From: Rein Henrichs <reinh@...>
Date: 2010-06-06T07:40:07+09:00
Subject: Re: comparing objects

On 2010-06-05 13:09:30 -0700, Robert Dober said:

> On Sat, Jun 5, 2010 at 8:55 PM, Rein Henrichs <reinh@reinh.com> wrote:
> <snip>
>> The Array#& operator, like its siblings, uses the #hash and #eql? methods of
>> the objects it compares. These must be the same for objects you want to be
>> considered equivalent.
>> 
> I must have made a stupid mistake in my example code, however, this is
> no reason to mess with #eql? and #hash, Be warned.
> In that case I stick with Robert's advice: Do not use Array#&, even
> MPing Array with something like #intersect_by would be preferable.
> 
> Cheers
> Robert

"Be warned"? "Do not use Array#&"? Enough of this baseless FUD. 
Understand the consequences of what you're doing, certainly, but don't 
shy away from techniques just because someone else cries wolf.

Array#& is meant to be used. Implementing #hash and #eql? in your 
classes is as normal as implementing #==, #<=> or #each. Ruby's duck 
typing is one of its most powerful features and should always be 
preferred over one-off monkey-patching. I'm afraid Robert has it 
precisely backwards.

-- 
Rein Henrichs
http://puppetlabs.com
http://reinh.com