A policy based reference counting implementation for compound objects

/////////////////////////////////
// graphs.hpp
//	generic graphs objects
//

#pragma once
#include "compounds.hpp"
#pragma message ("Compiling " __FILE__)


//arcs exists only between nodes

namespace GE_{ namespace stdx{ namespace graph {

	template<class Derived, class Node, class comp_traits>
	class arc;


	template<class Derived, class Arc, class comp_traits=comp_smart_traits>
	class node:
		public comp_traits::base
	{
	public:
		typedef comp_traits traits_t;
		typedef node node_t;
		typedef typename comp_traits::types<Derived>::value Node_t;
		typedef typename comp_traits::types<Derived>::ptr Node_p;
		typedef typename comp_traits::types<Derived>::wptr Node_wp;
		typedef typename comp_traits::types<Arc>::value Arc_t;
		typedef typename comp_traits::types<Arc>::ptr Arc_p;
		typedef typename comp_traits::types<Arc>::wptr Arc_wp;

	private:
		typedef std::list<Arc_p> Arclist_t;
		Arclist_t arcfrom, arcto;
        friend class arc;

	public:
		typedef derefiterator<typename Arclist_t::iterator, Arc&> arc_iterator;
		arc_iterator begin_arcfrom() { return arcfrom.begin(); }
		arc_iterator end_arcfrom() { return arcfrom.end(); }
		arc_iterator begin_arcto() { return arcto.begin(); }
		arc_iterator end_arcto()  { return arcto.end(); }

		void clear_incoming_arcs()
		{
			while(arcfrom.size()!=0)
				arcfrom.front()->unlink();
		}
		void clear_outgoing_arcs()
		{
			while(arcto.size()!=0)
				arcto.front()->unlink();
		}

	protected:

		
		//virtual in case of smart traits, alled automatillally.
		//for dumb traits, call it in the Derived destructor
		void on_lastrelease() 
		{
			clear_incoming_arcs();
			clear_outgoing_arcs();
		}
	};

	
	template<class Derived, class Node, class comp_traits=comp_smart_traits>
	class arc:
		public comp_traits::base
	{
	public:
		typedef comp_traits traits_t;
		typedef arc arc_t;
		typedef typename comp_traits::types<Derived>::value  Arc_t;
		typedef typename comp_traits::types<Derived>::ptr Arc_p;
		typedef typename comp_traits::types<Derived>::wptr Arc_wp;
		typedef typename comp_traits::types<Node>::value Node_t;
		typedef typename comp_traits::types<Node>::ptr Node_p;
		typedef typename comp_traits::types<Node>::wptr Node_wp;

	private:
		Node_wp nodefrom, nodeto;

	public:
		const Node_wp& get_from() const { return nodefrom; }
		const Node_wp& get_to() const { return nodeto; }
		void unlink()
		{
			Arc_p keep(static_cast<Derived*>(this));
			if(nodefrom) 
				nodefrom->arcto.remove(keep);
			if(nodeto) 
				nodeto->arcfrom.remove(keep);
			nodeto=0;
			nodefrom=0;
		}
		void link(const Node_wp& pFrom, const Node_wp& pTo)
		{
			Arc_p keep(static_cast<Derived*>(this));
			unlink();
			pFrom->arcto.push_front(keep);
			pTo->arcfrom.push_front(keep);
			nodefrom = pFrom; nodeto = pTo;
		}
	};

}}}