Swift语法笔记

类型

Int
Double
Float
Bool
String
Array
Tuple
Set
Dictionary

类型别名

使用 typealias 来声明类型别名

变量

let 声明常量
var 声明变量

默认情况下不需要加类型，有类型推导。如果需要指定类型，可以这么写：let myVar: Double = 2

还可以使用 \() 在字符串里进行运算，例如：

let apples = 3
let oranges = 4

print("\(apples) apples and \(oranges) oranges")

用三引号来包含换行的字符串。

let words = """
hello world
    world hello

hello world
world hello
    this that
"""

print(words)

使用中括号来创建数组和字典/哈希表：

var shoppingList = ["catfish", "water", "tulips"]
shoppingList[1] = "bottle of water"

var aDict: [String: Any] = [
    "hello": "world",
    "this": 1,
]

print(shoppingList, aDict)

如果要创建控字典或者数组：

let emptyArray = [String]()
let emptyDictionary = [String: Float]()

// 或者这样，当然只有在类型信息可以推导出来的时候才能这样
shoppingList = []
occupations = [:]

控制流

可以使用 for... in..., while..., repeat...while... 来进行循环。循环变量可以不写括号（当然也可以写）
if 后面只能接bool值，同时也可以接一个 let，用于判断值是否为空

var shoppingList: [String?] = ["hello", nil, "world"]

for i in shoppingList {
    if let item = i {
        print(item)
    }
}

?? 可以用来判断值是否为空，如果为空，就使用默认值，例如：

let nickName: String? = nil
let defaultNickname = "foo"

print("\(nickName ?? defaultNickname)")

switch...case... 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.")
}
// Prints "Is it a spicy red pepper?"

..< 和 ... 类似于Python中的range，前者不包括上界，后者包括上界：

for i in 0..<4 {
    print(i)
}

for i in 0...4 {
    print(i)
}

函数

使用 func 关键字声明函数，-> 指示函数返回类型

面向对象

class 关键字用于声明类

class NamedShape {
    var name: String

    init(name: String) {
        self.name = name
    }

    func SayHi() -> String {
        return "Hello, I'm shape \(self.name)"
    }
}

print(NamedShape(name: "foo").SayHi())

init 是类的构造器，deinit 是析构器
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"

如果不需要 getter 和 setter，但是需要前置和后置动作，可以使用 willSet, didSet

错误处理

使用 throw 来标记函数，表明这个函数可能会抛出异常
使用 do...catch... 来捕捉异常

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)
}