Swift 语言最小化
PauKohn
8年前
<p style="text-align:center"><img src="https://simg.open-open.com/show/a3b31a7d4655347ef58ecdb5c94aa953.jpg"></p> <p style="text-align:center">swift_tour_learning-swift.jpg</p> <p>在 WWDC 2014 上 Apple Duang!!! 一声发布了 Swift 。在那次发布会上， Apple 向外界宣布了，自己其实是一家软件公司。</p> <p>2015 年， Apple 又 Duang!!! 一声将 Swift 开源。这让 Swift 迅速攻占了服务器，这使 Swift 开发 Backend server 成为了可能（ Vapor ）。</p> <p>初次接触 Swift，让我看到了 Scala、C#、ES 6 的影子，并且语法层面兼容 Objective C。first-class functions 特性让语言并不局限于 OO，让 Swift 具有函数式编程语言的表达力。 同时，Swift 作者 Chris Lattner 这位传奇人物的存在，让 Swift 成为值得长期投资的一门语言。</p> <h2>变量</h2> <p>Swift 中可以使用 var 和 let 直接定义 变量 或 常量 。</p> <p>定义变量：</p> <p></p> <pre> <code class="language-swift">var age = 20// 定义变量 let name = "Halo" // 定义常亮 age = 21</code></pre> <p>声明类型：</p> <p>上段代码看起来有些类似 javascript 若类型语言的特性，Swift 本质上还是强类型的语言，声明变量的时候，可以指定数据类型：</p> <pre> <code class="language-swift">let cash: Float = 1.25 let money: Double = 1.252525 let dollar: String = "USD"</code></pre> <h2>使用 String</h2> <p>对于字符串，Swift 简化了 Objective C NSString 的定义方式： @"" ：</p> <pre> <code class="language-swift">let currencies = "AUD, " + dollar let rmb = "1 \(dollar) is 6 RMB" let formattedString = String(format: "%.2f \(dollar) is about 600 RMB", 100.0) // 100.00 USD is about 600 RMB</code></pre> <p>\(variable) 是 Swift 为字符串模板提供的支持。不过 Swift 还是支持类似 ES 6 或者 Ruby 中多行字符串模板。多行字符串还是需要 + 号拼接：</p> <pre> <code class="language-swift">let introduceSwift = "We are excited by this new chapter in the story of Swift. " + "After Apple unveiled the Swift programming language, it quickly became one of " + "the fastest growing languages in history. Swift makes it easy to write software " + "that is incredibly fast and safe by design. Now that Swift is open source, you can " + "help make the best general purpose programming language available everywhere."</code></pre> <h2>使用 tuple</h2> <p>tuple 是 Swift 引入的一种新的数据类型，它可以方便支持方法的多返回值：</p> <pre> <code class="language-swift">let numbersTuple = (1, 100, 1000) print("min: \(numbersTuple.0), max: \(numbersTuple.1), sum: \(numbersTuple.2)") let numbersNamedTuple = (min: 1, max: 100, sum: 1000) print("min: \(numbersNamedTuple.0), max: \(numbersNamedTuple.1), sum: \(numbersNamedTuple.2)") print("min: \(numbersNamedTuple.min), max: \(numbersNamedTuple.max), sum: \(numbersNamedTuple.sum)")</code></pre> <h2>Collections</h2> <p>创建集合：</p> <p>Swift 的集合类型主要还是 Array 和 Dictionary ：</p> <pre> <code class="language-swift">var fruits = ["apple", "banana", "oranage"] var fruitsPrice = [ "apple": 4.25, "banana": 6.2 ] print(fruitsPrice[fruits[1]]) // 6.2</code></pre> <p>定义空集合：</p> <pre> <code class="language-swift">var emptyArray = [String]() var emptyDictionary = [String: Float]()</code></pre> <p>将已有集合设置为空时，可以用如下简写：</p> <pre> <code class="language-swift">fruits = [] fruitsPrice = [:]</code></pre> <p>使用 for in 遍历集合：</p> <pre> <code class="language-swift">for score in [1,2,3,4,5,6] { print(score * score * score) } for (key, val) in ["one": 1, "two": 2] { print("\(val) is \(key)") }</code></pre> <h2>if else 和 Optional</h2> <p>Swift 中新增一种类型 Optional，这个概念来自 Scala。 Optional 类似一个包装器，它可以包装一个数值，但是 Optional 可能返回 nil ，可能返回数据。多用于错误处理，通常跟 if else 连用：</p> <p>声明 Optional：</p> <pre> <code class="language-swift">var optionalString: String? = nil //print(optionalString!) // nil 取值会报错 print(optionalString == nil) var optionalName: String? = "Jian" print(optionalName!)</code></pre> <p>String? 表示一个 String 类型的 Optional。只有 Optional 可以接受 nil 值。如果对一个 nil 的 Optional 取值会报错，一般取值前会对 Optional 做判断：</p> <pre> <code class="language-swift">var optionalString: String? = nil if optionalString != nil { let val = optionalString! } else { print("There is no value") }</code></pre> <p>if-else 简化 Optional 取值：</p> <p>Swift 为上面这种方式提供一种简写：</p> <pre> <code class="language-swift">if let val = optionalString { print("There is a value: \(val)") } else { print("There is no value") }</code></pre> <p>通常会将 if-else 和 Optional 这么使用：</p> <pre> <code class="language-swift">var optionalName: String? = "Jian" print(optionalName!) var greeting = "Hello!" if let name = optionalName { greeting = "Hello \(name)" }</code></pre> <p>Optional 默认值:</p> <p>使用 ?? 可以为 Optional 提供默认值：</p> <pre> <code class="language-swift">let fullName: String = "Jian" let nickName: String? = nil let displayName = "\(nickName ?? fullName)"</code></pre> <h2>switch</h2> <p>Swift 中的 switch 强大很多，支持 String，多值匹配，条件匹配：</p> <pre> <code class="language-swift">let vegetable = "red pepper" switch vegetable { case "celery": print("Add some raisins and make ants on a log.") case "cucumber", "watercress": print("Taht would make a good tea sandwich.") case let x where x.hasSuffix("pepper"): print("Is it a spicy \(x)?") // Is it a spicy red pepper? default: print("Everythink tasts good") }</code></pre> <h2>使用循环</h2> <p>for in 循环</p> <p>Swift 中的 for in 和 javascript 中的有点类似。使用 for in 便利 Dictionary：</p> <pre> <code class="language-swift">let numbersDict = [ "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 numbersDict { for number in numbers { number if number > largest { largest = number } } } print(largest) // 25</code></pre> <p>使用 for in 遍历 Range：</p> <pre> <code class="language-swift">var total = 0 for i in 0..<4 { total += i } print(total) // 6</code></pre> <p>while 循环</p> <p>一般语言都会提供 while 和 do {} while 循环。Swift 采用 while 和 repeat {} while ：</p> <pre> <code class="language-swift">var n = 1 while n < 100 { n += n } print(n) //128 var m = 1 repeat { m += m } while m < 100 print(m) // 128</code></pre> <h2>Functions</h2> <p>Swift 中的函数具有 javascript 和 objective c 的双重特征。并且函数在 Swift 中是一等公民(First-class type)，具有高阶函数的特性。</p> <p>定义函数</p> <p>一般情况下，跟 Objective C 方法一样，需要给函数参数提供 Label：</p> <pre> <code class="language-swift">func greet(person: String, day: String) -> String { return "Hello \(person), today is \(day)." } greet(person: "Jian", day: "Friday")</code></pre> <p>使用 _ 表示省略 Label：</p> <pre> <code class="language-swift">func greet(_ person: String, on day: String) -> String { return "Hello \(person), today is \(day)." } greet("Jian", on: "Friday")</code></pre> <p>函数可以使用 tuple 返回多个值：</p> <pre> <code class="language-swift">func calcStatistics(scores: [Int]) -> (min: Int, max: Int, sum: Int) { var min = scores[0] var max = scores[0] var sum = 0 for score in scores { if score > max { max = score } else if score < min { min = score } sum += score } return (min, max, sum) } let statistics = calcStatistics(scores: [5, 1, 100, 30, 90]) print(statistics.sum) // 226 print(statistics.2) // 226</code></pre> <p>无限参数：</p> <pre> <code class="language-swift">func sumOf(numbers: Int...) -> Int { return numbers.reduce(0, +) } sumOf() // 0 sumOf(numbers: 1, 2, 3, 4, 10) // 20</code></pre> <p>使用 Int... 在函数的最后一个参数，表示后面可以接受无限个整数参数。</p> <p>函数嵌套</p> <pre> <code class="language-swift">func returnFifteen() -> Int { var y = 10 func add() { y += 5 } add() return y } returnFifteen() // 15</code></pre> <p>高阶函数</p> <p>高阶函数( high-order function )，是函数是编程的一个概念，高阶函数的特点：</p> <ul> <li>可以将函数当做返回值，即：可以使用函数创建函数</li> <li>可以将函数当做参数接收</li> </ul> <p>使用函数创建另一个函数：</p> <pre> <code class="language-swift">func createIncrementer() -> ((Int) -> Int) { func plusOne(number: Int) -> Int { return 1 + number } return plusOne } let incrementer = createIncrementer() incrementer(10)</code></pre> <p>函数作为参数：</p> <pre> <code class="language-swift">func hasAnyMatches(_ list: [Int], matcher: (Int) -> Bool) -> Bool { for item in list { if matcher(item) { return true } } return false } func lessThanThen(number: Int) -> Bool { return number < 10 } hasAnyMatches([20, 10, 7, 12], matcher: lessThanThen)</code></pre> <h2>Closure （闭包）</h2> <p>Closure 可以理解匿名函数，在很多 Callback 和集合操作中使用：</p> <pre> <code class="language-swift">hasAnyMatches([20, 10, 7, 12]) { (item: Int) -> Bool in item < 10 } [20, 10, 7, 12].map { (item: Int) -> Int in return 3 * item } [20, 10, 7, 12].map({ item in 3 * item })</code></pre> <p>如果省略 () 后， Closure 是唯一的参数：</p> <pre> <code class="language-swift">let sortedNumbers = [20, 10, 7, 12].sorted { $0 > $1 } print(sortedNumbers)</code></pre> <h2>Objects and Classes</h2> <p>定义和使用类：</p> <pre> <code class="language-swift">class Shape { var numberOfSides = 0 func simpleDescription() -> String { return "A shap with \(numberOfSides) sides." } } let shape = Shape() shape.numberOfSides = 10 shape.simpleDescription()</code></pre> <p>使用继承:</p> <pre> <code class="language-swift">class NamedShape : Shape { var name: String init(name: String) { self.name = name } } // inherit and override 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 square = Square(sideLength: 10.0, name: "Jian's Square") square.area() square.simpleDescription()</code></pre> <p>使用属性</p> <p>Swift 中对属性的处理，有些像 C#。</p> <p>使用 getter/setter</p> <pre> <code class="language-swift">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 triangle with sides of length \(sideLength)" } } var triangle = EquilateralTriangle(sideLength: 3.1, name: "A triangle") print(triangle.perimeter) // 9.3 triangle.perimeter = 9.9 print(triangle.sideLength) // 3.3</code></pre> <p>使用 willSet：</p> <pre> <code class="language-swift">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: "other shape") print(triangleAndSquare.square.sideLength) // 10.0 print(triangleAndSquare.triangle.sideLength) // 10.0 triangleAndSquare.square = Square(sideLength: 50, name: "Large square") print(triangleAndSquare.triangle.sideLength) // 50.0</code></pre> <p>使用 willSet 保证 square 和 triangle 的 sideLength 始终相等。</p> <p>使用 Optional 类型</p> <p>使用 ?. 取值，当值为 nil 时返回 nil ，而不是报错。</p> <pre> <code class="language-swift">let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square") let sideLength = optionalSquare?.sideLength let nilSquare: Square? = nil let nilLength = nilSquare?.sideLength</code></pre> <h2>Enumerations</h2> <p>定义 enum 类型：</p> <pre> <code class="language-swift">enum Level: Int { case Zero, First, Second } Level.Zero.rawValue Level.First.rawValue</code></pre> <p>enum 的 rawValue 默认从 0 开始，依次递增。</p> <p>在 enum 中创建方法：</p> <pre> <code class="language-swift">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" } } }</code></pre> <p>定义特性类型的 enum：</p> <pre> <code class="language-swift">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.rawValue) } } } let ace = Rank.ace // ace let aceRawValue = ace.rawValue // 1</code></pre> <p>enum Rank: Int 设置 enum 的 rawValue 为 Int 。我们也可以通过 rawValue 来创建 enum ：</p> <pre> <code class="language-swift">if let convertedRank = Rank(rawValue: 3) { let threeDescription = convertedRank.simpleDescription() // 3 }</code></pre> <p>复杂的 enum ：</p> <pre> <code class="language-swift">enum ServerResponse { case result(String, String) case failure(String) } let success = ServerResponse.result("6:00 am", "8:00 pm") let failure = ServerResponse.failure("Out of cheese") switch success { case let .result(sunrise, sunset): print("Sunrise is at \(sunrise) and sunset is at \(sunset)") // Sunrise is at 6:00 am and sunset is at 8:00 pm case let .failure(message): print("Failure ... \(message)") }</code></pre> <h2>Structs</h2> <pre> <code class="language-swift">struct Card { var rank: Rank var suit: Suit func simpleDescript() -> String { return "The \(rank.simpleDescription()) of \(suit.simpleDescription())" } } let threeOfSpades = Card(rank: .three, suit: .spades) // Card print(threeOfSpades.simpleDescript()) // The 3 of spades</code></pre> <p>struct 和 class 最重要的区别是：</p> <ul> <li>struct 传递值，始终传递 copy</li> <li>class 传递引用。</li> </ul> <h2>Protocol</h2> <pre> <code class="language-swift">protocol ExampleProtocol { var simpleDescription: String { get } mutating func adjust() }</code></pre> <p>Protocol 与 Java 中的 Interface 概念类似。在 Swift 中，class、struct、enum、extension 都可以实现 Protocol：</p> <p>class 实现 protocol：</p> <pre> <code class="language-swift">class SimpleClass: ExampleProtocol { var simpleDescription: String = "A simple class." var moreProperty: Int = 315 func adjust() { simpleDescription += " Now 100% adjusted" } } var simpleClass = SimpleClass() simpleClass.adjust() print(simpleClass.simpleDescription) // A simple class. Now 100% adjusted</code></pre> <p>struct 实现 protocol：</p> <pre> <code class="language-swift">struct SimpleStructure: ExampleProtocol { var simpleDescription: String = "A simple structure" mutating func adjust() { simpleDescription += " (adjusted) " } } var simpleStruct = SimpleStructure() simpleStruct.adjust() print(simpleStruct.simpleDescription)</code></pre> <p>mutating 修饰符表示，当前方法在 struct 中可以修改 struct 的值。</p> <p>在 protocol 的应用中，可以使用 Java 中面向 Interface 编程：</p> <pre> <code class="language-swift">let protocolValue: ExampleProtocol = simpleStruct print(protocolValue.simpleDescription) // A simple structure (adjusted)</code></pre> <h2>Extensions</h2> <p>Swift 中的 extension 和 ruby 中的 Open Class 概念很像，在 ObjC 中是 Category 。它可以为已有类型添加新的特性：</p> <pre> <code class="language-swift">extension Int: ExampleProtocol { var simpleDescription: String { return "The number \(self)" } mutating func adjust() { self += 10 } } print(7.simpleDescription)</code></pre> <h2>Error Handling</h2> <p>throws 异常</p> <pre> <code class="language-swift">enum PointerError: Error { case outOfPaper case noToner case onFire } // throw error func send(job: Int, toPointer printerName: String) throws -> String { if printerName == "Never has toner" { throw PointerError.noToner } return "Job sent" }</code></pre> <p>catch 和处理异常</p> <p>对于具有 throws 声明的方法，需要使用 try 关键字调用，然后使用 do {} catch {} 包裹：</p> <pre> <code class="language-swift">do { let pointerResp = try send(job: 1024, toPointer: "Never has toner") print(pointerResp) } catch { // catch all errors print(error) // use error by default }</code></pre> <p>处理多个异常：</p> <pre> <code class="language-swift">do { let pointerResponse = try send(job: 1024, toPointer: "Jian") print(pointerResponse) throw PointerError.onFire } catch PointerError.onFire { print("I'll just put shi over here, with the result of the fire.") // I'll just put shi over here, with the result of the fire. } catch let pointerError as PointerError { print("Printer error: \(pointerError) .") } catch { print(error) }</code></pre> <p>通常 catch 多个 Error 时， catch 顺序需要从小异常，到范围更大的异常。</p> <p>使用 try?</p> <pre> <code class="language-swift">// try? -> Optional let pointerFailure = try? send(job: 1024, toPointer: "Never has toner") // nil let pointerSuccess = try? send(job: 2048, toPointer: "Good pointer") // Job sent</code></pre> <p>使用 defer</p> <p>在方法 throws 时，会终端当前函数后续的代码执行，使用 defer 可以确保 defer 代码段中的代码在函数返回前始终被执行。这个概念有些像 Java 的 try {} catch {} finally {} 中的 finally ：</p> <pre> <code class="language-swift">func ensureExecute() throws -> String { defer { print("Complete") } do { try send(job: 1024, toPointer: "Never has toner") } catch { throw error } return "Executed" } let executed = try? ensureExecute() // Complete</code></pre> <h2>Generic</h2> <p>Swift 开始支持泛型（Generic）：</p> <pre> <code class="language-swift">enum OptionalValue<Wrapped> { case none case some(Wrapped) } var possibleInteger: OptionalValue<Int> = .none // none possibleInteger = .some(100) // some(100)</code></pre> <p>使用 where 限定泛型的类型：</p> <pre> <code class="language-swift">func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool where T.Iterator.Element: Equatable, T.Iterator.Element == U.Iterator.Element { for lhsItem in lhs { for rhsItem in rhs { if lhsItem == rhsItem { return true } } } return false } anyCommonElements([1,2,3,4,5], [5])</code></pre> <p>where T.Iterator.Element: Equatable, T.Iterator.Element == U.Iterator.Element 限制 T 和 U 中的元素，必须实现 Equatable ，并且 T 和 U 中的元素是同一种类型。</p> <h2> </h2> <p> </p> <p>来自：http://www.jianshu.com/p/3d8963cdb0b9</p> <p> </p>