From: Christoph Rippel <crippel@...>
Date: 2001-03-20T13:34:41+09:00
Subject: [ruby-talk:12908] Re: Hash-Hash - behavior clarification?

> From: dave@thomases.com [mailto:dave@thomases.com]On Behalf Of Dave
[...]
> > `` Generates a Fixnum hash value for this object. This function must
> > have the property that a.eql?(b) implies a.hash == b.hash.... The
> > hash value is used by class  Hash. ...''
> > 
> > I finial realized that the #hash method of the Hash class it-self 
> > violates this  behavior it is simply id-based ...
> > 
> > h.hash == h.id # => true for any Hash object
> 
> While I agree that this may be unfortunate, in what way does having
> h.hash defined as h.id violate the rules? (If our statement is wrong
> I'd like to fix it).

It violates the rules because of

a = {}; b = {};
p a.eql? b          # => true , but
p a.hash == b.hash  # => false

Pointing out that the Hash Class itself is a notable exception from
this rule is probably enough - my guess is that Matz did not want to  
bother implementing a ``correct'' hashing scheme because of 
efficiency reasons. 
 

Christoph
[...]