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Re^2: Solving compositional problems with Perl 6 roles

by Ovid (Cardinal)
on Aug 22, 2004 at 14:41 UTC ( #384926=note: print w/ replies, xml ) Need Help??


in reply to Re: Solving compositional problems with Perl 6 roles
in thread Solving compositional problems with Perl 6 roles

Well, it depends. If you are using roles, there are a couple of ways of resolving conflicts, but basically it works out as:

class Elf is Character does Thief does Scout { method hide { .Scout::hide(@_) } ... }

However, if you prefer, you can have your cake and eat it too.

method hide ($self: $action) { # $self is required here because the topicalizer assigns # $action to $_ given $action { when Skulking { $self.Thief::hide($action) } when Stalking { $self.Scount::hide($action) } } }

And that's nice because theoretically, if your elf knows various professions, she should know how the activities with those professions vary, just as one person might know how to drive a race car but wouldn't think of doing that with a dump truck, even though both activies are driving.

Unfortunately, when it comes to your specific example with mixins, I'm a little less clear about disambiguation. When you use a role at runtime on an instance, you get new anonymous classes that are related to the instance via inheritance. Thus, the following has the inheritance ordering problem again:

$elf does Thief does Sentry;

In that example, $elf.hide calls Sentry.hide as Thief.hide is further up the inheritance tree. This seems to limit the utility of mixins, but I can't be sure. Further clarification would be nice.

Cheers,
Ovid

New address of my CGI Course.


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Re^3: Solving compositional problems with Perl 6 roles
by Velaki (Chaplain) on Aug 22, 2004 at 15:46 UTC

    Ultimately, it appears that the crux of the matter is defining what is a behavior vs. what is a trait.

    A thief IS a Character who "implements/HAS" the behavior/interface of methods associated with "thieving". An Elf is a Character who IS a type of Character, who HAS certain additional traits.

    It's all going to come down to whether you think of the character as an "elf type-of thief," or a "thief type-of elf." This will determine which is the child class by inheritance, and which is the child by "mix-in".

    Just some thoughts,
    -v
    "Perl. There is no substitute."
      Would be nice to NOT know whether $stranger is an "elf type-of thief" or "thief type-of elf" and be able to do this:
      # ".?" means "call if the obj CAN the method" acc. to Apoc12 $stranger.?steal; $stranger.?shoot_arrows;
      and expect DWIMming (doing both things in both cases). That's the whole point of polymorphism, is it not? :)

      Update: upgrade perl5 syntax to perl6 (Apoc12).

Re^3: Solving compositional problems with Perl 6 roles
by kappa (Chaplain) on Aug 23, 2004 at 12:39 UTC
    Your interesting node made me reread the Apocalypse. I stand admired (again) and await being able to call ALL the matching methods from all the roles of my little elf (via $elf.*hide) or even choose which ones I like to skip.

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