From: Robert Klemme <shortcutter@...>
Date: 2010-06-12T01:47:16+09:00
Subject: Re: comparing objects

On 10.06.2010 18:27, Robert Dober wrote:
> On Thu, Jun 10, 2010 at 6:10 PM, Robert Klemme
> <shortcutter@googlemail.com> wrote:
> 
>> http://blog.rubybestpractices.com/posts/rklemme/018-Complete_Class.html
>> http://blog.rubybestpractices.com/posts/rklemme/019-Complete_Numeric_Class.html
> I
> You define #eql? and #hash for your convenience. So good, so bad. My
> question simply was: Show my why *not* redefining #hash and #eql? will
> cause problems, because that was Wilson's statement. I am still
> waiting :(.

The advice to implement #eql? and #hash really only makes sense if 
equivalence can reasonably be defined for a class and if instances of 
that class should be used as Hash keys or in Set.  If not at least 
equivalence can be defined other than via identity (which is the 
default) then it is perfectly reasonable to not override both methods 
and go with the default implementation.

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/