From: David Simmons <pulsar@...>
Date: 2001-10-27T04:53:58+09:00
Subject: [ruby-talk:23508] Re: Overriding #== [numeric operators; hashing and comparison; binary selector

"Dave Harris" <brangdon@cix.co.uk> wrote in message
news:memo.20011026202623.39899C@brangdon.madasafish.com...
> pulsar@qks.com (David Simmons) wrote (abridged):
> > I suggest, taking it from SmallScript, that object-equivalence #(==~) is
> > what you are looking for.
>
> I read that name as saying, "approximately identical to", which is not
> what I am looking for. I want "identical to", in the same way that #=
> means "equal to". In my view both notions make sense at base-level (ie
> non-MOP level).
>
> #== is a natural name for the function I want, by analogy with #=. If
> there is to be some MOP test, perhaps it should be given the strange name,
> perhaps #basicIdentical:.
>
>
> >        hash/compare op correspondence
> > ---    ------------------------------
> > MOP    #basicHash (corresponding to [MOP] #==) [aliased as #identHash]
> > USER   #identEquivHash (corresponding to #==~) [not in QKS Smalltalk]
> > USER   #hash (corresponding to #= and #==~)
> > USER   #equivHash (corresponding to #=~)
>
> How can #==~ correspond to both #hash and #identEquivHash?

The second (#==~) associating it with #hash was my cut and paste goof.

However, as a folding function, any "weaker" hash function will do.

    #equivHash, #hash, #identEquivHash will all work for:
        #== or #==~

    #equivHash, #hash will all work for:
        #=

You just get a smaller distribution set.

-- Dave S. [www.smallscript.org]

>
>   Dave Harris, Nottingham, UK | "Weave a circle round him thrice,
>       brangdon@cix.co.uk      |   And close your eyes with holy dread,
>                               |  For he on honey dew hath fed
>  http://www.bhresearch.co.uk/ |   And drunk the milk of Paradise."