method_missing

method_missing.rb

class InfoDesk
  def trains
    :trains
  end
  def flights
    :flights
  end
  def buses
    :buses
  end
end

class Clock
  def self.lunch_time?
    true
  end
end

class Sign < BasicObject
  def initialize
    @desk = ::InfoDesk.new
  end

  def method_missing(method, *args, &block)
    return super unless @desk.respond_to?(method)

    singleton_class = class << self; self; end
    singleton_class.send(:define_method, method) do
      return 'out to lunch' if ::Clock.lunch_time?
      @desk.send(method, *args, &block)
    end
    __send__(method, *args, &block)
  end

  def respond_to?(method)
    @desk.respond_to?(method) || super
  end
end

sign = Sign.new
p sign.respond_to?(:trains)
p sign.trains