- 控制流：for-in、while、Repeat-While、if、switch
let someCharacter: Character = "z"
switch someCharacter {
case "a":
print("The first letter of the alphabet")
case "z":
print("The last letter of the alphabet")
default:
print("Some other character")
}
// 輸出 "The last letter of the alphabet"
let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a", "A":
print("The letter A")
default:
print("Not the letter A")
}
// 輸出 "The letter A
let approximateCount = 62
let countedThings = "moons orbiting Saturn"
var naturalCount: String
switch approximateCount {
case 0:
naturalCount = "no"
case 1..<5:
naturalCount = "a few"
case 5..<12:
naturalCount = "several"
case 12..<100:
naturalCount = "dozens of"
case 100..<1000:
naturalCount = "hundreds of"
default:
naturalCount = "many"
}
print("There are \(naturalCount) \(countedThings).") // 輸出 "There are dozens of moons orbiting Saturn."
//元組
let somePoint = (1, 1)
switch somePoint {
case (0, 0):
print("(0, 0) is at the origin")
case (_, 0):
print("(\(somePoint.0), 0) is on the x-axis")
case (0, _):
print("(0, \(somePoint.1)) is on the y-axis")
case (-2...2, -2...2):
print("(\(somePoint.0), \(somePoint.1)) is inside the box")
default:
print("(\(somePoint.0), \(somePoint.1)) is outside of the box")
}
// 輸出 "(1, 1) is inside the box"
//值綁定：
let anotherPoint = (2, 0)
switch anotherPoint {
case (let x, 0):
print("on the x-axis with an x value of \(x)")
case (0, let y):
print("on the y-axis with a y value of \(y)")
case let (x, y):
print("somewhere else at (\(x), \(y))")
}
// 輸出 "on the x-axis with an x value of 2"
//用where
let yetAnotherPoint = (1, -1)
switch yetAnotherPoint {
case let (x, y) where x == y:
print("(\(x), \(y)) is on the line x == y")
case let (x, y) where x == -y:
print("(\(x), \(y)) is on the line x == -y")
case let (x, y):
print("(\(x), \(y)) is just some arbitrary point")
}
// 輸出 "(1, -1) is on the line x == -y"
//貫穿：和C語言一樣執行下一個case
let integerToDescribe = 5
var description = "The number \(integerToDescribe) is"
switch integerToDescribe {
case 2, 3, 5, 7, 11, 13, 17, 19:
description += " a prime number, and also"
fallthrough
default:
description += " an integer."
}
print(description)
// 輸出 "The number 5 is a prime number, and also an integer."
- 轉移語句：continue、break、fallthrough、return、throw、guard-else
continue：繼續執行下一次循環
break：結束循環
fallthrough：貫穿，在switch中，可以執行下一個case
return：返回函數
throw：錯誤拋出
guard-else：提前退出
//標簽：
gameLoop: while square != finalSquare {
diceRoll += 1
if diceRoll == 7 { diceRoll = 1 }
switch square + diceRoll {
case finalSquare:
// 骰子數剛好使玩家移動到最終的方格里，游戲結束。
break gameLoop
case let newSquare where newSquare > finalSquare:
// 骰子數將會使玩家的移動超出最后的方格，那么這種移動是不合法的，玩家需要重新擲骰子
continue gameLoop
default:
// 合法移動，做正常的處理 square += diceRoll
square += board[square]
} }
print("Game over!")
- 函數：func 是一段完成特定任務的獨立代碼片段。
//可選元組返回類型
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)")
}
// 打印 "min is -6 and max is 109"
//
//可變參數的func（1個、2個、3個....）
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)
// 返回 3.0, 是這 5 個數的平均數。 arithmeticMean(3, 8.25, 18.75)
// 返回 10.0, 是這 3 個數的平均數。
//
//函數類型作為參數類型：
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
//用 chooseStepFunction(backward:) 來獲得兩個函數其中的一個
}
var currentValue = 3
let moveNearerToZero = chooseStepFunction(backward: currentValue > 0)
// moveNearerToZero 現在指向 stepBackward() 函數。
- 閉包：自包含的函數代碼塊。
三種形式的閉包： - 全局函數是一個有名字但不會捕獲任何值的閉包
- 嵌套函數是一個有名字并可以捕獲其封閉函數域內值的閉包
- 閉包表達式是一個利用輕量級語法所寫的可以捕獲其上下文中變量常量值的匿名閉包
閉包表達式：
//sorted方法：
let names = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
func backward(_ s1: String, _ s2: String) -> Bool {
return s1 > s2
}
var reversedNames = names.sorted(by: backward)
// reversedNames 為 ["Ewa", "Daniella", "Chris", "Barry", "Alex"]
//轉成閉包表達式：
reversedNames = names.sorted(by: { (s1: String, s2: String) -> Bool in
return s1 > s2
})
//根據上下文推斷類型
reversedNames = names.sorted(by: { s1, s2 in return s1 > s2 } )
//單表達式閉包隱式返回
reversedNames = names.sorted(by: { s1, s2 in s1 > s2 } )
尾隨閉包：
func someFunctionThatTakesAClosure(closure: () -> Void) {
// 函數體部分
}
// 以下是不使用尾隨閉包進行函數調用
someFunctionThatTakesAClosure(closure: {
// 閉包主體部分
})
// 以下是使用尾隨閉包進行函數調用
someFunctionThatTakesAClosure() {
// 閉包主體部分
}
捕獲值：
func makeIncrementer(forIncrement amount: Int) -> () -> Int {
var runningTotal = 0
func incrementer() -> Int {
runningTotal += amount
return runningTotal
}
return incrementer
}
逃逸閉包：@escaping
var completionHandlers: [() -> Void] = []
func someFunctionWithEscapingClosure(completionHandler: @escaping () -> Void) {
completionHandlers.append(completionHandler)
}
自動閉包：@autoclosure
一種自動創建的閉包，用于包裝傳遞給函數作為參數的表達式。不接受任何參數，當它被調用的時候，會返回被包裝在其中的表達式的值。
//延時求值：
var customersInLine = ["Chris", "Alex", "Ewa", "Barry", "Daniella"] print(customersInLine.count)
// 打印出 "5"
let customerProvider = { customersInLine.remove(at: 0) } print(customersInLine.count)
// 打印出 "5"
print("Now serving \(customerProvider())!") // Prints "Now serving Chris!" print(customersInLine.count)
// 打印出 "4"
//
// customersInLine is ["Ewa", "Barry", "Daniella"]
func serve(customer customerProvider: @autoclosure () -> String) {
print("Now serving \(customerProvider())!")
}
serve(customer: customersInLine.remove(at: 0)) // 打印 "Now serving Ewa!"
