Re: [Pharo-dev] hash and Collections

Oct. 9, 2015


      The identityHash should stay the same for any number of changes to the array..

| c1 c2 |

c1 := { #a . #b } asOrderedCollection.
c2 := { #a . #b } asOrderedCollection.

{ 
	c1 hash.
	c1 identityHash.
	c2 hash.
	c2 identityHash .
	(c2 add: #c; yourself) identityHash.
} "inspect"

Best regards,
Henrik

-----Original Message-----
From: Pharo-dev [mailto:pharo-dev-bounces@lists.pharo.org] On Behalf Of Esteban Lorenzano
Sent: Friday, October 9, 2015 4:08 PM
To: Pharo Development List <pharo-dev@lists.pharo.org>
Subject: Re: [Pharo-dev] hash and Collections

but thatâs an error, I think. 
a collection has to have always same hashâ¦ 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> 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 meanâ¦ a hash that changes when I add elements to the collectionâ¦ how can this work?
Esteban

Re: [Pharo-dev] hash and Collections

Henrik Nergaard