Swift-函數(shù)

定義和調(diào)用函數(shù)

定義：

func greet(person: String) -> String {
    let greeting = "Hello, " + person + "!"
    return greeting
}

調(diào)用：

print(greet(person: "Anna"))
// Prints "Hello, Anna!"
print(greet(person: "Brian"))
// Prints "Hello, Brian!"

func greetAgain(person: String) -> String {
    return "Hello again, " + person + "!"
}
print(greetAgain(person: "Anna"))
// Prints "Hello again, Anna!"

函數(shù)參數(shù)和返回值

沒有參數(shù)的函數(shù)

返回值為字符串的值

func sayHelloWorld() -> String {
    return "hello, world"
}
print(sayHelloWorld())
// Prints "hello, world"

具有多個參數(shù)的函數(shù)

一個參數(shù)名person 類型為字符串，另一個alreadyGreeted 類型為bool 返回一個字符串

func greet(person: String, alreadyGreeted: Bool) -> String {
    if alreadyGreeted {
        return greetAgain(person: person)
    } else {
        return greet(person: person)
    }
}
print(greet(person: "Tim", alreadyGreeted: true))
// Prints "Hello again, Tim!"

沒有返回值的函數(shù)

func greet(person: String) {
    print("Hello, \(person)!")
}
greet(person: "Dave")
// Prints "Hello, Dave!"

由于該函數(shù)的定義不需要返回值，因此它不包含返回箭頭（->）或返回類型
調(diào)用函數(shù)時脯颜，可以忽略其返回值：

func printAndCount(string: String) -> Int {
    print(string)
    return string.count
}
func printWithoutCounting(string: String) {
    let _ = printAndCount(string: string)
}
printAndCount(string: "hello, world")
// prints "hello, world" and returns a value of 12
printWithoutCounting(string: "hello, world")
// prints "hello, world" but does not return a value

具有多個返回值的函數(shù)

返回兩個返回值处坪，最大最小

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)
}

let bounds = minMax(array: [8, -6, 2, 109, 3, 71])
print("min is \(bounds.min) and max is \(bounds.max)")
// Prints "min is -6 and max is 109"

可選的元組返回類型

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)
}

if let bounds = minMax(array: [8, -6, 2, 109, 3, 71]) {
    print("min is \(bounds.min) and max is \(bounds.max)")
}
// Prints "min is -6 and max is 109"

隱式返回函數(shù)

func greeting(for person: String) -> String {
    "Hello, " + person + "!"
}
print(greeting(for: "Dave"))
// Prints "Hello, Dave!"

func anotherGreeting(for person: String) -> String {
    return "Hello, " + person + "!"
}
print(anotherGreeting(for: "Dave"))
// Prints "Hello, Dave!"

 func greeting(for person: String) -> String {
        "Hello, " + person + "!"
    }

 func greeting1(person: String) -> String {
          "Hello, " + person + "!"
      }

image.png

函數(shù)參數(shù)標(biāo)簽和參數(shù)名稱

func someFunction(firstParameterName: Int, secondParameterName: Int) {
    // In the function body, firstParameterName and secondParameterName
    // refer to the argument values for the first and second parameters.
}
someFunction(firstParameterName: 1, secondParameterName: 2)

指定參數(shù)標(biāo)簽

func someFunction(argumentLabel parameterName: Int) {
    // In the function body, parameterName refers to the argument value
    // for that parameter.
}

func greet(person: String, from hometown: String) -> String {
    return "Hello \(person)!  Glad you could visit from \(hometown)."
}
print(greet(person: "Bill", from: "Cupertino"))
// Prints "Hello Bill!  Glad you could visit from Cupertino."

image.png

在參數(shù)前面加from 和for類似隱式參數(shù)

省略參數(shù)標(biāo)簽

func someFunction(_ firstParameterName: Int, secondParameterName: Int) {
    // In the function body, firstParameterName and secondParameterName
    // refer to the argument values for the first and second parameters.
}

someFunction(1, secondParameterName: 2)

在參數(shù)名前面加_ 的時候在函數(shù)調(diào)用的時候參數(shù)名可以省略

默認(rèn)參數(shù)值

func someFunction(parameterWithoutDefault: Int, parameterWithDefault: Int = 12) {
    // If you omit the second argument when calling this function, then
    // the value of parameterWithDefault is 12 inside the function body.
}
someFunction(parameterWithoutDefault: 3, parameterWithDefault: 6) // parameterWithDefault is 6
someFunction(parameterWithoutDefault: 4) // parameterWithDefault is 12

如果是參數(shù)有默認(rèn)值那么驾茴，調(diào)用的時候可以默認(rèn)的參數(shù)可以忽略
someFunction(parameterWithoutDefault: 4)
如果都傳了參數(shù) 值那么會按照最新傳入的值進(jìn)行運算

可變參數(shù)

func arithmeticMean(_ numbers: Double...) -> Double {
    var total: Double = 0
    for number in numbers {
        total += number
    }
    return total / 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

求和锅必，numbers: Double... 寫法我現(xiàn)在也沒搞明白為嘛這么寫

輸入輸出參數(shù)

func swapTwoInts(_ a: inout Int, _ b: inout Int) {
    let temporaryA = a
    a = b
    b = temporaryA
}

var someInt = 3
var anotherInt = 107
swapTwoInts(&someInt, &anotherInt)
print("someInt is now \(someInt), and anotherInt is now \(anotherInt)")
// Prints "someInt is now 107, and anotherInt is now 3"

image.png

如果用inout修飾那么必須要有 &來獲取參數(shù)的值
傳入一個參數(shù)事格，調(diào)用函數(shù)后惕艳，返回一個 “&參數(shù)”的值

函數(shù)類型

使用函數(shù)類型

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

函數(shù)類型作為參數(shù)類型

var mathFunction: (Int, Int) -> Int = addTwoInts

image.png

定義一個方法搞隐，打印出來如上是function

mathFunction = multiplyTwoInts
print("Result: \(mathFunction(2, 3))")
// Prints "Result: 6"

函數(shù)類型作為返回類型

func printMathResult(_ mathFunction: (Int, Int) -> Int, _ a: Int, _ b: Int) {
    print("Result: \(mathFunction(a, b))")
}
printMathResult(addTwoInts, 3, 5)
// Prints "Result: 8"

image.png

函數(shù)作為一個參數(shù)，

函數(shù)類型作為返回類型

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

func chooseStepFunction(backward: Bool) -> (Int) -> Int {
    return backward ? stepBackward : stepForward
}

var currentValue = 3
let moveNearerToZero = chooseStepFunction(backward: currentValue > 0)
// moveNearerToZero now refers to the stepBackward() function

print("Counting to zero:")
// Counting to zero:
while currentValue != 0 {
    print("\(currentValue)... ")
    currentValue = moveNearerToZero(currentValue)
}
print("zero!")
// 3...
// 2...
// 1...
// zero!

嵌套函數(shù)

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!")
// -4...
// -3...
// -2...
// -1...
// zero!

image.png

返回的類型是函數(shù)類型函數(shù)的的返回值的類型是整形

OK
本期的 Swift-函數(shù)就到這里远搪。