ruby class var foo

test.rb

require 'active_support'
module ModuleA
  def self.included(c)
    c.class_attribute :foo
    c.extend ClassMethods
  end


  module ClassMethods
    def set_foo(value)
      self.foo = value
    end
  end
end

class ClassA
  include ModuleA
  set_foo 'foo'
end

class ClassAA
  include ModuleA
  set_foo 'bar'
end

class ClassB < ClassA
  
end

puts "A: #{ClassA.foo} (should be foo)"
puts "AA: #{ClassAA.foo} (should be bar)"
puts "B: #{ClassB.foo} (shoule be foo)"