From: Vincent Fourmond <vincent.fourmond@9online.fr>
Date: 2006-12-20T04:47:31+09:00
Subject: Re: what exactly does obj.is_a?  do?

Jon Garvin wrote:
> I've got a theory that I hope someone familiar with the deep recesses of
> Ruby's internals can confirm or deny.
> 
> According to the API, obj.is_a?     "Returns true if /class/ is the
> class of /obj/, or if /class/ is one of the superclasses of /obj/ or
> modules included in /obj/."
> For the purpose of this question, the only part I'm concerned with is
> "Returns true if /class/ is the class of /obj/", so let's ignore the rest.//
> 
> My theory is that Ruby is simply returning the result of...
> 
> @my_obj.class.object_id == Klass.object_id
> 
> when I do...
> 
> @my_obj.is_a?(Klass)

  No: is_a? also returns true when the @my_obj is an instance of a
subclass of Klass.

> (Don't forget we're ignoring the superclass and module stuff it does).
> 
> Can anyone confirm or deny this?
> 
> I'd also appreciate a hint pointing me to where I could have dredged up
> the answer to this one on my own.   Thanks, and happy holidays!

  If you do

ri is_a?

  on command-line, you'll get immediate answer.

	Vince

-- 
Vincent Fourmond, PhD student
http://vincent.fourmond.neuf.fr/