From: Daniel DeLorme <dan-ml@...42.com>
Date: 2006-08-09T12:13:19+09:00
Subject: Re: For Float#class why is '===' different from '=='

richB wrote:
> I appreciate the responses. I'm still puzzled. It seems that "case a"
> is different from "case a.class" and that the comparison being done by
> "===" in when is influenced by the type/class of the when operand.

Like most operators, === is just a method call. The following are equivalent:
   case a
   when b
and
   if b === a

Therefore the behavior of === depends on b. If b is a Class (e.g. Float), it's 
equivalent to a.is_a?(b). If b is a Float (e.g. 2.3), it's equivalent to b == a.

I usually view the === operator as the inclusion operator:
   b === a  ->  does b include a?

which brings me to... would there be any nasty side-effects to this?
   class Object
     def ===(other)
       if respond_to?(:include)
         self == other or include?(other)
       else
         self == other
       end
     end
   end

Daniel