SwiftのNeverとボトム型 / Never as a Bottom Type

第7回カンファレンス動画鑑賞会で供養したLTの資料です。

Transcript

1. 4XJGUͷ
   Never
   ͱ
 ϘτϜܕ 2019/04/14 ୈ7ճΧϯϑΝϨϯεಈըؑ৆ձ Mobile Act OSAKA #9 (ิܽ) try! Swift Tokyo 2019 (Backup)
2. About Me w ͻΖΜʢҰٶ
   ߒڭʣ
   w 5XJUUFS
   
   (JU)VC
   
 2JJUB
   
   4MJEF4IBSF
    4QFBLFS
   %FDL

   
   
   
   ˠ
   IJSPOZUJD
   w ಙౡࡏॅ
3. ݱ࣌఺ͷ
   4XJGU
   Ͱ͸
 Never
   ͸ϘτϜܕͰ͸͋Γ·ͤΜ
4. Agenda w Never
   ܕͬͯԿ͚ͩͬʁ
   w ϘτϜܕͬͯԿΑʁ
   w ΋͠
   Never
   ͕ϘτϜܕͩͬͨΒʁ
5. Never Type
6. func foo() -> Type foo
   ͸
   
   Type
   
   ͷΠϯελϯεΛฦ͢
7. func foo() -> Int foo
   ͸
   Int
   ͷΠϯελϯεΛฦ͢ -3, 0, 10, 42, …
8. func foo() -> Void foo
   ͸஋Λฦ͞ͳ͍
9. func foo() -> Type foo
   ͸
   
   Type
   
   ͷΠϯελϯεΛฦ͢
10. func foo() -> Void foo
    ͸
    
    Void
    
    ͷΠϯελϯεΛฦ͢
11. Void Type w ۭͷλϓϧܕͷΤΠϦΞε
    w ۭͷλϓϧͷܕ
    
    
    
    ʜ
    ()
    w ͦͷ།Ұͷ஋
    
    
    
    
    
    
    ʜ
    ()
13. func foo() -> Never foo
    ͸ฦͬͯ͜ͳ͍
14. func foo() -> Type foo
    ͸
    
    
    Type
    
    
    ͷΠϯελϯεΛฦ͢
15. func foo() -> Never foo
    ͸
    
    Never
    
    ͷΠϯελϯεΛฦ͢
16. Never Type w DBTF
    Λ࣋ͨͳ͍
    FOVN
    FOVN
    /FWFS
    \
    ^
    w ΠϯελϯεΛ࣋ͨͳ͍
    w ؔ਺͸
    /FWFS
    ͷΠϯελϯεΛฦͤͳ͍
    w ແݶϧʔϓɺΫϥογϡɺϓϩάϥϜऴྃɺྫ֎
17. Bottom Type
18. Subtype class Animal { ... } class Dog: Animal { ... } Animal Dog
19. Subtype Dog
    ͸
    Animal
    ͷαϒλΠϓ Dog
    ͷΠϯελϯεΛ
 Animal
    ͱͯ͠ѻ͑Δ Animal Dog
20. Animal Dog Cat Animal Dog Cat
21. Animal Dog Cat Plant Flower Star … ?
22. Animal Dog Cat Plant Flower Star … Any Top Type
23. Animal Dog Cat Plant Flower Star … Any Top Type ? Bottom Type
24. Bottom Type w ϘτϜܕ͸͢΂ͯͷܕͷαϒλΠϓ
    w ϘτϜܕͷΠϯελϯεΛͲͷܕͱͯ͠΋ѻ͑Δ
25. 4501ࡀະຬҿञ
    ະ੒೥ऀͷҿञ͸๏཯Ͱې͡ΒΕ͍ͯ·͢
26. Bottom Type w ϘτϜܕ͸͢΂ͯͷܕͷαϒλΠϓ
    w ϘτϜܕͷΠϯελϯεΛͲͷܕͱͯ͠΋ѻ͑Δ w ϘτϜܕ͸ΠϯελϯεΛ࣋ͨͳ͍ܕ
27. Imagine:
 Never as a Bottom Type
28. Case 1 class FooViewController: UIViewController { var label: UILabel! ... }
29. Case 1 class FooViewController: UIViewController { lazy var label: UILabel = fatalError() ... }
30. Case 2 let data: [String: String] = ... guard let name = data["name"] else { throw ParseError.missing("name") } speaker.name = name guard let icon = data["icon"] else { throw ParseError.missing("icon") } speaker.icon = icon
31. Case 2 let data: [String: String] = ... speaker.name = data["name"] ?? try missing("name") speaker.icon = data["icon"] ?? try missing("icon") func missing(_ key: String) throws -> Never { throw ParseError.missing(key) }
32. Case 2+ let data: [String: String] = ... speaker.name = data["name"] ?? throw ParseError.missing("name") speaker.icon = data["icon"] ?? throw ParseError.missing("icon") ͞Βʹ
    throw
    ͕
    Never
    Λฦࣜ͢ͳΒ
33. Case 3 enum Result<Value, Error: Swift.Error> { case success(Value) case failure(Error) } func foo() -> Result<String, Never> { ... } foo
    ͸ࣦഊ͠ͳ͍
34. Case 3 • 4XJGU
    Ͱ࣮ݱ͞Ε·ͨ͠
    
    4& https://github.com/apple/swift-evolution/blob/master/proposals/0215-conform-never-to- hashable-and-equatable.md
35. Case 3 w 4&ͷٞ࿦ʹͯ https://forums.swift.org/t/se-0215-conform-never-to-equatable-and-hashable/13586
36. Protocol • ΠϯελϯεϓϩύςΟ (var) • Πϯελϯεϝιου (func) • ܕϓϩύςΟ (static var) • ܕϝιου (static func) • ΠχγϟϥΠβ (init) Πϯελϯεʹର͢Δ
 ੍໿Ͱ͸ͳ͍
37. Recap
38. Recap w Never
    ܕͬͯԿ͚ͩͬʁ
    w ϘτϜܕͬͯԿΑʁ
    w ΋͠
    Never
    ͕ϘτϜܕͩͬͨΒʁ
 ˠ
    ΠϯελϯεΛ࣋ͨͳ͍ܕ
    ˠ
    ͢΂ͯͷܕͷαϒλΠϓʹͳΔܕ
    ˠ
    ͍Ζ͍ΖεοΩϦ͢Δ͜ͱ͕͋Δ
39. Never as a Bottom Type • SE-0215 - Conform Never to Equatable and Hashable
 https://forums.swift.org/t/se-0215-conform-never-to-equatable-and-hashable/13586 • SE-0102: Remove @noreturn attribute and introduce an empty Never type
 https://github.com/apple/swift-evolution/blob/master/proposals/0102-noreturn-bottom- type.md • [Pitch] Never as a bottom type
 https://forums.swift.org/t/pitch-never-as-a-bottom-type/5920
40. One more thing: Kotlin 4XJGU Void Never ,PUMJO Unit Nothing Nothing
    ͸ϘτϜܕ
41. Case 2 (Kotlin) val data: Map<String, String> = ... speaker.name = data["name"] ?: throw MissingException("name") speaker.icon = data["icon"] ?: throw MissingException("icon") throw
    ͸
    Nothing
    Λฦࣜ͢
42. ͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠