Swift的一些使用说明

Optionals

• swif不允许nil传入，如果要达到能够传nil使用如下方法添加?这个符号标识是

extension NSAttributedString {
     init(string str: String?)
}

• 返回一个可以为nil的返回值

func parseColorFromHexString(input: String) -> UIColor? {
     // ...
}

值类型与引用类型

• 值类型赋值和作为参数时都是复制的。值类型包括数字，字符串，数组，字典，枚举，元组和结构体

var a = "Hello"
var b = a
b.extend(", world")
println("a: \(a); b: \(b)") // a: Hello; b: Hello, world

• 引用类型可以有多所有者，一般类都是引用类型

var a = UIView()
var b = a
b.alpha = 0.5
println("a: \(a.alpha); b: \(b.alpha)") // a: 0.5; b: 0.5

函数

标准函数

func hello(name: String, age: Int, location: String) {
     println("Hello \(name). I live in \(location) too. When is your \(age + 1)th birthday?")
}
hello("Mr. Roboto", 5, "San Francisco")

外部参数

• 外部参数名称解决调用函数时不确定每个函数参数代表什么的问题

func hello(fromName name: String) {
     println("\(name) says hello to you!")
}
hello(fromName: "Mr. Roboto")

• 如需要外部参数和内部参数名相同，只需要在参数前加上#即可

func hello(#name: String) {
     println("hello \(name)")
}
hello(name: "Robot")

类中的方法

标准参数

• 类中的方法参数调用和函数不同，第一个参数不被外部包含，后面的的参数会被作为外部参数名和objective-c一样

class MyFunClass {
     func helloWithName(name: String, age: Int, location: String) {
          println("Hello \(name). I live in \(location) too. When is your \(age + 1)th birthday?")
     }
}
let myFunClass = MyFunClass()
myFunClass.helloWithName("Mr. Roboto", age: 5, location: "San Francisco")

• 如果不想显示外部参数名可以通过添加一个_解决

class MyFunClass {
     func helloWithName(name: String, _ age: Int, _ location: String) {
          println("Hello \(name). I live in \(location) too. When is your \(age + 1)th birthday?")
     }
}
let myFunClass = MyFunClass()
myFunClass.helloWithName("Mr. Roboto", 5, "San Francisco")

初始化

• 初始化时第一个参数必须是外部的

struct Celsius {
     var temperatureInCelsius: Double
     init(fromFahrenheit fahrenheit: Double) {
          temperatureInCelsius = (fahrenheit - 32.0) / 1.8
     }
     init(fromKelvin kelvin: Double) {
          temperatureInCelsius = kelvin - 273.15
     }
     init(_ celsius: Double) {
          temperatureInCelsius = celsius
     }
}

let boilingPointOfWater = Celsius(fromFahrenheit: 212.0)
// boilingPointOfWater.temperatureInCelsius 是 100.0

let freezingPointOfWater = Celsius(fromKelvin: 273.15)
// freezingPointOfWater.temperatureInCelsius 是 0.0

let bodyTemperature = Celsius(37.0)
// bodyTemperature.temperatureInCelsius 是 37.0

Optionals参数

• 传参是Optionals时，需要做拆包，如下

func myFuncWithOptionalType(optionalParameter: String?) {
     if let unwrappedOptional = optionalParameter {
          println("The optional has a value! It's \(unwrappedOptional)")
     } else {
          println("The optional is nil!")
     }
}

myFuncWithOptionalType("someString")
// optional has a value! It's someString

myFuncWithOptionalType(nil)
// The optional is nil

默认参数

• 设置参数默认值，一般都将默认参数放在后面

func hello(name: String = "you") {
     println("hello, \(name)")
}

hello(name: "Mr. Roboto")
// hello, Mr. Roboto

hello()
// hello, you

可变参数

• 可变参数，需要注意的是可变参数是在函数列表的最后一个

func helloWithNames(names: String...) {
     for name in names {
          println("Hello, \(name)")
     }
}

// 2 names
helloWithNames("Mr. Robot", "Mr. Potato")
// Hello, Mr. Robot
// Hello, Mr. Potato

// 4 names
helloWithNames("Batman", "Superman", "Wonder Woman", "Catwoman")
// Hello, Batman
// Hello, Superman
// Hello, Wonder Woman
// Hello, Catwoman

inout

• 使用引用来操纵外部变量

var name1 = "Mr. Potato"
var name2 = "Mr. Roboto"

func nameSwap(inout name1: String, inout name2: String) {
     let oldName1 = name1
     name1 = name2
     name2 = oldName1
}

nameSwap(&name1, &name2)

name1
// Mr. Roboto

name2
// Mr. Potato

泛型参数类型

• 一个函数中接受多个类型不定的参数。

func valueSwap(inout value1: T, inout value2: T) {
     let oldValue1 = value1
     value1 = value2
     value2 = oldValue1
}

var name1 = "Mr. Potato"
var name2 = "Mr. Roboto"

valueSwap(&name1, &name2)

name1 // Mr. Roboto
name2 // Mr. Potato

var number1 = 2
var number2 = 5

valueSwap(&number1, &number2)

number1 // 5
number2 // 2

• 更多可参考官方泛型说明：

多值返回

func findRangeFromNumbers(numbers: Int...) -> (min: Int, max: Int) {

     var min = numbers[0]
     var max = numbers[0]

     for number in numbers {
          if number > max {
               max = number
          }

          if number < min {
               min = number
          }
     }

     return (min, max)
}

findRangeFromNumbers(1, 234, 555, 345, 423)
// (1, 555)

let range = findRangeFromNumbers(1, 234, 555, 345, 423)
println("From numbers: 1, 234, 555, 345, 423. The min is \(range.min). The max is \(range.max).")
// From numbers: 1, 234, 555, 345, 423. The min is 1. The max is 555.

let (min, max) = findRangeFromNumbers(236, 8, 38, 937, 328)
println("From numbers: 236, 8, 38, 937, 328. The min is \(min). The max is \(max)")
// From numbers: 236, 8, 38, 937, 328. The min is 8. The max is 937

返回函数

• 返回一个函数

func myFuncThatReturnsAFunc() -> (Int) -> String {
     return { number in
          return "The lucky number is \(number)"
     }
}

let returnedFunction = myFuncThatReturnsAFunc()

returnedFunction(5) // The lucky number is 5

• 为返回的函数定义一个别名

typealias returnedFunctionType = (Int) -> String

func myFuncThatReturnsAFunc() -> returnedFunctionType {
     return { number in
          return "The lucky number is \(number)"
     }
}

let returnedFunction = myFuncThatReturnsAFunc()

returnedFunction(5) // The lucky number is 5

函数组装

• infix关键字表明运算符具有左右两个参数可以实现1 + 2 + 3 + 4 表达，比add(add(add(1, 2), 3), 4)这样更加容易理解

infix operator >|> { associativity left }

func >|> (filter1: Filter, filter2: Filter) -> Filter {
     return { img in filter2(filter1(img)) }
}

let myFilter = blur(blurRadius) >|> colorOverlay(overlayColor)
let result = myFilter(image)

语法参考

The Swift Programming Language》中文版：http://numbbbbb.gitbooks.io/-the-swift-programming-language-/