aproxacs

In ruby, there is no public variable. All variables in object are hidden encapsulated. To access objects’ variables, getter and setter methods are necessary. It may sound painful if I have to make all the getter/setter methods. But don’t worry. Ruby has a smart solution. attr_accessor.

attr_accessor :school
attr_reader :student
attr_writer :student

This is good. With a simple declaration, encapsulation is achieved. It is OK for instance variables, but what about class variables? Unfortunately, ruby core does not have the attr_xxx for class variables. However, It is not that difficult to implement.

class Class
  def cattr_accessor(name)
    class_eval <<-EOS
        unless defined? @@#{name}
          @@#{name} = nil
        end                      

        def self.#{name}
          @@#{name}
        end                      

        def self.#{name}=(obj)
          @@#{name} = obj
        end
    EOS
  end
end

class Test
  cattr_accessor :greet
end

Test.greet = "hello"
p Test.greet

ActiveSupport

There is a easier way if you set up your mind to use activesupport. Activesupport already implemented cattr_xxx and mattr_xxx serieses.

require "activesupport"
class ClassTest
  cattr_accessor :greet
end
module ModuleTest
  mattr_accessor :greet
end 

cattr_xxx works for class variables, and mattr_xxx wors for module variables.