继承（Inheritance）
-
值类型（枚举、结构体）不支持继承，只有类支持继承
-
没有父类的类，称为：基类
- Swift并没有像OC、Java那样的规定：任何类最终都要继承自某个基类
Note:
Swift classed do not inherit from a universal base class.Classes you define specifying a superclass automatically become base classes for you to build upon.
- 子类可以重写父类的下标、方法、属性，重写必须加上override关键字
内存结构
class Animal {
var age = 0
}
class Dog: Animal {
var weight = 0
}
class Erha: Dog {
var iq = 0
}
let a = Animal()
a.age = 10
print(Mems.size(ofRef: a))
print(Mems.memStr(ofRef: a))
/*
32
0x00000001000073e8
0x0000000000000002
0x000000000000000a
0x0000000000000023
*/
let d = Dog()
d.age = 10
d.weight = 20
print(Mems.size(ofRef: d))
print(Mems.memStr(ofRef: d))
/*
32
0x0000000100007498
0x0000000000000002
0x000000000000000a
0x0000000000000014
*/
let e = Erha()
e.age = 10
e.weight = 20
e.iq = 30
print(Mems.size(ofRef: e))
print(Mems.memStr(ofRef: e))
/*
48
0x0000000100007568
0x0000000000000002
0x000000000000000a
0x0000000000000014
0x000000000000001e
0x0000000100566500
*/
重写实例方法、下标
class Animal {
func speak() {
print("Animal speak")
}
subscript(index: Int) -> Int {
return index
}
}
class Cat: Animal {
override func speak() {
super.speak()
print("Cat speak")
}
override subscript(index: Int) -> Int {
return super[index] + 1
}
}
var animal: Animal
animal = Animal()
animal.speak()
print(animal[6])
animal = Cat()
animal.speak()
print(animal[6])
/*
Animal speak
6
Animal speak
Cat speak
7
*/
重写类型方法、下标
- 被class修饰的类型方法、下标，允许被子类重写
- 被static修饰的类型方法、下标，不允许被子类重写
class Animal {
class func speak() {
print("Animal speak")
}
class subscript(index: Int) -> Int {
return index
}
}
Animal.speak()
print(Animal[6])
/*
Animal speak
6
*/
class Cat: Animal {
override class func speak() {
super.speak()
print("Cat speak")
}
override class subscript(index: Int) -> Int {
return super[index] + 1
}
}
Cat.speak()
print(Cat[6])
/*
Animal speak
Cat speak
7
*/
重写属性
-
子类可以将父类的属性（存储、计算）重写为计算属性
-
子类不可以将父类属性重写为存储属性
-
只能重写var属性，不能重写let属性
-
重写时，属性名、类型要一致
-
子类重写后的属性权限 不能小于 父类属性的权限
如果父类属性是只读的，那么子类重写后的属性可以是只读的、也可以是可读写的
如果父类属性是可读写的，那么子类重写后的属性必须是可读写的
重写实例属性
class Circle {
var radius: Int = 0
var diameter:Int {
set {
print("Circle setDiameter")
radius = newValue / 2
}
get {
print("Circle getDiameter")
return radius * 2
}
}
}
var circle: Circle
circle = Circle()
circle.radius = 6
print(circle.diameter)
circle.diameter = 20
print(circle.radius)
/*
Circle getDiameter
12
Circle setDiameter
10
*/
class SubCircle: Circle {
override var radius: Int {
set {
print("SubCircle setRadius")
super.radius = newValue > 0 ? newValue : 0
}
get {
print("SubCircle getRadius")
return super.radius
}
}
override var diameter: Int {
set {
print("SubCircle setDiameter")
super.diameter = newValue > 0 ? newValue : 0
}
get {
print("SubCircle getDiameter")
return super.diameter
}
}
}
var circle = SubCircle()
circle.radius = 6
print(circle.diameter)
circle.diameter = 20
print(circle.radius)
/*
SubCircle setRadius
SubCircle getDiameter
Circle getDiameter
SubCircle getRadius
12
SubCircle setDiameter
Circle setDiameter
SubCircle setRadius
SubCircle getRadius
10
*/
- 被class修饰的计算类型属性，可以被子类重写
- 被static修饰的类型属性（存储、计算），不可以被子类重写
class Circle {
static var radius: Int = 0
class var diameter: Int {
set {
print("Circle setDiameter")
radius = newValue / 2
}
get {
print("Circle getDiameter")
return radius * 2
}
}
}
class SubCircle: Circle {
override static var diameter: Int {
set {
print("SubCircle setDiameter")
super.diameter = newValue > 0 ? newValue : 0
}
get {
print("SubCircle getDiameter")
return super.diameter
}
}
}
Circle.radius = 6
print(Circle.diameter)
Circle.diameter = 20
print(Circle.radius)
SubCircle.radius = 6
print(SubCircle.diameter)
SubCircle.diameter = 20
print(SubCircle.radius)
/*
Circle getDiameter
12
Circle setDiameter
10
SubCircle getDiameter
Circle getDiameter
12
SubCircle setDiameter
Circle setDiameter
10
*/
属性观察器
- 可以在子类中为父类属性（除了只读计算属性、let属性）增加属性观察器
class Circle {
var radius: Int = 1
}
class SubCircle: Circle {
override var radius: Int {
willSet {
print("SubCircle willSetRadius", newValue)
}
didSet {
print("SubCircle didSetRadius", oldValue, radius)
}
}
}
var circle = SubCircle()
circle.radius = 10
/*
SubCircle willSetRadius 10
SubCircle didSetRadius 1 10
*/
class Circle {
var radius: Int = 1 {
willSet {
print("Circle willSetRadius", newValue)
}
didSet {
print("Circle didSetRadius", oldValue, radius)
}
}
}
class SubCircle: Circle {
override var radius: Int {
willSet {
print("SubCircle willSetRadius", newValue)
}
didSet {
print("SubCircle didSetRadius", oldValue, radius)
}
}
}
var circle = SubCircle()
circle.radius = 10
/*
SubCircle willSetRadius 10
Circle willSetRadius 10
Circle didSetRadius 1 10
SubCircle didSetRadius 1 10
*/
class Circle {
var radius: Int {
set {
print("Circle setSetRadius", newValue)
}
get {
print("Circle getRadius")
return 20
}
}
}
class SubCircle: Circle {
override var radius: Int {
willSet {
print("SubCircle willSetRadius", newValue)
}
didSet {
print("SubCircle didSetRadius", oldValue, radius)
}
}
}
var circle = SubCircle()
circle.radius = 10
/*
Circle getRadius
SubCircle willSetRadius 10
Circle setSetRadius 10
Circle getRadius
SubCircle didSetRadius 20 20
*/
class Circle {
class var radius: Int {
set {
print("Circle setSetRadius", newValue)
}
get {
print("Circle getRadius")
return 20
}
}
}
class SubCircle: Circle {
override static var radius: Int {
willSet {
print("SubCircle willSetRadius", newValue)
}
didSet {
print("SubCircle didSetRadius", oldValue, radius)
}
}
}
SubCircle.radius = 10
/*
Circle getRadius
SubCircle willSetRadius 10
Circle setSetRadius 10
Circle getRadius
SubCircle didSetRadius 20 20
*/
final
- 被final修饰的方法、下标、属性，禁止被重写
- 被final修饰的类，禁止被继承
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