From: Eric Hodel <drbrain@...7.net>
Date: 2006-12-27T04:53:31+09:00
Subject: Re: Hash with two identical keys?

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.

> 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

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net

I LIT YOUR GEM ON FIRE!