# Point an element in Hash Object **URL:** \ **Category:** Ruby\ **Created:** [November 30, 2005, 11:05pm UTC](https://www.ruby-forum.com/t/point-an-element-in-hash-object/49178 "2005-11-30T23:05:46Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![andrew](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/f19dbf/32.png) [@andrew](https://www.ruby-forum.com/u/andrew)\ **Post date:** [November 30, 2005, 11:05pm UTC](https://www.ruby-forum.com/t/point-an-element-in-hash-object/49178/1 "2005-11-30T23:05:46Z")
I’m trying to create an hash object using object string for key and value. I need to link a key with another key as value… so an element of hash object can point to another element. But i need the link to the key and not a copy of the value. I have tried in this way: @my\_hash[“one”] = “First” @my\_hash[“two”] = “Second” @my\_hash[“three”] = “Third” @my\_hash[“four”] = @my\_hash[“T1”] Now if I modify @my\_hash[“one”] = “Modify” I would like to see the new value also for @my\_hash[“four”] =\> “Modify” but I see “First” because i think it do a copy. The problem is that i woult like to refer the element end not to copy it. Thanks so much and sorry for my english. Andreaw ---
**Author:** ![andrew](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/f19dbf/32.png) [@andrew](https://www.ruby-forum.com/u/andrew)\ **Post date:** [November 30, 2005, 11:44pm UTC](https://www.ruby-forum.com/t/point-an-element-in-hash-object/49178/2 "2005-11-30T23:44:16Z")
On Wed, 30 Nov 2005 22:05:53 -0000, Andrew [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > @my\_hash[“four”] = @my\_hash[“T1”] > > Andreaw (Caveat: Fairly new to Ruby) You actually do have a reference - AFAIU so far, pretty much everything is passed by reference (except references, which are passed by value ;)). Prior to your ‘@my\_hash[“one”] = “Modify”’ they do both reference the same object, but then you replace the reference with a new reference, to a string “Modify”. Swap ``` @my_hash["one"] = "Modify" ``` for ``` @my_hash["one"].sub!(/First/,'Modify') ``` and you should get the result you want, because ‘sub!’ modifies the receiver, so no new reference is assigned to @my\_hash[“one”]. (N.B. that this just illustrates the problem more, it’s not a general solution. For that I’d probably use a holder for the string (maybe an one-element array), but I don’t fully know what Ruby has to offer instead yet 😉 ---
**Author:** ![andrew](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/f19dbf/32.png) [@andrew](https://www.ruby-forum.com/u/andrew)\ **Post date:** [December 1, 2005, 12:40pm UTC](https://www.ruby-forum.com/t/point-an-element-in-hash-object/49178/3 "2005-12-01T12:40:50Z")
Ross B. a écrit : > > @my\_hash[“one”] = “First” > > The problem is that i woult like to refer the element end not to copy > > ;)). Prior to your ‘@my\_hash[“one”] = “Modify”’ they do both reference > > the same object, but then you replace the reference with a new > > reference, to a string “Modify”. > > Swap > > ``` > @my_hash["one"] = "Modify" > > ``` > > for > > ``` > @my_hash["one"].sub!(/First/,'Modify') > > ``` @my\_hash[“one”].replace ‘Modify’ is better > and you should get the result you want, because ‘sub!’ modifies the > receiver, so no new reference is assigned to @my\_hash[“one”]. > > (N.B. that this just illustrates the problem more, it’s not a general > solution. For that I’d probably use a holder for the string (maybe an > one-element array), but I don’t fully know what Ruby has to offer > instead yet 😉 – Lionel T. Personal web site: [http://users.skynet.be/lthiry/](http://users.skynet.be/lthiry/) ---
**Author:** ![andrew](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/f19dbf/32.png) [@andrew](https://www.ruby-forum.com/u/andrew)\ **Post date:** [December 1, 2005, 2:22pm UTC](https://www.ruby-forum.com/t/point-an-element-in-hash-object/49178/4 "2005-12-01T14:22:52Z")
Hi – On Thu, 1 Dec 2005, Ross B. wrote: > (P.s. is ‘replace’ one of the ‘!’ convention exceptions, or is there another > reason it doesn’t have a ‘!’ ?) It’s not an exception: the convention is that when there’s a pair of methods that differ only in that one is more “dangerous” than the other, they have the same name but the dangerous one has a ! on the end. replace isn’t part of a pair of that kind – it’s just its own thing. David ---
**Author:** ![andrew](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/f19dbf/32.png) [@andrew](https://www.ruby-forum.com/u/andrew)\ **Post date:** [December 1, 2005, 2:18pm UTC](https://www.ruby-forum.com/t/point-an-element-in-hash-object/49178/5 "2005-12-01T14:18:48Z")
On Thu, 01 Dec 2005 11:33:36 -0000, Lionel T. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > ``` > > @my_hash["one"].sub!(/First/,'Modify') > > > > ``` > > @my\_hash[“one”].replace ‘Modify’ > is better Definitely. Thanks. 🙂 (P.s. is ‘replace’ one of the ‘!’ convention exceptions, or is there another reason it doesn’t have a ‘!’ ?) ---
**Author:** ![andrew](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/f19dbf/32.png) [@andrew](https://www.ruby-forum.com/u/andrew)\ **Post date:** [December 1, 2005, 2:35pm UTC](https://www.ruby-forum.com/t/point-an-element-in-hash-object/49178/6 "2005-12-01T14:35:05Z")
On Thu, 01 Dec 2005 13:21:27 -0000, David A. Black [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Ahh, I see… I had the idea that the bang signified a method that modified self, regardless. A few other ‘exceptions’ make sense to me now, too 🙂 Thanks David.