Swift - 문법 (Object and Classes, Enumerations and Structures, Concurrency)

목차 Open

• Objects and Classes
• Enumerations and Structures
• Concurrency

Objects and Classes

• class → class

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

• use init to create initializer
  • self is used to distinguish the name property from the name argument to the initializer

class NamedShape {
    var numberOfSides: Int = 0
    var name: String
    init(name: String) {
       self.name = name
    }
}

• use deinit to deinitialize: perform cleanup before object is deallocated
• subclass → subclassName: superClassName
• override superclass’s implementation with override

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

• properties can have a getter and a setter
  • you can provide explicit name in parentheses after set

class EquilateralTriangle: NamedShape {
    var sideLength: Double = 0.0
    var perimeter: Double {
        get {
             return 3.0 * sideLength
        }
        set {
            sideLength = newValue / 3.0
        }
    }
}

• if value before ? is nil, everything after the ? is ignored and whole is nil
  • let sideLength = optionalSquare?.sideLength → nil if optionalSqaure is nil

Enumerations and Structures

• enumeration → enum
• enum can have methods with them

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)
        }
    }
}

• enum can have values associated with the case → values determined when instance is made

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)")
}

• structure → struct

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

• structures are always copied when passed around in code, but classes are passed by reference

Concurrency

• asynchronous function → async, await

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

• use async let to call asynchronous function run in parallel, and await to use the value it returns

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)
}

• use Task to call asynchronous functions from synchronous code, without waiting

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