On Tue, 20 Apr 2004, Luke Palmer wrote:
> John Williams writes:
> > On Tue, 20 Apr 2004, Luke Palmer wrote:
> > > There. Now here's the important part: in order to *use* all this, you
> > > import whatever module defines it, and then say:
> > >
> > > class Dog {
> > > method foo (?$arg) is accessor {
> > > # accessor code here
> > > }
> > > }
> > >
> > > If that's not easy enough for you, well, you're probably out of luck.
> >
> > It would be even easier if we could put the read-accessor-code and
> > write-accessor-code in different methods.
> >
> > class Dog {
> > multi method foo { ... }
> > multi method foo ($arg) is accessor { ... }
> > }
>
> Ugh! That's what I originally suggested, and it was shot down it was.
>
> My first solution to your problem introduced the traits C<get> and
> C<set>, allowing you to write it like this:
>
> class Dog {
> method foo ()
> will get { ... }
> will set { ... }
> { } # usually empty
> }
>
> I guess I bogged down that message with the implementation, so the
> result may have been easy to miss.
Well, I think we've come full circle. The get/set is the same as the
presumed current implementation, just with different keywords:
class Dog {
has $.foo
will FETCH { ... }
will STORE { ... }
;
}
I'm not saying there is anything wrong with that, but John Siracusa is
asking for something different, I think. A simple accessor which looks
like a method without having to play with Proxy, FETCH, STORE, etc.
If it still looks like $obj.foo = 1 outside the class, that's good too.
(Delphi and C# can do it; why can't we?)
Getting the multi-methods foo()/foo($) to automagically act as the
reader/writer for a virtual foo attibute seems like it would fulfill
his requirements. foo() already works for the reader, but foo($) needs
some help to make $obj.foo = 1 call $obj.foo(1).
Here's a feeble attempt to do what I suggested:
role accessor {
has $.accessor = 1;
multi sub trait_auxiliary:is( accessor $trait, &meth(Any) ) {
my $class = &meth.meta.class;
class $class is extended {
# class methods take precedence, so install a method
# in the class "is default" so it gets called first
multi method $meth.meta.name () is default {
return my $proxy is Proxy (
STORE => { &meth($^val) },
FETCH => {
my ($reader) =
grep !$_.meta.default ,
$class.meta.getmethods;
&$reader;
},
);
}
}
$meth does accessor;
}
}
class Dog {
multi method foo { ... }
multi method foo ($arg) is accessor { ... }
}
my Dog $spot;
$spot.foo++;
~ John Williams
