Swift Array - "Int.random(in: 0...25)" 和 "randomElement()" 之间的区别

Question

我最近开始通过在线课程快速学习。

我被赋予了从包含字符的给定数组中生成密码的任务。我们主要学习了两个代码示例，随机选择一个。

1. variable[Int.random(in: 0...25)]
2. variable.randomElement()

当从数组中拉出一个元素时，两者都可以正常工作，但variable[Int.random(in: 0...25)在多次与加号 (+) 组合时只能使用“ ”。

这是为什么？

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我查阅了文档但找不到答案

https://developer.apple.com/documentation/swift/array/2994747-randomelement

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解释：

此代码有效：

let alphabet = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]

//The number of letters in alphabet equals 26
var password = alphabet[Int.random(in: 0...25)] + alphabet[Int.random(in: 0...25)] + alphabet[Int.random(in: 0...25)] + alphabet[Int.random(in: 0...25)] + alphabet[Int.random(in: 0...25)] + alphabet[Int.random(in: 0...25)]  

print(password)

此代码不起作用，因为“randomElement()”在将多个与加号组合后变灰（为什么？）

let alphabet = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]

//The number of letters in alphabet equals 26
var password = alphabet.randomElement() + alphabet.randomElement() + alphabet.randomElement() + alphabet.randomElement() + alphabet.randomElement() + alphabet.randomElement()  

print(password)

编辑：感谢您的快速解释！

Answer 1

区别在于randomElement返回可选字符串 ( String?)，而不是返回非可选的下标。为什么randomElement返回可选字符串？那么，如果数组为空呢？

而且 Swift 无法弄清楚如何添加 2 个可选字符串（更不用说 6 个了！所以它就放弃了）。解决此问题的一种方法是强制解包 的返回值randomElement：

let password = alphabet.randomElement()! + alphabet.randomElement()! + alphabet.randomElement()! + alphabet.randomElement()! + alphabet.randomElement()! + alphabet.randomElement()!

我们知道数组不是空的，所以我们可以在这里安全地强制解包。

可以说，randomElement这里使用的是更好的方法，因为它迫使您考虑数组为空的情况，并相应地处理它。带下标的第一种方法没有检查数组是否为空，或者索引是否正确等。