From: Robert Klemme <shortcutter@...>
Date: 2010-06-11T01:10:06+09:00
Subject: Re: comparing objects

On 06/10/2010 05:27 PM, Rein Henrichs wrote:
> On 2010-06-10 06:59:40 -0700, Robert Dober said:
> 
>> On Thu, Jun 10, 2010 at 3:41 PM, Wilson Bilkovich <wilsonb@gmail.com> 
>> wrote:
>> Even if
>>> your code lives in isolation, ensuring proper semantics via these
>>> methods prevents a class of tricky bug that your successors may have
>>> to deal with.
>> Hmm? Would you care to show an example where overloading those methods
>> (#eql? and #hash) is needed to ensure proper behavior? I am willing to
>> learn. But I am not willing to accept this statement as such.
>> Cheers
>> R.
> 
> You have been presented with one in this very thread. The OP wants 
> objects of his class to have the correct semantics for Array#& and 
> Hash#[], etc. The correct answer is to implement #hash and #eql?, just 
> as implementing <=> provides objects of his class with the correct 
> semantics for Array#sort.

See also
http://blog.rubybestpractices.com/posts/rklemme/018-Complete_Class.html
http://blog.rubybestpractices.com/posts/rklemme/019-Complete_Numeric_Class.html

Cheers

	robert

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