Apple 的 A Swift Tour 程式碼重點整理 — 新手面試前的 Swift 複習聖經

Apple 官方的 Swift Book 是世界上最棒也最完整的 Swift 程式學習書籍，而書本開頭的 A Swift Tour 更是值得一讀，可以讓我們快速了解 Swift 的主要語法跟功能。

若是以下兩種人，更是推薦花個幾分鐘快速一讀 A Swift Tour:

• 正在準備 iOS App 工作面試的新手，想在面試前臨時抱佛腳，快速複習 Swift 語法。
• 已學過 Python, Java, C, JavaScript, Kotlin, Ruby 等程式語言，或是身為資工系學生或工程師，想快速認識 Swift 語法。

有興趣的朋友可從以下連結閱讀 A Swift Tour。

Documentation

以下則是彼得潘複製貼上 A Swift Tour 的程式碼。若是懶得看說明，想更快速複習 Swift 語法，也可直接參考以下程式。

constant & variable, var, let, type annotation

var myVariable = 42
myVariable = 50
let myConstant = 42
let implicitInteger = 70
let implicitDouble = 70.0
let explicitDouble: Double = 70
let label = "The width is "
let width = 94
let widthLabel = label + String(width)

string interpolation, \( )

let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit."

three double quotation marks, multiple lines

let quotation = """
I said "I have \(apples) apples."
And then I said "I have \(apples + oranges) pieces of fruit."
"""

array & dictionary

var shoppingList = ["catfish", "water", "tulips"]
shoppingList[1] = "bottle of water"
var occupations = [
    "Malcolm": "Captain",
    "Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"
shoppingList.append("blue paint")
print(shoppingList)
let emptyArray: [String] = []
let emptyDictionary: [String: Float] = [:]
shoppingList = []
occupations = [:]

for in & if else

let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
    if score > 50 {
        teamScore += 3
    } else {
        teamScore += 1
    }
}
print(teamScore)

optional, ?, nil, optional binding, if let

var optionalString: String? = "Hello"
print(optionalString == nil)
// Prints "false"
var optionalName: String? = "John Appleseed"
var greeting = "Hello!"
if let name = optionalName {
    greeting = "Hello, \(name)"
}

nil-coalescing, ??, default value

let nickname: String? = nil
let fullName: String = "John Appleseed"
let informalGreeting = "Hi \(nickname ?? fullName)"

if let shorthand

if let nickname {
    print("Hey, \(nickname)")
}

switch, where

let vegetable = "red pepper"
switch vegetable {
case "celery":
    print("Add some raisins and make ants on a log.")
case "cucumber", "watercress":
    print("That would make a good tea sandwich.")
case let x where x.hasSuffix("pepper"):
    print("Is it a spicy \(x)?")
default:
    print("Everything tastes good in soup.")
}
// Prints "Is it a spicy red pepper?"

for in & dictionary

let interestingNumbers = [
    "Prime": [2, 3, 5, 7, 11, 13],
    "Fibonacci": [1, 1, 2, 3, 5, 8],
    "Square": [1, 4, 9, 16, 25],
]
var largest = 0
for (_, numbers) in interestingNumbers {
    for number in numbers {
        if number > largest {
            largest = number
        }
    }
}
print(largest)
// Prints "25"

while & repeat while

var n = 2
while n < 100 {
    n *= 2
}
print(n)
// Prints "128"
var m = 2
repeat {
    m *= 2
} while m < 100
print(m)
// Prints "128"

for in & range, …, ..<

var total = 0
for i in 0..<4 {
    total += i
}
print(total)
// Prints "6"
total = 0
for i in 0...4 {
    total += i
}
print(total)
// Prints "10"

function

func greet(person: String, day: String) -> String {
    return "Hello \(person), today is \(day)."
}
greet(person: "Bob", day: "Tuesday")

custom argument label

func greet(_ person: String, on day: String) -> String {
    return "Hello \(person), today is \(day)."
}
greet("John", on: "Wednesday")

tuple

func calculateStatistics(scores: [Int]) -> (min: Int, max: Int, sum: Int) {
    var min = scores[0]
    var max = scores[0]
    var sum = 0
    for score in scores {
        if score > max {
            max = score
        } else if score < min {
            min = score
        }
        sum += score
    }
    return (min, max, sum)
}
let statistics = calculateStatistics(scores: [5, 3, 100, 3, 9])
print(statistics.sum)
// Prints "120"
print(statistics.2)
// Prints "120"

nested function

func returnFifteen() -> Int {
    var y = 10
    func add() {
        y += 5
    }
    add()
    return y
}
returnFifteen()

a function can return another function

func makeIncrementer() -> ((Int) -> Int) {
    func addOne(number: Int) -> Int {
        return 1 + number
    }
    return addOne
}
var increment = makeIncrementer()
increment(7)

A function can take another function as argument

func hasAnyMatches(list: [Int], condition: (Int) -> Bool) -> Bool {
    for item in list {
        if condition(item) {
            return true
        }
    }
    return false
}

func lessThanTen(number: Int) -> Bool {
    return number < 10
}

var numbers = [20, 19, 7, 12]
hasAnyMatches(list: numbers, condition: lessThanTen)

closure

numbers.map({ (number: Int) -> Int in
    let result = 3 * number
    return result
})

implicit returns from single-expression closure

let mappedNumbers = numbers.map({ number in 3 * number })
print(mappedNumbers)
// Prints "[60, 57, 21, 36]"

shorthand argument name & trailing closure, $0

let sortedNumbers = numbers.sorted { $0 > $1 }
print(sortedNumbers)
// Prints "[20, 19, 12, 7]"

class, property, method

class Shape {
    var numberOfSides = 0
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

object, instance

var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()

initializer, init, self

class NamedShape {
    var numberOfSides: Int = 0
    var name: String

    init(name: String) {
        self.name = name
    }

    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

inheritance, override

class Square: NamedShape {
    var sideLength: Double

    init(sideLength: Double, name: String) {
        self.sideLength = sideLength
        super.init(name: name)
        numberOfSides = 4
    }

    func area() -> Double {
        return sideLength * sideLength
    }

    override func simpleDescription() -> String {
        return "A square with sides of length \(sideLength)."
    }
}

let test = Square(sideLength: 5.2, name: "my test square")
test.area()
test.simpleDescription()

computed property, get, set

class EquilateralTriangle: NamedShape {
    var sideLength: Double = 0.0

    init(sideLength: Double, name: String) {
        self.sideLength = sideLength
        super.init(name: name)
        numberOfSides = 3
    }

    var perimeter: Double {
        get {
            return 3.0 * sideLength
        }
        set {
            sideLength = newValue / 3.0
        }
    }

    override func simpleDescription() -> String {
        return "An equilateral triangle with sides of length \(sideLength)."
    }
}

var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
print(triangle.perimeter)
// Prints "9.3"
triangle.perimeter = 9.9
print(triangle.sideLength)
// Prints "3.3000000000000003"

property observer, willSet, didSet

class TriangleAndSquare {
    var triangle: EquilateralTriangle {
        willSet {
            square.sideLength = newValue.sideLength
        }
    }

    var square: Square {
        willSet {
            triangle.sideLength = newValue.sideLength
        }
    }

    init(size: Double, name: String) {
        square = Square(sideLength: size, name: name)
        triangle = EquilateralTriangle(sideLength: size, name: name)
    }
}

var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
print(triangleAndSquare.square.sideLength)
// Prints "10.0"
print(triangleAndSquare.triangle.sideLength)
// Prints "10.0"
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
print(triangleAndSquare.triangle.sideLength)
// Prints "50.0"

optional chaining

let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square")
let sideLength = optionalSquare?.sideLength

enum, enumeration, raw value

enum Rank: Int {
    case ace = 1
    case two, three, four, five, six, seven, eight, nine, ten
    case jack, queen, king
    
    func simpleDescription() -> String {
        switch self {
        case .ace:
            return "ace"
        case .jack:
            return "jack"
        case .queen:
            return "queen"
        case .king:
            return "king"
        default:
            return String(self.rawValue)
        }
    }
}

let ace = Rank.ace
let aceRawValue = ace.rawValue
if let convertedRank = Rank(rawValue: 3) {
    let threeDescription = convertedRank.simpleDescription()
}

enum Suit {
    case spades, hearts, diamonds, clubs
    func simpleDescription() -> String {
        switch self {
        case .spades:
            return "spades"
        case .hearts:
            return "hearts"
        case .diamonds:
            return "diamonds"
        case .clubs:
            return "clubs"
        }
    }
}

let hearts = Suit.hearts
let heartsDescription = hearts.simpleDescription()

enum & associated value

enum ServerResponse {
    case result(String, String)
    case failure(String)
}

let success = ServerResponse.result("6:00 am", "8:09 pm")
let failure = ServerResponse.failure("Out of cheese.")
switch success {
case let .result(sunrise, sunset):
    print("Sunrise is at \(sunrise) and sunset is at \(sunset).")
case let .failure(message):
    print("Failure...  \(message)")
}
// Prints "Sunrise is at 6:00 am and sunset is at 8:09 pm."

struct, structure

struct Card {
    var rank: Rank
    var suit: Suit
    func simpleDescription() -> String {
        return "The \(rank.simpleDescription()) of \(suit.simpleDescription())"
    }
}

let threeOfSpades = Card(rank: .three, suit: .spades)
let threeOfSpadesDescription = threeOfSpades.simpleDescription()

concurrency, async

func fetchUserID(from server: String) async -> Int {
    if server == "primary" {
        return 97
    }
    return 501
}

await

func fetchUsername(from server: String) async -> String {
    let userID = await fetchUserID(from: server)
    if userID == 501 {
        return "John Appleseed"
    }
    return "Guest"
}

async let

func connectUser(to server: String) async {
    async let userID = fetchUserID(from: server)
    async let username = fetchUsername(from: server)
    let greeting = await "Hello \(username), user ID \(userID)"
    print(greeting)
}

Task

Task {
    await connectUser(to: "primary")
}
// Prints "Hello Guest, user ID 97"

protocol, mutating

protocol ExampleProtocol {
    var simpleDescription: String { get }
    mutating func adjust()
}

adopt and conform to protocol

class SimpleClass: ExampleProtocol {
    var simpleDescription: String = "A very simple class."
    var anotherProperty: Int = 69105
    func adjust() {
        simpleDescription += "  Now 100% adjusted."
    }
}

var a = SimpleClass()
a.adjust()
let aDescription = a.simpleDescription

struct SimpleStructure: ExampleProtocol {
    var simpleDescription: String = "A simple structure"
    mutating func adjust() {
        simpleDescription += " (adjusted)"
    }
}

var b = SimpleStructure()
b.adjust()
let bDescription = b.simpleDescription

extension

extension Int: ExampleProtocol {
    var simpleDescription: String {
        return "The number \(self)"
    }
    mutating func adjust() {
        self += 42
    }
}

print(7.simpleDescription)
// Prints "The number 7"

use a protocol name just like any other named type

let protocolValue: ExampleProtocol = a
print(protocolValue.simpleDescription)
// Prints "A very simple class.  Now 100% adjusted."
// print(protocolValue.anotherProperty)  // Uncomment to see the error

error handling, Error

enum PrinterError: Error {
    case outOfPaper
    case noToner
    case onFire
}

throw & throws

func send(job: Int, toPrinter printerName: String) throws -> String {
    if printerName == "Never Has Toner" {
        throw PrinterError.noToner
    }
    return "Job sent"
}

do catch, try

do {
    let printerResponse = try send(job: 1040, toPrinter: "Bi Sheng")
    print(printerResponse)
} catch {
    print(error)
}
// Prints "Job sent"

catch specific error

do {
    let printerResponse = try send(job: 1440, toPrinter: "Gutenberg")
    print(printerResponse)
} catch PrinterError.onFire {
    print("I'll just put this over here, with the rest of the fire.")
} catch let printerError as PrinterError {
    print("Printer error: \(printerError).")
} catch {
    print(error)
}
// Prints "Job sent"

try?

let printerSuccess = try? send(job: 1884, toPrinter: "Mergenthaler")
let printerFailure = try? send(job: 1885, toPrinter: "Never Has Toner")

defer

var fridgeIsOpen = false
let fridgeContent = ["milk", "eggs", "leftovers"]

func fridgeContains(_ food: String) -> Bool {
    fridgeIsOpen = true
    defer {
        fridgeIsOpen = false
    }
    let result = fridgeContent.contains(food)
    return result
}

fridgeContains("banana")
print(fridgeIsOpen)
// Prints "false"

generic function

func makeArray<Item>(repeating item: Item, numberOfTimes: Int) -> [Item] {
    var result: [Item] = []
    for _ in 0..<numberOfTimes {
        result.append(item)
    }
    return result
}

makeArray(repeating: "knock", numberOfTimes: 4)

generic type

// Reimplement the Swift standard library's optional type
enum OptionalValue<Wrapped> {
    case none
    case some(Wrapped)
}

var possibleInteger: OptionalValue<Int> = .none
possibleInteger = .some(100)

generic & where

func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool
    where T.Element: Equatable, T.Element == U.Element {
    for lhsItem in lhs {
        for rhsItem in rhs {
            if lhsItem == rhsItem {
                return true
            }
        }
    }
    return false
}
anyCommonElements([1, 2, 3], [3])

其它 Swift 的複習資源

kodeco 的 Swift Cookbook。

Swift Cookbook