[squeak-dev] Re: Object>>#is:?

Eliot Miranda eliot.miranda at gmail.com
Sun Mar 7 05:37:56 UTC 2010

On Thu, Mar 4, 2010 at 8:37 PM, Colin Putney <cputney at wiresong.ca> wrote:

> On 2010-03-04, at 1:18 PM, Stéphane Rollandin wrote:
> > I got it; see my answer to Juan. I guess I'm just programming in bad
> style: I do indeed consider that Object is part of my packages (or, more
> accurately, that Object is not a forbidden place for my package to go in).
> Hear hear. I've been wondering why people are so enthusiastic about #is: -
> good to see I'm not the only one.
> I think #isA: is fine, as an easy way to do #isKindOf: without a direct
> class reference. Being able to avoid class references makes it easier to
> avoid dependencies, which makes it easier to have a modular system.
> Juan's implementation of #is: puzzles me though. It replaces polymorphic
> dispatch with boolean logic. Good OO design generally goes in the opposite
> direction.
> Furthermore, Juan's version of #is: makes it more difficult to modularize
> the system. If I write a package that needs to add the concept of
> "greenness" to the system, I can add #isGreen extension methods wherever I
> want, without breaking any existing code. Somebody else can add #isPurple
> methods without breaking my code. But if we both need to override #is:, we
> have a gratuitous incompatibility.
> Note that #is: may work well in Cuis, but that's because Cuis is *not* a
> modular system.
> Finally, I also want to point out that "simpler" and "fewer methods" are
> not the same thing. Methods that answer booleans are dead simple to
> understand, no matter how many of them there are. A single #is: method
> increases incomplexity as the number of tests it encompasses increases.
> So, consider this moral support for Stéphane, since he seems to be beset on
> all sides. Also,
> +0 for #isA:
> -1 for #is:
> Colin

Hear, hear!
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