I'm trying to find a way to declare class variables in a module that can be mixed into class methods and retain scope for only that particular class instead of being defacto module-variables. Here's a simplified example (albeit somewhat silly) of what i'm trying to do: module Foo module Bar #...some instance methods def self.included(klass) klass.extend(BarClassMethods) end end module BarClassMethods def greeting @@greeting ||= self.determine_greeting end def determine_greeting hello end end end class A include Foo::Bar def self.hello "hello from A" end end class B include Foo::Bar def self.hello "hello from B" end end puts A.greeting #=> 'hello from A' puts B.greeting #=> 'hello from A' The result i would hope for is "hello from A" and "hello from B" respectively. But since @@greeting is really scoped module-wide it is only intialized once. How can i force the class variable to pertain only to the singelton class that mixes it in?
on 2007-01-25 01:56
on 2007-01-25 02:05
uuh-ooh. i guess i could use an instance variable for the Singleton class instead :) > def greeting > @greeting ||= self.determine_greeting > end It seems to have the exact same effect than a class variable defined in the class. Is this correct? On 2007-01-24 18:51:46 -0600, Sebastian <firstname.lastname@example.org> said:
on 2007-01-25 06:17
On Jan 24, 2007, at 8:05 PM, Sebastian wrote: > uuh-ooh. i guess i could use an instance variable for the Singleton > class instead :) > >> def greeting >> @greeting ||= self.determine_greeting >> end That isn't an instance variable for the singleton class. It is an instance variable associated with the class itself. The singleton class for an object acts as a container for method definitions but it is the object itself that has the instance variables. > It seems to have the exact same effect than a class variable > defined in the class. Is this correct? There are various differences but the biggest is that a class instance variable, just like all instance variables, is only accessible via the individual class object and not through any subclasses as would be the case with a class variable. Most Ruby veterans seem to shun Ruby class variables in favor of class instance variables. Despite the name, Ruby class variables are not like class variables in other object oriented languages. Almost always a 'class instance variable' is a better choice. Gary Wright
on 2007-01-25 13:57
> Posted by Sebastian (Guest) on 25.01.2007 01:56 > I'm trying to find a way to declare class variables in a module that > can be mixed into class methods and retain scope for only that > particular class instead of being defacto module-variables. Maybe check out: http://redcorundum.blogspot.com/2006/06/mixing-in-... Cheers, verno