反初始化（析构过程）（学习笔记）

环境Xcode 11.0 beta4 swift 5.1

• 反初始化（析构过程）
  • 类实例销毁之前会立即调用析构器，用关键字 deinit
• 反初始化（析构过程）如何工作
  • Swift仍然使用ARC管理机制，大部分情况下实例销毁不用手动清理；但有些情况下需要自己做一些额外的操作在实例销毁前，此时要可在析构器里实现

  • 一个类至多只有一个析构器

    deinit {
        // perform the deinitialization
    }

  • 析构器是自动调用

  • 析构调用之后实例才会被销毁，所以在析构器中可以访问实例的所有属性，可以修改这些属性的行为

• 析构器的运用

      // 示例程序
      class Bank {
          static var coinsInBank = 10_000
          static func distribute(coins numberOfCoinsRequested: Int) -> Int {
              let numberOfCoinsToVend = min(numberOfCoinsRequested, coinsInBank)
              coinsInBank -= numberOfCoinsToVend
              return numberOfCoinsToVend
          }
          static func receive(coins: Int) {
              coinsInBank += coins
          }
      }
      class Player {
          var coinsInPurse: Int
          init(coins: Int) {
              coinsInPurse = Bank.distribute(coins: coins)
          }
          func win(coins: Int) {
              coinsInPurse += Bank.distribute(coins: coins)
          }
          deinit {
              Bank.receive(coins: coinsInPurse)
          }
      }
      var playerOne: Player? = Player(coins: 100)
      print("A new player has joined the game with \(playerOne!.coinsInPurse) coins")
      // Prints "A new player has joined the game with 100 coins"
      print("There are now \(Bank.coinsInBank) coins left in the bank")
      // Prints "There are now 9900 coins left in the bank"
      playerOne!.win(coins: 2_000)
      print("PlayerOne won 2000 coins & now has \(playerOne!.coinsInPurse) coins")
      // Prints "PlayerOne won 2000 coins & now has 2100 coins"
      print("The bank now only has \(Bank.coinsInBank) coins left")
      // Prints "The bank now only has 7900 coins left"
      playerOne = nil
      print("PlayerOne has left the game")
      // Prints "PlayerOne has left the game"
      print("The bank now has \(Bank.coinsInBank) coins")
      // Prints "The bank now has 10000 coins"

  [Swift从入门到精通]