删除数组中的元素而不对索引进行硬编码？在斯威夫特

这是我的第一篇文章，我很高兴加入这个社区。我正在通过 Ray Wenderlich 的视频教程学习 Swift。我在第 3 课中遇到的挑战是删除数组中的元素而不对索引进行硬编码。我理解雷提供的正确答案，但只是不明白为什么我的答案不起作用。请参阅以下雷的回答以及我的回答。如果有人能为我解释一下，那就太好了！！谢谢：]

正确答案：

// Make an array with "C", "C++", and "Objective-C"
var programmingLanguages = ["C", "C++", "Objective-C"]

// Append "Swift" to the array
programmingLanguages += "Swift"

// Insert "Javascript" at Index 2
programmingLanguages.insert("Javscript", atIndex: 2)

// Remove "Objective-C" (without hard-coding the index)
let optIndex = find(programmingLanguages, "Objective-C")
if let defIndex = optIndex {
  programmingLanguages.removeAtIndex(defIndex)
}

programmingLanguages

我的回答1：

// Make an array with "C", "C++", and "Objective-C"
var programmingLanguages = ["C", "C++", "Objective-C"]

// Append "Swift" to the array
programmingLanguages += "Swift"

// Insert "Javascript" at Index 2
programmingLanguages.insert("Javscript", atIndex: 2)

// Remove "Objective-C" (without hard-coding the index)
programmingLanguages.removeAtIndex(find(programmingLanguages,"Objective-C")

programmingLanguages

我的回答2：

// Make an array with "C", "C++", and "Objective-C"
var programmingLanguages = ["C", "C++", "Objective-C"]

// Append "Swift" to the array
programmingLanguages += "Swift"

// Insert "Javascript" at Index 2
programmingLanguages.insert("Javscript", atIndex: 2)

// Remove "Objective-C" (without hard-coding the index)
let optIndex = find(programmingLanguages, "Objective-C")
programmingLanguages.removeAtIndex(optIndex)

programmingLanguages

当你使用find()它不保证返回结果（这里会发生什么？：find(programmingLanguages, "rick astley"))

考虑到这种可能性find()返回一个“optional https://developer.apple.com/library/prerelease/mac/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html#//apple_ref/doc/uid/TP40014097-CH5-XID_427“ - 这基本上意味着当它找不到匹配项时它将返回nil.

为了保护您不误使用nil在某些不知道如何处理它的地方，该语言将可选类型视为一种独特的类型。简而言之，你must当您获得可选值时检查是否为零。

主要方法是使用“if let”语法——如 Ray 的示例所示——但更简洁（也更常见）的方法如下所示：

if let defIndex = find(programmingLanguages, "Objective-C") {
  programmingLanguages.removeAtIndex(defIndex)
}

如果您确定该选项不是nil（就像如果你正在检查你想要的东西just插入）您可以使用“强制展开”从可选值中获取值（如果是，则会导致错误并崩溃nil).

您可以使用强制展开运算符（感叹号）进行强制展开!:

// defIndex is an optional
let defIndex = find(programmingLanguages, "Objective-C")

// defIndex!  <-- unwraps the optional but raises an error if it's nil
programmingLanguages.removeAtIndex(defIndex!)