Is this the proper way to do it?

[Jack via Digitalmars-d-learn]

I have a base class A, where I make specific operator depending 
on the derived class type. Currently I'm using something like 
this:

c is a class derived from A
bool shouldDoX = (cast(X)c) !is null || (cast(Y)c) !is null || 
(cast(K)c) !is null ... ;

as the number of cast(C) !is null is growing, I'm afraid of this 
being a inelegant or even poor performance approach. How would 
you do that?