From: Robert Dober <robert.dober@...>
Date: 2007-03-15T07:26:49+09:00
Subject: Re: Nil Comparable

On 3/14/07, Ronnie <koko@rpg-free.com> wrote:
> ara.t.howard@noaa.gov wrote:
> > On Wed, 14 Mar 2007, Trans wrote:
> >
> >> Does anyone see anything problematic about this?
> >>
> >>  class NilClass
> >>
> >>    include Comparable
> >>
> >>    def <=>(x)
> >>      x.nil? ? 0 : -1
> >>    end
> >>
> >>    def succ; nil; end
> >>
> >>  end
> >>
> >> It seems benign enough, and can be used to represent "always before".
> >> For instance, in Rake there is a class called EarlyTime: "EarlyTime is
> >> a fake timestamp that occurs before any other time value." And that's
> >> all that it does. If NilClass were comparable per the above then
> >> EarlyTime would not be needed.
> >
> > it could mask errors like
> >
> >   [42, nil].sort
> >
> > depending on the order of comparison it may or may not work since we
> > might get
> >
> >   42.send '<=>', nil
> >
> > or
> >
> >   nil.send '<=>', 42
> >
> > so it's a bit different in that it's weakly typed where as the
> > EarlyTime class
> > is strongly typed - it'll only compare with other times
> >
> > still - it __is__ handy.  if you search the archives i've suggeted that
> > -Infinity and Infinity have these kinds of properties wrst numerics a few
> > times.
> >
> > cheers.
> >
> > -a
> The Facets library includes all of the above-mentioned features of
> usefulness.
> http://facets.rubyforge.org/
> There are a lot of other extensions to the Ruby core in it, and they can
> mostly be included in small chunks, so they are easy to use.
> I hope this helps!
Well I guess Tom knows about Facets Ronnie :)
http://rubyforge.org/projects/facets/
as you might know this link :).
>
> Thus spake the monkey
>
>
It must be quite rewarding though to get pointed to your own project I
would love that ;)

Cheers
Robert
-- 
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw