From: ara.t.howard@...
Date: 2007-03-14T22:59:12+09:00
Subject: Re: Nil Comparable

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
-- 
be kind whenever possible... it is always possible.
- the dalai lama