> One more thing: If you really consider to implement the "isClass" check in
> two unrelated branches of an inheritance tree, you arguably have a design
> issue. Just use #respondsTo:. For example, TranscriptStream should not
> implement #isModel but rather implement the Model interface as needed.
> #respondsTo: will work fine.

How fast is #respondsTo:? Can it be used in a tight loop?

Stef