Swift5基本语法

import UIKit

var str = "Hello, playground"

//介绍swift5相关的语法


//********************常量和变量
/*
 1.常量定义时必须赋初值，
 2.变量定义时必须加 “!” or  “?”
 3.可以在一行中声明多个常量或者多个变量，用逗号隔开:
 */
let maximumNumberOfLoginAttempts = 10
var currentLoginAttempt = 0
var x = 0.0, y = 0.0, z = 0.0

var sgfdfd:Int?
var welcomeMessage: String!
var welcomeMessageInt: Int?

var optionalString: String? = "Hello"
print(optionalString == nil)
// Prints "false"

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


//********************条件语句
//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.")
}
// Prints "Is it a spicy red pepper?"

//for-in
//字典是无序的!!!
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 {
    print(kind)
    for number in numbers {
        if number > largest {
            largest = number
        }
    }
}
print(largest)


//while-repeat
var n = 2
while n < 100 {
    n *= 2
}
print(n)
// Prints "128"

var m = 2
repeat {
    m *= 2
} while m < 100
print(m)
// Prints "128"


//You can keep an index in a loop by using ..< to make a range of indexes.
var total = 0
for i in 0..<4 {
    total += i
}
print(total)










//********************数组和字典
//创建方式一
var shoppingList = ["catfish", "water", "tulips"]
shoppingList[1] = "bottle of water"

var occupations = [
    "Malcolm": "Captain",
    "Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"
shoppingList.append("blue paint")
print(shoppingList)
//创建方式二
let emptyArray = [String]()
let emptyDictionary = [String: Float]()
let individualScores = [75, 43, 103, 87, 12]
//注意if 语句的使用
var teamScore = 0
for score in individualScores {
    if score > 50 {
        teamScore += 3
    } else {
        teamScore += 1
    }
}
print(teamScore)
// Prints "11"


//********************Functions and Closures
/*
 函数实际上是闭包的一种特殊情况:
 
 
 方法名可以一样，但是方法里的参数设置不能一样，否则报错
 */

///简单方法
func greet(person: String, day: String) -> String {
    return "Hello \(person), today is \(day)."
}
func greet(_ person: String, on day: String) -> String {
    return "Hello \(person), today is \(day)."
}
func greet(_ person: String, ooon day: String) -> Int {
    return 15
}
greet(person: "Bob", day: "Tuesday")
greet("John", on: "Wednesday")
greet("Bill", ooon: "TOne")

///返回多个参数的方法[通过tuple 实现]
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"



///函数可以嵌套。嵌套函数可以访问在外部函数中声明的变量。可以使用嵌套函数在长函数或复杂函数中组织代码。
func returnFifteen() -> Int {
    var y = 10
    func add() {
        y += 5
    }
    add()
    return y
}
returnFifteen()
///函数可以返回另一个函数作为它的值。
func makeIncrementer() -> ((Int) -> Int) {
    func addOne(number: Int) -> Int {
        return 1 + number
    }
    return addOne
}
var increment = makeIncrementer()
increment(7)


///一个函数可以接受另一个函数作为它的参数之一。
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)

///函数实际上是闭包的一种特殊情况:
numbers.map({ (number: Int) -> Int in
    let result = 3 * number
    return result
})
///您有几个选项可以更简洁地编写闭包。当闭包的类型已知时，例如委托的回调，您可以省略它的参数类型、返回类型，或者两者都省略。单个语句闭包隐式地返回它们唯一语句的值。
let mappedNumbers = numbers.map({ number in 3 * number })
print(mappedNumbers)
// Prints "[60, 57, 21, 36]"






//********************Objects and Classes
//一个简单的类
class Shape {
    var numberOfSides = 0
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()

//一个有init 的类
class NamedShape {
    var numberOfSides: Int = 0
    var name: String
    
    init(name: String) {
        self.name = name
    }
    
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
    
}
//实现继承的类
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()


///除了存储的简单属性外，属性还可以有getter和setter。
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 = 9.9
print(triangle.sideLength)
// Prints "3.3000000000000003"


///如果您不需要计算属性，但仍然需要提供在设置新值之前和之后运行的代码，那么使用willSet和didSet。只要值在初始化器之外发生更改，就会运行您提供的代码。例如，下面的类确保三角形的边长总是与其正方形的边长相同。
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)
// Prints "10.0"
print(triangleAndSquare.triangle.sideLength)
// Prints "10.0"
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
print(triangleAndSquare.triangle.sideLength)
// Prints "50.0"


///当处理可选值时，您可以编写?在方法、属性和下标等操作之前。如果之前的值是?是nil吗?被忽略，整个表达式的值为nil。否则，可选值将被打开，并且在?作用于打开的值。在这两种情况下，整个表达式的值都是一个可选值。
let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square")
let sideLength = optionalSquare?.sideLength




//********************Enumerations and Structures
//使用枚举创建枚举。与类和所有其他命名类型一样，枚举可以具有与其关联的方法。
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
//使用init?(rawValue:)初始化器从原始值生成枚举的实例。如果没有匹配的秩，则返回匹配原始值的枚举用例或nil。
if let convertedRank = Rank(rawValue: 3) {
    let threeDescription = convertedRank.simpleDescription()
}

//枚举的大小写值是实际值，而不仅仅是编写原始值的另一种方式。事实上，在没有有意义的原始值的情况下，您不需要提供一个。
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()
//如果枚举具有原始值，这些值将作为声明的一部分确定，这意味着特定枚举用例的每个实例始终具有相同的原始值。枚举用例的另一个选择是拥有与该用例相关联的值——这些值是在创建实例时确定的，并且对于枚举用例的每个实例，它们可以是不同的。可以将关联值视为枚举用例实例的存储属性。例如，考虑从服务器请求日出和日落时间的情况。服务器要么响应所请求的信息，要么响应错误的描述。

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)")
}
// Prints "Sunrise is at 6:00 am and sunset is at 8:09 pm."



//使用struct创建结构。结构支持许多与类相同的行为，包括方法和初始化器。结构和类之间最重要的区别之一是，结构在代码中传递时总是被复制，但是类是通过引用传递的。
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()





//********************Protocols and Extensions
//使用协议声明协议。
//使用 mutating 关键字修饰方法是为了能在该方法中修改 struct 或是 enum 的变量，在设计接口的时候，也要考虑到使用者程序的扩展性。所以要多考虑使用mutating来修饰方法。
//注意，在SimpleStructure声明中使用mutating关键字来标记修改结构的方法。SimpleClass的声明不需要任何标记为mutating的方法，因为类上的方法总是可以修改该类。

protocol ExampleProtocol {
    var simpleDescription: String { get }
    mutating func adjust()
}

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


//使用扩展向现有类型添加功能，如新方法和计算属性。您可以使用扩展将协议一致性添加到在其他地方声明的类型，甚至添加到从库或框架导入的类型。
extension Int: ExampleProtocol {
    var simpleDescription: String {
        return "The number \(self)"
    }
    mutating func adjust() {
        self += 42
    }
}
print(7.simpleDescription)
// Prints "The number 7"

//您可以像使用任何其他命名类型一样使用协议名称—例如，创建具有不同类型但都符合单个协议的对象集合。当处理类型为协议类型的值时，不能使用协议定义之外的方法。
let protocolValue: ExampleProtocol = a
print(protocolValue.simpleDescription)
// Prints "A very simple class.  Now 100% adjusted."
// print(protocolValue.anotherProperty)  // Uncomment to see the error
//即使变量protocolValue有一个SimpleClass的运行时类型，编译器仍然将它视为给定类型的ExampleProtocol。这意味着除了协议一致性之外，您不能意外地访问类实现的方法或属性。



//********************Error Handling
//使用采用错误协议的任何类型表示错误。
enum PrinterError: Error {
    case outOfPaper
    case noToner
    case onFire
}
//使用throw来抛出错误，并使用throw来标记可能抛出错误的函数。如果在函数中抛出错误，函数将立即返回，调用该函数的代码将处理该错误。

func send(job: Int, toPrinter printerName: String) throws -> String {
    if printerName == "Never Has Toner" {
        throw PrinterError.noToner
    }
    return "Job sent"
}
//有几种方法可以处理错误。一种方法是使用do-catch。在do块内部，您可以通过在其前面编写try来标记可能抛出错误的代码。在catch块内部，除非您给它一个不同的名称，否则错误会自动给出名称错误。
do {
    let printerResponse = try send(job: 1040, toPrinter: "Bi Sheng")
    print(printerResponse)
} catch {
    print(error)
}
// Prints "Job sent"

//您可以提供多个catch块来处理特定的错误。在catch之后编写模式，就像在开关的case之后一样。
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)
}
// Prints "Job sent"

//另一种处理错误的方法是使用try?将结果转换为可选的。如果函数抛出错误，则丢弃特定的错误，结果为nil。否则，结果是一个可选的，包含函数返回的值。
let printerSuccess = try? send(job: 1884, toPrinter: "Mergenthaler")
let printerFailure = try? send(job: 1885, toPrinter: "Never Has Toner")

//使用defer编写一个代码块，该代码块在函数中所有其他代码之后，即函数返回之前执行。无论函数是否抛出错误，都会执行代码。您可以使用defer互相编写安装和清理代码，即使它们需要在不同的时间执行。
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)
// Prints "false"




//********************泛型
//在尖括号内编写一个名称，使其成为泛型函数或类型。
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)

//您可以创建函数和方法的通用形式，以及类、枚举和结构。
// Reimplement the Swift standard library's optional type
enum OptionalValue<Wrapped> {
    case none
    case some(Wrapped)
}
var possibleInteger: OptionalValue<Int> = .none
possibleInteger = .some(100)


//在正文前面指定需求列表的位置使用—例如，要求类型实现协议，要求两种类型相同，或者要求类具有特定的超类。
//sequence 是一个协议
//在 Swift 4 中可以在 associatedtype 后面声明的类型后追加 where 语句
func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool
    where T.Element: Equatable, T.Element == U.Element
{
    for lhsItem in lhs {
        for rhsItem in rhs {
            if lhsItem == rhsItem {
                return true
            }
        }
    }
    return false
}
anyCommonElements([1, 2, 3], [3])
//上面这个假定函数有两个类型参数。第一个类型参数T，有一个需要T必须遵循Sequence协议的类型约束；第二个类型参数U，有一个需要U必须遵循Sequence协议的类型约束。





print("end")