note 73380 deleted from language.oop5.interfaces by gwynne

Note Submitter: Chris ---- albert: Of course that doesn't work; it would violate the Liskov substitution principle. Namely: If Cmyqueue is-a Iqueue, then I must be able to do with an Cmyqueue anything I can do with an Iqueue. If I can call enqueue() on Iqueue passing any Object, I must be able to do the same with Cmyqueue. Restricting Cmyqueue::enqueue() to accept only a subclass of Object would break this. That's why generics (in languages supporting them) don't work like this: a List<String> cannot be "properly" converted to a List<Object>, because you can add Objects to a List<Object> but a List<String> should never contain Objects that are not Strings.