# Class Methods from Modules **URL:** \ **Category:** ruby-talk\ **Created:** [22 November 2007 17:58 UTC](https://rubytalk.org/t/class-methods-from-modules/42428 "2007-11-22T17:58:19Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Greg\_Willits](https://avatars.discourse-cdn.com/v4/letter/g/cab0a1/32.png) [@Greg\_Willits](https://rubytalk.org/u/Greg_Willits)\ **Post date:** [22 November 2007 17:58 UTC](https://rubytalk.org/t/class-methods-from-modules/42428/1 "2007-11-22T17:58:19Z")
Can't see the tree for the forest. Playing with how to integrate modules, classes, subclasses, and create instance methods and class methods from modules. In this play code below, I want to use initialize\_colors in either the class Shape or Square as a class method. At this point I'm sure I'm missing a very simple syntax rule explained very clearly in the books, but the code as is complains about initialize\_colors as being undefined, and I'm just not recognizing what I am missing. module Color   def initialize\_colors     @fill\_color = 'ffffff'     @border\_color = '000000'   end   def set\_fill\_rgb(color)     if color == 'white'       @fill\_color = 'ffffff'     elsif color == 'red'       @fill\_color = 'ff0000'     elsif color == 'blue'       @fill\_color = '0000ff'     elsif color == 'black'       @fill\_color = '000000'     end   end end class Shape   include Color   attr\_reader :fill\_color, :border\_color   def initialize     @fill\_color = String.new     @border\_color = String.new   end end class Square \< Shape   initialize\_colors end sq = Square.new puts sq.fill\_color sq.set\_fill\_rgb('red') puts sq.fill\_color > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Eric\_I2](https://avatars.discourse-cdn.com/v4/letter/e/22d042/32.png) [@Eric\_I2](https://rubytalk.org/u/Eric_I2)\ **Post date:** [22 November 2007 18:40 UTC](https://rubytalk.org/t/class-methods-from-modules/42428/2 "2007-11-22T18:40:03Z")
Hi Greg, Well the methods you can call \*as\* a class is being defined are \*class\* methods. initialize\_colors is an instance method, as it should be since it's setting instance variables. It seems to me that you want to call initialize\_colors not as the class is being defined but as instances are being created. And therefore the call to initialize\_colors should be inside Square's initialize method. Eric > **···** > > ==== > > Are you interested in on-site Ruby training that's been highly > reviewed by former students? [http://LearnRuby.com](http://LearnRuby.com) > > On Nov 22, 12:58 pm, Greg Willits \ wrote: > > > Can't see the tree for the forest. > > > > Playing with how to integrate modules, classes, subclasses, and create > > instance methods and class methods from modules. > > > > In this play code below, I want to use initialize\_colors in either the > > class Shape or Square as a class method. > > > > At this point I'm sure I'm missing a very simple syntax rule explained > > very clearly in the books, but the code as is complains about > > initialize\_colors as being undefined, and I'm just not recognizing what > > I am missing. > > > > module Color > > > >   def initialize\_colors > >     @fill\_color = 'ffffff' > >     @border\_color = '000000' > >   end > > > >   def set\_fill\_rgb(color) > >     if color == 'white' > >       @fill\_color = 'ffffff' > >     elsif color == 'red' > >       @fill\_color = 'ff0000' > >     elsif color == 'blue' > >       @fill\_color = '0000ff' > >     elsif color == 'black' > >       @fill\_color = '000000' > >     end > >   end > > end > > > > class Shape > > > >   include Color > > > >   attr\_reader :fill\_color, :border\_color > > > >   def initialize > >     @fill\_color = String.new > >     @border\_color = String.new > >   end > > end > > > > class Square \< Shape > > > >   initialize\_colors > > > > end > > > > sq = Square.new > > puts sq.fill\_color > > sq.set\_fill\_rgb('red') > > puts sq.fill\_color > > -- > > Posted viahttp://www.ruby-forum.com/. ---
**Author:** ![Gavin\_Kistner3](https://avatars.discourse-cdn.com/v4/letter/g/dfb087/32.png) [@Gavin\_Kistner3](https://rubytalk.org/u/Gavin_Kistner3)\ **Post date:** [23 November 2007 03:20 UTC](https://rubytalk.org/t/class-methods-from-modules/42428/3 "2007-11-23T03:20:00Z")
Greg Willits wrote: > In this play code below, I want to use initialize\_colors in either the > class Shape or Square as a class method. Including a module in a class causes instance methods of the module to be in the lookup path for instances of the class. Extending a class using a module causes instance methods of the module to be in the lookup path for the class itself. (See [http://phrogz.net/RubyLibs/RubyMethodLookupFlow.png\](http://phrogz.net/RubyLibs/RubyMethodLookupFlow.png%5C)) A common idiom to be able to cause a class to get both class and instance methods when including a single module follows: module Color   module ClassMethods     def initialize\_colors       p "woot!"     end   end   def giggle     puts "tee hee!"   end   def self.included(receiver)     receiver.extend ClassMethods   end end class Shape   include Color   initialize\_colors   #=\> "woot!" end Shape.new.giggle #=\> "tee hee!" ---
**Author:** ![Greg\_Willits](https://avatars.discourse-cdn.com/v4/letter/g/cab0a1/32.png) [@Greg\_Willits](https://rubytalk.org/u/Greg_Willits)\ **Post date:** [22 November 2007 18:57 UTC](https://rubytalk.org/t/class-methods-from-modules/42428/4 "2007-11-22T18:57:38Z")
Eric I. wrote: > Hi Greg, > > Well the methods you can call \*as\* a class is being defined are > \*class\* methods. initialize\_colors is an instance method, as it > should be since it's setting instance variables. > > It seems to me that you want to call initialize\_colors not as the > class is being defined but as instances are being created. And > therefore the call to initialize\_colors should be inside Square's > initialize method. The exercise is to figure how to make initialize\_colors work as a class method -- so if the instance vars are misleading, then it's those I would change. I am just experiementing to understand with working examples how various syntax and behavior are related in Ruby to acheive various levels of functionality at the class, instance, and module realms. Another way to look at this is that I'm trying to understand how some things in Rails work by replicating them on a micro scale -- in this case a good example might be how the validates\_ methods all work. They're called as class methods from within a subclass and I would expect they're implemented via modules. I've traced the source, but there's too much noise for me at this stage of my Ruby experience. -- gw > **···** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Greg\_Willits](https://avatars.discourse-cdn.com/v4/letter/g/cab0a1/32.png) [@Greg\_Willits](https://rubytalk.org/u/Greg_Willits)\ **Post date:** [23 November 2007 03:46 UTC](https://rubytalk.org/t/class-methods-from-modules/42428/5 "2007-11-23T03:46:13Z")
Gavin Kistner wrote: > Greg Willits wrote: > > > In this play code below, I want to use initialize\_colors in either the > > class Shape or Square as a class method. > > Including a module in a class causes instance methods of the module to > be in the lookup path for instances of the class. Extending a class > using a module causes instance methods of the module to be in the > lookup path for the class itself. > > (See [http://phrogz.net/RubyLibs/RubyMethodLookupFlow.png\](http://phrogz.net/RubyLibs/RubyMethodLookupFlow.png%5C)) > > A common idiom to be able to cause a class to get both class and > instance methods when including a single module follows: Cool, thanks. But... In this code the fill\_color is still never set to black. It seems to me that Module code even if added as class methods cannot access class variables?? -- gw module Color   module ClassMethods     def initialize\_colors       @@fill\_color = 'black'       p "woot!"     end   end   def self.included(receiver)     receiver.extend ClassMethods   end end class Shape   include Color   @@fill\_color = 'white'   initialize\_colors   def self.fill\_color     @@fill\_color   end end Shape.new p Shape.fill\_color > **···** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Greg\_Willits](https://avatars.discourse-cdn.com/v4/letter/g/cab0a1/32.png) [@Greg\_Willits](https://rubytalk.org/u/Greg_Willits)\ **Post date:** [22 November 2007 19:46 UTC](https://rubytalk.org/t/class-methods-from-modules/42428/6 "2007-11-22T19:46:18Z")
I found class \<\< self, but still here's an even simpler example that doesn't work as I thought it would: module Color   def set\_fill(color)     puts "testing"     @@fill\_color = color   end end class Shape   @@fill\_color = 'black'   class \<\< self     include Color   end   def self.fill\_color     @@fill\_color   end end Shape.new puts Shape.fill\_color Shape.set\_fill('red') puts Shape.fill\_color I get: black testing black --gw > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Greg\_Willits](https://avatars.discourse-cdn.com/v4/letter/g/cab0a1/32.png) [@Greg\_Willits](https://rubytalk.org/u/Greg_Willits)\ **Post date:** [23 November 2007 04:54 UTC](https://rubytalk.org/t/class-methods-from-modules/42428/7 "2007-11-23T04:54:42Z")
Greg Willits wrote: > Gavin Kistner wrote: > > > Greg Willits wrote: > > > > > In this play code below, I want to use initialize\_colors in either the > > > class Shape or Square as a class method. > > > > Including a module in a class causes instance methods of the module to > > be in the lookup path for instances of the class. Extending a class > > using a module causes instance methods of the module to be in the > > lookup path for the class itself. > > > > (See [http://phrogz.net/RubyLibs/RubyMethodLookupFlow.png\](http://phrogz.net/RubyLibs/RubyMethodLookupFlow.png%5C)) > > > > A common idiom to be able to cause a class to get both class and > > instance methods when including a single module follows: > > Cool, thanks. But... > > In this code the fill\_color is still never set to black. It seems to me > that Module code even if added as class methods cannot access class > variables? OK, nevermind -- I get it now. even though they have the same name they are actually two independent variables in the two separate "name spaces/realms" of the model & class containers. I thought the "inclusion" would fuse the two spaces into one. -- gw > **···** > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).