13 继承

class  {
    var currentSpeed = 0.0
    var description:String{
        return "traveling at (currentSpeed) miles per hour"
    }
    func makeNoise(){
        //什么也不做－因为车辆不一定有噪音
    }
}

let someVehicle = Vehicle()
println("Vehicle:(someVehicle.description)")

//继承Vehicle
class Bicycle: {
    var hasBasket = false
}
let bicycle = Bicycle()

//设置子类自己的实例属性
bicycle.hasBasket = true

//修改继承来的属性
bicycle.currentSpeed = 15.0

class Train:Vechicle 大专栏  13 继承span>{
    override func makeNoise(){
        println("Choo Choo")
    }
}
let train = Train()
train.makeNoise()

class Car: {
    var gear = 1
    override var description:String{
        return super.description + " in gear (gear)"
    }
}

let car = Car()
car.currentSpeed = 25.0
car.gear = 3
println("Car:(car.description)")
+ 重写属性观察器
1. 不可重写属性观察器的继承来的属性：常量存储属性、只读计算属性

class AutomaticCar:Car {
    //重写属性及其属性观察器
    override var currentSpeed:Double{
        didSet{
            gear = Int(currentSpeed / 10.0) + 1
        }
    }
}
let automatic = AutomaticCar()
automatic.currentSpeed = 35.0
println("AutomaticCar:(automatic.description)")