Hi Mariano, when I read this thread I was a bit confused that you wanted an IdentitySet that used #hash. From that statement it sounded like you just wanted a Set. This would allow any object to define its own hash and importantly what equality means with #=. So if you want to delegate that to the object use a Set.

However as the thread has gone on perhaps you want the identity relationship but you just wanted a bigger identity hash space?

IdentitySets are fast because they bypass any delegation. Once you have seen the object in your traversal (common usage pattern) that's it. You grab it's identity which is a pretty low level thing to do.

As for what happens with collections who knows. Depends. Relying on identity set semantics for a collection is easy. Set semantics is not so. Remember that both hash and equals are important to know if the set already contains the element. Depending on the collection implementation both of these could be composite in terms of the parts. Who knows where you end or how long it takes. I.e. if it is a function of the size of the collection and further collections are composite....

Cheers
Mike

On Tuesday, December 13, 2011, Carlo <snoobabk@yahoo.ie> wrote:
> Hi Mariano
> I'm no expert either ;)
> Without having access to the exact code it would look like either you have a collection that references itself (which would break all collection implementations) or maybe the tests have just slowed down to the point where you think it's 'crashed'.
> Do you have anymore info or perhaps which methods you changed on IdentitySet?
> Cheers
> Carlo
> On 13 Dec 2011, at 1:57 AM, Mariano Martinez Peck wrote:
>
>
> On Tue, Dec 13, 2011 at 12:32 AM, Mariano Martinez Peck <marianopeck@gmail.com> wrote:
>>
>>
>> On Mon, Dec 12, 2011 at 1:56 PM, Carlo <snoobabk@yahoo.ie> wrote:
>>>
>>> Hi
>>> Wouldn't the fact that you use hash cause potential loops now? e.g. collection refers to another object that refers to first collection. --> aCollection>>hash references an item which causes this current collection's hash to be called again?
>>
>> Hi Carlo. I am still newbie with Collections but I think I am having exactly that problem. During my tests, it loops in Collection >> #hash� when sending #hash to its elements.
>> Sorry, but I couldn't undertand what is the cause of the problem?� why it doesn't work while it does using #identityHash?� could you elaborate?
>>
>
> Well, now I understood, and I understand also why it doesn't happen with #identityHash. But what happens then with regular Dictionaries using #hash? why it doesn't happen there?
> �
>>
>> thanks
>> �
>>>
>>> identityHash is deterministic in this case.
>>> Does this help?
>>> Cheers
>>> Carlo
>>> On 12 Dec 2011, at 10:58 AM, Mariano Martinez Peck wrote:
>>> Hi guys. I hope this is not a very stupid question. Background: in Fuel we have a IdentityDictionary where we put each of the objects we find while traversing the graph. We need to use IdentitySet because we cannot have repetitions (and to avoid loops) so we NEED to use #==. In such dictionary we put ALL objects of the graph, so it can be very big. Since IdentitySet uses #identityHash, it means it will be using those ONLY 12 bits in the object header. It means that we have 2^12 = 4096� different values.�
>>>
>>> Question:� having explained the previous, I wanted to be able to use #hash rather than #identityHash since several classes implement #hash and hence I thought that using #hash I could have less colisions and hence a better performance. I tried to make a subclass of IdentitySet that uses #hash rather than #identityHash but my image freezes. I also tried something like:
>>>
>>> set := PluggableSet new.
>>> �� set hashBlock: [ :elem | elem hash ].
>>> �� set equalBlock: [ :a :b | a == b ].
>>>
>>> But it doesn't work either. I works with simple tests in a workspace but when I run the full tests of Fuel, it enters in a loop in the method #hash of Collection..
>>>
>>> Anyway, my question is, should that work? if not, what is the exact reason?
>>>
>>> Thanks in advance,
>>>
>>> --
>>> Mariano
>>> http://marianopeck.wordpress.com
>>>
>>>
>>
>>
>>
>> --
>> Mariano
>> http://marianopeck.wordpress.com
>>
>
>
>
> --
> Mariano
> http://marianopeck.wordpress.com
>
>
>