One other thing I forgot to mention, was when looking at the provided link http://geometrylibrary.geodan.nl/points.html The distance definition takes 2 templated point types but always returns a double. The lesson here is that the precision required for the the result may be more than the precision of the inputs. In this case the best strategy is to at the minimum return the same numeric type of the points as the result type or better. The other issue is that the points should be of the same type, not differing types. This strategy_traits approach where assuming there will be an implementation for the combination of types is not adequate, what if one of the types can be easily promoted to the other? eg: double conversion to my_super_duper_arbitrary_precision_floating_point_type via copy constructor? does that mean I have to provide a wrapper around the explicit call to my implementation of distance with my specific type? Arash Partow __________________________________________________ Be one who knows what they don't know, Instead of being one who knows not what they don't know, Thinking they know everything about all things. http://www.partow.net