From: Charles Mills <cmills@...>
Date: 2004-08-08T00:16:11+09:00
Subject: Re: Sets are not extensional

On Aug 7, 2004, at 6:11 AM, Kristof Bastiaensen wrote:

> Hi,
>
> On Fri, 06 Aug 2004 18:08:57 +0000, Csaba Henk wrote:
>> [snip]
>> I've read the thread spawned by this post, and now I summarize that 
>> part
>> of what was written there which is relevant to my original problem, 
>> and
>> wasn't stated there explicitly.
>>
>
> I think the thread was relevant to your post, since it described
> what was causing the bug.  The following should solve the problems
> (but can be very slow for large Hashes/Sets):
>
> class Array
>   def hash
>     to_a.hash
>   end
> end
>
I think you mean:

class Hash
   def hash
     to_a.hash
   end
end

-Charlie

> Regards,
> KB
>
>> "Set" can be forced to behave extensionally by doing so:
>>
>> class Set
>>   def eql? other
>>     subset? other and other.subset? self
>>   end
>>   def hash
>>     to_a.hash
>>   end
>> end
>>
>> -- as it seems to me, Array#uniq uses *both* of eql? and hash 
>> methods, and
>> to get rid of the (IMHO pathological) behaviour illustrated by the 
>> above
>> examples, both methods need to be overwritten. Concerning the above
>> re-implementation of these methods, what I did with "hash" is just a 
>> hack,
>> of course, I don't claim that it clean or right to do so, it just
>> something which does the job.
>
>