A code-ish description of the example depicted in the chapter 25 ("Layers and Boundaries") of "Clean Architecture" book by Bob Martin

layers_and_boundaries.rb

interface GameRulesInputBoundary
  void moveSouth()
end

interface GameRulesOutputBoundary
  void moveSouthSucceed()
end

class GameRules implements GameRulesInputBoundary
  def init(GameRulesOutputBoundary outputBoundary)
    this.outputBoundary = outputBoundary
  end

  @override
  def moveSouth()
    # do business logic
    this.outputBoundary.moveSouthSucceed()
  end
end

-----------------------

interface LanguageInputBoundary
  void parse(message)
end

interface LanguageOutputBoundary
  void movementSucceed()
end

class ItalianLanguageOutputBoundary implements GameRulesOutputBoundary
  def init(LanguageOutputBoundary languageOutputBoundary)
    this.languageOutputBoundary = languageOutputBoundary
  end

  @override
  void moveSouthSucceed()
    this.languageOutputBoundary.movementSucceed("Movimento completato")
  end
end

class ItalianLanguageInputBoundary implement LanguageInputBoundary
  def init(GameRulesInputBoundary gamerules)
    this.gamerules = gamerules
  end

  @override
  def parse(message)
    if message == "muovi sud"
      gamerules.moveSouth()
    end
  end
end

-------------------------

interface TextDeliveryInputBoundary
  void read_message()
end

class ConsoleTextDeliveryInputBoundary implements TextDeliveryInputBoundary
  def init(LanguageInputBoundary inputBoundary)
    this.inputBoundary = inputBoundary
  end

  @override
  void read_message
    message = read_from_command_line
    inputBoundary.parse(message)
  end
end

class ConsoleTextDeliveryOutputBoundary implements LanguageOutputBoundary
  @override
  void movementSucceed(message)
    system.println(message)
  end
end

------------

class main
  def init()
    LanguageOutputBoundary languageOutputBoundary = new ConsoleTextDeliveryOutputBoundary()
    GameRulesOutputBoundary gamerulesOutputBoundary = new ItalianLanguageOutputBoundary(languageOutputBoundary)
    GameRulesInputBoundary gamerules = new GameRules(gamerulesOutputBoundary)
    LanguageInputBoundary languageInputBoundary = new ItalianLanguageInputBoundary(gamerules)
    TextDeliveryInputBoundary textDeliveryInputBoundary = new ConsoleTextDeliveryInputBoundary(languageInputBoundary)

    while true
      textDeliveryInputBoundary.read_message()
    end
  end
end