Inheritance / override / final / super

// Base class
class ParentClass {
    func method() { }
    var property: Type { get }
}

// Inheritance
class ChildClass: ParentClass {
    // Override
    override func method() {
        super.method()  // Call the parent implementation
        // Additional logic
    }

    // Method that cannot be overridden further
    final func finalMethod() { }
}

// Base class
class Animal {
    var name: String

    init(name: String) {
        self.name = name
    }

    func speak() -> String {
        return "..."
    }

    func describe() -> String {
        return "\(name) says \(speak())"
    }
}

// Inheritance and override
class Dog: Animal {
    override func speak() -> String {
        return "Woof"
    }

    // Additional method
    func fetch() {
        print("\(name) fetched the ball")
    }
}

class Cat: Animal {
    var indoor: Bool

    init(name: String, indoor: Bool) {
        self.indoor = indoor
        super.init(name: name)  // Always call super.init
    }

    override func speak() -> String {
        return "Meow"
    }

    override func describe() -> String {
        let base = super.describe()
        return "\(base) (\(indoor ? "indoor" : "outdoor") cat)"
    }
}

let dog = Dog(name: "Rex")
let cat = Cat(name: "Whiskers", indoor: true)

print(dog.describe())
print(cat.describe())
dog.fetch()

// Polymorphism
let animals: [Animal] = [dog, cat, Animal(name: "Unknown creature")]
for animal in animals {
    print(animal.describe())
}

Swift supports only single inheritance — a class cannot have more than one parent class. When a subclass overrides an initializer, it must call super.init().

Marking a class, method, or property with final prevents it from being overridden or subclassed, which can also improve performance. Defining a method with the same name as a parent class method without the override keyword causes a compile error. Always use the override keyword when intentionally overriding.

For details on property types, see Stored Properties / Computed Properties / lazy.