   /// enable_if boost technique?

   template <typename _Base> 

   class AlterableUGraphExtender

     : public AlterableGraphExtender<_Base> {

   public:

     typedef AlterableUGraphExtender Graph;

     typedef AlterableGraphExtender<_Base> Parent;

     typedef typename Parent::UEdge UEdge;

     /// The edge observer registry.

     typedef AlterationNotifier<UEdge> UEdgeNotifier;

   protected:

     mutable UEdgeNotifier u_edge_notifier;

   public:

     using Parent::getNotifier;

     UEdgeNotifier& getNotifier(UEdge) const {

       return u_edge_notifier;

     }

     ~AlterableUGraphExtender() {

       u_edge_notifier.clear();

     }

   };

   template <typename _Base> 

   class AlterableUEdgeSetExtender

     : public AlterableEdgeSetExtender<_Base> {

   public:

     typedef AlterableUEdgeSetExtender Graph;

     typedef AlterableEdgeSetExtender<_Base> Parent;

     typedef typename Parent::UEdge UEdge;

     typedef AlterationNotifier<UEdge> UEdgeNotifier;

   protected:

     mutable UEdgeNotifier u_edge_notifier;

   public:

     using Parent::getNotifier;

     UEdgeNotifier& getNotifier(UEdge) const {

       return u_edge_notifier;

     }

     ~AlterableUEdgeSetExtender() {

       u_edge_notifier.clear();

     }

   };

   template <typename _Base>

   class AlterableBpUGraphExtender : public _Base {

   public:

     typedef _Base Parent;

     typedef AlterableBpUGraphExtender Graph;

     typedef typename Parent::Node Node;

     typedef typename Parent::BNode BNode;

     typedef typename Parent::ANode ANode;

     typedef typename Parent::Edge Edge;

     typedef typename Parent::UEdge UEdge;

     typedef AlterationNotifier<Node> NodeNotifier;

     typedef AlterationNotifier<BNode> BNodeNotifier;

     typedef AlterationNotifier<ANode> ANodeNotifier;

     typedef AlterationNotifier<Edge> EdgeNotifier;

     typedef AlterationNotifier<UEdge> UEdgeNotifier;

   protected:

     mutable NodeNotifier nodeNotifier;

     mutable BNodeNotifier bNodeNotifier;

     mutable ANodeNotifier aNodeNotifier;

     mutable EdgeNotifier edgeNotifier;

     mutable UEdgeNotifier uEdgeNotifier;

   public:

     NodeNotifier& getNotifier(Node) const {

       return nodeNotifier;

     }

     BNodeNotifier& getNotifier(BNode) const {

       return bNodeNotifier;

     }

     ANodeNotifier& getNotifier(ANode) const {

       return aNodeNotifier;

     }

     EdgeNotifier& getNotifier(Edge) const {

       return edgeNotifier;

     }

     UEdgeNotifier& getNotifier(UEdge) const {

       return uEdgeNotifier;

     }

     ~AlterableBpUGraphExtender() {

       nodeNotifier.clear();

       bNodeNotifier.clear();

       aNodeNotifier.clear();

       edgeNotifier.clear();

       uEdgeNotifier.clear();

     }

   };