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转自:http://letsswift.com/2014/06/swift_overview/
println("Hello, world")
var myVariable = 42 myVariable = 50 let myConstant = 42类型推导
let explicitDouble : Double = 70
let label = "The width is " let width = 94 let width = label + String(width)字符串格式化
let apples = 3 let oranges = 5 let appleSummary = "I have \(apples) apples." let appleSummary = "I have \(apples + oranges) pieces of fruit."
var shoppingList = ["catfish", "water", "tulips", "blue paint"] shoppingList[1] = "bottle of water" var occupations = [ "Malcolm": "Captain", "Kaylee": "Mechanic", ] occupations["Jayne"] = "Public Relations"一般使用初始化器(initializer)语法创建空数组和空字典:
let emptyArray = String[]() let emptyDictionary = Dictionary()
let individualScores = [75, 43, 103, 87, 12] var teamScore = 0 for score in individualScores { if score > 50 { teamScore += 3 } else { teamScore += 1 } }
var optionalString: String? = "Hello" optionalString == nil var optionalName: String? = "John Appleseed" var gretting = "Hello!" if let name = optionalName { gretting = "Hello, \(name)" }灵活的switch
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." }其它循环
let interestingNumbers = [ "Prime": [2, 3, 5, 7, 11, 13], "Fibonacci": [1, 1, 2, 3, 5, 8], "Square": [1, 4, 9, 16, 25], ] var largest = 0 for (kind, numbers) in interestingNumbers { for number in numbers { if number > largest { largest = number } } } largest
var n = 2 while n < 100 { n = n * 2 } n var m = 2 do { m = m * 2 } while m < 100 mSwift支持传统的for循环,此外也可以通过结合..(生成一个区间)和for-in实现同样的逻辑。
var firstForLoop = 0 for i in 0..3 { firstForLoop += i } firstForLoop var secondForLoop = 0 for var i = 0; i < 3; ++i { secondForLoop += 1 } secondForLoop注意:Swift除了..还有…:..生成前闭后开的区间,而…生成前闭后闭的区间。
func greet(name: String, day: String) -> String { return "Hello \(name), today is \(day)." } greet("Bob", "Tuesday")通过元组(Tuple)返回多个值:
func getGasPrices() -> (Double, Double, Double) { return (3.59, 3.69, 3.79) } getGasPrices()
func sumOf(numbers: Int...) -> Int { var sum = 0 for number in numbers { sum += number } return sum } sumOf() sumOf(42, 597, 12)函数也可以嵌套函数:
func returnFifteen() -> Int { var y = 10 func add() { y += 5 } add() return y }作为头等对象,函数既可以作为返回值,也可以作为参数传递:
func makeIncrementer() -> (Int -> Int) { func addOne(number: Int) -> Int { return 1 + number } return addOne } var increment = makeIncrementer() increment(7)
func hasAnyMatches(list: Int[], condition: Int -> Bool) -> Bool { for item in list { if condition(item) { return true } } return false } func lessThanTen(number: Int) -> Bool { return number < 10 } var numbers = [20, 19, 7, 12] hasAnyMatches(numbers, lessThanTen)闭包
numbers.map({ (number: Int) -> Int in let result = 3 * number return result })当闭包的类型已知时,可以使用下面的简化写法:
numbers.map({ number in 3 * number })此外还可以通过参数的位置来使用参数,当函数最后一个参数是闭包时,可以使用下面的语法:
sort([1, 5, 3, 12, 2]) { $0 > $1 }类和对象
class Shape { var numberOfSides = 0 func simpleDescription() -> String { return "A shape with \(numberOfSides) sides." } }创建Shape类的实例,并调用其字段和方法。
var shape = Shape() shape.numberOfSides = 7 var shapeDescription = shape.simpleDescription()
class NamedShape { var numberOfSides: Int = 0 var name: String init(name: String) { self.name = name } func simpleDescription() -> String { return "A shape with \(numberOfSides) sides." } }使用deinit进行清理工作。
class Square: NamedShape { var sideLength: Double init(sideLength: Double, name: String) { self.sideLength = sideLength super.init(name: name) numberOfSides = 4 } func area() -> Double { return sideLength * sideLength } override func simpleDescription() -> String { return "A square with sides of length \(sideLength)." } } let test = Square(sideLength: 5.2, name: "my test square") test.area() test.simpleDescription()注意:如果这里的simpleDescription方法没有被标识为override,则会引发编译错误。
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 triagle with sides of length \(sideLength)." } } var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle") triangle.perimeter triangle.perimeter = 9.9 triangle.sideLength注意:赋值器(setter)中,接收的值被自动命名为newValue。
class TriangleAndSquare { var triangle: EquilateralTriangle { willSet { square.sideLength = newValue.sideLength } } var square: Square { willSet { triangle.sideLength = newValue.sideLength } } init(size: Double, name: String) { square = Square(sideLength: size, name: name) triangle = EquilateralTriangle(sideLength: size, name: name) } } var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape") triangleAndSquare.square.sideLength triangleAndSquare.square = Square(sideLength: 50, name: "larger square") triangleAndSquare.triangle.sideLength从而保证triangle和square拥有相等的sideLength。
class Counter { var count: Int = 0 func incrementBy(amount: Int, numberOfTimes times: Int) { count += amount * times } } var counter = Counter() counter.incrementBy(2, numberOfTimes: 7)注意Swift支持为方法参数取别名:在上面的代码里,numberOfTimes面向外部,times面向内部。
let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square") let sideLength = optionalSquare?.sideLength
enum Rank: Int { case Ace = 1 case Two, Three, Four, Five, Six, Seven, Eight, Nine, Ten case Jack, Queen, King func simpleDescription() -> String { switch self { case .Ace: return "ace" case .Jack: return "jack" case .Queen: return "queen" case .King: return "king" default: return String(self.toRaw()) } } } let ace = Rank.Ace let aceRawValue = ace.toRaw()使用toRaw和fromRaw在原始(raw)数值和枚举值之间进行转换:
if let convertedRank = Rank.fromRaw(3) { let threeDescription = convertedRank.simpleDescription() }注意:枚举中的成员值(member value)是实际的值(actual value),和原始值(raw value)没有必然关联。
enum Suit { case Spades, Hearts, Diamonds, Clubs func simpleDescription() -> String { switch self { case .Spades: return "spades" case .Hearts: return "hearts" case .Diamonds: return "diamonds" case .Clubs: return "clubs" } } } let hearts = Suit.Hearts let heartsDescription = hearts.simpleDescription()除了可以关联方法,枚举还支持在其成员上关联值,同一枚举的不同成员可以有不同的关联的值:
enum ServerResponse { case Result(String, String) case Error(String) } let success = ServerResponse.Result("6:00 am", "8:09 pm") let failure = ServerResponse.Error("Out of cheese.") switch success { case let .Result(sunrise, sunset): let serverResponse = "Sunrise is at \(sunrise) and sunset is at \(sunset)." case let .Error(error): let serverResponse = "Failure... \(error)" }结构
struct Card { var rank: Rank var suit: Suit func simpleDescription() -> String { return "The \(rank.simpleDescription()) of \(suit.simpleDescription())" } } let threeOfSpades = Card(rank: .Three, suit: .Spades) let threeOfSpadesDescription = threeOfSpades.simpleDescription()
protocol ExampleProtocol { var simpleDescription: String { get } mutating func adjust() }类型、枚举和结构都可以实现(adopt)协议:
class SimpleClass: ExampleProtocol { var simpleDescription: String = "A very simple class." var anotherProperty: Int = 69105 func adjust() { simpleDescription += " Now 100% adjusted." } } var a = SimpleClass() a.adjust() let aDescription = a.simpleDescription struct SimpleStructure: ExampleProtocol { var simpleDescription: String = "A simple structure" mutating func adjust() { simpleDescription += " (adjusted)" } } var b = SimpleStructure() b.adjust() let bDescription = b.simpleDescription扩展
extension Int: ExampleProtocol { var simpleDescription: String { return "The number \(self)" } mutating func adjust() { self += 42 } } 7.simpleDescription泛型(generics)
func repeat(item: ItemType, times: Int) -> ItemType[] { var result = ItemType[]() for i in 0..times { result += item } return result } repeat("knock", 4)Swift也支持在类、枚举和结构中使用泛型:
// Reimplement the Swift standard library's optional type enum OptionalValue { case None case Some(T) } var possibleInteger: OptionalValue = .None possibleInteger = .Some(100)有时需要对泛型做一些需求(requirements),比如需求某个泛型类型实现某个接口或继承自某个特定类型、两个泛型类型属于同一个类型等等,Swift通过where描述这些需求:
func anyCommonElements本文转自 感谢原作者(lhs: T, rhs: U) -> Bool { for lhsItem in lhs { for rhsItem in rhs { if lhsItem == rhsItem { return true } } } return false } anyCommonElements([1, 2, 3], [3])
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