if 式と switch 式による SwiftUI のプレビューエラー対策

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1. potatotips #85 iOS/Android։ൃTipsڞ༗ձ 2023/11/14 @Voicy if ࣜͱ switch ࣜʹΑΔ SwiftUI ͷϓϨϏϡʔΤϥʔରࡦ ojun - DeNA Co., Ltd.
2. ࣗݾ঺հʢojunʣ • name: ojun • 2023೥৽ଔೖࣾ • iOSΤϯδχΞ @ojun_9
3. Xcode 15 ରԠਐΜͰ͍·͔͢ʁ
4. Xcode 15.0 Asset Catalogs / String Catalogs PreviewϚΫϩ Swift 5.9 ϒοΫϚʔΫػೳ ɾෳ਺ͷݴޠػೳͷ௥Ճ ɾσόοά࣌ʹม਺ͷ಺༰Λग़ྗ͢ΔͨΊʹར༻͢ΔpίϚϯυͱpoίϚϯυ ʹΑΔग़ྗ͕࣌ؒେ෯ʹ୹ॖ ͦͷଞ͍Ζ͍Ζ
5. Xcode 15.0 Asset Catalogs / String Catalogs PreviewϚΫϩ Swift 5.9 ϒοΫϚʔΫػೳ ɾෳ਺ͷݴޠػೳͷ௥Ճ ͦͷଞ͍Ζ͍Ζ ɾσόοά࣌ʹม਺ͷ಺༰Λग़ྗ͢ΔͨΊʹར༻ՄೳͳpίϚϯυͱpoίϚϯυ ʹΑΔग़ྗ͕࣌ؒେ෯ʹ୹ॖ
6. Swift 5.9: if ͱ switch ͷࣜදݱ
7. Swift 5.9: ifͱswitchͷࣜදݱ Swift 5.9͔ΒswitchͱifΛࣜͱͯ͠දݱͰ͖ΔΑ͏ʹͳͬͨ
8. Swift 5.9: ifͱswitchͷࣜදݱ Swift 5.9͔ΒswitchͱifΛࣜͱͯ͠දݱͰ͖ΔΑ͏ʹͳͬͨ
9. Swift 5.9: ifͱswitchͷࣜදݱ Swift 5.9͔ΒswitchͱifΛࣜͱͯ͠දݱͰ͖ΔΑ͏ʹͳͬͨ
10. Swift 5.9: ifͱswitchͷࣜදݱ Swift 5.9͔ΒswitchͱifΛࣜͱͯ͠දݱͰ͖ΔΑ͏ʹͳͬͨ
11. Swift 5.9: ifͱswitchͷࣜදݱ Swift 5.9͔ΒswitchͱifΛࣜͱͯ͠දݱͰ͖ΔΑ͏ʹͳͬͨ
12. Preview࣌ʹར༻͢Δ
13. Preview࣌ʹར༻͢Δ isSwiftͷBool஋ʹج͍ͮͯTextΛฦ͢
14. Preview࣌ʹར༻͢Δ isSwiftͷBool஋ʹج͍ͮͯTextΛฦ͢ ௨ৗͷϏϧυ 🎉 ໰୊ͳ͘੒ޭ͢Δ
15. Preview࣌ʹར༻͢Δ isSwiftͷBool஋ʹج͍ͮͯTextΛฦ͢ ௨ৗͷϏϧυ 🎉 ໰୊ͳ͘੒ޭ͢Δ Preview࣌ͷϏϧυ 😭 ίϯύΠϧΤϥʔ͕ൃੜ͢Δ
16. Preview࣌ʹར༻͢Δ isSwiftͷBool஋ʹج͍ͮͯTextΛฦ͢ ௨ৗͷϏϧυ 🎉 ໰୊ͳ͘੒ޭ͢Δ Preview࣌ͷϏϧυ 😭 ίϯύΠϧΤϥʔ͕ൃੜ͢Δ Preview ProviderΛར༻ͯ͠΋ಉ༷
17. Preview࣌ʹར༻͢Δ 'if' may only be used as expression in return, throw, or as the source of an assignment
18. ղܾํ๏
19. ղܾํ๏ 1. @ViewBuilderΩʔϫʔυΛ෇༩͢Δ 2. Opaque typeͰ͸ͳ͍໌֬ͳܕΛฦ͢ 3. Opaque Type Λ Existential Type ʹஔ͖׵͑Δ
20. @ViewBuilderΩʔϫʔυΛ෇༩͢Δ @ViewBuilderΩʔϫʔυΛ෇༩͢Δ ͜ͱͰPreview࣌ͷΤϥʔΛճආͰ͖Δ ௨ৗͷϏϧυ 🎉 ໰୊ͳ͘੒ޭ͢Δ Preview࣌ͷϏϧυ 🎉 ໰୊ͳ͘੒ޭ͢Δ
21. ໌֬ͳܕΛฦ͢ ௨ৗͷϏϧυ 🎉 ໰୊ͳ͘੒ޭ͢Δ Preview࣌ͷϏϧυ 🎉 ໰୊ͳ͘੒ޭ͢Δ `Text`ͷΑ͏ʹܕΛ໌֬ʹ͢Δ ͜ͱͰPreview࣌ͷΤϥʔΛճආͰ͖Δ
22. Opaque Type Λ Existential Type ʹஔ͖׵͑Δ ໭Γ஋Λany Viewʹ͢Δํ๏ ͨͩ͠ɺݺͼग़͠ݩͰܕΩϟετΛ ߦ͏ඞཁ͕͋Δ ௨ৗͷϏϧυ 🎉 ໰୊ͳ͘੒ޭ͢Δ Preview࣌ͷϏϧυ 🎉 ໰୊ͳ͘੒ޭ͢Δ
23. ໰୊ͷݪҼΛߟ࡯͢Δ ʢࠜຊݪҼ͸ಥ͖ࢭΊΒΕ·ͤΜͰͨ͠😢ʣ
24. ໰୊ͷݪҼΛߟ࡯͢Δ ContentView.1.preview-thunk.swift ͱ͍͏ϑΝΠϧ͕ҎԼʹଘࡏ͢Δ ~/Library/Developer/Xcode/DerivedData/MakeViewFromSwitch- fghepcludbkyehbmhgmucvzdrxsk/Build/Intermediates.noindex/Previews/ MakeViewFromSwitch/Intermediates.noindex/MakeViewFromSwitch.build/ Debug-iphonesimulator/MakeViewFromSwitch.build/Objects-normal/arm64
25. ContentViewͷPreviewϏϧυ͕૸Δͱ͜ͷϑΝΠϧ͕ߋ৽͞ΕΔ
26. ྫ͑͹ɺany ErrorΛฦ͢Α͏ͳϝιουΛ࣮૷͢Δͱ
27. ContentView.1.preview-thunk.swift ΋ߋ৽͞ΕΔ
28. ໭Γ஋ΛOpaque Typeʹ͢Δͱ ͨͩ͠
29. ContentView.1.preview-thunk.swift ͔ΒgetErrorͷॲཧ͕ফ͑Δ
30. ໰୊ͷݪҼΛߟ࡯͢Δ ίϯύΠϧΤϥʔʹͳ࣮ͬͨ૷͸ Opaque Typeͩͬͨ ௚઀తͳݪҼ͔͸Θ͔Βͳ͍͕͜Ε͕ ໰୊ʹͳ͍ͬͯΔՄೳੑ͕͋Δ
31. ·ͱΊ Swift 5.9͔Β͸ if ͱ switch Λࣜͱͯ͠ѻ͑ΔΑ͏ʹͳͬͨ if / switch ࣜΛ༻͍ͯSwiftUIͷViewΛʢopaque typeͱͯ͠ʣฦ͢ͱ Preview࣌ͷϏϧυͰͷΈίϯύΠϧΤϥʔ͕ൃੜ͢Δ ҎԼͷ͍ͣΕ͔ͷํ๏Ͱ໰୊ͷରԠΛ͢Δ͜ͱ͕Ͱ͖Δ 1. @ViewBuilderΩʔϫʔυΛ෇༩͢Δ 2. Opaque typeͰ͸ͳ͍໌֬ͳܕΛฦ͢ʢText ͳͲʣ 3. Opaque Type Λ Existential Type ʹஔ͖׵͑Δ
32. ͋Γ͕ͱ͏͍͟͝·ͨ͠ʂ