| 选择器 | 说明 |
|---|---|
div.classname | 具有特定类名的 Div |
div#idname | 具有特定 ID 的 Div |
div p | div中的段落 |
div > p | 所有 p 个标签 div 深处的一层 |
div + p | div 之后的 P 标签 |
div ~ p | div 前面的 P 标签 |
| 选择器 | 说明 |
|---|---|
div.classname | 具有特定类名的 div |
div#idname | 具有特定 ID 的 div |
div p | div 中的段落 |
div > p | div 子节点中的所有 P 标签 |
div + p | div 之后的 P 标签 |
div ~ p | div 前面的 P 标签 |
该备忘单提供了使用 Swift 的示例，涵盖 Swift 基础知识、控制流、类型、结构/类、运算符、函数方法等。
+var score = 0 // 变量
+let pi = 3.14 // 常数
+
+var greeting = "Hello"
+var numberOfToys = 8
+var isMorning = true
+
+var numberOfToys: Int = 8
+numberOfToys += 1
+print(numberOfToys) // 打印 "9"
+var greeting: String = "Hello"
+var numberOfToys: Int = 8
+var isMorning: Bool = true
+var price: Double = 8.99
++ 添加- 减法* 乘法/ 分配% 余数var x = 0
+x = 4 + 2 // x 现在是 6
+x = 4 - 2 // x 现在是 2
+x = 4 * 2 // x 现在是 8
+x = 4 / 2 // x 现在是 2
+x = 4 % 2 // x 现在是 0
+var numberOfDogs = 100
+numberOfDogs += 1
+print("有 \(numberOfDogs) 个斑点狗！")
+// 打印: 有 101 个斑点狗！
++= 添加和分配总和-= 减去并分配差值*= 乘并赋值/= 除并分配商%= 除并分配余数var apples = 6
+print("I have \(apples) apples!")
+// 打印: I have 6 apples!
+let myLongString = """
+Swift?
+这是我最喜欢的语言！
+"""
+// 这一行表示 Swift 中的注释。
+/*
+这都被注释掉了。
+没有一个会跑！
+*/
+let player = ("Maya", 5, 150)
+
+print(player) // ("Maya", 5, 150)
+print("\(player.0): level \(player.1), \(player.2) pts") // Maya: level 5, 150 pts
+let player = (name: "Maya", level: 5)
+let (currentName, curLevel) = player
+print("\(currentName): level \(curLevel)")
+// 打印: Maya: level 5
+// MARK: - 查看设置
+MARK 可用于在栏中显示评论
// TODO: 更新逻辑以适应数据更改
+TODO 用于显示需要完成的事情的提醒
// FIXME: 修复对现有条目进行更改时的故障行为
+FIXME 用于显示需要修复的内容的提醒
变量用 var 声明：
var greeting = "你好"
+var numberOfToys = 8
+var isMorning = true
+为了清楚起见，变量声明可以包含类型注释：
+var greeting: String = "你好"
+var numberOfToys: Int = 8
+var isMorning: Bool = true
+变量是可变的。 它们的值可以改变：
+var numberOfToys: Int = 8
+numberOfToys += 1
+print(numberOfToys) // 打印“9”
+常量用 let 声明：
let greeting = "Hello"
+let numberOfToys = 8
+let isMorning = true
+为清楚起见，常量声明可以包含类型注释：
+let greeting: String = "Hello"
+let numberOfToys: Int = 8
+let isMorning: Bool = true
+常量是不可变的。它们的值不能改变：
+让 numberOfToys: Int = 8
+numberOfToys += 1
+// ❌ 错误：numberOfToys 不可变
+import Foundation
+
+let df = DateFormatter()
+df.dateFormat = "d MMMM yyyy"
+
+var birth = df.date(from: "5 June 1999")!
+
+var age: Int {
+ Calendar.current
+ .dateComponents([.year],
+ from: birth,
+ to: Date()).year!
+}
+
+print(age) // 20
+birth = df.date(from: "5 June 2002")!
+print(age) // 17
+在下面的示例中，distanceInFeet 有一个 getter 和一个 setter。 因为有 setter，所以 getter 需要关键字 get：
var distanceInMeters: Float = 100
+
+var distanceInFeet: Float {
+ get {
+ distanceInMeters * 3.28
+ }
+ set(newDistance) {
+ distanceInMeters = newDistance / 3.28
+ }
+}
+
+print(distanceInMeters) // 100.0
+print(distanceInFeet) // 328.0
+
+distanceInFeet = 250
+print(distanceInMeters) // 76.21951
+print(distanceInFeet) // 250.0
+
+distanceInMeters = 800
+print(distanceInMeters) // 800.0
+print(distanceInFeet) // 2624.0
+var distance = 5 {
+ willSet {
+ print("距离将被设置")
+ }
+}
+
+distance = 10 // 打印: 距离将被设置
+可以在 willSet 中访问新值：
var distance = 5 {
+ willSet(newDistance) {
+ print("距离将被设置 \(newDistance)")
+ }
+}
+
+distance = 10 // 打印: 距离将被设置 10
+willSet 可用于在设置变量值之前执行一些代码
var distance = 5 {
+ didSet {
+ print("距离设置为 \(distance)")
+ print("它的旧值是： \(oldValue)")
+ }
+}
+distance = 10 // 打印: 距离将被设置 10
+ // 打印: 它的旧值是：5
+var distance = 5 {
+ willSet(newDistance) {
+ print("距离将设置为 \(newDistance)")
+ }
+ didSet {
+ print("距离设置为 \(distance)")
+ print("它的旧值是： \(oldValue)")
+ }
+}
+distance = 10
+var halloween = true
+if halloween {
+ print("不给糖就捣蛋！")
+}
+// 打印: 不给糖就捣蛋！
+if 5 > 3 {
+ print("5 大于 3")
+} else {
+ print("5 不超过 3")
+}
+// 输出: "5 大于 3"
+var turbulence = false
+
+if turbulence {
+ print("请坐好。")
+} else {
+ print("你可以自由地四处走动。")
+}
+// 打印: 你可以自由地四处走动。
+var weather = "rainy"
+if weather == "sunny" {
+ print("拿点防晒霜")
+} else if weather == "rainy" {
+ print("拿一把雨伞")
+} else if weather == "snowing" {
+ print("穿上你的雪地靴")
+} else {
+ print("无效天气")
+}
+// 打印: 拿一把雨伞
+5 > 1 // true
+6 < 10 // true
+2 >= 3 // false
+3 <= 5 // true
+"A" == "a" // false
+"B" != "b" // true
+< 小于> 大于<= 小于或等于>= 大于或等于== 等于!= 不等于var driverLicense = true
+
+driverLicense
+ ? print("驾驶座") : print("乘客座位")
+// 打印: 驾驶座
+var secondaryColor = "green"
+
+switch secondaryColor {
+ case "orange":
+ print("红色和黄色的混合")
+ case "purple":
+ print("红色和蓝色的混合")
+ default:
+ print("这可能不是辅助颜色")
+}
+// 打印: 蓝色和黄色的混合
+let year = 1905
+var artPeriod: String
+
+switch year {
+ case 1860...1885:
+ artPeriod = "印象派"
+ case 1886...1910:
+ artPeriod = "后印象派"
+ default:
+ artPeriod = "未知"
+}
+// 打印: 后印象派
+let service = "Seamless"
+
+switch service {
+ case "Uber", "Lyft":
+ print("旅行")
+ case "DoorDash", "Seamless", "GrubHub":
+ print("餐厅送餐")
+ case "Instacart", "FreshDirect":
+ print("杂货配送")
+ default:
+ print("未知服务")
+}
+// 打印: 餐厅外卖
+let num = 7
+
+switch num {
+ case let x where x % 2 == 0:
+ print("\(num) 是偶数")
+ case let x where x % 2 == 1:
+ print("\(num) 奇数")
+ default:
+ print("\(num) 无效")
+}
+
+// 打印: 7 奇数
+!true // false
+!false // true
+true && true // true
+true && false // false
+false && true // false
+false && false // false
+true || true // true
+true || false // true
+false || true // true
+false || false // false
+!false && true || false // true
+!false && true 首先计算并返回 true 然后，表达式，true || false 评估并返回最终结果 true
false || true && false // false
+true && false 首先计算返回 false 然后，表达式，false || false 评估并返回最终结果 false
// 没有括号：
+true || true && false || false
+// ----> true
+
+// 带括号：
+(true || true) && (false || false)
+// ----> false
+func greet(name: String?) {
+ guard let unwrapped = name else {
+ print("Hello guest!")
+ return
+ }
+ print("Hello \(unwrapped)!")
+}
+greet(name: "Asma") // 输出：Hello Asma!
+greet(name: nil) // 输出：Hello guest!
+let zeroToThree = 0...3
+// zeroToThree: 0, 1, 2, 3
+for oddNum in stride(from: 1, to: 5, by: 2) {
+ print(oddNum)
+}
+// 打印: 1
+// 打印: 3
+for char in "hehe" {
+ print(char)
+}
+// 打印: h
+// 打印: e
+// 打印: h
+// 打印: e
+for num in 0...5 {
+ if num % 2 == 0 {
+ continue
+ }
+ print(num)
+}
+// 打印: 1
+// 打印: 3
+// 打印: 5
+continue 关键字将强制循环继续进行下一次迭代
for char in "supercalifragilistice" {
+ if char == "c" {
+ break
+ }
+ print(char)
+}
+// 打印: s
+// 打印: u
+// 打印: p
+// 打印: e
+// 打印: r
+for _ in 1...3 {
+ print("Olé")
+}
+// 打印: Olé
+// 打印: Olé
+// 打印: Olé
+var counter = 1
+var stopNum = Int.random(in: 1...10)
+
+while counter < stopNum {
+ print(counter)
+ counter += 1
+}
+// 循环打印，直到满足停止条件
+while 循环接受一个条件，并在所提供的条件为 true 时持续执行其主体代码。如果条件从不为假，则循环将继续运行，程序将陷入无限循环
var scores = [Int]()
+// 数组为空：[]
+var grocery = ["🥓", "🥞", "🍪", "🥛", "🍊"]
+print(grocery.count)
+// 打印: 5
+索引是指项目在有序列表中的位置，使用下标语法 array[index] 从数组中检索单个元素。
var vowels = ["a", "e", "i", "o", "u"]
+
+print(vowels[0]) // 打印: a
+print(vowels[1]) // 打印: e
+print(vowels[2]) // 打印: i
+print(vowels[3]) // 打印: o
+print(vowels[4]) // 打印: u
+注意：Swift 数组是零索引的，这意味着第一个元素的索引为 0。
+// 使用类型推断：
+var snowfall = [2.4, 3.6, 3.4, 1.8, 0.0]
+// 明确类型：
+var temp: [Int] = [33, 31, 30, 38, 44]
+var gymBadges = ["Boulder", "Cascade"]
+gymBadges.append("Thunder")
+gymBadges += ["Rainbow", "Soul"]
+// ["Boulder", "Cascade", "Thunder",
+// "Rainbow", "Soul"]
+var moon = ["🌖", "🌗", "🌘", "🌑"]
+moon.insert("🌕", at: 0)
+// ["🌕", "🌖", "🌗", "🌘", "🌑"]
+
+moon.remove(at: 4)
+// ["🌕", "🌖", "🌗", "🌘"]
+var employees = ["小王", "张三", "王五"]
+for person in employees {
+ print(person)
+}
+// 打印: 小王
+// 打印: 张三
+// 打印: 王五
+var paintingsInMOMA: Set = [
+ "The Dream",
+ "The Starry Night",
+ "The False Mirror"
+]
+我们可以使用集合(Set)来存储相同数据类型的唯一元素
var team = Set<String>()
+
+print(team)
+// 打印: []
+var vowels: Set = ["a", "e", "i", "o","u"]
+要创建一个填充有值的集合，请在赋值运算符之前使用 Set 关键字。
var cookieJar: Set = [
+ "Chocolate Chip",
+ "Oatmeal Raisin"
+]
+// 添加一个新元素
+cookieJar.insert("Peanut Butter Chip")
+var oddNumbers: Set = [1, 2, 3, 5]
+
+// 移除现有元素
+oddNumbers.remove(2)
+// 删除所有元素
+oddNumbers.removeAll()
+var names: Set = ["Rosa", "Doug", "Waldo"]
+print(names.contains("Lola")) //打印: false
+
+if names.contains("Waldo"){
+ print("There's Waldo!")
+} else {
+ print("Where's Waldo?")
+}
+// 打印: There's Waldo!
+var recipe: Set = ["蛋", "面粉", "糖"]
+
+for ingredient in recipe {
+ print ("在配方中包含\(ingredient)")
+}
+var emptySet = Set<String>()
+print(emptySet.isEmpty) // 打印: true
+
+var populatedSet: Set = [1, 2, 3]
+print(populatedSet.isEmpty) // 打印: false
+var band: Set = ["张三", "王五", "赵六"]
+
+print("乐队有 \(band.count) 名演奏者。")
+// 打印: 乐队有 4 名演奏者。
+var setA: Set = ["A", "B", "C", "D"]
+var setB: Set = ["C", "D", "E", "F"]
+
+var setC = setA.intersection(setB)
+print(setC) // 打印: ["D", "C"]
+var setA: Set = ["A", "B", "C", "D"]
+var setB: Set = ["C", "D", "E", "F"]
+
+var setC = setA.union(setB)
+print(setC)
+// 打印: ["B", "A", "D", "F", "C", "E"]
+var setA: Set = ["A", "B", "C", "D"]
+var setB: Set = ["C", "D", "E", "F"]
+
+var setC = setA.symmetricDifference(setB)
+print(setC)
+// 打印: ["B", "E", "F", "A"]
+var setA: Set = ["A", "B", "C", "D"]
+var setB: Set = ["C", "D"]
+
+var setC = setA.subtracting(setB)
+print(setC)
+// 打印: ["B", "A"]
+var dictionaryName = [
+ "Key1": "Value1",
+ "Key2": "Value2",
+ "Key3": "Value3"
+]
+成对数据或键值对的无序集合
var fruitStand = [
+ "Coconuts": 12,
+ "Pineapples": 12,
+ "Papaya": 12
+]
+每个键都是唯一的，即使它们都包含相同的值
var numberOfSides = [
+ "triangle": 3,
+ "square": 4,
+ "rectangle": 4
+]
+仅包含 String 键和 Int 值
var employeeID = [
+ "Hamlet": 1367,
+ "Horatio": 8261,
+ "Ophelia": 9318
+]
+// 初始化器语法：
+var yearlyFishPopulation = [Int: Int]()
+
+// 空字典字面量语法：
+var yearlyBirdPopulation: [Int: Int] = [:]
+var pronunciation = [
+ "library": "lai·breh·ree",
+ "apple": "a·pl"
+]
+// 新键：“programming”，新值：“prow·gra”
+pronunciation["programming"] = "prow·gra"
+var bookShelf = [
+ "Goodnight": "Margaret Wise Brown",
+ "The BFG": "Roald Dahl",
+ "Falling Up": "Shel Silverstein",
+ "No, David!": "David Shannon"
+]
+
+// 通过将 key 设置为 nil 来删除值
+bookShelf["The BFG"] = nil
+
+// 使用 .removeValue() 删除值
+bookShelf.removeValue(forKey: "Goodnight")
+
+// 删除所有值
+bookShelf.removeAll()
+var change = [
+ "Quarter": 0.29,
+ "Dime": 0.15,
+ "Nickel": 0.05
+]
+
+// 使用下标语法更改值
+change["Quarter"] = .25
+
+// 使用 .updateValue() 更改值
+change.updateValue(.10, forKey: "Dime")
+要更改键值对的值，请使用 .updateValue() 方法或下标语法，通过将括号 [ ] 和其中的现有键附加到字典的名称，然后添加赋值运算符 (=) 后跟修改后的值
var bakery = [String:Int]()
+
+// 检查字典是否为空
+print(bakery.isEmpty) // 打印 true
+bakery["Cupcakes"] = 12
+// 检查字典是否为空
+print(bakery.isEmpty) // 打印 false
+var fruitStand = [
+ "Apples": 12,
+ "Oranges", 17
+]
+print(fruitStand.count) // 打印: 2
+var hex = [
+ "red": "#ff0000",
+ "yellow": "#ffff00",
+ "blue": "#0000ff",
+]
+
+print("蓝色十六进制代码 \(hex["blue"])")
+// 打印: 蓝色十六进制代码 Optional("#0000ff")
+
+if let redHex = hex["red"] {
+ print("红色的十六进制代码 \(redHex)")
+}
+// 打印: 红色的十六进制代码 #ff0000
+将键值对的值分配给变量将返回一个可选值。要提取值，请使用可选的展开
+var emojiMeaning = [
+ "🤔": "Thinking Face",
+ "😪": "Sleepy Face",
+ "😵": "Dizzy Face"
+]
+// 遍历键和值
+for (emoji, meaning) in emojiMeaning {
+ print("\(emoji)被称为'\(meaning)Emoji'")
+}
+// 仅通过键迭代
+for emoji in emojiMeaning.keys {
+ print(emoji)
+}
+// 仅通过值迭代
+for meaning in emojiMeaning.values {
+ print(meaning)
+}
+func washCar() -> Void {
+ print("Soap")
+ print("Scrub")
+ print("Rinse")
+ print("Dry")
+}
+func greetLearner() {
+ print("欢迎来到 Quick Reference!")
+}
+// 函数调用：
+greetLearner()
+// 打印: 欢迎来到 Quick Reference!
+let birthYear = 1994
+var currentYear = 2020
+
+func findAge() -> Int {
+ return currentYear - birthYear
+}
+
+print(findAge()) // 打印: 26
+func convertFracToDec(numerator: Double, denominator: Double) -> Double {
+ return numerator / denominator
+}
+
+let decimal = convertFracToDec(numerator: 1.0, denominator: 2.0)
+print(decimal) // Prints: 0.5
+func findDiff(_ a: Int, b: Int) -> Int {
+ return a - b
+}
+
+print(findDiff(6, b: 4)) // 打印: 2
+func smartphoneModel() -> (name: String, version: String, yearReleased: Int) {
+ return ("iPhone", "8 Plus", 2017)
+}
+
+let phone = smartphoneModel()
+
+print(phone.name) // 打印: iPhone
+print(phone.version) // 打印: 8 Plus
+print(phone.yearReleased) // 打印: 2017
+func findSquarePerimet(side: Int) -> Int {
+ return side * 4
+}
+
+let perimeter = findSquarePerimet(side: 5)
+print(perimeter) // 打印: 20
+
+// Parameter: side
+// Argument: 5
+func nextTotalSolarEclipse() -> String {
+ "April 8th, 2024 🌎"
+}
+
+print(nextTotalSolarEclipse())
+// 打印: April 8th, 2024 🌎
+func greet(person: String = "guest") {
+ print("Hello \(person)")
+}
+greet() // Hello guest
+greet(person: "Aliya") // Hello Aliya
+var currentSeason = "冬天"
+
+func season(month: Int, name: inout String) {
+ switch month {
+ case 1...2:
+ name = "冬天 ⛄️"
+ case 3...6:
+ name = "春天 🌱"
+ case 7...9:
+ name = "夏天 ⛱"
+ case 10...11:
+ name = "秋天 🍂"
+ default:
+ name = "未知"
+ }
+}
+
+season(monthNum: 4, name: ¤tSeason)
+
+print(currentSeason) // 春天 🌱
+func totalStudent(data: String...) -> Int {
+ let numStudents = data.count
+ return numStudents
+}
+
+print(totalStudent(data: "王五", "张三"))
+// 打印: 2
+func getFirstInitial(from name: String?) -> String? {
+ return name?.first
+}
+函数可以接受可选类型并返回可选类型。当一个函数不能返回请求类型的合理实例时，它应该返回 nil
struct Building {
+ var address: String
+ var floors: Int
+
+ init(address: String, floors: Int) {
+ self.address = address
+ self.floors = floors
+ }
+}
+结构或结构用于以编程方式在代码中表示现实生活中的对象。结构是使用 struct 关键字创建的，后跟其名称，然后是包含其属性和方法的主体
struct Car {
+ var numOfWheels = 4
+ var topSpeed = 80
+}
+
+var reliantRobin = Car(numOfWheels: 3)
+
+print(reliantRobin.numOfWheels) // 打印: 3
+print(reliantRobin.topSpeed) // 打印: 80
+struct Person {
+ var name: String
+ var age: Int
+
+ init(name: String, age: Int) {
+ self.name = name
+ self.age = age
+ }
+}
+
+// Person 实例：
+var morty = Person(name: "张三", age: 14)
+struct TV {
+ var size: Int
+ var type: String
+
+ init(size: Int, type: String) {
+ self.size = size
+ self.type = type
+ }
+}
+使用 TV 类
var newTV = TV(size: 65, type: "LED")
+print(type(of: "abc")) // 打印: String
+print(type(of: 123)) // 打印: 123
+struct Menu {
+ var menuItems = ["Fries", "Burgers"]
+ mutating func addToMenu(dish: String) {
+ self.menuItems.append(dish)
+ }
+}
+使用 Menu 类
var dinerMenu = Menu()
+dinerMenu.addToMenu(dish: "Toast")
+print(dinerMenu.menuItems)
+// 打印: ["Fries", "Burgers", "Toast"]
+struct Dog {
+ func bark() {
+ print("Woof")
+ }
+}
+let fido = Dog()
+fido.bark() // 打印: Woof
+class Player {
+ var name: String
+
+ init(name: String) {
+ self.name = name
+ }
+}
+
+var player1 = Player(name: "Tomoko")
+var player2 = player1
+player2.name = "Isabella"
+
+print(player1.name) // Isabella
+print(player2.name) // Isabella
+class Person {
+ var name = ""
+ var age = 0
+}
+
+var sonny = Person()
+// sonny 现在是 Person 的一个实例
+class Fruit {
+ var hasSeeds = true
+ var color: String
+
+ init(color: String) {
+ self.color = color
+ }
+}
+使用 Fruit 类
+let apple = Fruit(color: "red")
+可以使用 init() 方法和相应的初始化属性来初始化类，在 init() 方法中，self 关键字用于引用类分配属性值的实际实例
var ferris = Student()
+
+ferris.name = "Ferris Bueller"
+ferris.year = 12
+ferris.gpa = 3.81
+ferris.honors = false
+假设我们有一个 BankAccount 类：
+class BankAccount {
+ var balance = 0.0
+ func deposit(amount: Double) {
+ balance += amount
+ }
+ func withdraw(amount: Double) {
+ balance -= amount
+ }
+}
+SavingsAccount 继承 BankAccount 类
class SavingsAccount: BankAccount {
+ var interest = 0.0
+
+ func addInterest() {
+ let interest = balance * 0.005
+ self.deposit(amount: interest)
+ }
+}
+新的 SavingsAccount 类(子类)自动获得了 BankAccount 类(超类)的所有特征。 此外，SavingsAccount 类定义了一个 .interest 属性和一个 .addInterest() 方法。
使用数据类型
+class Student {
+ var name: String
+ var year: Int
+ var gpa: Double
+ var honors: Bool
+}
+使用默认属性值
+class Student {
+ var name = ""
+ var gpa = 0.0
+ var honors = false
+}
+struct Resolution {
+ var width = 0
+ var height = 0
+}
+class VideoMode {
+ var resolution = Resolution()
+ var interlaced = false
+ var frameRate = 0.0
+ var name: String?
+}
+Resolution 结构定义和 VideoMode 类定义仅描述 Resolution 或 VideoMode 的外观，创建结构或类的实例：
let resolution = Resolution(width: 1920)
+let someVideoMode = VideoMode()
+enum Day {
+ case monday
+ case tuesday
+ case wednesday
+ case thursday
+ case friday
+ case saturday
+ case sunday
+}
+
+let casualWorkday: Day = .friday
+enum Dessert {
+ case cake(flavor: String)
+ case vanillaIceCream(scoops: Int)
+ case brownie
+}
+
+let customerOrder: Dessert = .cake(flavor: "红色天鹅绒")
+switch customerOrder {
+ case let .cake(flavor):
+ print("你点了一个 \(flavor) 蛋糕")
+ case .brownie:
+ print("你点了一块巧克力蛋糕")
+}
+// 打印: "你点了一个红色天鹅绒蛋糕"
+enum Season: CaseIterable {
+ case winter
+ case spring
+ case summer
+ case fall
+}
+
+for season in Season.allCases {
+ print(season)
+}
+添加对 CaseIterable 协议的一致性以访问 allCases 属性，该属性返回枚举的所有案例的数组
enum Beatle: String {
+ case john, paul, george, ringo
+}
+
+print("披头士是 \(Beatle.john.rawValue).")
+// 打印: 披头士是 john.
+enum Dessert {
+ case cake(flavor: String)
+ case vanillaIceCream(scoops: Int)
+ case brownie
+}
+
+let order: Dessert = .cake(flavor: "红色天鹅绒")
+enum Traffic {
+ case light
+ case heavy
+
+ mutating func reportAccident() {
+ self = .heavy
+ }
+}
+
+var currentTraffic: Traffic = .light
+
+currentTraffic.reportAccident()
+// currentTraffic 现在是 .heavy
+就像类和结构一样，枚举也可以有实例方法。如果实例方法改变了枚举的值，则需要将其标记为 mutating
enum Hello: String {
+ case english = "Hello"
+ case japanese = "你好呀！"
+ case emoji = "👋"
+}
+let hello1 = Hello(rawValue: "你好呀！")
+let hello2 = Hello(rawValue: "Привет")
+print(hello1) // Optional(Hello.japanese)
+print(hello2) // nil
+enum ShirtSize: String {
+ case small = "S"
+ case medium = "M"
+ case large = "L"
+ case extraLarge = "XL"
+ var description: String {
+ return "这件衬衫尺码是 \(self.rawValue)"
+ }
+}
+