Swift — Classes

Basic class

class Person {
    var name: String
    var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }

    func greet() {
        print("Hi, I'm \(name)!")
    }
}

let alice = Person(name: "Alice", age: 30)
alice.greet()

Inheritance

class Animal {
    var name: String

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

    func speak() {
        print("\(name) makes a sound")
    }
}

class Dog: Animal {
    override func speak() {
        print("\(name) says Woof!")
    }
}

let dog = Dog(name: "Rex")
dog.speak() // Rex says Woof!

Properties

class BankAccount {
    private var _balance: Double

    var balance: Double {
        get { _balance }
        set { _balance = newValue }
    }

    init(balance: Double) {
        _balance = balance
    }

    func deposit(_ amount: Double) {
        _balance += amount
    }

    func withdraw(_ amount: Double) -> Bool {
        guard _balance >= amount else { return false }
        _balance -= amount
        return true
    }
}

Reference semantics

class Person {
    var name: String
    init(name: String) { self.name = name }
}

let p1 = Person(name: "Alice")
let p2 = p1
p2.name = "Bob"

print(p1.name) // Bob (shared reference)

Deinitializers

class Resource {
    let name: String

    init(name: String) {
        self.name = name
        print("Acquired: \(name)")
    }

    deinit {
        print("Released: \(name)")
    }
}

do {
    let r = Resource(name: "File")
    // Released here
}

Type casting

class MediaItem {
    var name: String
    init(name: String) { self.name = name }
}

class Movie: MediaItem {
    var director: String
    init(name: String, director: String) {
        self.director = director
        super.init(name: name)
    }
}

let items: [MediaItem] = [
    Movie(name: "Casablanca", director: "Curtiz"),
    Movie(name: "Citizen Kane", director: "Welles")
]

for item in items {
    if let movie = item as? Movie {
        print("\(movie.name) by \(movie.director)")
    }
}

Mini Practice

Write Swift code that:

1. Creates a class with inheritance
2. Overrides a method in a subclass
3. Demonstrates reference vs value semantics
4. Uses type casting with as?

Up Next

In the next lesson, you'll learn about Properties — stored and computed properties.