Naruki Chigira - Timers inc. GitHub: naru-jpn, Twitter: @naruchigi Unowned / Weak References with Closure 

ม਺ͷੜଘظؒɺؾʹͯ͠·͔͢ʁ 

Ϋϩʔδϟ಺Ͱอ࣋͞ΕΔม਺ɺ௥͑·͔͢ʁ 

DispatchQueue.main.async { [weak self] in // ... } 

Ϋϩʔδϟ಺Ͱʰ ͱΓ͋͑ͣ [weak self] ʱͯ͠·ͤΜ͔ʁ 

Playground ͰڍಈΛࡉ͔͘ݟͯΈΑ͏ https://gist.github.com/naru-jpn/fa4c39ce2eda8a803358dad75d04058d 

class Executor { // MARK: Exeute stored procedure let procedure: () -> () init(procedure: @escaping () -> ()) { self.procedure = procedure } func execute() { self.procedure() } // MARK: Static execution static func execute(procedure: () -> ()) { procedure() } } ΫϩʔδϟΛ࣮ߦ͢ΔΫϥε Executor 

class Object { var child: Object? weak var weakChild: Object? var closure: (() -> ())? weak var currentExecutor: Executor? } ؍ଌ༻Ϋϥε Object 

weak var weakObject: Object? = nil // スコープ内外での挙動を見るために if 文でネストさせる // object が解放されていれば weakObject の中身は nil になる if true { let object: Object = Object() weakObject = object print(“\(weakObject)") // nil or not nil? } print(“\(weakObject)") // nil or not nil? ม਺͕ղ์͞Ε͍ͯΔ͔Ͳ͏͔ͷ֬ೝ 

object object if true { let object: Object = Object() weakObject = object // 1 } // 2 1. ม਺͸είʔϓΛൈ͚ͨΒղ์͞ΕΔ 

object child object child if true { let object: Object = Object() object.child = object weakObject = object // 1 } // 2 weakObject?.child = nil 2. ࢀরʹΑΔϝϞϦϦʔΫ 

object child object child if true { let object: Object = Object() object.weakChild = object weakObject = object // 1 } // 2 weakObject?.child = nil 3. weak Λ࢖ͬͯϝϞϦϦʔΫ͠ͳ͍Α͏ʹͨ͠έʔε 

॥؀ࢀর͸౰વආ͚·͠ΐ͏ 

object closure object closure if true { let object: Object = Object() object.closure = { print("\(object)") } weakObject = object // 1 } // 2 weakObject?.closure = nil 4. Ϋϩʔδϟ͔ΒͷࢀরʹΑΔϝϞϦϦʔΫ 

object closure object closure if true { let object: Object = Object() object.closure = { [weak object] in print("\(object)") } weakObject = object // 1 } // 2 5. [weak ---] Λ࢖ͬͯϝϞϦϦʔΫ͠ͳ͍Α͏ʹͨ͠έʔε 

Ϋϩʔδϟͷ॥؀ࢀরʹ΋஫ҙ 

object closure object object closure object είʔϓ಺ ؔ਺࣮ߦ࣌ ؔ਺ऴྃ࣌ είʔϓ֎ Executor Executor extension Object { func printWeakSelf() { let executor: Executor = Executor(procedure: { [weak self] in debugPrint("\(self)") }) executor.execute() } } 6. Executor ͷΫϩʔδϟ಺Ͱ [weak self] Λ࢖͏৔߹ 

object closure object object closure object είʔϓ಺ ؔ਺࣮ߦ࣌ ؔ਺ऴྃ࣌ είʔϓ֎ Executor Executor if true { let object: Object = Object() object.printWeakSelf() weakObject = object } 6. Executor ͷΫϩʔδϟ಺Ͱ [weak self] Λ࢖͏৔߹ 

object closure object object closure object Executor Executor είʔϓ಺ ؔ਺࣮ߦ࣌ ؔ਺ऴྃ࣌ είʔϓ֎ extension Object { func printSelf() { let executor: Executor = Executor(procedure: { print("\(self)") }) executor.execute() } } 7. Executor ͷΫϩʔδϟ಺Ͱ [weak self] Λ࢖Θͳ͍৔߹ 

object closure object object closure object Executor Executor είʔϓ಺ ؔ਺࣮ߦ࣌ ؔ਺ऴྃ࣌ είʔϓ֎ if true { let object: Object = Object() object.printSelf() weakObject = object } 7. Executor ͷΫϩʔδϟ಺Ͱ [weak self] Λ࢖Θͳ͍৔߹ 

Ϋϩʔδϟ಺Ͱ self Λࢀরͯ͠΋ϦʔΫ͠ͳ͍৔߹΋͋Δ 

ඇಉظॲཧ଴ػ࣌ ඇಉظॲཧऴྃ࣌ ؔ਺࣮ߦ࣌ object closure closure Executor object closure Executor extension Object { func printAsynchronousWeakSelf() { let executor: Executor = Executor(procedure: { let time: DispatchTime = .now() + 1.0 DispatchQueue.global().asyncAfter(deadline: time, execute: { [weak self] in print("\(self)") }) }) executor.execute() self.currentExecutor = executor } } 8. ඇಉظॲཧͰ [weak self] Λ࢖͏৔߹ 

ඇಉظॲཧ଴ػ࣌ ඇಉظॲཧऴྃ࣌ ؔ਺࣮ߦ࣌ object closure closure Executor object closure Executor if true { let object: Object = Object() object.printAsynchronousSelf() weakObject = object } sleep(UInt32(3.0)) 8. ඇಉظॲཧͰ [weak self] Λ࢖͏৔߹ 

ඇಉظॲཧ଴ػ࣌ ඇಉظॲཧऴྃ࣌ ؔ਺࣮ߦ࣌ object closure object closure Executor object closure Executor extension Object { func printAsynchronousSelf() { let executor: Executor = Executor(procedure: { DispatchQueue.global().asyncAfter(deadline: .now() + 1.0, execute: { print("\(self)") }) }) executor.execute() self.currentExecutor = executor } } 9. ඇಉظॲཧͰ [weak self] Λ࢖Θͳ͍৔߹ 

ඇಉظॲཧ଴ػ࣌ ඇಉظॲཧऴྃ࣌ ؔ਺࣮ߦ࣌ object closure object closure Executor object closure Executor if true { let object: Object = Object() object.printAsynchronousSelf() weakObject = object } sleep(UInt32(3.0)) 9. ඇಉظॲཧͰ [weak self] Λ࢖Θͳ͍৔߹ 

ඇಉظॲཧͰ͸ίʔϧόοΫ࣌ʹ object ͕ੜଘ͍ͯ͠Δ͔Ͳ͏͔͕มΘͬͯ͘Δ 

ͨͩ͠ɺϦʔΫ͠ͳ͍͜ͱʹมΘΓ͸ͳ͍ 

໨తʹԠͯ͡࢖͍෼͚ΒΕΔΑ͏ʹͳΓ͍ͨͰ͢Ͷ 

͍͔ͭ [weak self] Λݟͨͱ͖ʹࢥ͍Λ஘ͤͯΈ͍ͯͩ͘͞ 

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Motivation / Concept https://developers.google.com/protocol-buffers/ Template message