Swift Initialization

swift-initialization.swift

/*
 Referenced from Stanford CS193p
 
 #: important
 ##: very important
 
 Initialization
 - Setting Initial Values for Stored Properties
 - ##Customizing Initialization
 - Default Initializers
 
 Reference: https://docs.swift.org/swift-book/LanguageGuide/Inheritance.html
 */

/*
 Setting Initial Values for Stored Properties
 */
// Initializers
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"

// Default Property Values
struct anotherFahrenheit {
    var temperature = 32.0
}

/*
 ##Customizing Initialization
 */
// Initialization Parameters
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

// Parameter Names and Argument Labels
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
    }
}

let magenta = Color(red: 1.0, green: 0.0, blue: 1.0)
let halfGray = Color(white: 0.5)

// Initializer Parameters Without Argument Labels
struct AnotherCelsius {
    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 = AnotherCelsius(37.0)
// bodyTemperature.temperatureInCelsius is 37.0

// Optional Property Types
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."

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

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

// Memberwise Initializers for Structure Types
struct Size {
    var width = 0.0, height = 0.0
}
let zeroByzero = Size()
let twoByTwo = Size(width: 2.0, height: 2.0)