From: Hugh Sasse <hgs@...>
Date: 2005-09-15T01:54:16+09:00
Subject: Re: Sets, uniqueness not unique.

On Thu, 15 Sep 2005, Christian Neukirchen wrote:

> This seems to be the canonical way to define compund hashes:
>
> class Student
>  def hash
>    [@forename, @surname, @birth_dt, @picture, @coll_status].hash
>  end
> end

That does seem to preserve the properties I need for strings, and is
probably cheaper than MD5sums.
>
         [...]
>
> Set uses a Hash to store the objects.
>
> That said, I think it would be nice to have something along this in
> the stdlib:
>
> class Student
>  equal_compares :@forename, :@surname, :@birth_dt, :@picture, :@coll_status
> end
>
> Above call should result in appropriate definitions of ==, eql? and

I don't know how it could know how to create the different
definitions correctly given a completely open spec as to what the
vars are.

> hash.  (Something like "ordered_by" would be pretty useful too.)

I think that could be tricky too.
>
Thank you.
         Hugh