Re: Naive, possibly silly question

From: Dave Harris (brangdon_at_cix.co.uk)
Date: 10/31/03 

Date: Fri, 31 Oct 2003 21:27 +0000 (GMT Standard Time)

mfeathers@objectmentorNOSPAM.com (Michael Feathers) wrote (abridged):
> There is a statically typed prototype-based language called Omega, but
> even that uses inheritance to share behavior.

I am not sure what sharing behaviour has to do with type-checking or
message dispatch. They seem to be 3 different things, more or less
orthogonal.

> The root thing is that when you have a statically typed OO language, the
> compiler has to know whether an object can accept a particular message.
> So, every instance has to be traced back to a particular specification
> of behavior.

I am not sure what you mean here. What is the "particular specification of
behaviour" for something like:

    template <typename T> T max( T a, T b ) { return a > b ? a : b; }

It's just invoking operator<() and hoping it does the right thing.

> I wouldn't count C++ templates, they are an entirely different kind of
> polymorphism.

Well, yes, but there's no reason why in some hypothetical language
something like the above couldn't be dispatched at run-time, using a
mechanism like Smalltalk's. Is there?

> I can imagine a statically-typed OO language that didn't use
> inheritance or delegation mimicking inheritance, but it would be
> pretty silly. Each instance would be a type and it would
> have its own method definitions.

Again you seem to be confusing reuse of method definitions with type
checking and/or polymorphism.

-- Dave Harris, Nottingham, UK

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