“字符不可用”，请直接使用字符串 [英] 'characters is unavailable' please use string directly

问题描述

我不知道如何解决它。我只想了解它的工作原理以及应该替换的内容。

I can't figure out how to fix it. I just want to understand how it works and what should be replaced.

我已经尝试删除个字符。

I've already tried to delete characters., but it still doesn't work.

import Foundation
var shrinking = String("hello")
repeat {
    print(shrinking)
    shrinking = String(shrinking.characters.dropLast())
}
while shrinking.characters.count > 0

我希望程序输出：

你好

地狱

hel

he

h

hello
hell
hel
he
h

，但根本不起作用。

推荐答案

您的代码如果删除字符应该可以正常工作，建议您创建一个新的Playground文件。顺便说一句，您可以简单地使用 RangeReplaceableCollection 变异方法 popLast 并在字符串不为空时进行迭代，以避免调用集合计数属性多次：

Your code should work as it is if you delete the characters I suggest you create a new playground file. Btw you can simply use RangeReplaceableCollection mutating method popLast and iterate while your string is not empty to avoid calling your collection count property multiple times:

var shrinking = "hello"
repeat {
    print(shrinking)
    shrinking.popLast()
} while !shrinking.isEmpty

这将打印

你好

hello

地狱

hel

he

h

或使用 removeLast 方法，但它要求字符串不为空，因此您需要在关闭前检查字符串是否为空：

or using removeLast method but it requires the string not to be empty so you would need to check if the string is empty at before the closure:

var shrinking = "hello"

while !shrinking.isEmpty {
    print(shrinking)
    shrinking.removeLast()
}

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