# Referencing an object through it's id string **URL:** \ **Category:** Ruby\ **Created:** [August 27, 2006, 12:33am UTC](https://www.ruby-forum.com/t/referencing-an-object-through-its-id-string/66559 "2006-08-27T00:33:19Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![orz42](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/45deac/32.png) [@orz42](https://www.ruby-forum.com/u/orz42)\ **Post date:** [August 27, 2006, 12:33am UTC](https://www.ruby-forum.com/t/referencing-an-object-through-its-id-string/66559/1 "2006-08-27T00:33:19Z")
Hello, how does one set a pointer to foo using an id string obtained through foo.object\_id for instance? Thanks in advance ---
**Author:** ![orz42](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/45deac/32.png) [@orz42](https://www.ruby-forum.com/u/orz42)\ **Post date:** [August 27, 2006, 1:50am UTC](https://www.ruby-forum.com/t/referencing-an-object-through-its-id-string/66559/2 "2006-08-27T01:50:10Z")
Alexandre H. wrote: > Hello, how does one set a pointer to foo using an id string obtained > through foo.object\_id for instance? obj = ObjectSpace.id2ref object\_id > Thanks in advance See ri ObjectSpace from your command-line. ---
**Author:** ![orz42](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/45deac/32.png) [@orz42](https://www.ruby-forum.com/u/orz42)\ **Post date:** [August 27, 2006, 4:56am UTC](https://www.ruby-forum.com/t/referencing-an-object-through-its-id-string/66559/3 "2006-08-27T04:56:41Z")
On Aug 26, 2006, at 7:38 PM, Alexandre H. wrote: > Hello, how does one set a pointer to foo using an id string obtained > through foo.object\_id for instance? > > Thanks in advance > > – > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ## ---------------------------------------------------- ObjectSpace#\_id2ref ObjectSpace.\_id2ref(object\_id) → an\_object ``` Converts an object id to a reference to the object. May not be called on an object id passed as a parameter to a finalizer. s = "I am a string" #=> "I am a string" r = ObjectSpace._id2ref(s.object_id) #=> "I am a string" r == s #=> true ``` Cheers- -Ezra ---
**Author:** ![orz42](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/45deac/32.png) [@orz42](https://www.ruby-forum.com/u/orz42)\ **Post date:** [August 27, 2006, 5:16am UTC](https://www.ruby-forum.com/t/referencing-an-object-through-its-id-string/66559/4 "2006-08-27T05:16:54Z")
Alexandre H. wrote: > Hello, how does one set a pointer to foo using an id string obtained > through foo.object\_id for instance? > > Thanks in advance Considering that object ids are only valid throughout one interpreter run… I’m curious: why pass around the object id instead of the object itself? David V. ---
**Author:** ![orz42](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/45deac/32.png) [@orz42](https://www.ruby-forum.com/u/orz42)\ **Post date:** [August 27, 2006, 6:33am UTC](https://www.ruby-forum.com/t/referencing-an-object-through-its-id-string/66559/5 "2006-08-27T06:33:04Z")
On Sun, 27 Aug 2006 12:16:11 +0900, David V. wrote: > Alexandre H. wrote: > > > Hello, how does one set a pointer to foo using an id string obtained > > through foo.object\_id for instance? > > > > Thanks in advance > > Considering that object ids are only valid throughout one interpreter > run… I’m curious: why pass around the object id instead of the object > itself? Have a look at how weakref.rb is implemented. It keeps track of the objects it’s referencing by object id, because the garbage collector can’t follow those, but the references can get their objects back using ObjectSpace.\_id2ref (assuming they haven’t been garbage collected). –Ken B. ---
**Author:** ![orz42](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/45deac/32.png) [@orz42](https://www.ruby-forum.com/u/orz42)\ **Post date:** [August 27, 2006, 12:56pm UTC](https://www.ruby-forum.com/t/referencing-an-object-through-its-id-string/66559/6 "2006-08-27T12:56:16Z")
Ken B. wrote: > > itself? > > Have a look at how weakref.rb is implemented. It keeps track of the > objects it’s referencing by object id, because the garbage collector can’t > follow those, but the references can get their objects back > using ObjectSpace.\_id2ref (assuming they haven’t been garbage collected). I figured as much, but that was the only behaviour I could think of that I’d implement using this. And since it’s in the standard library, I’d also probably use those weakrefs instead of rolling my own - I’m still living in the (naive?) idea that code that gets promoted into standard libraries works better than my implementations would. But then I still wonder. Why pass around object ids instead of weakrefs or object references themselves? David V. ---
**Author:** ![orz42](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/45deac/32.png) [@orz42](https://www.ruby-forum.com/u/orz42)\ **Post date:** [August 27, 2006, 1:54pm UTC](https://www.ruby-forum.com/t/referencing-an-object-through-its-id-string/66559/7 "2006-08-27T13:54:41Z")
Thanks for the information! David V. wrote: > Alexandre H. wrote: > > > Hello, how does one set a pointer to foo using an id string obtained > > through foo.object\_id for instance? > > > > Thanks in advance > > Considering that object ids are only valid throughout one interpreter > run… I’m curious: why pass around the object id instead of the object > itself? > > David V. I’m having trouble passing an object reference from a template (a form) to a controller method, what I’ve managed to return is the object’s id string. I’m guessing there’s a better way of doing this? ---
**Author:** ![orz42](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/45deac/32.png) [@orz42](https://www.ruby-forum.com/u/orz42)\ **Post date:** [August 27, 2006, 3:02pm UTC](https://www.ruby-forum.com/t/referencing-an-object-through-its-id-string/66559/8 "2006-08-27T15:02:32Z")
Alexandre H. wrote: > > run… I’m curious: why pass around the object id instead of the object > > itself? > > > > David V. > > I’m having trouble passing an object reference from a template (a form) > to a controller method, what I’ve managed to return is the object’s id > string. Is this a web application? (Rails maybe? Seeing as the words template and controller method cropped up.) It’s not quite best practice in that case since there are deployment models where this just doesn’t work - anything that involves several Ruby processes serving for instance. You also want to make sure the object doesn’t get garbage collected. But for simple cases, like a personal app, it’s pretty much the same thing as when you’d use a session I suppose. David V.