On Oct 9, 2015, at 7:51 AM, Henrik Johansen <henrik.s.johansen@veloxit.no> wrote:
On 09 Oct 2015, at 4:33 , Esteban Lorenzano <estebanlm@gmail.com> wrote:
On 09 Oct 2015, at 16:21, Gabriel Cotelli <g.cotelli@gmail.com> wrote:
If the collection implements = using the objects it holds then you need to consider at least some of them in the hash calculation. I can't conceive a hash calculation for this case independent of the contents (well, just hardcode a number but this will lead to always collide if used as a key in a hashed collection).
it is not :)
I'm with Levente here, I think the hash implementation is reasonable. And I wouldn't use a mutable object as key in a hashed collection.
no idea⦠Iâm not using it, just arrive to that method random and I cannot understand it. I still believe is wrong. It's not.
Either Dictionary >> #= or IdentityDictionary >> #species in Pharo *is* broken though.
dic1 := Dictionary newFrom:{1 -> 4}. dic2 := IdentityDictionary newFrom: dic1 associations .
dic1 = dic2 true dic1 hash = dic2 hash false
Cheers, Henry
+1. Henry is right. Esteban, given #(1 2 3) = #(1 2 3) and #(1 2 3) ~= #(1 2 3 4) we require that #(1 2 3) hash = #(1 2 3) hash and would like that #(1 2 3) hash ~= #(1 2 3 4) hash Now it's too much for me to type in my phone but exactly the same should be true of dictionaries. And given that a Dictionary with eg key/value pairs 1->a 2->b 3->c can have 4->d added to it it implies that if the hash function is good it will change when 4->d is added. And as others have said if you want a hash that doesn't change there is the identityHash and identity collections for that very purpose.