From: "David A. Black" <dblack@...>
Date: 2004-08-24T12:06:48+09:00
Subject: Re: *with* block?

Hi --

On Tue, 24 Aug 2004, zuzu wrote:

> On Tue, 24 Aug 2004 11:03:23 +0900, David A. Black <dblack@wobblini.net> wrote:
> > Every assignment to a bare identifier (x = 0) is parsed as an
> > assignment to a local variable.  If you want to call a "="-style
> > method, you have to give the receiver explicitly.  So I don't think a
> > "with" keyword would add much to what you can already do with
> > instance_eval:
> > 
> >   my_obj = BoxWidget.new
> >   my_obj.instance_eval do
> >     self.x = 0
> >     self.y = 0
> >     ...
> >   end
> > 
> > which then isn't a whole lot better than my_obj.x = 0 and so on.
> > 
> > Another thing people sometimes do is:
> > 
> >   my_obj = BoxWidget.new do |bw|
> >     bw.x = 0
> >     bw.y = 10
> >     ...
> >   end
> > 
> > which can be nice because it packages the initialization with the
> > creation of the object, but of course it only works if
> > BoxWidget#initialize yields the new object.
> 
> my very first thought was of .class_eval, but "obviously"
> .instance_eval is correct.
> 
> i find this interesting because this seems to me to be the way to do
> prototype-based objects rather than class-based objects in ruby;
> similar to the Self language w/r/t smalltalk.  (though offhand i'm not
> sure how an object would get cloned before doing this modifying.)

There's not really much object modifying here, compared to what you
*can* do :-) (adding methods to individual objects, etc.)  In general
I tend to think of Ruby objects as not very class-based: once an
object has been launched into objectspace by its class, it follows a
path of its own, in which the class of origin may play a role but
which is not constrained by it.  (And of course Class objects
themselves can change.)


David

-- 
David A. Black
dblack@wobblini.net