Larry Wall wrote:
> Jonathan Lang wrote:
> : In a similar vein, what about making a disjunction of classes in an
> : C<is> or C<isa> clause synonymous with a sequence of appropriate
> : clauses? Ditto with traits and C<is>, roles and C<does>, attributes
> : and C<has>, etc.; thus:
> :
> : class DangerousPet does Pet & Predator {
> : }
> :
> : would be the same as
> :
> : class DangerousPet does Pet does Predator {
> : }
>
> Depends on how you look at it. A DangerousPet is something that can
> act like either a Pet or a Predator, or both. Sometimes you want &
> and sometimes you want |. (Of course, a lawyer will tell you that
> "and" and "or" mean the same thing in a legal document.) I suppose
> there could even be some sense in
>
> class DangerousPet does Pet ^ Predator {
> }
>
> meaning it can be a Pet or a Predator but not both at the same time.
> Of course, that probably means that you can't actually have any
> objects of type DangerousPet. Or maybe it does, but you can't call
> any ambiguous DangerousPet methods without casting to either Pet or
> Predator. Hmm...
Since disjunctions are unambiguous in their membership, this isn't a
problem for them; only for disjunctions, ajunctions, and (horrors!)
injunctions. Admittedly, a class that C<is> an ajunction of classes would
be a cute way of creating something conceptually akin to a C union.
I could see practical uses for the disjunctive forms; even there, I'm not
sure that the coding required to make the compiler handle things would be
worth the time invested - but it just might be. I'm even less sure when
it comes to the other kinds of junctions.
> That would mean that C<does> implies a constraint test on typeof($self)
> rather than classof($self). (Presuming typed refs in the first place,
> of course.)
OTOH, C<is>, C<does>, and C<has> are declarative in nature, not
predicative; it's much like assignment vs. equality.
=====
Jonathan "Dataweaver" Lang
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