如何使用swift函数

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默认参数

func greet(_ person: String = "zhang san", _ hometown: String = "bei jing") -> String {    return "Hello \(person)! Glad you could visit from \(hometown)"}print(greet())//Hello zhang san! Glad you could visit from bei jing

不定参数个数

//不定参数个数func sum(_ nums: Int...) -> Int {    var ret = 0    for n in nums {        ret += n    }    return ret}print(sum(1,2,3))//6print(sum(1,2,3,4,5))//15

函数内改变函数外定义的参数值

//函数内改变函数外定义的参数值func swap(_ a: inout Int, _ b: inout Int) {    let temp = a    a = b    b = temp}var a = 1var b = 2swap(&a, &b)print(a)//2print(b)//1

函数类型变量

func add(_ a: Int, _ b: Int) -> Int {    return a + b}var addFunc: (Int, Int) -> Int = addprint(addFunc(1, 2))//3

函数类型参数

func printResult(_ f: (Int, Int) -> Int, _ a: Int, _ b: Int) {    print("Result: \(f(a, b))")}printResult(add, 1,2)//Result: 3

函数类型作为返回值

func forward(_ input: Int) -> Int {    return input + 1}func backward(_ input: Int) -> Int {    return input - 1}func step(isBack: Bool) -> (Int) -> Int {    return isBack ? backward : forward}//记数倒数到0var currValue = 3let moveNearerToZero = step(isBack: currValue > 0)print("Counting to zero:")while currValue != 0 {    print("\(currValue)...")    currValue = moveNearerToZero(currValue)}print("zero!")/* Counting to zero: 3... 2... 1... zero! */

内嵌函数

func chooseStepFunc(backward: Bool) -> (Int) -> Int {    func stepForward(input: Int) -> Int {        return input + 1    }    func stepBackward(input: Int) -> Int {        return input - 1    }    return backward ? stepBackward : stepForward}print("Counting to zero:")var cVal = -4let toZero = chooseStepFunc(backward: cVal > 0)while cVal != 0 {    print("\(cVal)...")    cVal = toZero(cVal)}print("zero!")/* Counting to zero: -4... -3... -2... -1... zero! */

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