定義function
func 自訂func名稱(參數1:資料類型, 參數2:資料類型, 參數3:資料類型) -> 傳出值資料類型{
code
return type
}
參數可以省略，return type也可空白！
呼叫function
let 接收物 = 自訂func名稱(引數1, 引數2, 引數3)
func greet(person:String) -> String {
let greeting = "Hello, " + person + "!";
return greeting
}
print(greet(person: "Anna"));
print(greet(person:"Brian"));
func greetAgain(person: String) -> String {
return "Hello again, " + person + "!"
}
print(greetAgain(person: "Anna"));
global Function：
apple 定義，使用者只呼叫
func greet(person:String) -> String{
let greeting = "Hello, " + person +"!";
return greeting;
}
func greetAgain(person:String) -> String{
return "Hello again, " + person +"!";
}
//function 沒有參數
//function 有傳出，就一定要有return！
func sayHelloWorld() -> String {
return "Hello, World";
}
//function 有多個參數
//function名稱相同，但參數名稱不同，或參數名稱相同，但參數的數量不同，皆視為不同的function
func greet(person:String, alreadyGreeted:Bool) -> Stringh{
if alreadyGreeted {
return greetAgain(person: String);
}
}
print(greet(person: "Tim", alreadyGreeted: true));
//function 沒有return值
//func greet(person:String) -> Void { }，-> Void：表示沒有傳出值！
func greet(person1:String){
print("Hello, \(person1)");
}
func printAndCount(string:String) -> Int{
print(string);
return string.count;
}
func printWithoutCounting(string:String){
let _ = printAndCount(string:string);
}
printWithoutCountin(string: "Hello, World!");
//利用tuple傳出多個值
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]);
bounds.max
bounds.min
//optional的寫法
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]){
bounds.max;
bounds.min;
}
//function的引數與參數名稱，
func someFunction(firstParameterName:Int, secondParameterName:Int){
}
someFunction(firstParameterName: 3, secondParameterName:2)
//自訂引數名稱 argumentLabel ，parameterName是參數名稱
func someFunction(argumentLabel parameterName:Int){
}
someFunction(argumentLabel: 54);
func greet(person:String, from hometown:String) -> String{
return "Hello \(person)! Glad you could visit from \(hometown)"
}
greet(person: "Bill", form: "Cupertino");
//省略引數名稱
func someFunction(_ firstParameterName:Int, secondParamaterName:Int){
}
someFunction(5, secondParamaterName:3)
//default parameter value，有default value的參數要寫在後面！
func someFunction(parameterWithoutDefault:Int,patameterWithDefault:Int = 12){
}
someFunction(parameterWithoutDefault: 3, patameterWithDefault: 6)
someFunction(parameterWithoutDefault: 5)
//不限參數數量，這時引述名稱大多省略！參數內容則為陣列！
func arithmeticMean(_ numbers:Double...) -> Double{
var total:Double = 0;
for number in numbers{
total += number
}
return total / Double(numbers.count)
}
arithmeticMean(1,2,3,4,5,6)
arithmeticMean(1.4,6,8,4.6,7.8)
//inout parameter，參數值為常數（let），無法變更！要在function內變更已設定的參數值，需用inout！
func swapTwoInt(_ a:inout Int, _ b:inout Int){
let temporaryA = a;
a = b;
b = temporaryA;
}
var someInt = 3;
var anotherInt = 107;
//inout參數的呼叫，名稱前會多&
swap(&someInt, &anotherInt);
someInt;
anotherInt;
//function type，不管function名稱，只管參數和return值
//function type可以被存在變數，可以當作引數，可以當return type
func addTwoInts(_ a:Int, _ b:Int) -> Int{
return a + b;
}
func mutiplyTwoInts(_ a:Int, _ b:Int) -> Int{
return a * b;
}
func printHelloWorld(){
print("hello, world");
}
//func printHelloWorld()的function type表示法：() -> Void
//將func addTwoInts指定給變數mathFunction，mathFunction的資料類型是function type:(Int, Int) -> Int
var mathFunction:(Int, Int) -> Int = addTwoInts;
print("result:\(mathFunction(2,3))");
mathFunction = mutiplyTwoInts
print("result:\(mathFunction(2, 3))");
//把function當作參數
func printMathResult(_ mathFunction:(Int, Int) -> Int, _ a:Int, _ b:Int) {
print("Result:\(mathFunction(a,b))")
}
printMathResult(addTwoInts, 3, 5);
Nested Function
//Nested Function
//傳出function
func chooseStepFunction(backward:Bool) -> (Int) -> Int{
func stepForward(input:Int) -> Int{
return input + 1
}
func stepBackward(input:Int) -> Int{
return input - 1
}
//三元運算式 Bool ?true的運算:false的運算
//下列只是傳出function，不是執行function，所以只輸入function名稱，沒有()！
return backward ? stepBackward : stepForward
}
var currentValue = -4;
let moveNearerToZero = chooseStepFunction(backward: currentValue > 0)
while currentValue != 0 {
print("\(currentValue)...");
currentValue = moveNearerToZero(currentValue)
}
Closure（閉鎖）--> 匿名的Function
用在當一個function的參數需求是一個function時，可以直接closure的方式給予。
Closure呼叫時語法：
mainFunction({
(參數名:資料類型,參數名:資料類型) -> return typr in
coding................
coding................
})
let names:[String] = ["Chris", "Alex", "Ewa", "Barry", "Daniella"];
let sotrdNames = names.sorted();
//定義一個function，省略參數名稱
func backward(_ s1:String,_ s2:String) -> Bool{
return s1 > s2;
}
//func sorted(by: (Element, Element) -> Bool) -> [Element]
//Returns the elements of the sequence, sorted using the given predicate as the comparison between elements.
var reverseNames = names.sorted(by: backward)
//closure 標準寫法
reverseNames = names.sorted(by: {
(s1:String, s2:String) -> Bool in
return s1 < s2;
})
//closure 的所有資料類型,可以省略,因為透過推測
reverseNames = names.sorted(by: {
(s1,s2) in
return s1 < s2
})
//如果只有一行,可以省略return
reverseNames = names.sorted(by: {
(s1,s2) in s1 < s2
})
//s1,s2也可以省略去定義,用$0,$1替代
reverseNames = names.sorted(by: { $0 < $1 })
//連$0，$1都省略
reverseNames = names.sorted(by: < )
//trailing closure,在最後一 個參數
reverseNames = names.sorted(){
$0 < $1;
}
//trailing closure,在最後一 個參數，連()都省略！
reverseNames = names.sorted{
$0 < $1;
}
let numbers = [16, 58, 510];
let numberStrings = numbers.map({
(n:Int) -> String in
return String(n*2)
})
