From: Mathieu Bouchard <matju@...>
Date: 2001-08-08T17:40:54+09:00
Subject: [ruby-talk:19362] Re: Perl/Python/Ruby common backend (Parrot, can Ruby play too?)


On Wed, 8 Aug 2001, Ned Konz wrote:
> On Tuesday 07 August 2001 10:37 pm, Mathieu wrote:
> > Ruby has this thing called "mixins" that afaik is not in Python (unless
> 
> 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 

although method lookup is depth-first, when you call SUPER it does it in
the sub-hierarchy of __PACKAGE__ only, and so never backtracks past the
point where SUPER was called.

> dynamically as I've wanted it to). I could see wanting to do a breadth-first 

I'm not talking about breadth-first and I wouldn't see the advantage of
it.

> > 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.

Not sure what you mean. In Perl you can access the symbol table of a
package fairly easily, and then you can access @ISA (the superclass
list) even more easily. That's about the same amount of reflection as you
have in Ruby.

> And added the ability to smoothly make singleton classes, 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.

Now this is nice. =) I think I recall Damian briefly presenting it at
YAPC-NA-2000. (Or else he presented similar stuff)

> > 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.

Perl doesn't have the "&" slot in its messages; it only has @_ in which
$_[0] is the receiver.

> 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.

There isn't, and there could be, although it breaks some assumptions that
Ruby code (and especially C code of extensions) may have.

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

you can't. You could add this at the C level but you may have to
learn Ruby's internal "proxy classes" before (I haven't). It possibly
would break also some assumptions.

I think though that changing the class of an object and the superclass of
a class is of somewhat lesser importance when you have Ruby-style mixins.
OTOH they also can be a good complement to Ruby-style mixins, especially
if you have Object#unextend and Module#uninclude...

matju