10.函数(function)

函数

• kotlin_函数

函数是有名字的一段代码
包含参数和返回值,参数可以有默认值

fun add (x: Int ,y:Int = 0):Int{
    return x + y
}

fun main(args:Array<String>){
    //调用是可打参数名,可读性更好(但调用java函数无效)
    val b  add(x : 2)
    println(b)
    val a = intArryOf(1,2,3,5,100)
    println(sum (*a))
}
//可变参数修饰符vararg
fun sum(vararg x: Int) : Int{
     var total = 0
     for(i in x){
        total += i
     }
    return total
}

• swift_函数

无参数函数
func helloworld() ->String{
   return "hello,world"
}
多参数函数
func greet(person:String,age:Int) -> String{
   if age >= 20 {
     print(person)
   } else {
      print(person)
   }
}
无返回值函数
func helloWorld(){
   print("helloworld")
}
多重返回值函数
func minMax(array: [Int]) -> (min: Int, max: Int) {
    var currentMin = array[0]
    var currentMax = array[0]
    for value in array[1..<array.count] {
        if value < currentMin {
            currentMin = value
        } else if value > currentMax {
            currentMax = value
        }
    }
    return (currentMin, currentMax)
}
可选元组返回类型
func minMax(array: [Int]) -> (min: Int, max: Int)? {
    if array.isEmpty { return nil }
    var currentMin = array[0]
    var currentMax = array[0]
    for value in array[1..<array.count] {
        if value < currentMin {
            currentMin = value
        } else if value > currentMax {
            currentMax = value
        }
    }
    return (currentMin, currentMax)
}
函数类型作为参数类型
func printMathResult(_ mathFunction: (Int, Int) -> Int, 
_ a: Int, _ b: Int) {
    print("Result: \(mathFunction(a, b))")
}
printMathResult(addTwoInts, 3, 5)
嵌套函数
func chooseStepFunction(backward: Bool) -> (Int) -> Int {
    func stepForward(input: Int) -> Int { return input + 1 }
    func stepBackward(input: Int) -> Int { return input - 1 }
    return backward ? stepBackward : stepForward
}
var currentValue = -4
let moveNearerToZero = chooseStepFunction(backward: currentValue > 0)
// moveNearerToZero now refers to the nested stepForward() function
while currentValue != 0 {
    print("\(currentValue)... ")
    currentValue = moveNearerToZero(currentValue)
}
print("zero!")