From: Ronnie <koko@...>
Date: 2007-03-15T00:12:27+09:00
Subject: Re: Nil Comparable

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!

Thus spake the monkey