From: Jason Creighton <androflux@...>
Date: 2003-07-21T08:17:48+09:00
Subject: Re: chaining comparisons

On Sun, 20 Jul 2003 14:22:37 +0900
Joel VanderWerf <vjoel@PATH.Berkeley.EDU> wrote:

> Jason Creighton wrote:
> > On Sat, 19 Jul 2003 14:58:51 +0900
> > "Kurt M. Dresner" <kdresner@cs.utexas.edu> wrote:
> > 
> > 
> >>When I learned python I was overjoyed that I could evaluate 1 < 2 < 3
> >>and get "true".  I just realized that you can't do that in Ruby.  Is
> >>there a reason why?  Is it good?  I know I can use "between", but
> >>still...
> > 
> > 
> > http://www.rubygarden.org/article.php?sid=286
> > 
> > So basically, it's because it's hard to implement, even more so because
> > true/false/nil are singleton objects. (So you can't, for instance, save state
> > in a particular instance of 'true', because there's only one.)
> 
> As you say, there is only one true; but you still can save state in it:
> 
> irb(main):001:0> true.instance_eval {@x = 1}
> 1
> irb(main):002:0> true.instance_eval {@x}
> 1
> 
> Not that it's relevant to the 1 < 2 < 3 discussion, but it's kinda cute...

Yeah, it is kinda cute. How does that work? It works for Fixnum objects,
too.....

>> (0..16).each { |n| n.instance_eval { @square = n*n } }
=> 0..16
>> 5.instance_eval { @square }
=> 25

How can that work when Fixnum is stored in VALUE? And that's another thing:
VALUE is either an immediate value (Fixnum/true/false/nil) or a pointer to an
object. Doesn't that mean there's only 31 bits (on 32 bit machins) available
for the pionter? How can that work? I always thought that pointers would have
to be able to cover the whole address space....

Jason Creighton