Variance

fun main(args : Array<String>){
    val car = Car(200)
    val motorCycle = MotorCycle(100)
    var vehicle: Vehicle = car
    vehicle = motorCycle
    
    //
    val carList = listOf(Car(100), Car(120))
    val vehicleList = carList
}

abstract  class Vehicle(wheel: Int)
class Car(speed: Int) : Vehicle(4)
class MotorCycle(speed: Int) : Vehicle(2)