Optionals
- swif不允許nil傳入，如果要達到能夠傳nil使用如下方法添加?這個符號標識是
extension NSAttributedString {
init(string str: String?)
}
- 返回一個可以為nil的返回值
func parseColorFromHexString(input: String) -> UIColor? {
// ...
}
值類型與引用類型
- 值類型賦值和作為參數時都是復制的。值類型包括數字，字符串，數組，字典，枚舉，元組和結構體
var a = "Hello"
var b = a
b.extend(", world")
println("a: \(a); b: \(b)") // a: Hello; b: Hello, world
- 引用類型可以有多所有者，一般類都是引用類型
var a = UIView()
var b = a
b.alpha = 0.5
println("a: \(a.alpha); b: \(b.alpha)") // a: 0.5; b: 0.5
函數
標準函數
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")
外部參數
- 外部參數名稱解決調用函數時不確定每個函數參數代表什么的問題
func hello(fromName name: String) {
println("\(name) says hello to you!")
}
hello(fromName: "Mr. Roboto")
- 如需要外部參數和內部參數名相同，只需要在參數前加上#即可
func hello(#name: String) {
println("hello \(name)")
}
hello(name: "Robot")
類中的方法
標準參數
- 類中的方法參數調用和函數不同，第一個參數不被外部包含，后面的的參數會被作為外部參數名和objective-c一樣
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")
- 如果不想顯示外部參數名可以通過添加一個_解決
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
- 初始化時第一個參數必須是外部的
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參數
- 傳參是Optionals時，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
默認參數
- 設置參數默認值，一般都將默認參數放在后面
func hello(name: String = "you") {
println("hello, \(name)")
}
hello(name: "Mr. Roboto")
// hello, Mr. Roboto
hello()
// hello, you
可變參數
- 可變參數，需要注意的是可變參數是在函數列表的最后一個
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
- 使用引用來操縱外部變量
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
泛型參數類型
- 一個函數中接受多個類型不定的參數。
func valueSwap<T>(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
- 更多可參考官方泛型說明：<https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Generics.html>
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
返回函數
- 返回一個函數
func myFuncThatReturnsAFunc() -> (Int) -> String {
return { number in
return "The lucky number is \(number)"
}
}
let returnedFunction = myFuncThatReturnsAFunc()
returnedFunction(5) // The lucky number is 5
- 為返回的函數定義一個別名
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
函數組裝
- infix關鍵字表明運算符具有左右兩個參數可以實現1 + 2 + 3 + 4 表達，比add(add(add(1, 2), 3), 4)這樣更加容易理解
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)
語法參考
The Swift Programming Language》中文版：http://numbbbbb.gitbooks.io/-the-swift-programming-language-/
