クラス変数とモジュール

a.rb

class A
  @@a = 1
end

b.rb

class B < A
  @@b = 2
  m_def
end

c.rb

class B < A
  puts "can access @@a #{@@a}" rescue puts "cannot access @@a"
  puts "can access @@b #{@@b}" rescue puts "cannot access @@b"
  puts "can access @@mv1 #{@@mv1}" rescue puts "cannot access @@mv1"
  puts "can access @@mv2 #{@@mv2}" rescue puts "cannot access @@mv2"
  mm1 rescue puts "cannot call mm1"
  mm2 rescue puts "cannot call mm2"
end

class A
  puts "can access @@a #{@@a}" rescue puts "cannot access @@a"
  puts "can access @@b #{@@b}" rescue puts "cannot access @@b"
  puts "can access @@mv1 #{@@mv1}" rescue puts "cannot access @@mv1"
  puts "can access @@mv2 #{@@mv2}" rescue puts "cannot access @@mv2"
  mm1 rescue puts "cannot call mm1"
  mm2 rescue puts "cannot call mm2"
end

m.rb

module M
  extend ActiveSupport::Concern

  module ClassMethods
    def m_def
      self.class_eval do
        @@mv1 = 3

        def self.mm1
          puts 'called mm1'
        end
      end

      self.class_eval <<-EOS
        @@mv2 = 4

        def self.mm2
          puts 'called mm2'
        end
      EOS

      def mm3
        puts 'called mm3'
      end
    end
  end
end

A.send :include, M

test.rb

require 'rubygems'
require 'active_support'
require './a'
require './m'
require './b'
require './c'