Inicjalizatory i deinit (klasy)

struct User {
    var name: String = "Guest"   // default value
    var age: Int

    // memberwise init is synthesized: User(name:age:)
}
let u1 = User(name: "Ada", age: 20)
let u2 = User(age: 0)            // uses default name
print(u1.name, u2.name)

class Person {
    let name: String
    let id: Int

    // Designated initializer: fully initializes stored properties
    init(name: String, id: Int) {
        self.name = name
        self.id = id
    }
}
let p = Person(name: "Bob", id: 1)
print(p.name, p.id)

class Rectangle {
    var width: Double
    var height: Double

    // Designated
    init(width: Double, height: Double) {
        self.width = width
        self.height = height
    }

    // Convenience must call a designated initializer
    convenience init(square side: Double) {
        self.init(width: side, height: side)
    }
}
print(Rectangle(square: 3).width)

struct Email {
    let value: String
    init?(_ raw: String) {
        guard raw.contains("@") else { return nil } // fail to initialize
        self.value = raw
    }
}
print(Email("a@b.com")?.value ?? "invalid")
print(Email("not email")?.value ?? "invalid")

class TempResource {
    let id: Int
    init(id: Int) { self.id = id }
    deinit { print("Releasing resource", id) }
}
do {
    let r = TempResource(id: 42)
    print("Using", r.id)
} // r goes out of scope; ARC may call deinit here