From: Christoph Rippel <crippel@...>
Date: 2001-03-20T09:39:43+09:00
Subject: [ruby-talk:12894] Hash-Hash - behavior clarification?

Hi,

I have been investigating and using Hash-Hashes and their behavior
completely defied my understanding of them. Quote from Dave's and 
Andy's book ..
 
`` 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

As a consequence it's impossible to form Hash-Hashes - for example
(Ruby syntax rules do allow something like {{1=> 1} => {1 =>1}} )

e = {}; h = {}           
p ({ e => 1 } == {f => 1}) # => false 

This would be easy to fix with something like (un-efficient and 
recursion unprotected - note the internal Hash implementation  
ignores this ``corrected'' hash #method.) 

class Hash
def hash
	res = 0
	each do |l,r| 
		res = (l.hash<<1)  + r.hash  + 1 
     end
    res
 end   
end

My guess is that this was not done on purpose but figured
I ask anyway if the semantically incorrect #hash Hash method
is here to stay? 

Christoph