From: Ned Konz <ned@...>
Date: 2001-08-08T14:49:13+09:00
Subject: [ruby-talk:19351] Re: Perl/Python/Ruby common backend (Parrot, can Ruby play too?)

On Tuesday 07 August 2001 10:37 pm, Mathieu wrote:

> Ruby has this thing called "mixins" that afaik is not in Python (unless
> it's quite recent) and is not in Perl. In Perl you have multiple
> inheritance, but the dispatch is C++-style, so calling SUPER looks
> always upwards. Ruby backtracks in the method lookup. (Damian wants that
> in Perl6)

I don't understand what you mean. In Perl, the method lookup is first in the 
current class, and then depth-first through the @ISA (parent) list. Calling, 
say, $self->SUPER::method merely skips the current class (and only works if 
written in the namespace (package) of the class that's being defined, not 
dynamically as I've wanted it to). I could see wanting to do a breadth-first 
search through @ISA, or make SUPER work outside of the original namespace.

> Ruby also has metaclasses (singleton classes that inherit from the Class
> class). Perl doesn't even have Class objects.

We've (Toby Everett and I) added a reflection layer to Perl, at least. And 
added the ability to smoothly make singleton classes, or to adjust 
inheritance dynamically.

> Oh, Ruby also has singleton classes, which implement adding methods and
> superclasses to objects.

We did this for Perl also (see Class::Prototyped). Works fine, actually. You 
can inherit from these singleton classes and/or regular classes, and change 
the inheritance on the fly.

> Ruby has closures, which allow to modify existing variables of the
> enclosing binding. For closures there is a special slot "&" in every
> message that allows for the #each{} kind of methods.

Perl has closures, of course.

> This is a small and possibly incomplete list.
>
> OTOH, Ruby *doesn't* allow to change an object's class, unlike Perl and
> Python. The exception to that is when a object has class=Foo and
> changes to class=(new singleton class inheriting from Foo).

You know, I've been meaning to ask how to do this (change the class of an 
object). Is there something akin to Smalltalk's "become:" in which two 
objects swap identities? That's one way to do this, of course.

Also, how can one change the superclass of an existing class in Ruby?

-- 
Ned Konz
currently: Stanwood, WA
email:     ned@bike-nomad.com
homepage:  http://bike-nomad.com