Swift簡介

1. swift初始來源

    沒有了解過swift能夠先參考Brec VictorInventing on Principle ,Swift編程環境的大部分概念都源自於Brec這個演講。express

2. swift是啥

Swift是蘋果在WWDC 2014發佈的新的編程語言,這裏引用The Swift Programming Language的原文:編程

Swift is a new programming language for iOS and OS X apps that builds on the best of C and Objective-C, without the constraints of C compatibility.swift

Swift adopts safe programming patterns and adds modern features to make programming easier, more flexible and more fun.vim

Swift’s clean slate, backed by the mature and much-loved Cocoa and Cocoa Touch frameworks, is an opportunity to imagine how software development works.數組

Swift is the first industrial-quality systems programming language that is as expressive and enjoyable as a scripting language.閉包

簡單的說:app

  1. Swift用來寫iOS和OS X程序。(估計也不會支持其它屌絲系統)
  2. Swift吸收了C和Objective-C的優勢,且更增強大易用。
  3. Swift可使用現有的Cocoa和Cocoa Touch框架。
  4. Swift兼具編譯語言的高性能(Performance)和腳本語言的交互性(Interactive)。

3.Swift語言概覽

基本概念

注:這一節的代碼源自The Swift Programming Language中的A Swift Tour框架

Hello, world

相似於腳本語言,下面的代碼便是一個完整的Swift程序。less

1 println("Hello, world")

變量與常量

Swift使用var聲明變量,let聲明常量。編程語言

1 var myVariable = 42
2 myVariable = 50
3 let myConstant = 42

類型推導

Swift支持類型推導(Type Inference),因此上面的代碼不需指定類型,若是須要指定類型:

1 let explicitDouble : Double = 70

 

Swift不支持隱式類型轉換(Implicitly casting),因此下面的代碼須要顯式類型轉換(Explicitly casting):

1 let label = "The width is "
2 let width = 94
3 let width = label + String(width)

 

字符串格式化

Swift使用\(item)的形式進行字符串格式化:

1 let apples = 3
2 let oranges = 5
3 let appleSummary = "I have \(apples) apples."
4 let appleSummary = "I have \(apples + oranges) pieces of fruit."

 

數組和字典

Swift使用[]操做符聲明數組(array)和字典(dictionary):

1 var shoppingList = ["catfish", "water", "tulips", "blue paint"]
2 shoppingList[1] = "bottle of water"
3 
4 var occupations = [
5     "Malcolm": "Captain",
6     "Kaylee": "Mechanic",
7 ]
8 occupations["Jayne"] = "Public Relations"

 

通常使用初始化器(initializer)語法建立空數組和空字典:

1 let emptyArray = String[]()
2 let emptyDictionary = Dictionary<String, Float>()

 

若是類型信息已知,則可使用[]聲明空數組,使用[:]聲明空字典。

控制流

概覽

Swift的條件語句包含ifswitch,循環語句包含for-inforwhiledo-while,循環/判斷條件不須要括號,但循環/判斷體(body)必需括號:

1 let individualScores = [75, 43, 103, 87, 12]
2 var teamScore = 0
3 for score in individualScores {
4     if score > 50 {
5         teamScore += 3
6     } else {
7         teamScore += 1
8     }
9 }

 

可空類型

結合iflet,能夠方便的處理可空變量(nullable variable)。對於空值,須要在類型聲明後添加?顯式標明該類型可空。

1 var optionalString: String? = "Hello"
2 optionalString == nil
3 
4 var optionalName: String? = "John Appleseed"
5 var gretting = "Hello!"
6 if let name = optionalName {
7     gretting = "Hello, \(name)"
8 }

 

靈活的switch

Swift中的switch支持各類各樣的比較操做:

let vegetable = "red pepper"
switch vegetable {
case "celery":
    let vegetableComment = "Add some raisins and make ants on a log."
case "cucumber", "watercress":
    let vegetableComment = "That would make a good tea sandwich."
case let x where x.hasSuffix("pepper"):
    let vegetableComment = "Is it a spicy \(x)?"
default:
    let vegetableComment = "Everything tastes good in soup."
}

 

其它循環

for-in除了遍歷數組也能夠用來遍歷字典:

 1 let interestingNumbers = [
 2     "Prime": [2, 3, 5, 7, 11, 13],
 3     "Fibonacci": [1, 1, 2, 3, 5, 8],
 4     "Square": [1, 4, 9, 16, 25],
 5 ]
 6 var largest = 0
 7 for (kind, numbers) in interestingNumbers {
 8     for number in numbers {
 9         if number > largest {
10             largest = number
11         }
12     }
13 }
14 largest

 

while循環和do-while循環:

 1 var n = 2
 2 while n < 100 {
 3     n = n * 2
 4 }
 5 n
 6 
 7 var m = 2
 8 do {
 9     m = m * 2
10 } while m < 100
11 m

 

Swift支持傳統的for循環,此外也能夠經過結合..(生成一個區間)和for-in實現一樣的邏輯。

 1 var firstForLoop = 0
 2 for i in 0..3 {
 3     firstForLoop += i
 4 }
 5 firstForLoop
 6 
 7 var secondForLoop = 0
 8 for var i = 0; i < 3; ++i {
 9     secondForLoop += 1
10 }
11 secondForLoop

 

注意:Swift除了..還有.....生成前閉後開的區間,而...生成前閉後閉的區間。

函數和閉包

函數

Swift使用func關鍵字聲明函數:

1 func greet(name: String, day: String) -> String {
2     return "Hello \(name), today is \(day)."
3 }
4 greet("Bob", "Tuesday")

 

經過元組(Tuple)返回多個值:

1 func getGasPrices() -> (Double, Double, Double) {
2     return (3.59, 3.69, 3.79)
3 }
4 getGasPrices()

 

支持帶有變長參數的函數:

1 func sumOf(numbers: Int...) -> Int {
2     var sum = 0
3     for number in numbers {
4         sum += number
5     }
6     return sum
7 }
8 sumOf()
9 sumOf(42, 597, 12)

 

函數也能夠嵌套函數:

1 func returnFifteen() -> Int {
2     var y = 10
3     func add() {
4         y += 5
5     }
6     add()
7     return y
8 }
9 returnFifteen()

 

做爲頭等對象,函數既能夠做爲返回值,也能夠做爲參數傳遞:

1 func makeIncrementer() -> (Int -> Int) {
2     func addOne(number: Int) -> Int {
3         return 1 + number
4     }
5     return addOne
6 }
7 var increment = makeIncrementer()
8 increment(7)

 

 1 func hasAnyMatches(list: Int[], condition: Int -> Bool) -> Bool {
 2     for item in list {
 3         if condition(item) {
 4             return true
 5         }
 6     }
 7     return false
 8 }
 9 func lessThanTen(number: Int) -> Bool {
10     return number < 10
11 }
12 var numbers = [20, 19, 7, 12]
13 hasAnyMatches(numbers, lessThanTen)

 

閉包

本質來講,函數是特殊的閉包,Swift中能夠利用{}聲明匿名閉包:

1 numbers.map({
2     (number: Int) -> Int in
3     let result = 3 * number
4     return result
5     })

 

當閉包的類型已知時,可使用下面的簡化寫法:

1 numbers.map({ number in 3 * number })

 

此外還能夠經過參數的位置來使用參數,當函數最後一個參數是閉包時,可使用下面的語法:

1 sort([1, 5, 3, 12, 2]) { $0 > $1 }

 

類和對象

建立和使用類

Swift使用class建立一個類,類能夠包含字段和方法:

1 class Shape {
2     var numberOfSides = 0
3     func simpleDescription() -> String {
4         return "A shape with \(numberOfSides) sides."
5     }
6 }

 

建立Shape類的實例,並調用其字段和方法。

1 var shape = Shape()
2 shape.numberOfSides = 7
3 var shapeDescription = shape.simpleDescription()

 

經過init構建對象,既可使用self顯式引用成員字段(name),也能夠隱式引用(numberOfSides)。

 1 class NamedShape {
 2     var numberOfSides: Int = 0
 3     var name: String
 4 
 5     init(name: String) {
 6         self.name = name
 7     }
 8 
 9     func simpleDescription() -> String {
10         return "A shape with \(numberOfSides) sides."
11     }
12 }

 

使用deinit進行清理工做。

繼承和多態

Swift支持繼承和多態(override父類方法):

 1 class Square: NamedShape {
 2     var sideLength: Double
 3 
 4     init(sideLength: Double, name: String) {
 5         self.sideLength = sideLength
 6         super.init(name: name)
 7         numberOfSides = 4
 8     }
 9 
10     func area() -> Double {
11         return sideLength * sideLength
12     }
13 
14     override func simpleDescription() -> String {
15         return "A square with sides of length \(sideLength)."
16     }
17 }
18 let test = Square(sideLength: 5.2, name: "my test square")
19 test.area()
20 test.simpleDescription()

 

注意:若是這裏的simpleDescription方法沒有被標識爲override,則會引起編譯錯誤。

屬性

爲了簡化代碼,Swift引入了屬性(property),見下面的perimeter字段:

 1 class EquilateralTriangle: NamedShape {
 2     var sideLength: Double = 0.0
 3 
 4     init(sideLength: Double, name: String) {
 5         self.sideLength = sideLength
 6         super.init(name: name)
 7         numberOfSides = 3
 8     }
 9 
10     var perimeter: Double {
11     get {
12         return 3.0 * sideLength
13     }
14     set {
15         sideLength = newValue / 3.0
16     }
17     }
18 
19     override func simpleDescription() -> String {
20         return "An equilateral triagle with sides of length \(sideLength)."
21     }
22 }
23 var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
24 triangle.perimeter
25 triangle.perimeter = 9.9
26 triangle.sideLength

 

注意:賦值器(setter)中,接收的值被自動命名爲newValue

willSet和didSet

EquilateralTriangle的構造器進行了以下操做:

  1. 爲子類型的屬性賦值。
  2. 調用父類型的構造器。
  3. 修改父類型的屬性。

若是不須要計算屬性的值,但須要在賦值先後進行一些操做的話,使用willSetdidSet

 1 class TriangleAndSquare {
 2     var triangle: EquilateralTriangle {
 3     willSet {
 4         square.sideLength = newValue.sideLength
 5     }
 6     }
 7     var square: Square {
 8     willSet {
 9         triangle.sideLength = newValue.sideLength
10     }
11     }
12     init(size: Double, name: String) {
13         square = Square(sideLength: size, name: name)
14         triangle = EquilateralTriangle(sideLength: size, name: name)
15     }
16 }
17 var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
18 triangleAndSquare.square.sideLength
19 triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
20 triangleAndSquare.triangle.sideLength

 

從而保證trianglesquare擁有相等的sideLength

調用方法

Swift中,函數的參數名稱只能在函數內部使用,但方法的參數名稱除了在內部使用外還能夠在外部使用(第一個參數除外),例如:

1 class Counter {
2     var count: Int = 0
3     func incrementBy(amount: Int, numberOfTimes times: Int) {
4         count += amount * times
5     }
6 }
7 var counter = Counter()
8 counter.incrementBy(2, numberOfTimes: 7)

 

注意Swift支持爲方法參數取別名:在上面的代碼裏,numberOfTimes面向外部,times面向內部。

?的另外一種用途

使用可空值時,?能夠出如今方法、屬性或下標前面。若是?前的值爲nil,那麼?後面的表達式會被忽略,而原表達式直接返回nil,例如:

1 let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional 
2 square")
3 let sideLength = optionalSquare?.sideLength

 

optionalSquarenil時,sideLength屬性調用會被忽略。

枚舉和結構

枚舉

使用enum建立枚舉——注意Swift的枚舉能夠關聯方法:

 1 enum Rank: Int {
 2     case Ace = 1
 3     case Two, Three, Four, Five, Six, Seven, Eight, Nine, Ten
 4     case Jack, Queen, King
 5         func simpleDescription() -> String {
 6         switch self {
 7             case .Ace:
 8                 return "ace"
 9             case .Jack:
10                 return "jack"
11             case .Queen:
12                 return "queen"
13             case .King:
14                 return "king"
15             default:
16                 return String(self.toRaw())
17         }
18     }
19 }
20 let ace = Rank.Ace
21 let aceRawValue = ace.toRaw()

 

使用toRawfromRaw在原始(raw)數值和枚舉值之間進行轉換:

1 if let convertedRank = Rank.fromRaw(3) {
2     let threeDescription = convertedRank.simpleDescription()
3 }

 

注意枚舉中的成員值(member value)是實際的值(actual value),和原始值(raw value)沒有必然關聯。

一些狀況下枚舉不存在有意義的原始值,這時能夠直接忽略原始值:

 1 enum Suit {
 2     case Spades, Hearts, Diamonds, Clubs
 3         func simpleDescription() -> String {
 4         switch self {
 5             case .Spades:
 6                 return "spades"
 7             case .Hearts:
 8                 return "hearts"
 9             case .Diamonds:
10                 return "diamonds"
11             case .Clubs:
12                 return "clubs"
13         }
14     }
15 }
16 let hearts = Suit.Hearts
17 let heartsDescription = hearts.simpleDescription()

 

除了能夠關聯方法,枚舉還支持在其成員上關聯值,同一枚舉的不一樣成員能夠有不一樣的關聯的值:

 1 enum ServerResponse {
 2     case Result(String, String)
 3     case Error(String)
 4 }
 5 
 6 let success = ServerResponse.Result("6:00 am", "8:09 pm")
 7 let failure = ServerResponse.Error("Out of cheese.")
 8 
 9 switch success {
10     case let .Result(sunrise, sunset):
11         let serverResponse = "Sunrise is at \(sunrise) and sunset is at \(sunset)."
12     case let .Error(error):
13         let serverResponse = "Failure... \(error)"
14 }

 

結構

Swift使用struct關鍵字建立結構。結構支持構造器和方法這些類的特性。結構和類的最大區別在於:結構的實例按值傳遞(passed by value),而類的實例按引用傳遞(passed by reference)。

1 struct Card {
2     var rank: Rank
3     var suit: Suit
4     func simpleDescription() -> String {
5         return "The \(rank.simpleDescription()) of \(suit.simpleDescription())"
6     }
7 }
8 let threeOfSpades = Card(rank: .Three, suit: .Spades)
9 let threeOfSpadesDescription = threeOfSpades.simpleDescription()

 

協議(protocol)和擴展(extension)

協議

Swift使用protocol定義協議:

1 protocol ExampleProtocol {
2     var simpleDescription: String { get }
3     mutating func adjust()
4 }

 

類型、枚舉和結構均可以實現(adopt)協議:

 1 class SimpleClass: ExampleProtocol {
 2     var simpleDescription: String = "A very simple class."
 3     var anotherProperty: Int = 69105
 4     func adjust() {
 5         simpleDescription += " Now 100% adjusted."
 6     }
 7 }
 8 var a = SimpleClass()
 9 a.adjust()
10 let aDescription = a.simpleDescription
11 
12 struct SimpleStructure: ExampleProtocol {
13     var simpleDescription: String = "A simple structure"
14     mutating func adjust() {
15         simpleDescription += " (adjusted)"
16     }
17 }
18 var b = SimpleStructure()
19 b.adjust()
20 let bDescription = b.simpleDescription

 

擴展

擴展用於在已有的類型上增長新的功能(好比新的方法或屬性),Swift使用extension聲明擴展:

1 extension Int: ExampleProtocol {
2     var simpleDescription: String {
3         return "The number \(self)"
4     }
5     mutating func adjust() {
6         self += 42
7     }
8 }
9 7.simpleDescription

 

泛型(generics)

Swift使用<>來聲明泛型函數或泛型類型:

1 func repeat<ItemType>(item: ItemType, times: Int) -> ItemType[] {
2     var result = ItemType[]()
3     for i in 0..times {
4         result += item
5     }
6     return result
7 }
8 repeat("knock", 4)

 

Swift也支持在類、枚舉和結構中使用泛型:

1 // Reimplement the Swift standard library's optional type
2 enum OptionalValue<T> {
3     case None
4     case Some(T)
5 }
6 var possibleInteger: OptionalValue<Int> = .None
7 possibleInteger = .Some(100)

 

有時須要對泛型作一些需求(requirements),好比需求某個泛型類型實現某個接口或繼承自某個特定類型、兩個泛型類型屬於同一個類型等等,Swift經過where描述這些需求:

 
 1 func anyCommonElements <T, U where T: Sequence, U: Sequence, T.GeneratorType.Element: Equatable, T.GeneratorType.Element == U.GeneratorType.Element> (lhs: T, rhs: U) -> Bool {
 2     for lhsItem in lhs {
 3         for rhsItem in rhs {
 4             if lhsItem == rhsItem {
 5                 return true
 6             }
 7         }
 8     }
 9     return false
10 }
11 anyCommonElements([1, 2, 3], [3])

 


Swift語言概覽就到這裏,有興趣的朋友請進一步閱讀The Swift Programming Language。本文摘自http://zh.lucida.me/blog/an-introduction-to-swift/的部份內容。

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