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学习 swift。

我的任务是从给定的包含字符的数组中生成密码。 我们主要学习了两个代码示例来随机选择一个。

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

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

这是为什么呢？

---

我查阅了文档，但找不到答案

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

---

说明：

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： 感谢你们的快速解释！

Answer 1

不同之处在于randomElement 返回一个可选字符串（String?），而不是返回非可选的下标。为什么randomElement 返回一个可选字符串？那么，如果数组为空呢？

而且 Swift 不知道如何添加 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开 randomElement 的返回值：

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 是在这里使用的更好方法，因为它迫使您考虑数组为空的情况，并进行相应的处理。第一种带下标的方法没有检查数组是否为空，或者索引是否正确等。

Answer 2

这是因为两种方法的返回类型不同。

如您所料，对字符串数组进行索引会返回该索引处的字符串。

但是.randomElement() 函数具有不同的签名：它返回序列的可选元素，在您的情况下是可选字符串（字符串？）。

“+”运算符是为字符串定义的，但不是为可选字符串定义的。要将.randomElement() 返回的元素加在一起，您需要先将它们解包。鉴于你有一个封闭的序列，你可以安全地用'！'强制解开它们：

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

Answer 3

不要多次编写相同的代码，而是尝试一些循环：

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"]
var i = 0
var temp = ""
    //The number of letters in alphabet equals 26
while i < 6 {
    temp = temp + alphabet[Int.random(in: 0...25)]
    i += 1
}
let password = temp
    
print(password)

Answer 4

初学者快速使用以下解决方案

let passwordChrt:Array = [
    "A", "a", "B", "b", "C" , "c", "D", "d", "E", "e", "F", "f", "G", "g", "H", "h",
    "I", "i", "J", "j", "K", "k", "L", "l", "M", "m","N", "n", "O", "o", "P", "p",
    "Q", "q", "R", "r", "S", "s", "T", "t", "U", "u", "V", "v", "W", "w","X", "x", "Y",
    "y", "Z", "z", 1, 2, 3, 4, 5, 6, 7 , 8 ,9, 0, "!", "@", "#", "$", "%", "^", "&", "*"] as [Any] 

var password:String = "" 
passwordChrt.shuffled()
for _ in passwordChrt {
    if password.count < 6 {
        password.append("\(passwordChrt.randomElement() ?? <#default value#>)")

    }
     } 
print(password)

Answer 5

更新，更新的版本：

func randomPassword(length: Int) -> String {
  let letters = "abcdefghijklmnopqrstuvwxyz"
  return String((0..<length).map { _ in letters.randomElement()! })
}
    
print(randomPassword(length: 6)) // e.g. output: "deckro"