RE: A12: default accessors and encapsulation

[Austin Hastings]

> -----Original Message-----
> From: Aaron Sherman [mailto:[EMAIL PROTECTED]
> Sent: Friday, 23 April, 2004 03:12 PM
> To: John Siracusa
> Cc: Perl 6 Language
> Subject: Re: A12: default accessors and encapsulation
>
>
> On Tue, 2004-04-20 at 10:13, John Siracusa wrote:
> > On 4/19/04 7:20 PM, Larry Wall wrote:
> > > On Mon, Apr 19, 2004 at 06:53:29PM -0400, John Siracusa wrote:
> > > : Yeah, that's exactly what I don't want to type over and over :)
> > >
> > > I really don't understand what you're getting at here.  First you
> > > complain that you'd rather write an ordinary method, and then you
> > > complain that you have to.  Have I met someone lazier than me?  :-)
> >
> > Possibly :)  Here's what I'm saying.  In the first version of a
> class, there
> > will probably be a lot of simple get/set attributes.  It's
> convenient not to
> > have to write any explicit methods for those.
> >
> > If I accept the default accessors that you get "for free" when
> a class  "has
> > $.foo is rw", then that means the users of my class can do $obj.foo =
> > whatever in order to set the foo attribute.
>
> And if you override the accessor, you can:
>
>       multi method foo(Str $blah = undef) is rw($new) {
>               (my($old),$.foo)=($.foo,$blah//$new);
>               .update_the_world_in_some_cool_way();
>               return $old
>       }

I don't understand this.

What's the $new doing?

And if you've only got one of them, do you need multi, or just an optional
argument?

method foo(Str ?$new) is rw {
  my $old = $.foo;
  if (defined($new)) {
    $.foo = $new;
    .update_the_world();
  }
  return $old;
}