Swift Function函数

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"))
• // prints "Hello, 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 }
•     varcurrentMin =array[0] 
•     varcurrentMax =array[0]
•     forvalueinarray[1..<array.count] {
•         if value < currentMin {
•             currentMin = value
•         } else if value >currentMax {
•             currentMax = value
•         }
•     }
•     return (currentMin,currentMax)
• }

• ifletbounds =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"

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) {
•     // function body goes here
•     // 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,3,5)
• // 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

原文地址:

https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Functions.html#//apple_ref/doc/uid/TP40014097-CH10-ID158