Properties

// STRUCT PROPERTIES
// Properties are variables/constants that belong to a struct

// STORED PROPERTIES
struct Rectangle {
    var width: Double   // Stored property (variable)
    var height: Double  // Stored property (variable)
    let color: String   // Stored property (constant)
}

var rect = Rectangle(width: 10, height: 5, color: "blue")
rect.width = 15  // OK - var can change
// rect.color = "red"  // ERROR - let cannot change

// COMPUTED PROPERTIES
struct Circle {
    var radius: Double

    // Computed property (read-only)
    var diameter: Double {
        radius * 2
    }

    var area: Double {
        Double.pi * radius * radius
    }

    var circumference: Double {
        2 * Double.pi * radius
    }
}

let circle = Circle(radius: 5)
print(circle.diameter)      // 10.0
print(circle.area)          // 78.54...

// GETTER AND SETTER
struct Temperature {
    var celsius: Double

    var fahrenheit: Double {
        get {
            celsius * 9/5 + 32
        }
        set {
            celsius = (newValue - 32) * 5/9
        }
    }
}

var temp = Temperature(celsius: 0)
print(temp.fahrenheit)  // 32.0

temp.fahrenheit = 212
print(temp.celsius)     // 100.0

// PROPERTY OBSERVERS
struct Player {
    var score: Int = 0 {
        willSet {
            print("Score will change to \(newValue)")
        }
        didSet {
            print("Score changed from \(oldValue)")
            if score > oldValue {
                print("Great job! +\(score - oldValue) points!")
            }
        }
    }
}

var player = Player()
player.score = 10

// LAZY PROPERTIES
struct DataManager {
    var filename: String

    lazy var data: [String] = {
        print("Loading data...")
        return ["item1", "item2", "item3"]
    }()
}

var manager = DataManager(filename: "data.txt")
print("Manager created")  // data NOT loaded yet
print(manager.data)       // NOW data is loaded

// TYPE PROPERTIES (Static)
struct AppConfig {
    static let appName = "SwiftApp"
    static var version = "1.0.0"
    static var userCount = 0
}

print(AppConfig.appName)  // SwiftApp
AppConfig.userCount += 1
print(AppConfig.userCount)  // 1