函数Function

1.无参数无返回值

• funcprintHelloWorld() {
• print("hello,world")
• }

2.有参数无返回值

• funcsayGoodbye(personName:String) {
• print("Goodbye,\(personName)!")
• }
• sayGoodbye("Dave")
• // prints "Goodbye,Dave!"

3.一个参数

• funcsayHello(personName:String) -> String{
• letgreeting ="Hello," +personName +"!"
• returngreeting
• }

• print(sayHello("Anna"))
• // prints "Hello,Anna!"
• print(sayHello("Brian"))

函数名 参数名 参数类型 返回值类型

func sayHello(personName:String) -> String

4.多个参数

• funcsayHello(personName:String,alreadyGreeted: Bool) -> String{
• ifalreadyGreeted {
• returnsayHelloAgain(personName)
• } else {
• returnsayHello(personName)
• }
• }
• print(sayHello("Tim",alreadyGreeted:true))
• // prints "Hello again,Tim!"

上面的在函数的调用过程中,参数里面可以带参数名称的: alreadyGreeted:true

多参数之间使用”,”分开.

5.多值返回

• funcminMax(array: [Int]) -> (min:Int,max: Int) {
• varcurrentMin =array[0]
• varcurrentMax =array[0]
• forvalueinarray[1..<array.count] {
• if value < currentMin {
• currentMin = value
• } else if value >currentMax {
• currentMax = value
• }
• }
• return (currentMin,currentMax)
• }

• letbounds =minMax([8,-6,2,109,3,71])
• print("min is \(bounds.min) and max is\(bounds.max)")
• // prints "min is -6 and max is 109"

6.可选元组返回

• funcminMax(array: [Int]) -> (min:Int,max: Int)? {
• if array.isEmpty {returnnil }
• )
• }

• ifletbounds =minMax([8,71]) {
• print("min is\(bounds.min) and max is\(bounds.max)")
• }
• // prints "min is -6 and max is 109"

和上面的多值返回相比 在函数{}前多了一个”?”.

7.指定外部参数名称

• funcsayHello(toperson:String,and anotherPerson:String) ->String{
• return"Hello\(person) and\(anotherPerson)!"
• }
• print(sayHello(to:"Bill",and: "Ted"))
• // prints "Hello Bill and Ted!"

8.省去外部参数名

• funcsomeFunction(firstParameterName:Int,_ secondParameterName:Int) {
• // function body goes here
• // firstParameterName and secondParameterName refer to
• // the argument values for the first and second parameters
• print(“result is\(firstParameterName + secondParameterName)")
• }
• someFunction(1,2)

// prints “result is 3”

9.带初始参数

• funcsomeFunction(parameterWithDefault:Int = 12) {
• // if no arguments are passed to the function call,
• // value of parameterWithDefault is 12
  • returnparameterWithDefault
• }
• someFunction(6)// parameterWithDefault is 6
• someFunction()// parameterWithDefault is 12

10.不定参数个数

• funcarithmeticMean(numbers:Double...) -> Double {
• var total: Double = 0
• fornumberinnumbers {
• total += number
• }
• returntotal /Double(numbers.count)
• }
• arithmeticMean(1,2,3,4,5)
• // returns 3.0,which is the arithmetic mean of these five numbers
• arithmeticMean(3,8.25,18.75)
• // returns 10.0,which is the arithmetic mean of these three numbers

11.常亮和变量参数

• funcalignRight(varstring:String,totalLength:Int,pad:Character) -> String{
• letamountToPad =totalLength -string.characters.count
• if amountToPad < 1 {
• return string
• }
• letpadString =String(pad)
• for _ in1...amountToPad {
• string =padString +string
• }
• return string
• }
• letoriginalString ="hello"
• letpaddedString =alignRight(originalString,totalLength:10,pad:"-")
• // paddedString is equal to "-----hello"
• // originalString is still equal to "hello"

12.In-Out 参数

• func swapTwoInts(inouta:Int,inout _ b: Int) {
• lettemporaryA =a
• a = b
• b =temporaryA
• }

• varsomeInt =3
• varanotherInt =107
• swapTwoInts(&someInt,&anotherInt)
• print("someInt is now\(someInt),and anotherInt is now\(anotherInt)")
• // prints "someInt is now 107,and anotherInt is now 3"

in-out参数不能有初始默认值,inout参数不能是变量.上面的函数swapTwoInts

没有返回参数但是也完成了相似的功能.

13.函数赋值函数

• funcaddTwoInts(a:Int,_ b:Int) -> Int{
• return a + b
• }

varmathFunction: (Int,Int ) ->Int= addTwoInts

• print("Result: \(mathFunction(2,3))")
• // prints "Result: 5"

14.函数作为参数

• funcprintMathResult(mathFunction: (Int, Int ) -> Int,_a:Int ,_b: Int) {
• print("Result:\(mathFunction(a,b))")
• }
• printMathResult(addTwoInts,17)"> // prints "Result: 8"

15.函数作为返回值

• funcstepForward(input:Int) -> Int{
• return input + 1
• }
• funcstepBackward(input:Int) -> Int{
• return input - 1
• }

• funcchooseStepFunction(backwards:Bool) -> ( Int) -> Int{
• returnbackwards ?stepBackward :stepForward
• }

• varcurrentValue =3
• letmoveNearerToZero =chooseStepFunction(currentValue >0)
• // moveNearerToZero now refers to the stepBackward() function