Originally it was stored in the method, but that required copying each type's methods (and each parents' methods) into an object on instantiation, which was a pretty much unacceptable performance hit.

I think more a typical solution is to dynamically bind `self` like you do now on normal method calls. But when a reference to a method is stored, you bind `self` to the original receiver at that point in time.

Basically, you treat it like a closure.