@@ -49,10 +49,16 @@ using namespace std;
 // occurs in stl headers
 #pragma warning( disable : 4786 )
 
+template <class T> class AStarState;
+
 // The AStar search class. UserState is the users state space type
 template <class UserState> class AStarSearch
 {
 
+#if (defined(__cplusplus) && __cplusplus > 199711L) || (defined(_MSC_VER) && _MSC_VER >= 1600)
+	static_assert(is_base_of<AStarState<UserState>, UserState>::value, "UserState must be derived from AStarState!");
+#endif
+
 public: // data
 
 	enum
@@ -778,6 +784,17 @@ template <class UserState> class AStarSearch
 
 };
 
+template <class T> class AStarState
+{
+public:
+	virtual ~AStarState() {}
+	virtual float GoalDistanceEstimate( T &nodeGoal ) = 0; // Heuristic function which computes the estimated cost to the goal node
+	virtual bool IsGoal( T &nodeGoal ) = 0; // Returns true if this node is the goal node
+	virtual bool GetSuccessors( AStarSearch<T> *astarsearch, T *parent_node ) = 0; // Retrieves all successors to this node and adds them via astarsearch.addSuccessor()
+	virtual float GetCost( T &successor ) = 0; // Computes the cost of travelling from this node to the successor node
+	virtual bool IsSameState( T &rhs ) = 0; // Returns true if this node is the same as the rhs node
+};
+
 #endif