Swift ensures that all properties of a derived class are initialised before calling its base class. The compiler will generate a warning. Just move the statement below the assignment to remove the warning. Compared to Java, this is safe. See: http://stackoverflow.com/questions/3404301/whats-wrong-with-overridable-method-calls-in-constructors

SuperclassCallsOverridableMethod.playground

import Cocoa

class Plane
{
    init()
    {
        readyToTakeOff();
    }
    
    func readyToTakeOff(){
    }
}

class HighSpeedPlane : Plane
{
    var speed : Int
    
    init(speed: Int) {
        super.init() //compiler warning: "Property 'self.speed' not initialized at super.init call"
        self.speed = speed
    }
    
    override func readyToTakeOff()
    {
        super.readyToTakeOff()
        println("Travelling at the speed of \(self.speed)")
    }
}

let plane = HighSpeedPlane(speed: 200);