Classes in Swift

// Class definition
class Vehicle {
    var currentSpeed = 0.0
    var description: String {
        return "traveling at \(currentSpeed) mph"
    }

    func makeNoise() {
        // Base implementation
    }

    init(speed: Double) {
        self.currentSpeed = speed
    }
}

// Inheritance
class Bicycle: Vehicle {
    var hasBasket = false

    override func makeNoise() {
        print("Ring ring!")
    }
}

// Reference semantics
let bike1 = Bicycle(speed: 15)
let bike2 = bike1  // Same reference
bike2.currentSpeed = 20
print(bike1.currentSpeed)  // 20