存在型に `any` を付けていないときにコンパイルエラーにする / How to produce a compile error when writing an existential type without the `any` keyword

存在型に `any` を付けていないときにコンパイルエラーにする / How to produce a compile error when writing an existential type without the `any` keyword

potatotips #81 iOS/Android開発Tips共有会
2023/02/21 19:00〜
https://potatotips.connpass.com/event/272353/

登壇ノートはこちら: https://zenn.dev/treastrain/articles/555d4a2fc1b40b

Transcript

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   3ZPHB 1 potatotips #81 
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5. Copyright © 2023 treastrain / Tanaka RyogaɹAll rights reserved. ଘࡏܕ &YJTUFOUJBM
   5ZQFT 5 protocol Fruit {} struct Apple: Fruit {} struct Banana: Fruit {} func fruit1() -> Fruit { Apple() } var fruit2: Fruit = fruit1() fruit2 = Banana() // ✅
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    ʣ 6 protocol Fruit {} struct Apple: Fruit {} struct Banana: Fruit {} // Swift 5.1+ func fruit3() -> some Fruit { Apple() } // Swift 5.7+ var fruit4: some Fruit = fruit3() fruit4 = Banana() // ❌ Cannot assign value of type 'Banana' to type 'some Fruit'
7. Copyright © 2023 treastrain / Tanaka RyogaɹAll rights reserved. ଘࡏܕ &YJTUFOUJBM
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    ʣ 7 protocol Fruit {} struct Apple: Fruit {} struct Banana: Fruit {} // Swift 5.6+ func fruit5() -> any Fruit { Apple() } // Swift 5.6+ var fruit6: any Fruit = fruit5() fruit6 = Banana() // ✅
8. Copyright © 2023 treastrain / Tanaka RyogaɹAll rights reserved. ଘࡏܕ &YJTUFOUJBM
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   ΑΓ΋લ·Ͱʣ 8 protocol Fruit {} func fruit1() -> Fruit { /* ... */ } var fruit2: Fruit = fruit1() protocol Fruit {} func fruit5() -> any Fruit { /* ... */ } var fruit6: any Fruit = fruit5()
9. Copyright © 2023 treastrain / Tanaka RyogaɹAll rights reserved. ଘࡏܕ &YJTUFOUJBM
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   Ҏ߱Ͱ͸ʣ 9 protocol Fruit {} func fruit1() -> Fruit { /* ... */ } var fruit2: Fruit = fruit1() protocol Fruit {} func fruit5() -> any Fruit { /* ... */ } var fruit6: any Fruit = fruit5()
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13. Copyright © 2023 treastrain / Tanaka RyogaɹAll rights reserved. -enable-upcoming-feature ExistentialAny 4XJGU
    
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    ͷ࢖༻ྫ potatotips #81 
 iOS / Android ։ൃ Tips ڞ༗ձ #potatotips