let 来声明常量，使用 var 来声明变量。
常量let 只能赋值1次，变量var 可以多次。不同类型的常量变量运算，需要强转：
例：
let label = "The width is"
let width = 94
let widthLabel = label + String(width)
强转字符串可以简化：加反斜杠括号 \
let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit."
- 使用 [] 来创建数组和字典
var shoppingList = ["catfish", "water", "tulips", "blue paint"]
shoppingList[1] = "bottle of water"
//字符数组
var occupations = [
"Malcolm": "Captain",
"Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"
//字典：键值对
let emptyArray = [String]() //空字符数组
let emptyDictionary = [String: Float]() //空字典
- 使用 if 和 switch 来进行条件操作，使用 for-in 、 for 、 while 和 repeat-while 来进行循环。
..< 来表示范围——半闭半开
... 来表示范围——闭区间
//for-in循环
let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
if score > 50 {
teamScore += 3
} else {
teamScore += 1
} }
print(teamScore)
var total = 0
for i in 0..<4 {
total += i }
print(total)
//while循环
var n = 2
while n < 100 {
n=n* 2
}
print(n)
var m = 2
repeat {
m=m* 2
} while m < 100
print(m)
//switch条件
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.")
}
//注：不用加break
- 函数和闭包：func声明函数 ->指定返回值类型
func greet(_person: String, day: String) -> String {
return "Hello \(person), today is \(day)."
}
greet(person:"Bob", day: "Tuesday")
//返回值可以有多个
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)
//参数可以有多个
func sumOf(numbers: Int...) -> Int {
var sum = 0
for number in numbers {
sum += number
}
return sum }
sumOf()
sumOf(numbers: 42, 597, 12)
闭包：用 {} 来创建 一个匿名闭包。使用 in 将参数和返回值类型声明与闭包函数体进行分离。
//闭包
numbers.map({
(number: Int) -> Int in
let result = 3 * number
return result
})
//单个语句闭包会把它语句的值当做结果返回
let mappedNumbers = numbers.map({ number in 3 * number })
print(mappedNumbers)
//当一个闭包是传给函数的唯一参数，你可以完全忽略括号。
let sortedNumbers = numbers.sort { $0 > $1 }
print(sortedNumbers)
- 类与对象
//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."
}
}
//子类
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()
方法、属性和子脚本)之前加 ? 。如果 ? 之前的值是 nil ， ? 后面 的东西都会被忽略，并且整个表达式返回 nil 。否则， ? 之后的东西都会被运行
let optionalSquare: Square? = Square(sideLength: 2.5, name:"optional square")
let sideLength = optionalSquare?.sideLength
- 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
- 协议protocol
protocol ExampleProtocol {
var simpleDescription: String { get }
mutating func adjust()
}
//类、枚举和结构体都可以实现协议。
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
- 错误处理：采用Error协议的类型来表示错误
enum PrinterError: Error {
case OutOfPaper
case NoToner
case OnFire
}
使用 throw 来抛出一个错误并使用 throws 来表示一个可以抛出错误的函数。如果在函数中抛出一个错误，这个函 数会立刻返回并且调用该函数的代码会进行错误处理。
func send(job: Int, toPrinter printerName: String) throws -> String {
if printerName == "Never Has Toner" {
throw PrinterError.noToner
}
return "Job sent"
}
有多种方式可以用来进行错误处理。一种方式是使用 do-catch 。在 do 代码块中，使用 try 来标记可以抛出错误 的代码。在 catch 代码块中，除非你另外命名，否则错误会自动命名为 error 。
do {
let printerResponse = try send(job: 1040, toPrinter: "Bi Sheng")
print(printerResponse)
} catch {
print(error)
}
//catch可以使用多个 来解决不同的特定的错误
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 defer 代码块来表示在函数返回前，函数中最后执行的代码。无论函数是否会抛出错误，这段代码都将执 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)
- 泛型：尖括号<>可创建泛型函数、方法、类、枚举和结构体
func repeatItem<Item>(repeating item: Item, numberOfTimes: Int) ->[Item] {
var result = [Item]()
for _ in 0..<numberOfTimes {
result.append(item)
}
return result
}
repeatItem(repeating: "knock", numberOfTimes:4)
