class DBObject {
private:
	. . . // state
public:
	void saveState() { . .. }
	void loadState() { . .. }
	. . .
}

class StorableShape : Shape {
	private DBObj ect _store;
	alias _store this;
	this( ) {
		_store = new DBObj ect;
	}
	. . .
}

unittest {
	auto s = new StorableShape;
	s. draw( ) ; 		// call a Shape method
	s. saveState() ; 	// call a DBObject method
				// gets rewritten as s._store.saveState()
	Shape sh = s; 		// normal upcast derived -> base
	DBObj ect db = s; 	// rewritten as DBObject db = s._store
}