Swift 继承

//定义基类
class Veh {
var number: Int
var max: Int
func descrip() -> String {
return"\(number)----\(max)"
}
//init()是构造器,在实例化这个类的时候调用它
init() {
number = 0
max = 1
}
}
let someV = Veh()

//定义子类
class Child : Veh {
override init(){
super.init()//初始化父类
number = 2  //重新初始化父类属性
}
}
let child = Child()
print(child.descrip())

//方法重写
//子类能够重写父类的方法,属性,下标
class Car: Veh {
var speed: Double = 0.0
override init() {
super.init()
max = 5
number = 4
}
override func descrip() -> String {  //重写的方法前面要添加关键字override
//super指代父类实例
return super.descrip() + "----\(speed)"
}

}
let car = Car()
print(car.descrip())

//属性重写
//主要是对属性的get,set访问器的重写
class SpeedL: Car {
override var speed: Double {
get {
return super.speed
}
set {
super.speed = min(newValue, 40.0)
}
}
}
let lim = SpeedL()
lim.speed = 60.0
print(lim.descrip())