最近学习很迷茫，深入学不懂，源码看不明白，迷茫之下，学一点其他的东西充实自己
因为上周看了Swift ui，感觉很不错，和flutter简直是一个模子里刻出来的，于是准备在正式版出来之前学习学习
变量声明
var声明变量let声明常量
变量类型跟在变量名后
如 var str:String = "hello"
可选值
var optionalString: String? = "Hello" // String 或者nil字符串
使用\()引用变量
如：
let apples = 3let oranges = 5let appleSummary = "I have \(apples) apples."let fruitSummary = "I have \(apples + oranges) pieces of fruit."多行字符串
使用"""
如：
let quotation = """I said "I have \(apples) apples."And then I said "I have \(apples + oranges) pieces of fruit.""""数组和字典
数组
var shoppingList = ["catfish", "water", "tulips"]shoppingList[1] = "bottle of water"字典
var occupations = [ "Malcolm": "Captain", "Kaylee": "Mechanic",]创建空数组或字典
let emptyArray = [String]()let emptyDictionary = [String: Float]()如果类型不确定
shoppingList = []occupations = [:]流程控制
for-in,if
let individualScores = [75, 43, 103, 87, 12]var teamScore = 0for score in individualScores { if score > 50 { teamScore += 3 } else { teamScore += 1 }}print(teamScore)// Prints "11"if-let
var optionalName: String? = "John Appleseed"var greeting = "Hello!"if let name = optionalName { greeting = "Hello, \(name)"}当optionalName不为nil时，会赋值给name并执行代码块中的代码
空值判断符??
let nickName: String? = nillet fullName: String = "John Appleseed"let informalGreeting = "Hi \(nickName ?? fullName)"当??左边当值为nil时，会返回??右边的值
switch
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.")}switch中可以支持任何数据当比较
for-in 迭代字典
let interestingNumbers = [ "Prime": [2, 3, 5, 7, 11, 13], "Fibonacci": [1, 1, 2, 3, 5, 8], "Square": [1, 4, 9, 16, 25],]var largest = 0for (kind, numbers) in interestingNumbers { for number in numbers { if number > largest { largest = number } }}print(largest)// Prints "25"for第一个是键名，第二个是值
while
var n = 2while n < 100 { n *= 2}print(n)// Prints "128"repeat
var m = 2repeat { m *= 2} while m < 100print(m)// Prints "128"这就是do-while吗?
for 循环指定范围
..< 不包含最后一项
var total = 0for i in 0..<4 { total += i}print(total)// Prints "6"等于 => for i in [0,1,2,3]
... 包含最后一项
var total = 0for i in 0..<4 { total += i}等于 => for i in [0,1,2,3,4]
函数
func greet(person: String, day: String) -> String { return "Hello \(person), today is \(day)."}greet(person: "Bob", day: "Tuesday")使用 func关键字声明，->表示函数返回值当类型
使用元组返回多个值
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)// Prints "120"print(statistics.2)// Prints "120"元组当值可以用名字或数字来使用
函数嵌套
func makeIncrementer() -> ((Int) -> Int) { func addOne(number: Int) -> Int { return 1 + number } return addOne}var increment = makeIncrementer()increment(7)函数里可以声明新的函数，也可以将这个函数作为返回值返回
匿名函数
numbers.map({ (number: Int) -> Int in let result = 3 * number return result})使用花括号，in关键字来分割参数和函数体
let mappedNumbers = numbers.map({ number in 3 * number })print(mappedNumbers)// Prints "[60, 57, 21, 36]"一直参数类型和返回类型时，可以省略参数类型和return关键字
let sortedNumbers = numbers.sorted { $0 > $1 }print(sortedNumbers)// Prints "[20, 19, 12, 7]"可以不使用名字，使用编号来引用变量
类
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)// Prints "9.3"triangle.perimeter = 9.9print(triangle.sideLength)// Prints "3.3000000000000003"使用class关键字来声明一个类，init为构造函数，继承父类使用:符号，self调用实例类对象的变量，super调用父类,override关键字重写父类方法
getter和setter使用关键字get和set
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 "hi queen" case .king: return "king" default: return String(self.rawValue) } }}let ace = Rank.acelet aceRawValue = ace.rawValueprint(Rank.queen.simpleDescription()) // "hi queen"枚举可以自定义初始值，如果需要获取枚举的数字值，使用rawValue，枚举里也可以写方法
使用构造函数直接通过数字取得值
Rank(rawValue: 3) // three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()使用stuct关键字声明结构体，结构体和类相似，不过不能继承,并且类总是以引用传递，结构体以复制传递
规则
protocol ExampleProtocol { var simpleDescription: String { get } mutating func adjust()}使用protocol关键字声明一个规则
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.simpleDescriptionstruct SimpleStructure: ExampleProtocol { var simpleDescription: String = "A simple structure" mutating func adjust() { simpleDescription += " (adjusted)" }}var b = SimpleStructure()b.adjust()let bDescription = b.simpleDescription类，枚举和结构体，都可以继承这个规则
结构体需要使用mutating关键字来标记修改结构体的方法
扩展
extension Int: ExampleProtocol { var simpleDescription: String { return "The number \(self)" } mutating func adjust() { self += 42 }}print(7.simpleDescription)// Prints "The number 7"使用extension关键字来向现有类型添加新方法
小结
这里只是文档首页的一篇简述教程，深入学习还需要仔细阅读文档
在枚举、结构体、枚举之前的东西多少能懂七七八八，看见swift的这些，颠覆了我以前学c++，c# 对这些类型对概念，咋个还能这样写，我也不知道算不算反人类，至少oc是真的反人类
简单入门，深入学习看文档去了~