# Bug in Hash#hash? (Ruby 1.8.4) **URL:** \ **Category:** Ruby\ **Created:** [September 20, 2006, 4:42pm UTC](https://www.ruby-forum.com/t/bug-in-hash-hash-ruby-1-8-4/69365 "2006-09-20T16:42:58Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Eyal\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/7ba0ec/32.png) [@Eyal\_O](https://www.ruby-forum.com/u/Eyal_O)\ **Post date:** [September 20, 2006, 4:42pm UTC](https://www.ruby-forum.com/t/bug-in-hash-hash-ruby-1-8-4/69365/1 "2006-09-20T16:42:58Z")
Hi, say one = {:a=\>:b} then one.hash != one.clone.hash is that a bug or correct? (using ruby 1.8.4 (2005-12-24) [i486-linux]) second question:I want to index use a hash as key in a hashtable, but it doesnt work (probably because of above problem) one = {:a=\>:b} two = {:a=\>:b} test[one] = 1 test[two] … nil test.include? one … true test.include? two … false although one == two … true on the other hand, one.eql?(two) … false (which seems wrong to me, as matz indicated in 2004, see [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/122510](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/122510)) and also one.hash != two.hash (as pointed out above, and seems to be the source of the problem) so it seems: - hash.eql? is wrong (see matz’ earlier message) - hash.hash is wrong (try it with dup of itself) or do i miss something? ---
**Author:** ![Eyal\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/7ba0ec/32.png) [@Eyal\_O](https://www.ruby-forum.com/u/Eyal_O)\ **Post date:** [September 20, 2006, 5:05pm UTC](https://www.ruby-forum.com/t/bug-in-hash-hash-ruby-1-8-4/69365/2 "2006-09-20T17:05:01Z")
Hi, In message “Re: Bug in Hash#hash? (Ruby 1.8.4)” on Wed, 20 Sep 2006 23:40:11 +0900, “Eyal O.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: |say one = {:a=\>:b} |then one.hash != one.clone.hash |is that a bug or correct? | |(using ruby 1.8.4 (2005-12-24) [i486-linux]) Currently it’s an intended behavior. Hash is not designed to be hash key (two hashes are considered to be a same key if they are exactly the same object). It’s not likely to change in 1.8 series. In 1.9, maybe. ``` matz. ``` ---
**Author:** ![Eyal\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/7ba0ec/32.png) [@Eyal\_O](https://www.ruby-forum.com/u/Eyal_O)\ **Post date:** [September 21, 2006, 2:36am UTC](https://www.ruby-forum.com/t/bug-in-hash-hash-ruby-1-8-4/69365/3 "2006-09-21T02:36:20Z")
On 9/20/06, Yukihiro M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Currently it’s an intended behavior. Hash is not designed to be hash > key (two hashes are considered to be a same key if they are exactly > the same object). It’s not likely to change in 1.8 series. In 1.9, > maybe. And I think more precisely, it’s that hash needs to be implemented so that a.eql?(b) implies a.hash == b.hash one = {:a =\> :b} two = one.clone one == two #=\> true one.eql?(two) #=\> false Smalltalkers might recall that Smalltalk has both a Hash which uses Smalltalks equivalents to Ruby’s hash and ==, and IdentityHash which uses Smalltalks equivalents to Ruby’s object\_id for the hash, and equal? – Rick DeNatale My blog on Ruby [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) IPMS/USA Region 12 Coordinator [http://ipmsr12.denhaven2.com/](http://ipmsr12.denhaven2.com/) Visit the Project Mercury Wiki Site [http://www.mercuryspacecraft.com/](http://www.mercuryspacecraft.com/) ---
**Author:** ![Eyal\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/7ba0ec/32.png) [@Eyal\_O](https://www.ruby-forum.com/u/Eyal_O)\ **Post date:** [September 21, 2006, 3:30am UTC](https://www.ruby-forum.com/t/bug-in-hash-hash-ruby-1-8-4/69365/4 "2006-09-21T03:30:22Z")
On 9/20/06, Yukihiro M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Recently, 1.9 added Hash#compare\_by\_identity method which makes Hash > to compare its keys by identity. And I showed my age, they say that the memory is the second thing to go, but I forget what the first thing is. In Smalltalk it’s Dictionary, and IdentityDictionary, but other than the names Dictionary is a Hash. – Rick DeNatale My blog on Ruby [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) ---
**Author:** ![Eyal\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/7ba0ec/32.png) [@Eyal\_O](https://www.ruby-forum.com/u/Eyal_O)\ **Post date:** [September 21, 2006, 12:17pm UTC](https://www.ruby-forum.com/t/bug-in-hash-hash-ruby-1-8-4/69365/5 "2006-09-21T12:17:21Z")
Yukihiro M. wrote: > > |say one = {:a=\>:b} > > |then one.hash != one.clone.hash > > |is that a bug or correct? > > Currently it’s an intended behavior. Hash is not designed to be hash > > key (two hashes are considered to be a same key if they are exactly > > the same object). It’s not likely to change in 1.8 series. In 1.9, > > maybe. > > thanks for the clarification. > > why was this decided? is it not useful to have a hash as hash-key? I often use hashes to emulate named parameter-values, and if I have say a connection pool I would like to index it based on the connection-parameters (which are given as a hash of key-value pairs). does this scenario make sense? ---
**Author:** ![Eyal\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/7ba0ec/32.png) [@Eyal\_O](https://www.ruby-forum.com/u/Eyal_O)\ **Post date:** [September 21, 2006, 3:18am UTC](https://www.ruby-forum.com/t/bug-in-hash-hash-ruby-1-8-4/69365/6 "2006-09-21T03:18:22Z")
Hi, In message “Re: Bug in Hash#hash? (Ruby 1.8.4)” on Thu, 21 Sep 2006 09:34:17 +0900, “Rick DeNatale” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: |Smalltalkers might recall that Smalltalk has both a Hash which uses |Smalltalks equivalents to Ruby’s hash and ==, and IdentityHash which |uses Smalltalks equivalents to Ruby’s object\_id for the hash, and |equal? Recently, 1.9 added Hash#compare\_by\_identity method which makes Hash to compare its keys by identity. ``` matz. ``` ---
**Author:** ![Eyal\_O](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/e/7ba0ec/32.png) [@Eyal\_O](https://www.ruby-forum.com/u/Eyal_O)\ **Post date:** [September 21, 2006, 4:38pm UTC](https://www.ruby-forum.com/t/bug-in-hash-hash-ruby-1-8-4/69365/7 "2006-09-21T16:38:15Z")
On 9/21/06, Eyal O. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Yukihiro M. wrote: > > > > |say one = {:a=\>:b} > > > |then one.hash != one.clone.hash > > > |is that a bug or correct? > > > Currently it’s an intended behavior. Hash is not designed to be hash > > > key (two hashes are considered to be a same key if they are exactly > > > the same object). > is it not useful to have a hash as hash-key? I often use hashes to > emulate named parameter-values, and if I have say a connection pool I > would like to index it based on the connection-parameters (which are > given as a hash of key-value pairs). Not entirely to the point, but… One issue you have to be aware of if you have a Hash with keys that are mutable, is that if a key mutates so as to affect the results of eql?/hash then the hash needs to be rehashed or strange events can ensue. – Rick DeNatale My blog on Ruby [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)