Swift 闭包Closures

概述什么是Closures? Closures是自包含的代码块,在代码中使用或是作为参数传值,和OC中的blocks类似. Swift中闭包的优势 1.根据上下文推断参数和返回值类型 2.隐式返回(可以省略return) 3.简化参数(如$0,$1;从0开始表示第n个参数) 4.Trailing闭包表达式 闭包表达式形式 具体实例: // 使用函数let names = ["Chris", "Ale 什么是Closures?
Closures是自包含的代码块,在代码中使用或是作为参数传值,和OC中的blocks类似.
Swift中闭包的优势
1.根据上下文推断参数和返回值类型
2.隐式返回(可以省略return)
3.简化参数(如$0,$1;从0开始表示第n个参数)
4.Trailing闭包表达式

闭包表达式形式

具体实例:

// 使用函数let names = ["Chris","Alex","Ewa","barry","DanIElla"]func backwards(s1: String,_ s2: String) -> Bool {    return s1 > s2}var reversed = names.sort(backwards)// reversed = ["Ewa","DanIElla","Chris","Alex"]// 使用闭包reversed = names.sort({ (s1: String,s2: String) -> Bool in    return s1 > s2})// reversed = ["Ewa","Alex"]reversed = names.sort( { s1,s2 in return s1 > s2 } )// reversed = ["Ewa","Alex"]reversed = names.sort( {  >  } ) // 简写参数 隐式返回// reversed = ["Ewa","Alex"]reversed = names.sort {  >  }    // 进一步简写// reversed = ["Ewa","Alex"]reversed = names.sort() {  >  }  // Trailing闭包// reversed = ["Ewa","Alex"]reversed = names.sort(>)             // Operator Functions Swift中定义了一个>作为函数,并返回一个bool类型的数据// reversed = ["Ewa","Alex"]let digitnames = [    0: "Zero",1: "One",2: "Two",3: "Three",4: "Four",5: "Five",6: "Six",7: "Seven",8: "Eight",9: "Nine"]let numbers = [16,58,510]//  map(_:) 遍历numberslet strings = numbers.map {    (number) -> String in    var number = number    var output = ""    while number > 0 {        output = digitnames[number % 10]! + output  // 先取出个位        number /= 10                                // 取出十位    }    print("output = \(output)")  // 依次打印:Onesix,FiveEight,FiveOneZero    return output}// 值捕获func makeIncrementer(forIncrement amount: Int) -> () -> Int {    var runningTotal = 0    func incrementer() -> Int {        runningTotal += amount        return runningTotal    }    return incrementer}// 引用闭包let incrementByTen = makeIncrementer(forIncrement: 10)print("incrementByTen = \(incrementByTen())") // incrementByTen = 10print("incrementByTen = \(incrementByTen())") // incrementByTen = 20print("incrementByTen = \(incrementByTen())") // incrementByTen = 30// NonescaPing 闭包func someFunctionWithNonescaPingClosure(@noescape closure: () -> VoID) {    closure()}var completionHandlers: [() -> VoID] = []func someFunctionWithEscaPingClosure(completionHandler: () -> VoID) {    completionHandlers.append(completionHandler)}class SomeClass {    var x = 10    func doSomething() {        someFunctionWithEscaPingClosure { self.x = 100 }        someFunctionWithNonescaPingClosure { x = 200 }    }}let instance = SomeClass()instance.doSomething()print(instance.x)// Prints "200"completionHandlers.first?()print(instance.x)// Prints "100"

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