Re: Importance of Polymorphism

[Brian Rogoff <bpr@shell5.ba.best.com>]

On 10 Feb 1998, Nick Roberts wrote:
> It's the world's most contended subject, I get the impression, but my own
> take on it is: I believe it is dynamic polymorphism which really defines
> the _key_ advantage of object oriented programming.  It's perhaps not so
> obvious in a compiled language such as Ada, especially where there is not
> (yet) a culture of using dynamic polymorphism very heavily.

Also a key disadvantage. No, I'm not saying that dynamic dispatch is bad
or evil, just that there are costs (which function am I really calling?, 
why do I have to have this tag on everything? etc...).

> In the future, it may well be that Ada gets rather like SmallTalk --

I hope we get block closures, or at least some limited closure facility, 
but I think Smalltalk style OO and Ada style OO (with static typing) won't 
mix well. More likely would be some Java interface type mechanism, and
maybe a limited form of multi-dispatch. We're already seeing a bit of this 
now in GNAT ("downward funargs" via Unrestricted_Access) and the
Intermetrics Java Mapping (pragma Convention( Java_Interface, ... ) ) but 
I doubt we'll see a "doesNotUnderstand" message at runtime soon :-).

-- Brian