[Swift 공식 문서] 14. Initialization

init() { // perform some initialization here } init(temparautre: Double) { }

struct Fahrenheit { var temperature: Double init() { temperature = 32.0 } } var f = Fahrenheit() print("The default temperature is \(f.temperature)° Fahrenheit") // Prints "The default temperature is 32.0° Fahrenheit"

struct Fahrenheit { var temperature = 32.0 }

struct Celsius { var temperatureInCelsius: Double init(fromFahrenheit fahrenheit: Double) { temperatureInCelsius = (fahrenheit - 32.0) / 1.8 } init(fromKelvin kelvin: Double) { temperatureInCelsius = kelvin - 273.15 } } let boilingPointOfWater = Celsius(fromFahrenheit: 212.0) // boilingPointOfWater.temperatureInCelsius is 100.0 let freezingPointOfWater = Celsius(fromKelvin: 273.15) // freezingPointOfWater.temperatureInCelsius is 0.0

struct Color { let red, green, blue: Double init(red: Double, green: Double, blue: Double) { self.red = red self.green = green self.blue = blue } init(white: Double) { red = white green = white blue = white } } //파라미터의 이름을 통해 생성자를 구분한다. let magenta = Color(red: 1.0, green: 0.0, blue: 1.0) let halfGray = Color(white: 0.5) //이러한 argument lable 없이 생성자를 호출하면 오류가 발생한다. let veryGreen = Color(0.0, 1.0, 0.0) // this reports a compile-time error - argument labels are required

struct Celsius { var temperatureInCelsius: Double init(fromFahrenheit fahrenheit: Double) { temperatureInCelsius = (fahrenheit - 32.0) / 1.8 } init(fromKelvin kelvin: Double) { temperatureInCelsius = kelvin - 273.15 } init(_ celsius: Double) { temperatureInCelsius = celsius } } let bodyTemperature = Celsius(37.0) // bodyTemperature.temperatureInCelsius is 37.0

class SurveyQuestion { var text: String var response: String? init(text: String) { self.text = text } func ask() { print(text) } } let cheeseQuestion = SurveyQuestion(text: "Do you like cheese?") cheeseQuestion.ask() // Prints "Do you like cheese?" cheeseQuestion.response = "Yes, I do like cheese."

class SurveyQuestion { let text: String var response: String? init(text: String) { self.text = text } func ask() { print(text) } } let beetsQuestion = SurveyQuestion(text: "How about beets?") beetsQuestion.ask() // Prints "How about beets?" beetsQuestion.response = "I also like beets. (But not with cheese.)"

class ShoppingListItem { var name: String? var quantity = 1 var purchased = false } var item = ShoppingListItem()

struct Size { var width = 0.0, height = 0.0 } let twoByTwo = Size(width: 2.0, height: 2.0)

let zeroByTwo = Size(height: 2.0) print(zeroByTwo.width, zeroByTwo.height) // Prints "0.0 2.0" let zeroByZero = Size() print(zeroByZero.width, zeroByZero.height) // Prints "0.0 0.0"

struct Size { var width = 0.0, height = 0.0 } struct Point { var x = 0.0, y = 0.0 }

struct Rect { var origin = Point() var size = Size() //어떠한 생성자도 정의하지 않았을 때 제공되는 기본 생성자와 동일 //기본값으로 초기화된 인스턴스를 리턴함. init() {} init(origin: Point, size: Size) { self.origin = origin self.size = size } init(center: Point, size: Size) { let originX = center.x - (size.width / 2) let originY = center.y - (size.height / 2) //기존에 존재하는 생성자와 중복되는 코드 >> self.init 으로 대체 self.init(origin: Point(x: originX, y: originY), size: size) } }

let basicRect = Rect() // basicRect's origin is (0.0, 0.0) and its size is (0.0, 0.0) let originRect = Rect(origin: Point(x: 2.0, y: 2.0), size: Size(width: 5.0, height: 5.0)) // originRect's origin is (2.0, 2.0) and its size is (5.0, 5.0) let centerRect = Rect(center: Point(x: 4.0, y: 4.0), size: Size(width: 3.0, height: 3.0)) // centerRect's origin is (2.5, 2.5) and its size is (3.0, 3.0)

class Person { var name: String var age: Int var gender: String init(name: String, age: Int, gender: String) { self.name = name self.age = age self.gender = gender } convenience init(age: Int, gender: String) { self.init(name: "zedd", age: age, gender: gender) } }

init(parameters) { statements }

convenience init(parameters) { statements }

class Vehicle { var numberOfWheels = 0 var description: String { return "\(numberOfWheels) wheel(s)" } } let vehicle = Vehicle() print("Vehicle: \(vehicle.description)") // Vehicle: 0 wheel(s) class Bicycle: Vehicle { override init() { super.init() numberOfWheels = 2 } } let bicycle = Bicycle() print("Bicycle: \(bicycle.description)") // Bicycle: 2 wheel(s)

class Hoverboard: Vehicle { var color: String init(color: String) { self.color = color // super.init() 암묵적 생략 } override var description: String { return "\(super.description) in a beautiful \(color)" } } let hoverboard = Hoverboard(color: "silver") print("Hoverboard: \(hoverboard.description)") // Hoverboard: 0 wheel(s) in a beautiful silver

class Food { var name: String init(name: String) { self.name = name } convenience init() { self.init(name: "[Unnamed]") } } let namedMeat = Food(name: "Bacon") // namedMeat's name is "Bacon" let mysteryMeat = Food() // mysteryMeat's name is "[Unnamed]" class RecipeIngredient: Food { var quantity: Int init(name: String, quantity: Int) { self.quantity = quantity super.init(name: name) } //override 키워드를 작성하는 이유 => 상위 클래스에 동일한 파라미터의 생성자가 존재하기 때문. //상위클래스의 지정 생성자를 상속 override convenience init(name: String) { self.init(name: name, quantity: 1) } }

let oneMysteryItem = RecipeIngredient() let oneBacon = RecipeIngredient(name: "Bacon") let sixEggs = RecipeIngredient(name: "Eggs", quantity: 6)

class ShoppingListItem: RecipeIngredient { var purchased = false var description: String { var output = "\(quantity) x \(name)" output += purchased ? " ✔" : " ✘" return output } } var breakfastList = [ ShoppingListItem(), ShoppingListItem(name: "Bacon"), ShoppingListItem(name: "Eggs", quantity: 6), ] breakfastList[0].name = "Orange juice" breakfastList[0].purchased = true for item in breakfastList { print(item.description) } // 1 x Orange juice ✔ // 1 x Bacon ✘ // 6 x Eggs ✘

let wholeNumber: Double = 12345.0 let pi = 3.14159 if let valueMaintained = Int(exactly: wholeNumber) { print("\(wholeNumber) conversion to Int maintains value of \(valueMaintained)") } // Prints "12345.0 conversion to Int maintains value of 12345" let valueChanged = Int(exactly: pi) // valueChanged is of type Int?, not Int if valueChanged == nil { print("\(pi) conversion to Int doesn't maintain value") } // Prints "3.14159 conversion to Int doesn't maintain value"

struct Animal { let species: String init?(species: String) { if species.isEmpty { return nil } self.species = species } } let someCreature = Animal(species: "Giraffe") // someCreature is of type Animal?, not Animal if let giraffe = someCreature { print("An animal was initialized with a species of \(giraffe.species)") } // Prints "An animal was initialized with a species of Giraffe" // let anonymousCreature = Animal(species: "") // anonymousCreature is of type Animal?, not Animal if anonymousCreature == nil { print("The anonymous creature couldn't be initialized") } // Prints "The anonymous creature couldn't be initialized"

enum TemperatureUnit { case kelvin, celsius, fahrenheit init?(symbol: Character) { switch symbol { case "K": self = .kelvin case "C": self = .celsius case "F": self = .fahrenheit default: //어떠한 case 에도 해당되지 않는 경우 생성 실패 return nil } } } let fahrenheitUnit = TemperatureUnit(symbol: "F") if fahrenheitUnit != nil { print("This is a defined temperature unit, so initialization succeeded.") } // Prints "This is a defined temperature unit, so initialization succeeded." let unknownUnit = TemperatureUnit(symbol: "X") if unknownUnit == nil { print("This isn't a defined temperature unit, so initialization failed.") } // Prints "This isn't a defined temperature unit, so initialization failed."

enum TemperatureUnit: Character { case kelvin = "K", celsius = "C", fahrenheit = "F" } let fahrenheitUnit = TemperatureUnit(rawValue: "F") if fahrenheitUnit != nil { print("This is a defined temperature unit, so initialization succeeded.") } // Prints "This is a defined temperature unit, so initialization succeeded." let unknownUnit = TemperatureUnit(rawValue: "X") if unknownUnit == nil { print("This isn't a defined temperature unit, so initialization failed.") } // Prints "This isn't a defined temperature unit, so initialization failed."

class Product { let name: String init?(name: String) { if name.isEmpty { return nil } self.name = name } } class CartItem: Product { let quantity: Int init?(name: String, quantity: Int) { if quantity < 1 { return nil } self.quantity = quantity super.init(name: name) } } if let twoSocks = CartItem(name: "sock", quantity: 2) { print("Item: \(twoSocks.name), quantity: \(twoSocks.quantity)") } // Prints "Item: sock, quantity: 2" if let zeroShirts = CartItem(name: "shirt", quantity: 0) { print("Item: \(zeroShirts.name), quantity: \(zeroShirts.quantity)") } else { print("Unable to initialize zero shirts") } // Prints "Unable to initialize zero shirts" if let oneUnnamed = CartItem(name: "", quantity: 1) { print("Item: \(oneUnnamed.name), quantity: \(oneUnnamed.quantity)") } else { print("Unable to initialize one unnamed product") } // Prints "Unable to initialize one unnamed product"

class Document { var name: String? // this initializer creates a document with a nil name value init() {} // 항상 name 을 가지는 인스턴스를 생성 init?(name: String) { if name.isEmpty { return nil } self.name = name } } class AutomaticallyNamedDocument: Document { override init() { super.init() self.name = "[Untitled]" } //failable 을 override 했지만 실패하지 않음. override init(name: String) { super.init() if name.isEmpty { self.name = "[Untitled]" } else { self.name = name } } } class UntitledDocument: Document { override init() { super.init(name: "[Untitled]")! } }

class SomeClass { required init() { // initializer implementation goes here } } class SomeSubclass: SomeClass { required init() { super.init() // subclass implementation of the required initializer goes here } }

class SomeClass { let someProperty: SomeType = { // create a default value for someProperty inside this closure // someValue must be of the same type as SomeType return someValue }() }

struct Chessboard { let boardColors: [Bool] = { var temporaryBoard: [Bool] = [] var isBlack = false for i in 1...8 { for j in 1...8 { temporaryBoard.append(isBlack) isBlack = !isBlack } isBlack = !isBlack } return temporaryBoard }() func squareIsBlackAt(row: Int, column: Int) -> Bool { return boardColors[(row * 8) + column] } } let board = Chessboard() print(board.squareIsBlackAt(row: 0, column: 1)) // Prints "true" print(board.squareIsBlackAt(row: 7, column: 7)) // Prints "false"