函數(shù)的定義
func pi() -> Double {
return 3.14
}
//形參默認(rèn)是let, 也只能是let常量
func sum(v1: Int, v2: Int) -> Int {
return v1 + v2
}
//無返回值
func sayHello() -> Void {
print("hello")
}
func sayHello() -> () {
print("hello")
}
func sayHello() {
print("hello")
}
隱式返回(Implicit Return)
如果整個函數(shù)體是一個單一表達(dá)式, 那么函數(shù)會隱式返回這個表達(dá)式:
func sum(v1: Int, v2: Int) -> Int {
v1 + v2
}
sum(v1: 10, v2: 20) //30
返回元祖: 實現(xiàn)多返回值
func calculate(v1: Int, v2: Int) -> (sum: Int, difference: Int, average: Int){
let sum = v1 + v2
return (sum, v1 - v2, sum >> 1)
}
let result = calculate(v1: 20, v2: 10)
result.sum //30
result.difference //10
result.average //15
參數(shù)標(biāo)簽(Argument Label)
可以修改參數(shù)標(biāo)簽:
func goToWork(at time: String) {
print("This time is \(time)")
}
goToWork(at: "08:00")
// This time is 08:00
可以使用下劃線 _ 省略參數(shù)標(biāo)簽
func sum(_ v1: Int, _ v2: Int) -> Int {
v1 + v2
}
sum(10,20)
默認(rèn)參數(shù)值(Default Parameter Value)
func check(name: String = "nobody", age: Int, job: String = "none") {
print("name=\(name), age=\(age), job=\(job)")
}
check(name: "Jack", age: 20, job: "Doctor") //name=Jack, age=20, job=Doctor
check(name: "Rose", age: 18) //name=Rose, age=18, job=none
check(age: 10, job: "Batman") //name=nobody, age=10, job=Batman
check(age: 15) //name=nobody, age=15, job=none
C++的默認(rèn)參數(shù)值有個限制: 必須從右往左設(shè)置, 由于Swift擁有參數(shù)標(biāo)簽, 因此沒有類似限制
但是在省略參數(shù)標(biāo)簽時, 需要特別注意, 避免出錯
//這里的middle不可以省略參數(shù)標(biāo)簽
func test(_ first: Int = 10, middle: Int, _ last: Int = 30) {}
test(middle: 20)
可變參數(shù)(Variadic Parameter)
func sum(_ numbers: Int...) -> Int {
var total = 0
for number in numbers {
total += number
}
return total
}
sum(10, 20, 30, 40) //100
一個函數(shù)最多只能有1個可變參數(shù)
緊跟在可變參數(shù)后面的參數(shù)不能省略參數(shù)標(biāo)簽
//參數(shù)string不能省略標(biāo)簽
func test(_ numbers: Int..., string: String, _ other: String) { }
test(10, 20, 30, string: "Jack", "Rose")
輸入輸出參數(shù)(In-Out Parameter)
可以用inout定義一個輸入輸出參數(shù):可以在函數(shù)內(nèi)部修改外部實參的值
可變參數(shù)不能標(biāo)記為inout
inout參數(shù)不能有默認(rèn)值
inout參數(shù)只能傳入可以被多次賦值的
inout參數(shù)的本質(zhì)是地址傳遞(引用傳遞)
func swapValues(_ v1: inout Int, _ v2: inout Int) {
let tmp = v1
v1 = v2
v2 = tmp
}
var num1 = 10
var num2 = 20
swapValues(&num1, &num2)
func swapValues(_ v1: inout Int, _ v2: inout Int) {
(v1, v2) = (v2, v1)
}
函數(shù)重載(Function Overload)
規(guī)則
函數(shù)名相同
參數(shù)個數(shù)不同 || 參數(shù)類型不同 || 參數(shù)標(biāo)簽不同
func sum(v1: Int, v2: Int) -> Int { v1 + v2 }
func sum(v1: Int, v2: Int, v3: Int) -> Int { v1 + v2 + v3 } // 參數(shù)個數(shù)不同
sum(v1: 10, v2: 20) // 30
sum(v1: 10, v2: 20, v3: 30) // 60
sum(v1: 10, v2: 20.0) // 30.0
sum(v1: 10.0, v2: 20) // 30.0
sum(10, 20) // 30
sum(a: 10, b: 20) // 30
func sum(v1: Int, v2: Double) -> Double { Double(v1) + v2 } // 參數(shù)類型不同
func sum(v1: Double, v2: Int) -> Double { v1 + Double(v2) } // 參數(shù)類型不同
func sum(_ v1: Int, _ v2: Int) -> Int { v1 + v2 } // 參數(shù)標(biāo)簽不同
func sum(a: Int, b: Int) -> Int { a + b } // 參數(shù)標(biāo)簽不同
函數(shù)重載注意點
返回值類型與函數(shù)重載無關(guān)
func sum(v1: Int, v2: Int) -> Int { v1 + v2 }
func sum(v1: Int, v2: Int) {}
sum(v1: 10, v2: 20) //報錯 有歧義
默認(rèn)參數(shù)值和函數(shù)重載一起使用產(chǎn)生二義性時叨叙，編譯器并不會報錯(在C++中會報錯)
func sum(v1: Int, v2: Int) -> Int {
v1 + v2
}
func sum(v1: Int, v2: Int, v3: Int = 10) -> Int {
v1 + v2 + v3
}
// 會調(diào)用sum(v1: Int, v2: Int) sum(v1: 10, v2: 20)
函數(shù)重載注意點
可變參數(shù)锭弊、省略參數(shù)標(biāo)簽、函數(shù)重載一起使用產(chǎn)生二義性時擂错，編譯器有可能會報錯
func sum(v1: Int, v2: Int) -> Int {
v1 + v2
}
func sum(_ v1: Int, _ v2: Int) -> Int {
v1 + v2
}
func sum(_ numbers: Int...) -> Int {
var total = 0
for number in numbers {
total += number
}
return total
}
// error: ambiguous use of 'sum'
sum(10, 20)
函數(shù)類型(Function Type)
每一個函數(shù)都是有類型的味滞，函數(shù)類型由形式參數(shù)類型、返回值類型組成
func test() { } // () -> Void 或者 () -> ()
func sum(a: Int, b: Int) -> Int { a+b } // (Int, Int) -> Int
// 定義變量
var fn: (Int, Int) -> Int = sum fn(2, 3) // 5钮呀，調(diào)用時不需要參數(shù)標(biāo)簽
函數(shù)類型作為函數(shù)參數(shù)
func sum(v1: Int, v2: Int) -> Int {
v1 + v2
}
func difference(v1: Int, v2: Int) -> Int { v1 - v2 }
func printResult(_ mathFn: (Int, Int) -> Int, _ a: Int, _ b: Int) {
print("Result: \(mathFn(a, b))")
}
printResult(sum, 5, 2) // Result: 7
printResult(difference, 5, 2) // Result: 3
函數(shù)類型作為函數(shù)返回值
func next(_ input: Int) -> Int {
input + 1
}
func previous(_ input: Int) -> Int { input - 1 }
func forward(_ forward: Bool) -> (Int) -> Int {
forward ? next : previous
}
forward(true)(3) // 4
forward(false)(3) // 2
返回值是函數(shù)類型的函數(shù)剑鞍，叫做高階函數(shù)(Higher-Order Function)
typealias
typealias用來給類型起別名
typealias Byte = Int8
typealias Short = Int16
typealias Long = Int64
typealias Date = (year: Int, month: Int, day: Int)
func test(_ date: Date) {
print(date.0)
print(date.year)
}
test((2011, 9, 10))
按照Swift標(biāo)準(zhǔn)庫的定義，Void就是空元組()
public typealias Void = ()
typealias IntFn = (Int, Int) -> Int
func difference(v1: Int, v2: Int) -> Int {
v1 - v2
}
let fn: IntFn = difference
fn(20, 10) // 10
func setFn(_ fn: IntFn) { }
setFn(difference)
func getFn() -> IntFn { difference }
public typealias Void = ()
嵌套函數(shù)(Nested Function)
將函數(shù)定義在函數(shù)內(nèi)部
func forward(_ forward: Bool) -> (Int) -> Int {
func next(_ input: Int) -> Int {
input + 1
}
func previous(_ input: Int) -> Int {
input - 1
}
return forward ? next : previous
}
forward(true)(3) // 4
forward(false)(3) // 2
