meta.rb

module Runnable
  def run(command, *args)
    fail "#{command} is not a valid action!" unless actions.include? command
    send(command, *args)
  end

  def runnables(*args)
    define_singleton_method(:actions) do
      args.map(&:to_s)
    end
  end
end
  
class MyObj
  extend Runnable
  runnables :hello

  def self.hello(name)
    puts "hello #{name}"
  end
end

puts MyObj.actions # ["hello"]
puts MyObj.run("hello", "Bob") #hello bob