Question

我试图以相反的顺序迭代但是在while循环中它无限期地运行并打印4 ...

func countDown(start: Int) -> AnyIterator<Int> { 
var i = start
return AnyIterator {
    guard i > 0 else { return nil }
    i -= 1
    return i
    }
}

let  i = 5
while let x = countDown(start: i).next() {
    print("Element x: \(x)" ) // It iterates indefinitely.
}

Answer 1

因为每次都会调用该函数，并且每次都在创建一个新的迭代器。

let  i = 5
let it = countDown(start: i)
while let x = it.next() {
    print("Element x: \(x)" ) // It no longer iterates indefinitely.
}

为什么，while循环在这里无限期运行？

1 个答案: