函数基本使用
关键字:func
func hello(name:String) ->String { let result = "Hello,"+name return result } hello(name: "imagine")
可选型：
func hello(name:String?,greet:String) ->String { let result = greet+","+(name)! return result } var nickname:String? //nil nickname = "imagine" hello(name: nickname,greet: "Good Night") //Good Night,imagine"
无参数函数，直接返回一个字符串类型的函数：
func sayHello() ->String { return "Welcome to imaginecode" } sayHello() //"Welcome to imaginecode"
空类型void / () ,不返回任何值
func sayVoid() ->Void{ print("it is a void func") }
使用元组让函数返回多个值
func maxminScores( scores:[Int]) -> ( maxscore:Int,minscore:Int)? //元组的可选型 { if scores.isEmpty{ return nil } var curmax = scores[0] ,curmin = scores[0] for score in scores[1..<scores.count]{ curmax = max(curmax, score) curmin = min(curmin, score) } return (curmax,curmin) } var scores:[Int]? = [12,60,71,81,91,100] //可选型数组 scores = scores ?? [] if let result = maxminScores(scores: scores!) { print(result.maxscore) print(result.minscore) }
内部参数名和外部参数名
func hello(userName nickname:String,greeting greet:String) -> String{ //内部参数nickname,greet,属于函数体 let result = greet+":"+nickname return result } hello(userName: "imagine", greeting: "codeing") //给参数nickname与greet起了外部参数名userName和greeting
参数的默认值
func hello(nickname:String,greet:String = "hello") -> String{ //给greet默认值hello let result = greet+":"+nickname return result } hello(nickname: "imagine") //"hello:imagine"
func hello(nickname:String,greet:String = "hello",other:String = "nihao") -> String{ //给greet默认值hello let result = greet+":"+nickname+other return result } hello(nickname: "imagine",other:"how do you do") //"hello:imaginehow do you do"
可变参数
- 一个函数最好只能设置一个可变参数，并且该可变参数只能放在这个函数参数列表的最后一个位置
- 必须参数 > 默认值参数 > 可变参数
func add(a:Int,b:Int,others:Int ... ) ->Int //others是可变参数 ... 将其解析为数组 { var result = a + b for num in others { result += num } return result } var res = add(a: 2, b: 3) res = add(a: 2, b: 3, others: 4,5,6) NSLog(format: String, args: CVarArg...) //CvarArg也是可变参数
inout参数 - 引用传递
- inout用于声明数据是地址传递，也称之为引用传递；
- inout修饰的参数是不能有默认值的，有范围的参数集合也不能被修饰；
- 一个参数一旦被inout修饰，就不能再被var和let修饰了。
func swapTwoInts( a:inout Int,b:inout Int) { let t = a; a = b b = t } var x = 0, y = 100 swapTwoInts(a: &x, b: &y) //传入引用参数
函数类型
func add(a:Int,b:Int) -> Int { return a+b } let anotherAdd:(Int,Int)->Int = add //参数为两个Int,返回类型为Int ,add 作为变量 anotherAdd(3,4)
func changeScores1(scores:inout [Int]) { for i in 0..<scores.count { scores[i] = Int(sqrt(Double(scores[i]))*10) } } func changeScores2(scores:inout [Int]) { for i in 0..<scores.count { scores[i] = Int(sqrt(Double(scores[i]))/150.0 * 100.0) } } func changeScores3(scores:inout [Int]) { for i in 0..<scores.count { scores[i] += 3 } } var scores1 = [20,40,60,80,90] changeScores1(scores: &scores1) var scores2 = [20,40,60,80,90] changeScores2(scores: &scores2) var scores3 = [20,40,60,80,90] changeScores3(scores: &scores3)
改进：
func changeScores(op:(Int)->Int, scores:inout [Int]) { for i in 0..<scores.count{ scores[i] = op(scores[i]) } } func op1(x:Int)->Int {return Int(sqrt(Double(x))*10)} func op2(x:Int)->Int {return Int(sqrt(Double(x))/150.0*100.0)} func op3(x:Int)->Int {return x + 3} var scores1 = [20,40,60,80,90] changeScores(op: op1, scores: &scores1) var scores2 = [20,40,60,80,90] changeScores(op: op2, scores: &scores2) var scores3 = [20,40,60,80,90] changeScores(op: op3, scores: &scores3)
var arr = [Int]() for _ in 1...20 { arr.append(Int(arc4random()%100)) } arr func compareTwoInts(a:Int,b:Int) -> Bool{return a>b } arr.sort()
返回函数类型的返回值、函数嵌套
//邮费计算 func mailcost1(weight:Int) -> Int { return 1*weight } func mailcost2(weight:Int) -> Int { return 2*weight } func chooseMailCostMethod(weight:Int) -> (Int)->Int //返回一个Int类型的函数，解耦作用 { return weight <= 10 ? mailcost1 : mailcost2 } func totalCost(price:Int,weight:Int) -> Int { let mailCost:(Int)->Int = chooseMailCostMethod(weight: weight) return mailCost(weight) + price*weight }
另一种写法：函数嵌套
func mailcost1(weight:Int) -> Int { return 1*weight } func mailcost2(weight:Int) -> Int { return 2*weight } func totalCost(price:Int,weight:Int) -> Int { func chooseMailCostMethod(weight:Int) -> (Int)->Int //函数嵌套 { return weight <= 10 ? mailcost1 : mailcost2 } let mailCost:(Int)->Int = chooseMailCostMethod(weight: weight) return mailCost(weight) + price*weight }
