> Is there a way to make it accept all the instances inheriting from Curve?
As that question arises often, I tried to explain that in my book (with geometric shapes). [http://ssalewski.de/nimprogramming.html#_object_orientated_programming_and_inheritance](http://ssalewski.de/nimprogramming.html#_object_orientated_programming_and_inheritance) It is still not clear enough?
