From: Robert Klemme <bob.news@...>
Date: 2004-08-06T19:11:26+09:00
Subject: Re: Sets are not extensional


"Charles Mills" <cmills@freeshell.org> schrieb im Newsbeitrag
news:2B60D928-E751-11D8-AF77-000A95A27A10@freeshell.org...
>
> On Aug 5, 2004, at 6:41 PM, George Ogata wrote:
>
> > Kristof Bastiaensen <kristof@vleeuwen.org> writes:
> >
> >> {}.hash == {}.hash
> >> => false
> >> Set[].hash == Set[].hash
> >> => false
> >> [].hash == [].hash
> >> => true
> >>
> >> I have no idea for the reason why different hashes have different
> >> hashvalues, while different arrays may get the same value (based on
> >> the
> >> contents of the array).
> >
> > This seems like a blatant bug to me.  `a.eql? b' must imply `a.hash ==
> > b.hash', yet:

Yes, this issue has come up before IIRC.  Maybe Matz did something about
this but it's not included in a release version.

> I agree:
>  > a = {} #=> {}
>  > a.hash #=> 1650134
>  > a.id #=> 1650134
>  > b = {} #=> {}
>  > b.hash #=> 1639814
> # So hash on an empty hash returns the objects id....
>  > a = {"a"=>"b"} #=> {"a"=>"b"}
>  > a.hash #=> 1682094
>  > a.clear #=> {}
>  > a.hash #=> 1682094
> # Looks like no two hashes hash to one another...
> # Here is the reason
> /* in object.c */
>      rb_mKernel = rb_define_module("Kernel");
>      rb_include_module(rb_cObject, rb_mKernel);
> /* ..snip.. */
>      rb_define_method(rb_mKernel, "object_id", rb_obj_id, 0);
> /* in hash.c the "hash" method is never overridden.  So rb_obj_id() is
> the "hash" method for hashes. */

Where do you take that conclusion from?  From the source quotes you name,
there is no indication of a connection between #hash and #id.  And you're
showing code for Kernel which is unrelated to this thread.  The only
conclusion so far is, that Hash#hash is Object#hash (because it's not
overridden as you state) and thus can't take into account the contents of
the Hash.  Can you please clarify this?

Kind regards

    robert