# Something changed an instance variable ... and now I'm confused **URL:** \ **Category:** Ruby\ **Created:** [January 8, 2010, 6:05pm UTC](https://www.ruby-forum.com/t/something-changed-an-instance-variable-and-now-im-confused/181281 "2010-01-08T18:05:48Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![ralphshnelvar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e19adc/32.png) [@ralphshnelvar](https://www.ruby-forum.com/u/ralphshnelvar)\ **Post date:** [January 8, 2010, 6:05pm UTC](https://www.ruby-forum.com/t/something-changed-an-instance-variable-and-now-im-confused/181281/1 "2010-01-08T18:05:48Z")
Newbie here. Consider this irb session … F:\InstantRails-2.0-win\rails\_apps\>irb irb(main):001:0\> class X irb(main):002:1\> attr\_accessor :x, :y irb(main):003:1\> end =\> nil irb(main):004:0\> irb(main):005:0\* x1 = X.new =\> #\ irb(main):006:0\> irb(main):007:0\* x1.x = 5; irb(main):008:0\* x1.y = 6; irb(main):009:0\* irb(main):010:0\* irb(main):011:0\* irb(main):012:0\* class X irb(main):013:1\> def x=(arg) irb(main):014:2\> puts “arg=” + arg.to\_s irb(main):015:2\> @x = arg irb(main):016:2\> puts “whoopy” irb(main):017:2\> @x irb(main):018:2\> end irb(main):019:1\> irb(main):020:1\* def make\_x irb(main):021:2\> self.x = “xyzzy” irb(main):022:2\> end irb(main):023:1\> end =\> nil irb(main):024:0\> irb(main):025:0\* irb(main):026:0\* x1.x = “hello” arg=hello whoopy =\> “hello” irb(main):027:0\> x1 =\> #\ irb(main):028:0\> x1.make\_x arg=xyzzy whoopy =\> “xyzzy” irb(main):029:0\> x1 =\> #\ irb(main):030:0\> The background … I am debugging an RoR application and noticed that the @activation\_code instance variable was being modified _somewhere_. I couldn’t tell where. So I added a method to the User class def activation\_code=(arg) puts at\_file\_line\_msg( **FILE** , **LINE** ) puts “arg=” + arg @activation\_code=arg debugger @activation\_code end When I look at the value of @activation\_code in the debugger (at the debuuger breakpoint), it has the right value … but when I look at self in the debugger, the activation\_code field is nil. I do not understand why things seem to work in the snippet of code I provided, above, in irb … but do not work in the far more complex RoR environment. ---
**Author:** ![ralphshnelvar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e19adc/32.png) [@ralphshnelvar](https://www.ruby-forum.com/u/ralphshnelvar)\ **Post date:** [January 8, 2010, 9:34pm UTC](https://www.ruby-forum.com/t/something-changed-an-instance-variable-and-now-im-confused/181281/2 "2010-01-08T21:34:12Z")
On Fri, Jan 8, 2010 at 12:05 PM, Ralph S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > irb(main):004:0\> > irb(main):014:2\> puts “arg=” + arg.to\_s > irb(main):024:0\> > =\> “xyzzy” > So I added a method to the User class > When I look at the value of @activation\_code in the debugger (at the debuuger breakpoint), it has the right value … > > but when I look at self in the debugger, the activation\_code field is nil. > > I do not understand why things seem to work in the snippet of code I provided, above, in irb … but do not work in the far more complex RoR environment. Is activation\_code an attribute of an ActiveRecord model? If so then the value isn’t stored in an instance variable, the accessors are actually handled via method\_missing. By defining activation\_code= you are preventing activerecord from doing it’s thing. You need something like: def activation\_code=(arg) puts at\_file\_line\_msg( **FILE** , **LINE** ) puts “arg=” + arg self[‘activation\_code’] =arg debugger arg # strictly speaking you don’t really need this since ruby assignments via an x= method ignore the return value end – Rick DeNatale Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) Twitter: [http://twitter.com/RickDeNatale](http://twitter.com/RickDeNatale) WWR: [http://www.workingwithrails.com/person/9021-rick-denatale](http://www.workingwithrails.com/person/9021-rick-denatale) LinkedIn: [Rick DeNatale - Developer - IBM | LinkedIn](http://www.linkedin.com/in/rickdenatale) ---
**Author:** ![ralphshnelvar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e19adc/32.png) [@ralphshnelvar](https://www.ruby-forum.com/u/ralphshnelvar)\ **Post date:** [January 8, 2010, 9:45pm UTC](https://www.ruby-forum.com/t/something-changed-an-instance-variable-and-now-im-confused/181281/3 "2010-01-08T21:45:32Z")
Rick Denatale wrote: > Is activation\_code an attribute of an ActiveRecord model? > > If so then the value isn’t stored in an instance variable I believe it’s stored in @attributes (which is a Hash) > You need something like: > > def activation\_code=(arg) > puts at\_file\_line\_msg( **FILE** , **LINE** ) > puts “arg=” + arg > self[‘activation\_code’] =arg > debugger > arg # strictly speaking you don’t really need this since ruby > assignments via an x= method ignore the return value > end Should be cleaner to use: write\_attribute(‘activation\_code’, arg) If you have the Agile Web D. with Rails book, look up ‘facade columns’ in the index. ---
**Author:** ![ralphshnelvar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e19adc/32.png) [@ralphshnelvar](https://www.ruby-forum.com/u/ralphshnelvar)\ **Post date:** [January 9, 2010, 6:44am UTC](https://www.ruby-forum.com/t/something-changed-an-instance-variable-and-now-im-confused/181281/4 "2010-01-09T06:44:17Z")
Brian, Friday, January 8, 2010, 1:45:34 PM, you wrote: BC\> Rick Denatale wrote: > > Is activation\_code an attribute of an ActiveRecord model? > > If so then the value isn’t stored in an instance variable BC\> I believe it’s stored in @attributes (which is a Hash) > > You need something like: > > def activation\_code=(arg) > > puts at\_file\_line\_msg( **FILE** , **LINE** ) > > puts “arg=” + arg > > self[‘activation\_code’] =arg > > debugger > > arg # strictly speaking you don’t really need this since ruby > > assignments via an x= method ignore the return value > > end BC\> Should be cleaner to use: write\_attribute(‘activation\_code’, arg) BC\> If you have the Agile Web D. with Rails book, look up ‘facade BC\> columns’ in the index. To both Brian and Rick, thank you. Is there another way to determine why a particular value changed and/or when it is assigned to?