Swift概览 - 代码速读

1.简单值

//常量
let myConstant = 42

//变量
var myVariable = 42
myVariable = 50

//指定类型变量（不指定的话自动判断）
let explicitDouble: Double = 70

//类型转换
let label = "The width is "
let width = 94
let widthLabel = label + String(width)

//字符串拼接
let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit."

//数组
let emptyArray = [String]() //数组初始化
var shoppingList = ["catfish", "water", "tulips", "blue paint"]
shoppingList[1] = "bottle of water" //指定元素修改

//字典
let emptyDictionary = [String: Float]() //字典初始化
var occupations = [
    "Malcolm": "Captain",
    "Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations" //指定元素修改

2.控制流

//for循环遍历数组
let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
    if score > 50 {
        teamScore += 3
    } else {
        teamScore += 1
    }
}
print(teamScore)

//for循环遍历字典
let interestingNumbers = [
    "Prime": [2, 3, 5, 7, 11, 13],
    "Fibonacci": [1, 1, 2, 3, 5, 8],
    "Square": [1, 4, 9, 16, 25],
]
var largest = 0
for (kind, numbers) in interestingNumbers {
    for number in numbers {
        if number > largest {
            largest = number
        }
    }
}
print(largest)
//..<来创建一个不包含最大值的区间，使用 ... 来创造一个包含最大值和最小值的区间
var total = 0
for i in 0..<4 {
    total += i
}
print(total)

//问号表示可选
var optionalString: String? = "Hello"
print(optionalString == nil)

//if判断
var optionalName: String? = "John Appleseed"
var greeting = "Hello!"
if let name = optionalName {
    greeting = "Hello, \(name)"
}

//双问号判断是否nil
let nickName: String? = nil
let fullName: String = "John Appleseed"
let informalGreeting = "Hi \(nickName ?? fullName)"

//switch控制（default必须有）
let vegetable = "red pepper"
switch vegetable {
case "celery":
    print("Add some raisins and make ants on a log.")
case "cucumber", "watercress":
    print("That would make a good tea sandwich.")
case let x where x.hasSuffix("pepper"):
    print("Is it a spicy \(x)?")
default:
    print("Everything tastes good in soup.")
}

//while循环（条件在前）
var n = 2
while n < 100 {
    n = n * 2
}
print(n)

//while循环（条件在后）
var m = 2
repeat {
    m = m * 2
} while m < 100
print(m)

3.函数和闭包

//函数
//person: String, day: String表示参数，-> String表示返回值
func greet(person: String, day: String) -> String {
    return "Hello \(person), today is \(day)."
}
greet(person: "Bob", day: "Tuesday")

//on表示形式参数，方法调用的时候提示用的。如果用下划线可以避免形式参数
func greet2(person: String, on day: String) -> String {
    return "Hello \(person), today is \(day)."
}
greet2(person: "Bob", on: "Tuesday")

//使用元组来从函数中返回多个值。元组中的元素可以通过名字或者数字调用。
func calculateStatistics(scores: [Int]) -> (min: Int, max: Int, sum: Int) {
    var min = scores[0]
    var max = scores[0]
    var sum = 0
    
    for score in scores {
        if score > max {
            max = score
        } else if score < min {
            min = score
        }
        sum += score
    }
    
    return (min, max, sum)
}
let statistics = calculateStatistics(scores: [5, 3, 100, 3, 9])
print(statistics.sum)
print(statistics.2)

//函数同样可以接受多个参数，然后把它们存放进数组当中。
func sumOf(numbers: Int...) -> Int {
    var sum = 0
    for number in numbers {
        sum += number
    }
    return sum
}
sumOf()
sumOf(numbers: 42, 597, 12)

//内嵌函数
func returnFifteen() -> Int {
    var y = 10
    func add() {
        y += 5
    }
    add()
    return y
}
returnFifteen()

//把函数作为值来返回（就是说函数的返回值是另一个函数）
func makeIncrementer() -> ((Int) -> Int) {
    func addOne(number: Int) -> Int {
        return 1 + number
    }
    return addOne
}
var increment = makeIncrementer()
increment(7)

//函数作为另一个函数的参数
func hasAnyMatches(list: [Int], condition: (Int) -> Bool) -> Bool {
    for item in list {
        if condition(item) {
            return true
        }
    }
    return false
}
func lessThanTen(number: Int) -> Bool {
    return number < 10
}
var numbers = [20, 19, 7, 12]
hasAnyMatches(list: numbers, condition: lessThanTen)

//闭包
numbers.map({
    (number: Int) -> Int in
    let result = 3 * number
    return result
})

//单语句闭包隐式地返回语句执行的结果
let mappedNumbers = numbers.map({ number in 3 * number })
print(mappedNumbers)

//如果闭包是函数的唯一参数，你可以去掉圆括号直接写闭包
let sortedNumbers = numbers.sorted { $0 > $1 }
print(sortedNumbers)

4.对象和类

//类
class Shape {
    var numberOfSides = 0
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

//实例化类
var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()

//init来创建一个初始化器
//使用 deinit来创建一个反初始化器，如果你需要在释放对象之前执行一些清理工作的话
class NamedShape {
    var numberOfSides: Int = 0
    var name: String
    
    init(name: String) {
        self.name = name
    }
    
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

//类的继承和方法重写
class Square: NamedShape {
    var sideLength: Double
    
    init(sideLength: Double, name: String) {
        self.sideLength = sideLength
        super.init(name: name)
        numberOfSides = 4
    }
    
    func area() ->  Double {
        return sideLength * sideLength
    }
    
    override func simpleDescription() -> String {
        return "A square with sides of length \(sideLength)."
    }
}
let test = Square(sideLength: 5.2, name: "my test square")
test.area()
test.simpleDescription()

//带有getter和setter的计算属性
class EquilateralTriangle: NamedShape {
    var sideLength: Double = 0.0
    
    init(sideLength: Double, name: String) {
        self.sideLength = sideLength
        super.init(name: name)
        numberOfSides = 3
    }
    
    var perimeter: Double {
        get {
            return 3.0 * sideLength
        }
        set {
            sideLength = newValue / 3.0
        }
    }
    
    override func simpleDescription() -> String {
        return "An equilateral triangle with sides of length \(sideLength)."
    }
}
var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
print(triangle.perimeter)
triangle.perimeter = 9.9
print(triangle.sideLength)

//willSet和didSet
class TriangleAndSquare {
    var triangle: EquilateralTriangle {
        willSet {
            square.sideLength = newValue.sideLength
        }
    }
    var square: Square {
        willSet {
            triangle.sideLength = newValue.sideLength
        }
    }
    init(size: Double, name: String) {
        square = Square(sideLength: size, name: name)
        triangle = EquilateralTriangle(sideLength: size, name: name)
    }
}
var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
print(triangleAndSquare.square.sideLength)
print(triangleAndSquare.triangle.sideLength)
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
print(triangleAndSquare.triangle.sideLength)

5.枚举和结构体

//枚举
enum Rank: Int {
    case ace = 1
    case two, three, four, five, six, seven, eight, nine, ten
    case jack, queen, king
    func simpleDescription() -> String {
        switch self {
        case .ace:
            return "ace"
        case .jack:
            return "jack"
        case .queen:
            return "queen"
        case .king:
            return "king"
        default:
            return String(self.rawValue)
        }
    }
}
let ace = Rank.ace
let aceRawValue = ace.rawValue

//枚举成员的值是实际的值，不是原始值的另一种写法
enum Suit {
    case spades, hearts, diamonds, clubs
    func simpleDescription() -> String {
        switch self {
        case .spades:
            return "spades"
        case .hearts:
            return "hearts"
        case .diamonds:
            return "diamonds"
        case .clubs:
            return "clubs"
        }
    }
}
let hearts = Suit.hearts
let heartsDescription = hearts.simpleDescription()

//结构体（结构体传值，类传递引用）
struct Card {
    var rank: Rank
    var suit: Suit
    func simpleDescription() -> String {
        return "The \(rank.simpleDescription()) of \(suit.simpleDescription())"
    }
}
let threeOfSpades = Card(rank: .three, suit: .spades)
let threeOfSpadesDescription = threeOfSpades.simpleDescription()

6.协议和扩展

//声明一个协议
protocol ExampleProtocol {
    var simpleDescription: String { get }
    mutating func adjust()
}

//类和结构体，都可以继承自同一个协议
class SimpleClass: ExampleProtocol {
    var simpleDescription: String = "A very simple class."
    var anotherProperty: Int = 69105
    func adjust() {
        simpleDescription += "  Now 100% adjusted."
    }
}
var a = SimpleClass()
a.adjust()
let aDescription = a.simpleDescription

struct SimpleStructure: ExampleProtocol {
    var simpleDescription: String = "A simple structure"
    mutating func adjust() {
        simpleDescription += " (adjusted)"
    }
}
var b = SimpleStructure()
b.adjust()
let bDescription = b.simpleDescription

//类的方法可以修改类的属性，但是结构体的方法，无法修改自身的属性。如果要修改，需要在方法前加 mutating
extension Int: ExampleProtocol {
    var simpleDescription: String {
        return "The number \(self)"
    }
    mutating func adjust() {
        self += 42
    }
}
print(7.simpleDescription)

7.错误处理

enum PrinterError: Error {
    case outOfPaper
    case noToner
    case onFire
}
//使用 throw 来抛出一个错误
func send(job: Int, toPrinter printerName: String) throws -> String {
    if printerName == "Never Has Toner" {
        throw PrinterError.noToner
    }
    return "Job sent"
}

//使用do-catch处理错误
do {
    let printerResponse = try send(job: 1040, toPrinter: "Bi Sheng")
    print(printerResponse)
} catch {
    print(error)
}

//提供多个catch代码块来处理特定的错误
do {
    let printerResponse = try send(job: 1440, toPrinter: "Gutenberg")
    print(printerResponse)
} catch PrinterError.onFire {
    print("I'll just put this over here, with the rest of the fire.")
} catch let printerError as PrinterError {
    print("Printer error: \(printerError).")
} catch {
    print(error)
}

//使用try处理错误
let printerSuccess = try? send(job: 1884, toPrinter: "Mergenthaler")
let printerFailure = try? send(job: 1885, toPrinter: "Never Has Toner")

//使用 defer 来写在函数返回后也会被执行的代码块
var fridgeIsOpen = false
let fridgeContent = ["milk", "eggs", "leftovers"]
func fridgeContains(_ food: String) -> Bool {
    fridgeIsOpen = true
    defer {
        fridgeIsOpen = false
    }
    
    let result = fridgeContent.contains(food)
    return result
}
fridgeContains("banana")
print(fridgeIsOpen)

8.泛型

//把名字写在尖括号里来创建一个泛型方法或者类型
func makeArray<Item>(repeating item: Item, numberOfTimes: Int) -> [Item] {
    var result = [Item]()
    for _ in 0..<numberOfTimes {
        result.append(item)
    }
    return result
}
makeArray(repeating: "knock", numberOfTimes:4)

//你可以从函数和方法同时还有类，枚举以及结构体创建泛型
enum OptionalValue<Wrapped> {
    case none
    case some(Wrapped)
}
var possibleInteger: OptionalValue<Int> = .none
possibleInteger = .some(100)

//在类型名称后紧接 where来明确一系列需求——比如说，来要求类型实现一个协议，要求两个类型必须相同，或者要求类必须继承自特定的父类
func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool
    where T.Iterator.Element: Equatable, T.Iterator.Element == U.Iterator.Element {
        for lhsItem in lhs {
            for rhsItem in rhs {
                if lhsItem == rhsItem {
                    return true
                }
            }
        }
        return false
}
anyCommonElements([1, 2, 3], [3])
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