swift 函数特性

//函数体内享有外部所有作用域
let global = "global"
func fn (args: String, args2: String) -> String {
print(global)
return args + "\t" + args2
}

var return_string: String =  fn("string1", args2: "string3331");
print(return_string)

//元组返回
func minMax(array: [Int]) -> (Int,Int)? {
if array.isEmpty {
return nil
}
var curren_min = array[0]
var curren_max = curren_min
//array[1..<2] 数组截取
for value in array[1..<array.count] {
if curren_min > value {
curren_min = value
}else if curren_max < value {
curren_max = value
}
}
return (curren_min, curren_max)
}

print(minMax([1,2,3,5,2,99,0]))

//外部参数名

func fnOutParams(in1 args1: String, in2 args2: String) {
print(args1 + "  " + args2)
}
fnOutParams(in1: "aa", in2: "bb")

//省略外部参数名

func fnOutParams(args1: String, _ args2: String) {
print(args1 + "  " + args2)
}
fnOutParams("aa", "bb")

//可变参数

func avgNumbers(numbers: Double...) -> Double {
var total: Double = 0
for number in numbers {
total += number
}
return total/Double(numbers.count)
}
print(avgNumbers(1,2,3,4,5.9,6,9,22))

//参数重赋值(默认let 常量参数)

func reFn(var args: String) {
args = "cs";
print(args)
}
reFn("reFn");

//inout 指针传值

func swapVariable(inout args: String, inout _ args2: String) {
let tmp: String  = args
args = args2
args2 = tmp
}
var a = "args1"
var b = "args2"
swapVariable(&a, &b)
print(a + "\t" + b)

// 函数类型

func addTwoInts(a: Int, _ b: Int) -> Int {
return a + b
}
func multiplyTwoInts(a: Int, _ b: Int) -> Int {
return a * b
}

let addTwoInts2 = addTwoInts;
print(addTwoInts2(1, 2));

let variable_fn: (Int, Int) -> Int  = multiplyTwoInts;

print(variable_fn(1, 2));

//函数作为参数

func fnArgments(args: (Int, Int)-> Int, _ args2: Int, _ args3: Int) -> Int{
return args(args2, args3)
}

print(fnArgments(addTwoInts2, 2, 3))

//函数作为返回值

func fnRetruns(args: (Int, Int) -> Int) -> (Int, Int) -> Int{
return args
}

let return_value = fnRetruns(multiplyTwoInts)(1, 5)
print(return_value);

//嵌套函数

func fnNesting(bool: Bool) -> (Int) -> Int{

func stepForward(input: Int) -> Int {
return input + 1
}

func stepBackward(input: Int) -> Int {
return input - 1
}

return bool ? stepForward : stepBackward
}

print(fnNesting(true)(2))