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weak vs unowned
2018/09/02 @iOSDC Japan 2018
Yutaro Muta @yutailang0119
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• Yutaro Muta @yutailang0119
• Hatena Co., Ltd. @Kyoto
• Conference Staff
• builderscon 2017, 2018
• PyCon JP 2016, 2017
• and more
•
Who am I ?
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https://fortee.jp/iosdc-japan-2018/proposal/b84477b0-a13b-4994-a250-ad2300229e83
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Goal
• Ͳ͏͍͚Δ͖͔ΛΔ
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Agenda
• ॥ࢀরͷ෮श
• Strong, Weak, Unowned
• WeakͷϝϦοτ/σϝϦοτ
• UnownedͷϝϦοτ/σϝϦοτ
• ·ͱΊ
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॥ࢀরͷ෮श
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ਓྨɺ͍͔ͭΒ·͞Ε͍ͯΔͷ͔
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https://qiita.com/susieyy/items/39efd4d34cf4c1f9d3ef
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Sample
https://github.com/yutailang0119/iOSDC2018Sample
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^
॥ࢀরͷ෮श
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Strong Reference
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Weak Reference
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Unowned Reference
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^
^
॥ࢀর͠ͳ͍ύλʔϯ
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Strong ReferenceͰ॥ࢀরͯ͠ͳ͍
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༨ஊ: weakΩϟϓνϟ self Ҏ֎Ͱ͖Δ
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^
^
^
^
※ͨͩ͠ɺunownedͰ͖ͳ͍
`property` may only be applied to class and class-bound protocol types, not ‘Type'
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WeakͷϝϦοτ/σϝϦοτ
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WeakͷϝϦοτ/σϝϦοτ
• ϝϦοτ
• ࣮֬ʹΫϥογϡΛ͛Δ
• σϝϦοτ
• ʹͳΔ͜ͱ͕͋Δ
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ϝϦοτ: UnownedͰΫϥογϡ͢Δঢ়گճආͰ͖Δ
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σϝϦοτ: ʹͳΔ͜ͱ͕͋Δ
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if let guard let ͰʹΞΫηε੍ޚ͢Δඞཁ͕ग़ͨΓ͢Δ
ಛʹ self Shadowingͷ͕͋Δ
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UnownedͷϝϦοτ/σϝϦοτ
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UnownedͷϝϦοτ/σϝϦοτ
• ϝϦοτ
• WeakʹൺͯύϑΥʔϚϯε͕༏ҐͰ͋Δ
• ΞΫηε࣌ʹnilͰͳ͍͜ͱΛ໌ࣔͰ͖Δ (อূͰ͖ͳ͍)
• σϝϦοτ
• దʹ༻͠ͳ͚ΕɺΫϥογϡ͢Δ͜ͱ͕͋Δ
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UnownedͷϝϦοτ/σϝϦοτ
• ϝϦοτ
• WeakʹൺͯύϑΥʔϚϯε͕༏ҐͰ͋Δ
• ΞΫηε࣌ʹnilͰͳ͍͜ͱΛ໌ࣔͰ͖Δ (อূͰ͖ͳ͍)
• σϝϦοτ
• దʹ༻͠ͳ͚ΕɺΫϥογϡ͢Δ͜ͱ͕͋Δ
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Copyright © 2018 Apple Inc. All rights reserved.
https://help.apple.com/instruments/mac/current/
ݕূ: WeakʹൺͯύϑΥʔϚϯε͕༏ҐͰ͋Δͷ͔
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ݕূ: WeakʹൺͯύϑΥʔϚϯε͕༏ҐͰ͋Δͷ͔
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No content
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ࠓճͷαϯϓϧϨϕϧͰɺ
༏ҐͳࠩݟΒΕͳ͔ͬͨ
-> ଞͷύϑΥʔϚϯεΛ
্ͤͨ͞ํ͕ے͕͍͍
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Stack Overflow
weak vs unowned in Swift. What are the internal differences?
https://stackoverflow.com/a/42847825
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Stack Overflow
weak vs unowned in Swift. What are the internal differences?
https://stackoverflow.com/a/42847825
> In my usage, the common case arises in situations where a closure needs a capture list
involving self in order to avoid a retain cycle. In such a situation, it is almost always
possible to say [unowned self] in the capture list. When we do:
> * It is more convenient for the programmer because there is nothing to unwrap. [weak
self] would be an Optional in need of unwrapping in order to use it.
> * It is more efficient, partly for the same reason (unwrapping always adds an extra level
of indirection) and partly because it is one fewer weak reference for the runtime's
scratchpad list to keep track of.
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Stack Overflow
weak vs unowned in Swift. What are the internal differences?
https://stackoverflow.com/a/42847825
> In my usage, the common case arises in situations where a closure needs a capture list
involving self in order to avoid a retain cycle. In such a situation, it is almost always
possible to say [unowned self] in the capture list. When we do:
> * It is more convenient for the programmer because there is nothing to unwrap. [weak
self] would be an Optional in need of unwrapping in order to use it.
> * It is more efficient, partly for the same reason (unwrapping always adds an extra level
of indirection) and partly because it is one fewer weak reference for the runtime's
scratchpad list to keep track of.
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UnownedͷϝϦοτ/σϝϦοτ
• ϝϦοτ
• WeakʹൺͯύϑΥʔϚϯε͕༏ҐͰ͋Δ
• ΞΫηε࣌ʹOJMͰͳ͍͜ͱΛ໌ࣔͰ͖Δ (อূͰ͖ͳ͍)
• σϝϦοτ
• దʹ༻͠ͳ͚ΕɺΫϥογϡ͢Δ͜ͱ͕͋Δ
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The Swift Programing Language
Automatic Reference Counting / Unowned References
> Unlike a weak reference, however, an unowned reference is used when
the other instance has the same lifetime or a longer lifetime. You indicate
an unowned reference by placing the unowned keyword before a property
or variable declaration.
> An unowned reference is expected to always have a value. As a result,
ARC never sets an unowned reference’s value to nil, which means that
unowned references are defined using nonoptional types.
https://docs.swift.org/swift-book/LanguageGuide/AutomaticReferenceCounting.html
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The Swift Programing Language
Automatic Reference Counting / Unowned References
> Unlike a weak reference, however, an unowned reference is used when
the other instance has the same lifetime or a longer lifetime. You indicate
an unowned reference by placing the unowned keyword before a property
or variable declaration.
> An unowned reference is expected to always have a value. As a result,
ARC never sets an unowned reference’s value to nil, which means that
unowned references are defined using nonoptional types.
https://docs.swift.org/swift-book/LanguageGuide/AutomaticReferenceCounting.html
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ϓϩάϥϚͷҙਤ͕ٴͿൣғͰɺ
ཧ͕ͳΔ͘ίʔυʹ
ө͞Ε͍ͯΔํ͕·͍͠
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·ͱΊ
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Ͳ͏͍͚Δ͖͔
• ϝϞϦղ์ͷλΠϛϯά͕ෆ໌ͳ߹ɺweakΛ༻
• ࣮ߦ࣌ͷڍಈΛཧղͰ͖Δࣗ৴͕ͳ͍߹ɺweak͕ແ
• γϯϓϧͳΞϓϦέʔγϣϯͰɺύϑΥʔϚϯεʹࠩग़ʹ͍͘
ͷͰɺ҆৺ײΛಘΔͨΊͷweak͋Γͱݴ͑Δ
• ϝϞϦղ์͕ߦΘΕͳ͍͜ͱ͕લఏͷॲཧͰɺ·ͨͦΕΛอূͰ͖Δ
߹ɺunownedΛ͏
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ओ؍
Swift͕weakͱunownedͷ2ͭΛఏڙ͍ͯ͠ΔͷͳΒɺ
ϓϩάϥϚͷҙ͕ࣝհࡏ͢ΔίʔυʹͳΔΑ͏ʹ
͍͚͍ͨ
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Reference
• https://qiita.com/susieyy/items/39efd4d34cf4c1f9d3ef
• https://docs.swift.org/swift-book/LanguageGuide/AutomaticReferenceCounting.html
• https://github.com/yutailang0119/iOSDC2018Sample
• https://help.apple.com/instruments/mac/current/
• https://stackoverflow.com/questions/42842336/weak-vs-unowned-in-swift-what-are-
the-internal-differences
• http://www.apeth.com/iOSBook/ch12.html#_property_memory_management_policies
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ͯͳͰɺ͜Μͳݴ༿͕͞ΔਓΛืू͍ͯ͠·͢ʂ
ϓϩάϥϚͷҙਤ͕ٴͿൣғͰɺ
ཧ͕ͳΔ͘ίʔυʹ
ө͞Ε͍ͯΔํ͕·͍͠
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