2009/10/26 Alexandre Bergel <[email protected]>:
> Hi Igor,
>
>> Trait named: #TraitGroup
>> uses: TraitA + TraitB + .... TraitN
>> category: 'foo'
>>
>> and suppose i want to use TraitGroup in one of my classes, but
>> excluding one of the traits in the list above.. i.e. something like:
>>
>> Object subclass: #Myclass
>> uses: TraitGroup - TraitA
>> ..
>>
>> but the above code don't seem to work..
>> Any clues, how i can do that?
>
> The exclusion is specified between a trait and a set of selectors, not
> between two traits.
>
> You need to write for example:
>> Object subclass: #Myclass
>> uses: TraitGroup - {#m1 . #m2}
>
>
> If #m1 and #m2 are two methods of TraitA (i.e., defined on or acquired
> by TraitA).
>
Yes, i know Alex.
And this is awkward , because i can't control composition _indirectly_
, only directly.
The problem i want to solve is following:
A base trait (BaseTrait) provides a protocol , which implies
accessing/using some state.
This means, that trait having all methods which potential class would
have, including accessors.
But accessors is implemented as: 'self shouldBeImplemented'.
In this way, i creating an error-proof and self-documenting trait ,
because developer could clearly see
what methods should be overridden in a class which using the trait.
Now for this trait, i creating a basic class, which implemets
necessary methods by overriding some trait methods.
Object subclass: #MyBase
uses: BaseTrait
now if i make a subclass of it,
MyBase subclass: #NextClass
i know, that its already implementing a protocol of BaseTrait.
However, i want to add more things to it, because i having a:
Trait named: #CompositeTrait
uses: BaseTrait + TraitA + TraitB + ...
Next, i want to reuse the MyBase behavior by inheritance, and
CompositeTrait by using it:
Mystate subclass: #NextClass
uses: CompositeTrait
But here the problem: if i apply CompositeTrait, it will override all
of the BaseTrait methods again,
leaving no way how i can reuse the MyBase class methods, unless i'm explicitly
specify all protocol of BaseTrait for exclusion..
Which is really awkward. Just compare this:
Mystate subclass: #NextClass
uses: CompositeTrait - {#foo. #bar. #baz. ....... a list could be very long }
and this:
Mystate subclass: #NextClass
uses: CompositeTrait - BaseTrait
moreover, whenever i change the BaseTrait protocol, i would need to
revisit the NextClass declaration
again and again, instead of doing nothing :(
Of course, you could say that solution is to not include the BaseTrait
in CompositeTrait
at first place.
But i indend to do so, because in this way i'm clearly stating what
interfaces the class should support, otherwise
the only way how i would tell developer to not forget to include
BaseTrait is write in CompositeTrat comment:
'Hey, pal, if you want to use thit trait, make sure that your class
implements the BaseTrait protocol'. :)
Of course, these problems would go away if we could afford stateful
traits(aka mixins)..
Then really, there would be no need to use a class inheritance, and
all classes could be composed from traits
having an Object class as base class.
But until then, i need to use some tricks , to deal with state.
> Cheers,
> Alexandre
>
> --
> _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:
> Alexandre Bergel http://www.bergel.eu
> ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
>
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--
Best regards,
Igor Stasenko AKA sig.
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