兩階段初始化

Two-Phase Initialization

Implicit super.init()

If a subclass initializer:

• performs no customization in phase 2 of the initialization process

• the superclass has a zero-argument designated initializer

you can omit a call to super.init() after assigning values to all of the subclass’s stored properties

Cat

class Cat : Animal {

  override init() {
    print("Cat created")
    // super.init() implicitly called here. ⭐
  }

  override func makeNoise() {
    print("Mews")
  }
  
}

Animal

class Animal {

  init() {
    print("Animal Created")
  }

  func makeNoise() {
    fatalError("Must Override to get specific Noise")
  }
  
}

main

let cat = Cat()
cat.makeNoise()

// output:
// Cat created
// Animal created
// Mews

🔗 原始碼：repl.it