Weak, Strong, Unowned, Oh My!

Let’s dig into something we’re all afraid to look at talk about. ARC is that family member that we all hate to love. Unfortunately, he needs our help quite often (more often than we’d like!). I want to discuss retain cycles. Swift is much better at helping us help ARC know how to manage our memory by giving us cool little things like capture lists, unowned, and weak references. We’ll generate some retain cycles of our own, explore how to debug them with Instruments, and learn how to use the tools Swift gives us to have clear, expressive, non-leaky code.

Transcript

1. Weak, Strong, Unowned Oh, My!
2. Quick Intro
3. Hi! I'm Hector Matos
5. Sr. Software Engineer @ Capital One
6. @allonsykraken on the Twitters
7. Father of KrakenDev.io
8. ARC
9. - (void)releaseTheKraken { Kraken *kraken = [[Kraken alloc] init]; //+1 retain [kraken release]; //generated by ARC }
10. Magic has it's limitations And so does ARC
11. Leaked Memory & Retain Cycles
14. Strong References Default in Swift
15. Now Stop, Example Time //Kraken holds a strong reference to the yummy human. class Kraken { var yummyHuman: Human }
16. // The animation closure holds a strong reference to self // self.retainCount is 1 here UIView.animateWithDuration(0.3) { // self.retainCount is 2 here self.view.alpha = 0.0 }
17. Questions?
18. Weak References Safe - Independent
19. Stop, Collaborate, & Listen! (to my next example) class KrakensFace: UIView { @IBOutlet weak var razorSharpTeeth: UIView! } KrakenAPI.eat(yummyHuman, whenFinished: { [weak self] in self?.waitForNextMealTime() })
20. WTF is "[weak self] in"?!
21. Capture Lists It's just an array. That's all it is. There, there. It's all over now. !
22. KrakenAPI.eat(yummyHuman, finished: { [weak self, unowned lovedOne = yummyHuman.lovedOne] in self?.waitForNextMealTime() })
23. Questions?
24. Unowned References Mutual Dependence
25. class Human { var heart: ! func seeKrakenComing() { heart.haveHeartAttack() } } class !: Organ { unowned let human: Human init(human: Human) { self.human = human } func haveHeartAttack() { human.die() } } let human = Human() human.heart = !(human: human)
26. Questions?
28. ❤