From: Austin Ziegler <austin@...>
Date: 2002-06-14T00:09:47+09:00
Subject: Re: Relational operators redux (returning RHS)

On Thu, 13 Jun 2002 23:26:52 +0900, Martin Weber wrote:
> On Thu, Jun 13, 2002 at 11:13:03PM +0900, Austin Ziegler wrote:
>> [...]
>> In [ruby-talk:6572], Hugh says he'd probably exclude == and !=.
>> 
>> I don't honestly know the state of this proposal (there's no
>> mention of it in the Pickaxe book, which may or may not mean
>> anything), but I think it would be a very good thing, and
>> disagree that == and != should be excluded.
> Imagine == and != returned rhs:
> 
> t == nil ?
> nil == t ?
> t != nil ?
> nil != t ?

True enough. I'm not sure that simple RHS return would be good in
the event that one of the values is nil; but I think that the idea
is fundamentally sound (warning; the following is untested
air-code).

alias :oeq, :==

def == (other)
    if other.nil?
        false
    elsif oeq(other)
        other
    else
        false
    end
end

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.

-austin
-- Austin Ziegler, austin@halostatue.ca on 2002.06.13 at 10.41.47