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. Esteban
On Fri, Oct 9, 2015 at 11:07 AM, Esteban Lorenzano <estebanlm@gmail.com <mailto:estebanlm@gmail.com>> wrote: but thatâs an error, I think. a collection has to have always same hash⦠no matter its size (because is not an array) and no matter his elements.
On 09 Oct 2015, at 15:21, Levente Uzonyi <leves@elte.hu <mailto:leves@elte.hu>> wrote:
You simply don't modify _objects_ which are used as keys in hashed collections. Or if you do so, you'll have to deal with the consequences yourself.
Levente
On Fri, 9 Oct 2015, Esteban Lorenzano wrote:
Hi,
Can anyone explain me how this is correct?
Collection>>#hash "Answer an integer hash value for the receiver such that, -- the hash value of an unchanged object is constant over time, and -- two equal objects have equal hash values"
| hash |
hash := self species hash. self size <= 10 ifTrue: [self do: [:elem | hash := hash bitXor: elem hash]]. ^hash bitXor: self size hash
I mean⦠a hash that changes when I add elements to the collection⦠how can this work?
Esteban