Swift从入门到精通第十二篇 - 反初始化（析构过程） 初识

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"