# What is "dynamic constant assignment" **URL:** \ **Category:** ruby-talk\ **Created:** [14 August 2007 08:03 UTC](https://rubytalk.org/t/what-is-dynamic-constant-assignment/39881 "2007-08-14T08:03:05Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Sean\_Liu](https://avatars.discourse-cdn.com/v4/letter/s/a4c791/32.png) [@Sean\_Liu](https://rubytalk.org/u/Sean_Liu)\ **Post date:** [14 August 2007 08:03 UTC](https://rubytalk.org/t/what-is-dynamic-constant-assignment/39881/1 "2007-08-14T08:03:05Z")
hi, all today i defined a class like this: class C   AB = 10   def self.set(value)      AB = value   end end then i got this error: SyntaxError: compile error (irb):10: dynamic constant assignment. Constants can be changed after initialization, but what does this error mean? Any explanations will be appreciated. ---
**Author:** ![Nikos\_Kanellopoulos](https://avatars.discourse-cdn.com/v4/letter/n/c5a1d2/32.png) [@Nikos\_Kanellopoulos](https://rubytalk.org/u/Nikos_Kanellopoulos)\ **Post date:** [14 August 2007 08:23 UTC](https://rubytalk.org/t/what-is-dynamic-constant-assignment/39881/2 "2007-08-14T08:23:37Z")
Variable AB is a contant, because it starts with a capital letter. You can only assign a contant value (or expression) to it, once. > **···** > > 2007/8/14, sean liu \: > > > hi, all > > > > today i defined a class like this: > > class C > >   AB = 10 > >   def self.set(value) > >      AB = value > >   end > > end > > then i got this error: SyntaxError: compile error (irb):10: dynamic constant > > assignment. > > Constants can be changed after initialization, but what does this error > > mean? > > Any explanations will be appreciated. ---
**Author:** ![Stefano\_Crocco](https://avatars.discourse-cdn.com/v4/letter/s/5f9b8f/32.png) [@Stefano\_Crocco](https://rubytalk.org/u/Stefano_Crocco)\ **Post date:** [14 August 2007 08:27 UTC](https://rubytalk.org/t/what-is-dynamic-constant-assignment/39881/3 "2007-08-14T08:27:36Z")
Alle martedì 14 agosto 2007, Nikos Kanellopoulos ha scritto: > \> hi, all > \> > \> today i defined a class like this: > \> class C > \> AB = 10 > \> def self.set(value) > \> AB = value > \> end > \> end > \> then i got this error: SyntaxError: compile error (irb):10: dynamic > \> constant assignment. > \> Constants can be changed after initialization, but what does this error > \> mean? > \> Any explanations will be appreciated. > > Variable AB is a contant, because it starts with a capital letter. > You can only assign a contant value (or expression) to it, once. That's not true. You can assign a value to a constant more than once, even if ruby will issue a warning: irb: 001\> A = 1 1 irb: 002\> A = 2 (irb):2: warning: already initialized constant A 2 I guess that the 'dynamic constant assignment' means that you can assing to a constant in a method. Stefano > **···** > > > 2007/8/14, sean liu \: ---
**Author:** ![Logan\_Capaldo](https://avatars.discourse-cdn.com/v4/letter/l/7ea924/32.png) [@Logan\_Capaldo](https://rubytalk.org/u/Logan_Capaldo)\ **Post date:** [14 August 2007 10:10 UTC](https://rubytalk.org/t/what-is-dynamic-constant-assignment/39881/4 "2007-08-14T10:10:38Z")
> Alle martedì 14 agosto 2007, Nikos Kanellopoulos ha scritto: > \> \> hi, all > \> \> > \> \> today i defined a class like this: > \> \> class C > \> \> AB = 10 > \> \> def self.set(value) > \> \> AB = value > \> \> end > \> \> end > \> \> then i got this error: SyntaxError: compile error (irb):10: dynamic > \> \> constant assignment. > \> \> Constants can be changed after initialization, but what does this > error > \> \> mean? > \> \> Any explanations will be appreciated. > \> > \> Variable AB is a contant, because it starts with a capital letter. > \> You can only assign a contant value (or expression) to it, once. > > That's not true. You can assign a value to a constant more than once, even > if > ruby will issue a warning: > > irb: 001\> A = 1 > 1 > irb: 002\> A = 2 > (irb):2: warning: already initialized constant A > 2 > > I guess that the 'dynamic constant assignment' means that you can assing > to a > constant in a method. And the work around is def self.set(value)   const\_set("AB". value) end Although it might make more sense to do @AB = 10 def self.AB   @AB end def self.AB=(value)   @AB = value end Stefano > **···** > > On 8/14/07, Stefano Crocco \ wrote: > > > \> 2007/8/14, sean liu \: ---
**Author:** ![Marc\_Heiler](https://avatars.discourse-cdn.com/v4/letter/m/e8c25b/32.png) [@Marc\_Heiler](https://rubytalk.org/u/Marc_Heiler)\ **Post date:** [14 August 2007 10:15 UTC](https://rubytalk.org/t/what-is-dynamic-constant-assignment/39881/5 "2007-08-14T10:15:32Z")
"Any explanations will be appreciated." Ruby does not allow redefinitions of constants in a method. > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Roger\_Pack4](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@Roger\_Pack4](https://rubytalk.org/u/Roger_Pack4)\ **Post date:** [26 September 2008 17:03 UTC](https://rubytalk.org/t/what-is-dynamic-constant-assignment/39881/6 "2008-09-26T17:03:00Z")
> > I guess that the 'dynamic constant assignment' means that you can assing > > to a > > constant in a method. > > And the work around is > def self.set(value) >   const\_set("AB". value) > end Or, if you aren't in a class method def set(value) self.class.const\_set(:AB, value) # can use a symbol end Cheers. -=R > **···** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).