From: "David A. Black" <dblack@...>
Date: 2005-08-12T07:22:19+09:00
Subject: Re: NEWBIE QUESTION: pattern with nil

Hi --

On Thu, 11 Aug 2005, Austin Ziegler wrote:

> The problem, as others have stated, is that adding #empty? to
> NilClass implies a containment. I'd have as big a problem if we
> added #empty? to Fixnum so that 0 returned true and everything else
> returned false. (Indeed, would that be correct? Would -3.empty? be
> true or false?)

I'd say it's undefined, or just meaningless.  One could say that -3
"contains" three -1's... but I don't find that compelling.  It could
be said, equally (and equally wrongly, in my view), to "contain" a 5
and a -8.

I don't consider something a container unless there's some meaning to
the concept of inserting, removing, counting, iterating over elements.
Even in the case of, say, a frozen array, there's still a meaning to
the concept of altering the collection.  You can't remove a 1 from 3.
You can subtract 1 from 3, but that doesn't change 3.  If it were
otherwise, then the expression "3 - 1" would turn 3 into 2, which
would cause lots of problems :-)

I would say that propagating the notion of emptiness to
non-collections definitely isn't the way to address nil-related
issues.


David

-- 
David A. Black
dblack@wobblini.net