沒有了解過swift能夠先參考Brec Victor的Inventing on Principle ,Swift編程環境的大部分概念都源自於Brec這個演講。express
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
注:這一節的代碼源自The Swift Programming Language中的A Swift Tour。框架
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")
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
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)
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."
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。
Swift的條件語句包含if
和switch
,循環語句包含for-in
、for
、while
和do-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 }
結合if
和let
,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 }
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." }
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。
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)
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 }
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。
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。
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
。
EquilateralTriangle
的構造器進行了以下操做:
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willSet
和didSet
:
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triangle
和square
擁有相等的sideLength
。
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。
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
當optionalSquare
爲nil
時,sideLength
屬性調用會被忽略。
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toRaw
和fromRaw
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 }
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()
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
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。