11-繼承

• 繼承(Inheritance)

• 值類型(枚舉、結構體)不支援繼承，隻有類支援繼承

• 沒有父類的類，稱為：基類

  Swift 并沒有像 OC、Java 那樣的規定：任何類最終都要繼承自某個基類

• 子類可以重寫父類的下标、方法、屬性，重寫必須加上 override

• 記憶體結構

class Animal {
    var age = 0
}

class Dog: Animal {
    var weight = 0
}

class Erha: Dog {
    var iq = 0
}

let a = Animal()
a.age = 10
// 32
print(Mems.size(ofRef: a))

/*
 0x00000001000073c8
 0x0000000000000002
 0x000000000000000a
 0x0000000000000000
 */
print(Mems.memStr(ofRef: a))

let d = Dog()
d.age = 10
d.weight = 20

// 32
print(Mems.size(ofRef: d))

/*
 0x0000000100007478
 0x0000000000000002
 0x000000000000000a
 0x0000000000000014
 */
print(Mems.memStr(ofRef: d))

let e = Erha()
e.age = 10
e.weight = 20
e.iq = 30

// 48
print(Mems.size(ofRef: e))

/*
0x0000000100007548
 0x0000000000000002
 0x000000000000000a
 0x0000000000000014
 0x000000000000001e
 0x0000000000000000
 */
print(Mems.memStr(ofRef: e))
           

• 重寫執行個體方法、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 anim: Animal
anim = Animal()

anim.speak()    // Animal speak

print(anim[6])  // 6

anim = Cat()

// Animal speak
// Cat speak
anim.speak()

// 7
print(anim[6])
           

• 重寫類型方法、下标

• 被 class 修飾的類型方法、下标，允許被子類重寫
• 被 static 修飾的類型方法、下标，不允許被子類重寫

class Animal {
    class func speak() {
        print("Animal speak")
    }
    
    class subscript(index: Int) -> Int {
        return index
    }
}
// Animal speak
Animal.speak()
// 6
print(Animal[6])

class Cat: Animal {
    
    override class func speak() {
        super.speak()
        print("Cat speak")
    }
    
    override class subscript(index: Int) -> Int {
        return super[index] + 1
    }
}
// Animal speak
// Cat speak
Cat.speak()
// 7
print(Cat[6])
           

• 重寫屬性

• 子類可以将父類的屬性(存儲、計算)重寫為計算屬性
• 子類不可以将父類屬性重寫為存儲屬性
• 隻能重寫 var 屬性，不能重寫 let 屬性
• 重寫時，屬性名，類名要一緻
• 子類重寫後的屬性權限不能小于父類屬性的權限

1. 如果父類屬性隻是隻讀的，那麼子類重寫後的屬性可以是隻讀的，也可以是可讀寫的
2. 如果父類屬性時可讀寫的，那麼子類重寫後的屬性也必須是可讀寫的

• 重寫執行個體屬性

class Circle {
    var radius: Int = 0
    var diameter: Int {
        set {
            print("Circle setDiameter")
            radius = newValue / 2
        }
        get {
            print("Circle getDiameter")
            return radius * 2
        }
    }
}

var c: Circle
c = Circle()
c.radius = 6

// Circle getDiameter
// 12
print(c.diameter)

// Circle setDiameter
c.diameter = 20

// 10
print(c.radius)
           

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 getRadius")
            return super.diameter
        }
    }
}

c = SubCircle()
// SubCircle setRadius
c.radius = 6

// SubCircle getRadius
// Circle getDiameter
// SubCircle getRadius
// 12
print(c.diameter)

// SubCircle setDiameter
// Circle setDiameter
// SubCircle setRadius
c.diameter = 20

// SubCircle getRadius
// 10
print(c.radius)
           

• 屬性觀察器

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 c = SubCircle()

// SubCircle willSetRadius 10
// SubCircle didSetRadius 1 10
c.radius = 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 c = SubCircle()

// SubCircle willSetRadius 10
// Circle willSetRadius 10
// Circle didSetRadius 1 10
// SubCircle didSetRadius 1 10
c.radius = 10
           

class Circle {
    var radius: Int {
        set {
            print("Circle setRadius", 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 c = SubCircle()

//Circle getRadius
//SubCircle willSetRadius 10
//Circle setRadius 10
//Circle getRadius
//SubCircle didSetRadius 20 20
c.radius = 10
           

• final

• 被 final 修飾的方法、下标、屬性，禁止被重寫
• 被 final 修飾的類，禁止被繼承

本文章隻是本人的學習筆記！