property magic for inerfaces (please!)

[Hasan Aljudy]

Reiner Pope wrote:
> == 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

Yeah, and it's not like the interface is sooo abstract that it doesn't 
define anything at all! It does define something; it defines "what" 
should be done.