From: Robert Klemme <shortcutter@...>
Date: 2006-08-01T20:45:06+09:00
Subject: Re: Weird elusive bug using Comparable

Pedro C�rte-Real wrote:
> On 7/31/06, Robert Klemme <shortcutter@googlemail.com> wrote:
>> > I thought date1 == date2 was the same as (date1 <=> date2> == 0 but
>> > apparently not.
>>
>> No, it's differently implemented.
> 
> How then? According to the docs if you implement <=> and include
> Comparable you get ==. But my second assertion is failing when it
> should be blowing up when trying to do nil <=> nil.

You get == but if you implement it yourself your version will shadow the 
one from Comparable:

 >> class Foo
 >> def <=>(o) 0 end
 >> include Comparable
 >> end
=> Foo
 >> Foo.instance_method :==
=> #<UnboundMethod: Foo(Comparable)#==>

Now we add it to Foo:

 >> class Foo
 >> def ==(o) false end
 >> end
=> nil
 >> Foo.instance_method :==
=> #<UnboundMethod: Foo#==>
 >> Foo.ancestors
=> [Foo, Comparable, Object, Kernel]

Kind regards

	robert