Swift Language Guide - Inheritance

ONLY Reference Type has Inheritance.

Initializers

Subclass initializers are NOT inherited by default. So, subclass MUST invoke Designated initializers of superclass in its initializers.

  class Color {
      let red = 0.0, green = 0.0, blue = 0.0

      init(red: Double, green: Double, blue: Double) {
          self.red = red
          self.green = green
          self.blue = blue
      }

      convenience init() {
          self.init(red: 128.0, green: 128.0, blue: 128.0)

      }

  }

  class AlphaColor : Color {
      let alpha = 255.0

      init(alpha: Double) {
          super.init(red: 0.0, green: 0.0, blue: 0.0)
          self.alpha = alpha
      }
  }

  let c1 = AlphaColor(alpha: 128.0)

  println("(\(c1.red), \(c1.green), \(c1.blue), \(c1.alpha))")    <-- (0.0, 0.0, 0.0, 128.0)

  class Color {
      let red = 0.0
      var green = 0.0, blue = 0.0

      init(red: Double, green: Double, blue: Double) {
          self.red = red
          self.green = green
          self.blue = blue
      }

      convenience init() {
          self.init(red: 128.0, green: 128.0, blue: 128.0)

      }

  }

  class AlphaColor : Color {
      let alpha = 255.0

      init(alpha: Double) {
          super.init()            <-- Error, invoke convenience initializers of superclass
          self.alpha = alpha
      }
  }

  class Color {
      let red = 0.0
      var green = 0.0, blue = 0.0

      init(red: Double, green: Double, blue: Double) {
          self.red = red
          self.green = green
          self.blue = blue
      }

      convenience init() {
          self.init(red: 128.0, green: 128.0, blue: 128.0)

      }

  }

  class AlphaColor : Color {
      let alpha = 255.0

      init(alpha: Double) {
          super.init(red: 0.0, green: 0.0, blue: 0.0)
          self.alpha = alpha
      }

      convenience init() {
          super.init()    <-- Error, Must invoke designated initializers of superclass
      }
  }

Subclass can NOT modify Constant properties of superclass.

  class Color {
      let red = 0.0   <-- Constant
      var green = 0.0, blue = 0.0

      init(red: Double, green: Double, blue: Double) {
          self.red = red
          self.green = green
          self.blue = blue
      }

      convenience init() {
          self.init(red: 128.0, green: 128.0, blue: 128.0)

      }

  }

  class AlphaColor : Color {
      let alpha = 255.0

      init(alpha: Double) {
          super.init(red: 0.0, green: 0.0, blue: 0.0)
          self.alpha = alpha
          self.green = 128.0  
          self.red = 255.0        <-- Error, Can not modify constant properties of superclass
      }
  }

Override

Use override to override methods, properties, and Subscripts

Subclass can NOT override Stored properties of superclass Directly.

  class Color {
      let red = 0.0
      var green = 0.0, blue = 0.0

      init(red: Double, green: Double, blue: Double) {
          self.red = red
          self.green = green
          self.blue = blue
      }

      convenience init() {
          self.init(red: 128.0, green: 128.0, blue: 128.0)

      }

  }

  class AlphaColor : Color {
      let alpha = 255.0
      override var green = 128.0  <-- Error, can not override stored properties of superclass.

      init(alpha: Double) {
          super.init(red: 0.0, green: 0.0, blue: 0.0)
          self.alpha = alpha
          self.green = 128.0
      }


  }

Subclass CAN override Stored properties of superclass with Computed ones.

  class Color {
      let red = 0.0, green = 0.0, blue = 0.0
      var count = 0           <-- a stored property

      init(red: Double, green: Double, blue: Double) {
          self.red = red
          self.green = green
          self.blue = blue
      }

      convenience init() {
          self.init(red: 128.0, green: 128.0, blue: 128.0)

      }


  }

  class AlphaColor : Color {
      let alpha = 255.0

      init(alpha: Double) {
          super.init(red: 0.0, green: 0.0, blue: 0.0)
          self.alpha = alpha
      }

      override var count : Int {      <-- override count with computed property
          get {
              return super.count
          }

          set {
              super.count = newValue
          }
      }

  }

  let c1 = AlphaColor(alpha: 128.0)

  println(c1)

Subclass CAN override Computed properties of superclass.

  class Color : Printable {
      let red = 0.0, green = 0.0, blue = 0.0

      init(red: Double, green: Double, blue: Double) {
          self.red = red
          self.green = green
          self.blue = blue
      }

      convenience init() {
          self.init(red: 128.0, green: 128.0, blue: 128.0)

      }

      var description : String {
          return "(\(red), \(green), \(blue))"
      }

  }

  class AlphaColor : Color {
      let alpha = 255.0

      init(alpha: Double) {
          super.init(red: 0.0, green: 0.0, blue: 0.0)
          self.alpha = alpha
      }

      override var description : String { <-- Override computed properties.
          return "(\(red), \(green), \(blue), \(alpha))"
      }
  }

  let c1 = AlphaColor(alpha: 128.0)

  println(c1)

Subclass can Add Property Observers to Stored and Computed properties with Override (override)

  class Color {
      let red = 0.0, green = 0.0, blue = 0.0
      var count = 0           <-- Stored Property

      var count2 : Int {      <-- Computed Property
          get {
              println("count2 getter")
              return self.count
          }

          set {
              println("count2 setter")
              count = newValue
          }
      }

      init(red: Double, green: Double, blue: Double) {
          self.red = red
          self.green = green
          self.blue = blue
      }

      convenience init() {
          self.init(red: 128.0, green: 128.0, blue: 128.0)

      }


  }

  class AlphaColor : Color {
      let alpha = 255.0
      var cc : Int = 0

      init(alpha: Double) {
          super.init(red: 0.0, green: 0.0, blue: 0.0)
          self.alpha = alpha
      }

      override var count2 : Int {         <-- Add property observer to computed property
          didSet {
              cc += 1
              println("didset: cc = \(cc)")
          }

          willSet {
              cc += 2
              println("willset: cc = \(cc)")
          }
      }

      override var count: Int {           <-- Add property observer to stored property
          didSet {
              println("didset: count = \(count)")
          }

          willSet {
              println("willset: count = \(count)")
          }
      }


  }

  let c1 = AlphaColor(alpha: 128.0)
  println("before setter")
  c1.count2 = 20
  println("after setter")
  println(c1.count)
  println(c1.cc)

Preventing Overrides

Use final to prevent overrides, even adding property observers.

class Color {
    let red = 0.0, green = 0.0, blue = 0.0
    final var count = 0         <-- Final Stored Property

    final var count2 : Int {    <-- Final Computed Property
        get {
            println("count2 getter")
            return self.count
        }

        set {
            println("count2 setter")
            count = newValue
        }
    }

    init(red: Double, green: Double, blue: Double) {
        self.red = red
        self.green = green
        self.blue = blue
    }

    convenience init() {
        self.init(red: 128.0, green: 128.0, blue: 128.0)

    }


}

class AlphaColor : Color {
    let alpha = 255.0
    var cc : Int = 0

    init(alpha: Double) {
        super.init(red: 0.0, green: 0.0, blue: 0.0)
        self.alpha = alpha
    }

    override var count2 : Int {     <-- Error, can NOT override
        didSet {
            cc += 1
            println("didset: cc = \(cc)")
        }

        willSet {
            cc += 2
            println("willset: cc = \(cc)")
        }
    }

    override var count: Int {       <-- Error, can NOT override
        didSet {
            println("didset: count = \(count)")
        }

        willSet {
            println("willset: count = \(count)")
        }
    }


}

工程師的筆記本

2014年8月11日星期一