iOS-swift4学习（函数）

1. 忽略参数标签 _ xx: xxx

func greet(_ name:String) ->String{
    
    return "hello,\(name)"
}
let kname = greet("jack")

2. 设置默认参数值

func someFunction(parameterWithoutDefault: Int, parameterWithDefault: Int = 2 ){
     如果你在调用时候不传第二个参数，parameterWithDefault 会值为 12 传入到函数体中。
}

3. 可变参数 一个函数最多只能拥有一个可变参数。

func arithmeticMean(_ numbers: Double...) -> Double {
    var total: Double = 0
    for number in numbers {
        total += number
    }
    return total / Double(numbers.count)
}
print(arithmeticMean(1,2,3))

4. 输入输出参数 函数修改变量 - inout

func swapTwoInts(_ a: inout Int, _ b: inout Int) {
    let temporaryA = a
    a = b
    b = temporaryA
}
var height = 120
var width = 60
swapTwoInts(&height, &width)
// height = 60, width = 120

5. 函数类型作为返回类型

func stepBackward(_ input: Int) -> Int {
    return input - 1
}
func stepForward(_ input: Int) -> Int {
    return input + 1
}
func chooseStepFunction(backward: Bool) -> (Int) -> Int {
    return backward ? stepBackward : stepForward
}

6. 闭包表达式语法

let blockHs = {(s1:String, s2:String) ->Bool in

    return s1.count > s2.count
}

7. 尾随闭包

func someFunctionThatTakesAClosure(closure: () -> Void) {
    // 函数体部分
}
/*以下是不使用尾随闭包进行函数调用*/
someFunctionThatTakesAClosure(closure: {
    // 闭包主体部分
})

/*以下是使用尾随闭包进行函数调用*/
someFunctionThatTakesAClosure() {
    // 闭包主体部分
}

8. 逃逸闭包 - @escaping

var completionHandlers: [() -> Void] = []
func someFunctionWithEscapingClosure(completionHandler: @escaping () -> Void) {
    completionHandlers.append(completionHandler)
}

9. 自动闭包 自动闭包让你能够延迟求值

var customersInLine = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
let customerProvider = { customersInLine.remove(at: 0) }
print(customersInLine.count) // 打印出 5
customerProvider() // 执行
print(customersInLine.count) // 打印出 4

10. 将闭包作为参数传递给函数时

func serve(customer customerProvider: () -> String) {
    print("Now serving \(customerProvider())!")
}
serve(customer: {customersInLine.remove(at: 0) })
 // 打印出 "Now serving Alex!"

11. 将参数标记为 @autoclosure 来接收一个自动闭包

func serveE(customer customerProvider: @autoclosure () -> String) {
    print("Now serving \(customerProvider())!")
}
serveE(customer: customersInLine.remove(at: 0))

12. 泛型函数

func swapTwoValues<T>(_ a: inout T, _ b: inout T){
    
    let temporaryA = a
    a = b
    b = temporaryA
}

13. 枚举语法

enum CompassPoint {
    case north
    case south
    case east
    case west
}
var directionToHead = CompassPoint.west

swift学习电梯：
swift-基础类型
swift-函数
swift-类和结构体

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