[squeak-dev] Re: On traits composition

Andreas Raab andreas.raab at gmx.de
Tue Dec 8 08:32:59 UTC 2009

Igor Stasenko wrote:
> T1+T2
> should mean 'apply T1 then T2', but not 'apply combination of T1 and T2'.
> Its much easier to implement as well as easy to understand & follow.

That's what I'm thinking as well.

> Also, in Pharo list i suggested extension to exclusion operator:
> in addition to:
> T1 - selectorsArray "{ #sel1. #sel2 }"
> also have:
> T1 - T2
> which should transparently behave as:
> T1 - (T2 selectors)
> and mean: apply all from T1 , except selectors in T2.

I'll leave this as an exercise for the interested reader :)

> Btw, i am curious about one thing:
> Since traits allowed to hold method for both instance side and class side.

Ah, yes. Classes and metaclasses and traits. Last time we had this 
discussion it was pretty clear that this whole area is not 
well-understood. That you can only apply a trait without class-side 
methods to a class for example, causes all sorts of irritation when you 
later add a class method to the trait, thereby making it non-applicable 
to compositions where it's already used. It's inconsistent at least 
(broken as far as I'm concerned since you can create compositions that 
can't be recreated).

> Now, how i can specify a composition, which applies my trait, except
> #isel1 and #csel2 ?
> So, final class should have #isel2 method at instance side and
> #csel2 at class side, but not #isel1 and not #csel2.
> And what is a correct syntax for defining such composition in class definition?

Yes, that's just more inconsistencies resulting from the same basic problem.

   - Andreas

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