property magic for inerfaces (please!)

[Reiner Pope]

== Quote from Lionello Lunesu (lionello at lunesu.remove.com)'s article
> What if getChildren() is a costly function, that, say, does an SELECT on a
> remote database? You would not want it to have that particular
> implementation since it would not need to collect the children first, just
> to check whether there are any.
> Unfortunately, the only correct way to work with interfaces *is* declaring
> all the functions virtual. You want to do getChildren().length because you
> already know the implementation of getChildren, which is not a fair way to
> look at it.
> L.

But you could apply this sort of argument ("we want to allow people to implement
it differently") everywhere so, by that logic, we shouldn't have final methods,
since there *might* sometime be a reason to reimplement them (and you could even
extend this argument to disallow every function which isn't a class, since none of
them involve a virtual function lookup!). There is a limit to how much flexibility
can be achieved in an API, and it is sometimes useful to final methods. If the
interface expects that getChildren will run in a reasonable time, then it violates
the Liskov Substitution principle if an implementing class takes too long on it.

Cheers,

Reiner