From: Paul Brannan <pbrannan@...>
Date: 2004-06-18T23:49:56+09:00
Subject: Re: How to make generic #== method?

On Fri, Jun 18, 2004 at 10:15:44AM +0900, Joel VanderWerf wrote:
> One way I've done it is this:
> 
> module ContentEquality
>   def hash
>     content.hash
>   end
> 
>   def eql?(other)
>     content.eql? other.content
>   end
> 
>   def ==(other)
>     # self.class == other.class and # optional
>     content == other.content
>   end
> end

I like this, and since content is ordered, it's possible to write this
too:

module ContentEquality
  def <=>(other)
    content.each_with_index do |member, idx|
      result = member <=> other.content[idx]
      return result if result != 0
    end
    return 0
  end

  include Comparable
end

The only thing I don't like is that content doesn't carry any
information about what it holds, so it's entirely possible to
inadvertently compare apples and oranges.

Paul