From: Guillaume Marcais <guslist@...>
Date: 2003-06-27T22:37:51+09:00
Subject: Re: Using & for arrays of objects

On Fri, 2003-06-27 at 07:26, nobu.nokada@softhome.net wrote:
> Hi,
> 
> At Fri, 27 Jun 2003 09:48:56 +0900,
> Krishna Dole wrote:
> > I'm having trouble using the & (intersection) method on two arrays of
> > objects. I know that if the objects don't have comparison methods, & won't
> > work because it is looking at the object IDs rather than values stored in
> > the objects, but I can't seem to get & to use the comparison methods I want.
> 
> Array#& uses Hash internally due to performance, so you need to
> define #hash and #eql? methods.
> 
> -- 
> Nobu Nakada
> 

I barely dare asking this because I know how tedious of a task
maintaning documentation is. Nevertheless, could it be made clearer
throughout the documentation what equality operator (hash/eql? or ==) a
method relies on. It is not the first time I see confusion about it and
I am a little confused myself from time to time.

Just looking at the Array class, at least the following methods rely on
an equality operator of its elements:

-, &, delete (with no block), uniq, uniq!, eql?, <=>, ==, include?,
index, rassoc, rindex.

The methods from eql? on already specify which equality operator is
being used.

Thanks in advance,
Guillaume.