Swift 快速入门
变量
let apple = 3 //不可变变量
var orange = 5 //可变变量显式类型声明和类型转换
let num:Float = 4
let hello:String = "hello"
print(hello + num) //报错，不同类型
print(hello + String(num)) //正确方式
print("\(hello), \(num)") //字符插值方式List和Map
//空数组和空map
let emptyArray = [String]()
let emptyDictionary = [String: Float]()
var shoppingList = ["catfish", "water", "tulips", "blue paint"]
shoppingList[1] = "bottle of water"
var occupations = [
"Malcolm": "Captain",
"Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"控制流
let scores = [75, 24, 34, 33, 56, 74, 66]
var sum = 0
for score in scores {
if score > 60 {
sum += 1
} else {
sum -= 1
}
}
print(sum)可选值
var optionalString: String? = "Hello"
print(optionalString == nil)
var optionalName: String? = "John Appleseed"
var greeting = "Hello!"
if let name = optionalName {
greeting = "Hello, \(name)"
}默认值
let nickName: String? = nil
let fullName: String = "John Appleseed"
let informalGreeting = "Hi \(nickName ?? fullName)"switch语句
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.")
}循环
//for
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)
//while
var n = 2
while n < 100 {
n = n * 2
}
print(n)
//repeat
var m = 2
repeat {
m = m * 2
} while m < 100
print(m)区间
var total = 0
for i in 0..<4 {//4次
print(i)
}
for i in 1...5 {//5次
print(i)
}函数
func greet(person: String, day: String) -> String {
return "Hello \(person), today is \(day)."
}
greet(person: "Bob", day: "Tuesday")
//可变参数
func sumOf(numbers: Int...) -> Int {
var sum = 0
for number in numbers {
sum += number
}
return sum
}
sumOf()
sumOf(numbers: 42, 597, 12)元组
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)嵌套函数
func returnFifteen() -> Int {
var y = 10
func add() {
y += 5
}
add()
return y
}
returnFifteen()
//函数类型返回值
func makeIncrementer() -> ((Int) -> Int) {
func addOne(number: Int) -> Int {
return 1 + number
}
return addOne
}
var increment = makeIncrementer()
increment(7)
//函数参数
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
let mappedNumbers = numbers.map({ number in 3 * number })
print(mappedNumbers)类
class Shape {
var numberOfSides = 0
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
//创建对象
var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()
//继承
class Square: NamedShape {
var sideLength: Double
//构造函数
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 4
}
func area() -> Double {
return sideLength * sideLength
}
//重写父类方法
override func simpleDescription() -> String {
return "A square with sides of length \(sideLength)."
}
//带getter和setter的属性
var perimeter: Double {
get {
return 3.0 * sideLength
}
set {
sideLength = newValue / 3.0
}
}
}
let test = Square(sideLength: 5.2, name: "my test square")
test.area()
test.simpleDescription()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
//带属性的枚举
enum ServerResponse {
case result(String, String)
case failure(String)
}
let success = ServerResponse.result("6:00 am", "8:09 pm")
let failure = ServerResponse.failure("Out of cheese.")
switch success {
case let .result(sunrise, sunset):
print("Sunrise is at \(sunrise) and sunset is at \(sunset).")
case let .failure(message):
print("Failure... \(message)")
}结构体
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()结构体跟类几乎一样，区别就是结构体在传递的时候是复制自身，类是传递引用
协议(接口)
protocol ExampleProtocol {
var simpleDescription: String { get }
mutating func adjust()
}类，枚举以及结构体都可以使用协议，mutating关键字的作用是在enum和struct中可以让协议方法修改对象的属性，类中不需要，可以直接修改
拓展
extension Int: ExampleProtocol {
var simpleDescription: String {
return "The number \(self)"
}
mutating func adjust() {
self += 42
}
}
print(7.simpleDescription)给已有的类型添加新功能
错误处理
enum PrinterError: Error {
case outOfPaper
case noToner
case onFire
}
func send(job: Int, toPrinter printerName: String) throws -> String {
if printerName == "Never Has Toner" {
throw PrinterError.noToner
}
return "Job sent"
}
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)
}泛型
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)
