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Re: Roles and Mix-ins?
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From:
Joe Gottman
Date:
January 6, 2004 20:08
Subject:
Re: Roles and Mix-ins?
Message ID:
005f01c3d4d4$17304320$42404a18@carolina.rr.com
----- Original Message -----
From: "Luke Palmer" <fibonaci@babylonia.flatirons.org>
To: "Joe Gottman" <jgottman@carolina.rr.com>
Cc: "Perl6" <perl6-language@perl.org>
Sent: Tuesday, January 06, 2004 9:34 PM
Subject: [perl] Re: Roles and Mix-ins?
> Joe Gottman writes:
> >
> > ----- Original Message -----
> > From: "Luke Palmer" <fibonaci@babylonia.flatirons.org>
> > To: <perl6-language@perl.org>
> > Sent: Tuesday, January 06, 2004 4:51 AM
> > Subject: [perl] Re: Roles and Mix-ins?
> >
> >
> > > David Storrs writes:
> > > >
> > > > On Sat, Dec 13, 2003 at 11:12:31AM -0800, Larry Wall wrote:
> > > > > On Sat, Dec 13, 2003 at 04:57:17AM -0700, Luke Palmer wrote:
> > > >
> > > > > : For one, one role's methods don't silently override another's.
> > Instead,
> > > > > : you get, er, role conflict and you have to disambiguate
yourself.
> > > >
> > > > How do you disambiguate?
> > >
> > > Let's see...
> > >
> > > role Dog {
> > > method bark() { print "Ruff!" }
> > > }
> > > role Tree {
> > > method bark() { print "Rough!" }
> > > }
> > > class Trog
> > > does Dog does Tree {
> > > method bark() { .Dog::bark() }
> > > }
> > > }
> > >
> > > Perhaps something like that. In any case, you do it by putting the
> > > offending method directly in the aggregating class.
> > >
> >
> > How about something like
> > class Trog
> > does Dog {bark=>dogBark} does Tree {bark=>treeBark}
> > {...}
> >
> > Then we could have code like
> > my Trog $foo = Trog.new();
> > my Dog $spot := $foo;
> > my Tree $willow := $foo;
> > $spot.bark(); # calls dogBark()
> > $willow.bark(); #calls treeBark()
> >
> > This works better when Dog::bark and Tree::bark are both needed but
they
> > do different things.
>
> Renaming methods defeats the purpose of roles. Roles are like
> interfaces inside-out. They guarantee a set of methods -- an interface
> -- except they provide the implementation to (in terms of other,
> required methods). Renaming the method destroys the interface
> compatibility.
>
> Your renaming can be done easily enough, and more clearly (IMO) with:
>
> class Trog
> does Dog does Tree {
> method bark() { ... } # Explicitly remove the provided method
> method dogBark() { .Dog::bark() }
> method treeBark() { .Tree::bark() }
> }
But won't explicitly removing bark() from the class also disable
Dog::bark() and Tree::bark() for the class? Renaming would work if other
methods in Dog are directed to dogBark() when they call bark(), and other
methods in Tree are redirected to treeBark().
Joe Gottman
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