Objective C — narrow instance variable types in subclasses?

Question

Is it possible to narrow the allowed type of an ivar in a subclass. Something like this:

@interface person: NSObject {
  NSArray *friendArray;
}

@interface         


        

Answer 1

@class doesn't make sense at all... it should be @interface. So the first error is purely syntactical.

And no, you cannot change the type of an ivar. And that's for a good reason: Narrowing it down (as you do) can't work, because the parent class might rely on a different implementation. Widening it can't work as well (mainly for the analogous reason.