From: Bill Kelly <billk@...>
Date: 2002-08-13T10:47:45+09:00
Subject: Re: class === class often false?

Hi Hal,

From: "Hal E. Fulton" <hal9000@hypermetrics.com>
>
> From: "Bill Kelly" <billk@cts.com>
> 
> > I'm just noticing that some classes return true when testing 
> > themselves with #===, while others return false.  For instance:
> > 
> > (ruby 1.6.6 (2001-12-26) [i586-mswin32])
> > irb> Bignum === Bignum
> > false
> > irb> Kernel === Kernel
> > true
> > irb> Object === Object
> > true
> > irb> Comparable === Comparable
> > false
>
[...]
> Then note that there is some circularity in Ruby's
> object paradigm. Everything is an object. Even the
> class Class is an object. Note that these are 
> both true:
> 
>   Class.is_a? Object
>   Object.is_a? Class
> 
> I have spent many hours lying in bed thinking about
> this. :)

:-)

> I think the cases where you're getting a "true" for
> "klass === klass" are the ones where the circularity
> is asserting itself.
> 
> For example: Kernel is-a Object, but Object is-a Kernel.
> Or more indirectly: Kernel is-a Module is-a Object is-a 
> Kernel. There are probably other paths (through Class, 
> which is-a Module).
> 
> For the cases where you get false, I can't see any
> way of tracing back to oneself. For example, Bignum
> is-a Object, or is-a Class, or is-a Kernel... but these
> don't ever lead back to Bignum.
> 
> Help any?

Interesting... further tests in irb seem to support your
hypothesis.

Thanks!  . . . Actually what I finally realized was that
Ruby was already doing what I wanted in case statements.
I'm dealing with an instance, so === doing is_a? is just
what I want after all.  I had been trying:

  case some_instance.class
    when Bignum
  etc.

Where I can simply do (of course)

  case some_instance
    when Bignum 
  etc.

Which is great (as usual.)

Regards,

Bill