传递和返回功能

以下函数返回另一个函数作为其结果，稍后可以将其分配给变量并调用：

func jediTrainer () -> ((String, Int) -> String) {
  func train(name: String, times: Int) -> (String) {
    return "\(name) has been trained in the Force \(times) times"
  }
  return train
}

let train = jediTrainer()
train("Obi Wan", 3)