From: Jean-Hugues ROBERT <jean_hugues_robert@...>
Date: 2004-04-08T06:38:25+09:00
Subject: Re: IdentityHash, like Hash but with keys using equals? vs eql?

At 05:58 08/04/2004 +0900, you wrote:
>Jean-Hugues ROBERT (jean_hugues_robert@yahoo.com) wrote:
>
> > I just encountered a rare case where I need a Hash where keys
> > are object id. Class Hash compares keys by value. As a result
> > two different String with the same value are considered the
> > same key. This is fine in most cases. But right now I need to
> > be more restrictive and I need two String objects to be treated
> > as two keys even if they have the same value.
>
>Not entirely true.
>
>Hash uses #hash and #eql? to decide how to store entries.  Some objects
>(String) implement #hash, but by default Ruby uses #object_id for #hash:

Thanks for the clarification.

> > I think IdentityHash is a probable name for such a beast, yet
> > I could not find one in Ruby and I don't see any method in
> > class Hash that I could redefine in a derived class to change
> > the way keys are compared.
>
>How about instead extending Strings you want stored uniquely to return
>#object_id for #hash?

Would be OK if my IdentityHash were to contain strings only. But I
need to put arbitrary objects in it.

BTW: I need that to detect "true" circular paths when walking a tree/graph.
Rigth now I detect false circulars when nodes' values compare equal
where in fact it is two different node objects (with the same "value").

Thanks.

Jean-Hugues



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