以下函数返回另一个函数作为其结果，可以稍后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)