使用class_eval和instance_eval访问Ruby类变量

I have the following:

我有以下几点:

class Test
    @@a = 10

    def show_a()
        puts "a: #{@@a}"
    end

    class << self
      @@b = '40'

      def show_b
        puts "b: #{@@b}"
    end
  end
end
class Test