# \[Nuby\] Object ID Lookup? **URL:** \ **Category:** ruby-talk\ **Created:** [12 December 2003 22:05 UTC](https://rubytalk.org/t/nuby-object-id-lookup/9308 "2003-12-12T22:05:58Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Jim\_Moy](https://avatars.discourse-cdn.com/v4/letter/j/7ea924/32.png) [@Jim\_Moy](https://rubytalk.org/u/Jim_Moy)\ **Post date:** [12 December 2003 22:05 UTC](https://rubytalk.org/t/nuby-object-id-lookup/9308/1 "2003-12-12T22:05:58Z")
Hi all, a Ruby Nuby here with a question. Is there a way to lookup an object reference from the object’s id? Something to do like the following, but without the need for the lookup hash: a = { “a” =\> 1, “b” =\> 2 } b = { “c” =\> 4, “d” =\> 3 } arr = [a, b] ids = arr.collect {|h| [h.id](http://h.id)} lookup = {} arr.each { |h| lookup[[h.id](http://h.id)] = h } cmp = ids.collect {|id| lookup[id]} ids == cmp =\> true In my instance, I’ve got a reference set of hashes that I’m pointing to from multiple arrays. Those arrays are manipulated depending on sorting and other factors. I don’t want to get Hash#== involved so I’m using the Hash object id’s. After processing is completed, I’d like to get back from the IDs to the object references. The lookup is working, but I was wondering if there was a better method. Thanks for any suggestions, Jim Moy Fort Collins, Colorado USA ---
**Author:** ![Joel\_VanderWerf1](https://avatars.discourse-cdn.com/v4/letter/j/94ad74/32.png) [@Joel\_VanderWerf1](https://rubytalk.org/u/Joel_VanderWerf1)\ **Post date:** [12 December 2003 22:11 UTC](https://rubytalk.org/t/nuby-object-id-lookup/9308/2 "2003-12-12T22:11:01Z")
Jim Moy wrote: > Is there a way to lookup an object reference from the object’s id? You can use ObjectSpace.\_id2ref(x.id) to get a reference to x. ---
**Author:** ![Eric\_Hodel1](https://avatars.discourse-cdn.com/v4/letter/e/a9adbd/32.png) [@Eric\_Hodel1](https://rubytalk.org/u/Eric_Hodel1)\ **Post date:** [15 December 2003 23:12 UTC](https://rubytalk.org/t/nuby-object-id-lookup/9308/3 "2003-12-15T23:12:28Z")
Not seeing the internals of your code, will Object#equal? (identical object ids) be able to replace #==? > **···** > > Jim Moy ([web@jimmoy.com](mailto:web@jimmoy.com)) wrote: > > > Hi all, a Ruby Nuby here with a question. > > > > Is there a way to lookup an object reference from the object’s id? > > Something to do like the following, but without the need for the lookup > > hash: > > > > a = { “a” =\> 1, “b” =\> 2 } > > b = { “c” =\> 4, “d” =\> 3 } > > arr = [a, b] > > ids = arr.collect {|h| h.id} > > lookup = {} > > arr.each { |h| lookup[h.id] = h } > > cmp = ids.collect {|id| lookup[id]} > > ids == cmp =\> true > > > > In my instance, I’ve got a reference set of hashes that I’m pointing to > > from multiple arrays. Those arrays are manipulated depending on sorting > > and other factors. > > > > I don’t want to get Hash#== involved so I’m using the Hash object id’s. > > After processing is completed, I’d like to get back from the IDs to the > > object references. The lookup is working, but I was wondering if there > > was a better method. > > – > Eric Hodel - [drbrain@segment7.net](mailto:drbrain@segment7.net) - [http://segment7.net](http://segment7.net) > All messages signed with fingerprint: > FEC2 57F1 D465 EB15 5D6E 7C11 332A 551C 796C 9F04 ---
**Author:** ![Jim\_Moy](https://avatars.discourse-cdn.com/v4/letter/j/7ea924/32.png) [@Jim\_Moy](https://rubytalk.org/u/Jim_Moy)\ **Post date:** [13 December 2003 00:48 UTC](https://rubytalk.org/t/nuby-object-id-lookup/9308/4 "2003-12-13T00:48:59Z")
> Jim Moy wrote: > > > Is there a way to lookup an object reference from the object’s id? > > You can use ObjectSpace.\_id2ref(x.id) to get a reference to x. Thanks for the answer. My Ruby in a Nutshell says this is an “internal use only” method, is that still the case as of 1.8? Jim ---
**Author:** ![Jim\_Moy](https://avatars.discourse-cdn.com/v4/letter/j/7ea924/32.png) [@Jim\_Moy](https://rubytalk.org/u/Jim_Moy)\ **Post date:** [16 December 2003 01:29 UTC](https://rubytalk.org/t/nuby-object-id-lookup/9308/5 "2003-12-16T01:29:39Z")
> > a = { “a” =\> 1, “b” =\> 2 } > > b = { “c” =\> 4, “d” =\> 3 } > > arr = [a, b] > > ids = arr.collect {|h| h.id} > > lookup = {} > > arr.each { |h| lookup[h.id] = h } > > cmp = ids.collect {|id| lookup[id]} > > ids == cmp =\> true > > > > In my instance, I’ve got a reference set of hashes that I’m > > pointing to from multiple arrays. Those arrays are manipulated > > depending on sorting and other factors. > > > > I don’t want to get Hash#== involved so I’m using the Hash > > object id’s. After processing is completed, I’d like to get > > back from the IDs to the object references. The lookup is > > working, but I was wondering if there was a better method. > > Not seeing the internals of your code, will Object#equal? (identical > object ids) be able to replace #==? Yes, the code similar to the above example works as-is with the hash ids, as I wanted to avoid Hash#== and all the comparisons it will perform. Judging by the replies so far, I think I’ll keep the lookup hash. Jim > **···** > > > Eric Hodel ([drbrain@segment7.net](mailto:drbrain@segment7.net)) wrote: ---
**Author:** ![Yukihiro\_Matsumoto2](https://avatars.discourse-cdn.com/v4/letter/y/b9e5f3/32.png) [@Yukihiro\_Matsumoto2](https://rubytalk.org/u/Yukihiro_Matsumoto2)\ **Post date:** [13 December 2003 02:26 UTC](https://rubytalk.org/t/nuby-object-id-lookup/9308/6 "2003-12-13T02:26:21Z")
Hi, > **···** > > In message “Re: [Nuby] Object ID Lookup?” on 03/12/13, “Jim Moy” [web@jimmoy.com](mailto:web@jimmoy.com) writes: > > > > You can use ObjectSpace.\_id2ref(x.id) to get a reference to x. > > > > Thanks for the answer. My Ruby in a Nutshell says this is an “internal > > use only” method, is that still the case as of 1.8? > > I don’t recommend you to use it too often, because it’s difficult to > use it right. The referencing object may be recycled by GC. > > ``` > matz. > > ```