前言
本章内容完全是描写苹果新语言的基础练习，对于初学者来说是非常好用，好学、升级了编辑器Xcode9快速体验Swift4语法
print("Hello, world!")就是这么简单的打印
该内容基于语法教程，更多内容可以去Develpoer去看API
内容概括
- 简单值
- 控制流
- 函数和闭包
- 对象和类
- 枚举和结构体
- 协议和扩展
- 错误处理
- 泛型
简单值
- 使用 let 来声明常量，使用 var 来声明变量。
var myVariable = 42
myVariable = 50
let myConstant = 42
- 不用明确地声明类型，声明的同时赋值的话，编译器会自动推断类型
let implicitInteger = 70
let implicitDouble = 70.0
let explicitDouble: Double = 70
- 值永远不会被隐式转换为其他类型。如果你需要把一个值转换成其他类型，请显式转换
let label = "The width is"
let width = 94
let widthLabel = label + String(width)
- 有一种更简单的把值转换成字符串的方法：把值写到括号中，并且在括号之前写一个反斜杠
let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit."
- 使用方括号 [] 来创建数组和字典，并使用下标或者键（key）来访问元素。最后一个元素后面允许有个逗号。
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
- 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
let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
if score > 50 {
teamScore += 3
} else {
teamScore += 1
}
}
print(teamScore)
- 使用 while 来重复运行一段代码直到不满足条件。循环条件也可以在结尾，保证能至少循环一次。
var n = 2
while n < 100 {
n = n * 2
}
print(n)
var m = 2
repeat {
m = m * 2
} while m < 100
print(m)
var total = 0
for i in 0..<4 {
total += i
}
print(total)
函数和闭包
- 闭包和函数是一个重点，也是难点，比较难学
- 简单函数比如
func greet(person: String, day: String) -> String {
return "Hello \(person), today is \(day)."
}
greet(person:"Bob", day: "Tuesday")
- 使用元组来让一个函数返回多个值。该元组的元素可以用名称或数字来表示
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)
对象和类
- 使用 class 和类名来创建一个类。类中属性的声明和常量、变量声明一样，唯一的区别就是它们的上下文是类。同样，方法和函数声明也一样。
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()
枚举和结构体
- 使用 enum 来创建一个枚举。就像类和其他所有命名类型一样，枚举可以包含方法
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
协议和扩展
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
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 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)