From: Christoph <chr_news@...>
Date: 2002-06-14T02:05:07+09:00
Subject: Re: Relational operators redux (returning RHS)


"Austin Ziegler" <austin@halostatue.ca> wrote in
....
> is fundamentally sound (warning; the following is untested
> air-code).

Still way above my standard;-)

>
> alias :oeq, :==
>
> def == (other)
>     if other.nil?
>         false
>     elsif oeq(other)
>         other
>     else
>         false
>     end
> end

This would also imply  false == false # => false

>
> It would be necessary to replace NilClass#== with
>
> class NilClass
>     def ==(other)
>         false
>     end
> end
>
> to handle nil on the LHS.
>
> If we have the NilClass replacement and the first code in Fixnum,
> then:
>
> x = 5
> y = 6
>
> p x == x        #=> 5
> p x == y        #=> false
> p x == nil      #=> false
> p nil == x      #=> false
>
> Unfortunately, because != is simply syntactic sugar for ! (x == x),
> the != tests aren't as clean:
>
> p x != x        #=> false
> p x != y        #=> true
> p x != nil      #=> true
> p nil != x      #=> true
>
> This means that if this were to become normative behaviour, x != y
> would produce surprising results. I'm not quite sure what the proper
> answer to this is, but it's just a thought or two.
>
> As I said, I *like* the idea that nil isn't equal to anything,
> including nil.

I don't like this idea, and I am not so  sure if the C-heritage of

   nan = 0.0 / 0.0
   nan.equal? nan # => true but
   nan == nan      # => false

is really such a good idea.


/Christoph