From: Trans <transfire@...>
Date: 2006-12-27T05:09:30+09:00
Subject: Re: Hash with two identical keys?


Eric Hodel wrote:
> On Dec 26, 2006, at 11:22, Trans wrote:
> > Trans wrote:
> >> thanks Ara and Jon,
> >>
> >> I see what your saying. I was using #== not #eql? in comparing the
> >> keys. So I see why it's faling now. How do I get aorund this? I'm
> >> caching object based on therr initialization paramaters, which has to
> >> be an array. Is there a simpler way or do I have to do something
> >> like:
> >>
> >>   class Parameters < Array
> >>     alias :eql? :==
> >>   end
> >
> > Ugh. Nothing like that works either. It's not using eql? or equal?,
> > but
> > rather #hash (I guess that's actually what you were trying to say
> > Ara).
>
> A Hash only asks if one object is #eql? to another when they have the
> same #hash.  You can't use a Hash as a Hash key because Hash#hash is
> not implemented that way.

I see. So it's not using object_id but

  a.hash == b.hash && a.eql?(b)

Is that right?

> > This doen't make any sense to me. Why do identical strings and arrays
> > have the same #hash value but not hashes?
>
> Likely because:
>
> s = ''
> s.hash
>
> and:
>
> a = []
> a << a
> a.hash
>
> are easier to compute than:
>
> h = {}
> h[h] = h
> h.hash

Hmm... the expection gums up the works.

T.