Swift 编程语言学习笔记#

Swift 是 Apple 于 2014 年推出的现代编程语言，用于开发 iOS、macOS、watchOS 和 tvOS 应用。

基础语法#

变量与常量#

1
// 使用 let 声明常量
2
let maxLoginAttempts = 10
3
let welcomeMessage: String = "Hello, Swift!"
4

5
// 使用 var 声明变量
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var currentLoginAttempt = 0
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var x = 0.0, y = 0.0, z = 0.0
8

9
// 类型推断
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let meaningOfLife = 42        // Int
11
let pi = 3.14159              // Double
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let anotherPi = 3 + 0.14159   // Double

数据类型#

1
// 整数类型
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let minValue = UInt8.min    // 0
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let maxValue = UInt8.max    // 255
4

5
// 浮点数
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let floatValue: Float = 3.14
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let doubleValue = 3.14159265359
8

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// 字符串
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let name = "Swift"
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let greeting = "Hello, \(name)!"  // 字符串插值
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// 数组
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var skills = ["Python", "JavaScript"]
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skills.append("Swift")
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let immutableArray = [1, 2, 3]
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// 字典
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var userInfo: [String: Any] = [
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    "name": "John",
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    "age": 25,
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    "isDeveloper": true
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]
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userInfo["city"] = "Beijing"
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// 集合
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var favoriteGenres: Set<String> = ["Rock", "Classical", "Hip hop"]
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favoriteGenres.insert("Jazz")

控制流#

条件语句#

1
// if 语句
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let temperature = 22
3
if temperature <= 18 {
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    print("天气较凉")
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} else if temperature >= 30 {
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    print("天气炎热")
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} else {
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    print("天气舒适")
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}
10

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// 三元运算符
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let status = temperature >= 25 ? "温暖" : "凉爽"
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14
// switch 语句
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let fruit = "Apple"
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switch fruit {
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case "Apple":
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    print("这是一个苹果")
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case "Banana":
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    print("这是一根香蕉")
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case "Orange", "Mango":      // 多个值匹配
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    print("这是橙子或芒果")
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default:
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    print("未知水果")
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}
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// 范围匹配
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let score = 85
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switch score {
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case 0..<60:
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    print("不及格")
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case 60..<80:
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    print("及格")
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case 80..<90:
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    print("良好")
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case 90...100:
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    print("优秀")
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default:
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    print("超出范围")
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}

循环语句#

1
// for-in 循环
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for i in 1...5 {
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    print(i)  // 1, 2, 3, 4, 5
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}
5

6
for fruit in ["Apple", "Banana", "Orange"] {
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    print(fruit)
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}
9

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for (index, item) in ["A", "B", "C"].enumerated() {
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    print("Index: \(index), Value: \(item)")
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}
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// while 循环
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var counter = 0
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while counter < 5 {
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    counter += 1
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    print(counter)
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}
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21
// repeat-while (do-while)
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repeat {
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    print("至少执行一次")
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} while false

函数#

基本函数#

1
// 无参数无返回值
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func sayHello() {
3
    print("Hello!")
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}
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// 有参数
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func greet(name: String) -> String {
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    return "Hello, \(name)!"
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}
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// 多参数
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func calculateArea(width: Double, height: Double) -> Double {
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    return width * height
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}
15

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// 无标签参数
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func sum(_ a: Int, _ b: Int) -> Int {
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    return a + b
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}
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// 参数标签
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func introduce(person name: String, from city: String) {
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    print("\(name) 来自 \(city)")
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}
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introduce(person: "张三", from: "北京")
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28
// 默认参数
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func log(message: String, level: String = "INFO") {
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    print("[\(level)] \(message)")
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}
32

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log(message: "程序启动")           // [INFO] 程序启动
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log(message: "发生错误", level: "ERROR")

函数类型#

1
// 函数类型作为参数
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func operation(a: Int, b: Int, function: (Int, Int) -> Int) -> Int {
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    return function(a, b)
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}
5

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let add: (Int, Int) -> Int = { $0 + $1 }
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let multiply: (Int, Int) -> Int = { $0 * $1 }
8

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print(operation(a: 5, b: 3, function: add))       // 8
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print(operation(a: 5, b: 3, function: multiply))  // 15
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// 函数类型作为返回值
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func chooseOperation(operator op: String) -> (Int, Int) -> Int {
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    switch op {
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    case "+":
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        return { $0 + $1 }
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    case "*":
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        return { $0 * $1 }
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    default:
20
        return { $0 - $1 }
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    }
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}
23

24
let chooseAdd = chooseOperation(operator: "+")
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print(chooseAdd(10, 20))  // 30

闭包#

1
// 基本语法
2
let greetClosure = { (name: String) in
3
    return "Hello, \(name)"
4
}
5

6
// 尾随闭包
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numbers.map { $0 * 2 }
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9
// 捕获值
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func makeIncrementer(forIncrement amount: Int) -> () -> Int {
11
    var runningTotal = 0
12
    func incrementer() -> Int {
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        runningTotal += amount
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        return runningTotal
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    }
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    return incrementer
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}
18

19
let incrementByTwo = makeIncrementer(forIncrement: 2)
20
print(incrementByTwo())  // 2
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print(incrementByTwo())  // 4
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print(incrementByTwo())  // 6

面向对象#

类与结构体#

1
// 结构体 - 值类型
2
struct Point {
3
    var x: Double
4
    var y: Double
5

6
    init(x: Double, y: Double) {
7
        self.x = x
8
        self.y = y
9
    }
10

11
    func distance(to other: Point) -> Double {
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        let dx = other.x - x
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        let dy = other.y - y
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        return sqrt(dx * dx + dy * dy)
15
    }
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}
17

18
// 类 - 引用类型
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class Vehicle {
20
    var currentSpeed = 0.0
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    let maxSpeed: Double
22

23
    init(maxSpeed: Double) {
24
        self.maxSpeed = maxSpeed
25
    }
26

27
    func description() -> String {
28
        return "当前速度: \(currentSpeed) km/h"
29
    }
30

31
    // 子类可重写
32
    func makeSound() {
33
        // 默认实现
34
    }
35
}
36

37
class Car: Vehicle {
38
    var brand: String
39

40
    init(brand: String, maxSpeed: Double) {
41
        self.brand = brand
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        super.init(maxSpeed: maxSpeed)
43
    }
44

45
    override func makeSound() {
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        print("嘟嘟嘟~")
47
    }
48

49
    // 属性观察者
50
    var speedInKmh: Double {
51
        get {
52
            return currentSpeed
53
        }
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        set {
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            currentSpeed = newValue
56
        }
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    }
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}

继承与多态#

1
class Shape {
2
    var area: Double { return 0 }
3

4
    func describe() {
5
        print("这是一个图形")
6
    }
7
}
8

9
class Rectangle: Shape {
10
    var width: Double
11
    var height: Double
12

13
    init(width: Double, height: Double) {
14
        self.width = width
15
        self.height = height
16
    }
17

18
    override var area: Double {
19
        return width * height
20
    }
21

22
    override func describe() {
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        print("这是一个矩形, 面积: \(area)")
24
    }
25
}
26

27
class Circle: Shape {
28
    var radius: Double
29

30
    init(radius: Double) {
31
        self.radius = radius
32
    }
33

34
    override var area: Double {
35
        return .pi * radius * radius
36
    }
37
}
38

39
// 多态
40
let shapes: [Shape] = [
41
    Rectangle(width: 5, height: 3),
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    Circle(radius: 2)
43
]
44

45
for shape in shapes {
46
    shape.describe()
47
}

协议#

1
// 定义协议
2
protocol Drawable {
3
    func draw()
4
    var lineColor: String { get set }
5
}
6

7
protocol Movable {
8
    func move(to point: Point)
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}
10

11
// 协议继承
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protocol ShapeProtocol: Drawable, Movable {
13
    var area: Double { get }
14
}
15

16
// 类遵守协议
17
class CircleShape: ShapeProtocol {
18
    var center: Point
19
    var radius: Double
20
    var lineColor: String
21

22
    init(center: Point, radius: Double, lineColor: String) {
23
        self.center = center
24
        self.radius = radius
25
        self.lineColor = lineColor
26
    }
27

28
    func draw() {
29
        print("画圆, 圆心: (\(center.x), \(center.y)), 半径: \(radius)")
30
    }
31

32
    func move(to point: Point) {
33
        center = point
34
        print("圆移动到: (\(point.x), \(point.y))")
35
    }
36

37
    var area: Double {
38
        return .pi * radius * radius
39
    }
40
}
41

42
// 协议扩展
43
extension Drawable {
44
    func drawWithBorder() {
45
        print("边框颜色: \(lineColor)")
46
        draw()
47
    }
48
}

泛型#

1
// 泛型函数
2
func swapValues<T>(_ a: inout T, _ b: inout T) {
3
    let temp = a
4
    a = b
5
    b = temp
6
}
7

8
var a = 1, b = 2
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swapValues(&a, &b)
10
print("a = \(a), b = \(b)")  // a = 2, b = 1
11

12
// 泛型类型
13
struct Stack<Element> {
14
    private var items: [Element] = []
15

16
    mutating func push(_ item: Element) {
17
        items.append(item)
18
    }
19

20
    mutating func pop() -> Element? {
21
        return items.popLast()
22
    }
23

24
    var isEmpty: Bool {
25
        return items.isEmpty
26
    }
27
}
28

29
var intStack = Stack<Int>()
30
intStack.push(1)
31
intStack.push(2)
32
print(intStack.pop())  // 2
33

34
// 泛型协议
35
protocol Container {
36
    associatedtype Item
37
    mutating func append(_ item: Item)
38
    var count: Int { get }
39
    subscript(i: Int) -> Item { get }
40
}

错误处理#

1
// 定义错误类型
2
enum DataError: Error {
3
    case notFound
4
    case unauthorized
5
    case invalidData(String)
6
    case networkError(Int)
7
}
8

9
// 抛出错误
10
func fetchData(from url: String) throws -> Data {
11
    guard url.hasPrefix("https://") else {
12
        throw DataError.invalidData("URL 必须以 https:// 开头")
13
    }
14

15
    // 模拟网络请求
16
    throw DataError.notFound
17
}
18

19
// 处理错误
20
do {
21
    let data = try fetchData(from: "http://example.com")
22
} catch DataError.notFound {
23
    print("数据未找到")
24
} catch DataError.unauthorized {
25
    print("未授权访问")
26
} catch let DataError.invalidData(message) {
27
    print("无效数据: \(message)")
28
} catch {
29
    print("发生未知错误: \(error)")
30
}
31

32
// try? - 将错误转换为可选值
33
let result = try? fetchData(from: "https://example.com")
34
// 如果出错, result 为 nil
35

36
// try! - 断言不会出错 (慎用!)
37
let forcedResult = try! fetchData(from: "https://example.com")
38

39
// defer - 延迟执行
40
func processFile() throws {
41
    let file = openFile()
42
    defer {
43
        closeFile(file)  // 无论是否出错,都会执行
44
    }
45

46
    try writeData(to: file)
47
    try anotherOperation()
48
}

可选链与空合运算符#

1
// 可选链
2
class Person {
3
    var residence: Residence?
4
}
5

6
class Residence {
7
    var address: Address?
8
}
9

10
class Address {
11
    var street: String = ""
12
    var city: String = ""
13
    var zipCode: String?
14
}
15

16
let john = Person()
17
let street = john.residence?.address?.street  // 如果任何环节为 nil, 返回 nil
18

19
// 空合运算符 ??
20
let defaultCity = "北京"
21
let city = john.residence?.address?.city ?? defaultCity
22

23
// 可选绑定
24
if let street = john.residence?.address?.street {
25
    print("街道: \(street)")
26
} else {
27
    print("地址信息不完整")
28
}
29

30
// 隐式展开可选
31
var assumedString: String! = nil
32
// 直接使用,无需解包
33
let implicitString: String = assumedString

内存管理#

1
// 强引用循环
2
class Person {
3
    var name: String
4
    var apartment: Apartment?
5

6
    init(name: String) {
7
        self.name = name
8
    }
9

10
    deinit {
11
        print("\(name) 被释放")
12
    }
13
}
14

15
class Apartment {
16
    var tenant: Person?
17

18
    deinit {
19
        print("公寓被释放")
20
    }
21
}
22

23
// 解决: 使用 weak 或 unowned
24
class Person2 {
25
    var name: String
26
    weak var apartment: Apartment2?  // weak
27

28
    init(name: String) {
29
        self.name = name
30
    }
31
}
32

33
class Apartment2 {
34
    var tenant: Person2?
35
    unowned let building: Building   // unowned
36

37
    init(building: Building) {
38
        self.building = building
39
    }
40
}

访问控制#

1
// open - 最高权限,可跨模块访问和继承
2
open class OpenClass {}
3

4
// public - 跨模块访问,不可继承
5
public class PublicClass {}
6

7
// internal - 默认,模块内访问
8
class InternalClass {}
9

10
// fileprivate - 文件内访问
11
fileprivate class FilePrivateClass {}
12

13
// private - 当前作用域内访问
14
private class PrivateClass {
15
    private var secret: String = "机密"
16

17
    func access() {
18
        let secret2 = secret  // 可以访问
19
    }
20
}

总结#

Swift 是一门现代、安全、高效的编程语言：

安全性: 强类型系统、可选类型、自动内存管理
现代性: 语法简洁、支持泛型、函数式编程特性
高性能: 编译型语言,性能接近 C++
易用性: 丰富的标准库、优秀的错误处理机制

掌握 Swift 的核心概念是开发 Apple 平台应用的基础。

Swift 编程语言学习笔记#

基础语法#

变量与常量#

数据类型#

控制流#

条件语句#

循环语句#

函数#

基本函数#

函数类型#

闭包#

面向对象#

类与结构体#

继承与多态#

协议#

泛型#

错误处理#

可选链与空合运算符#

内存管理#

访问控制#

总结#

参考资源#