inherit.rb

module InGem
  class BlueController
    def index
      puts 'in gem'
    end

    class BlueTemplate
      def path
        'blue_template'
      end
    end
  end
end

module Main
  class BlueController < InGem::BlueController
    def index
      puts 'main'
    end

    class BlueTemplate < BlueTemplate
      def path
        'main'
      end
    end
  end
end