Function Builders in Swift 5.1

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1. Function Builders in Swift 5.1 Christopher Rogers Twitter: @christorogers /

   GitHub: @ChristopherRogers

2. Function Builder ͱ͸ʁ ؔ਺ΛϏϧμʔߏจʹมߋͰ͖Δ৽ػೳ1 • Embedded Domain-Specific Language (eDSL) •

   SwiftUI ͷͨΊʁ • GM·ͰมΘΔՄೳੑ͕ߴ͍ 1 https://forums.swift.org/t/function-builders/25167

3. var body: some View { HStack { Image(uiImage: profile.image) Spacer()

   Text(profile.name) } }

4. var body: some View { /* return লུ */ HStack

   { // ͔͜͜Β͕ function builder ߏจ Image(uiImage: profile.image) Spacer() Text(profile.name) } } public HStack { public init(@ViewBuilder _ content: () -> Content) }

5. var body: some View { /* return লུ */ HStack

   { // ͔͜͜Β͕ function builder ߏจ Image(uiImage: profile.image) Spacer() Text(profile.name) } }

6. var body: some View { /* return লུ */ HStack

   { // ͔͜͜Β͕ function builder ߏจ let _v0 = Image(uiImage: profile.image) let _v1 = Spacer() let _v2 = Text(profile.name) return ViewBuilder.buildBlock(_v0, _v1, _v2) } }

7. • ܕΛఆٛ͢Δ • ܕͷએݴΛ @_functionBuilder Ͱम০͢Δ • ಛఆͷϝιουΛ࣮૷͢Δ • ४ڌ͢Δ

   protocol ͸ͳ͍ • ʢݱ࣌఺Ͱ͸ʣϝιου͸͢΂ͯ static • Ҿ਺ͱฦΓ஋ͷܕ͸͋Δఔ౓ࣗ༝ • ਂ͞༏ઌ୳ࡧͰࣜΛධՁͯ͠ม׵͍ͯ͘͠ @_functionBuilder public struct ViewBuilder { public static func buildBlock<Content>(_ content: Content) -> Content where Content: View }

8. buildBlock • །Ұඞਢͷϝιου • จʢ{}Λ࢖ͬͨͱ͜Ζʣ୯ҐͰม׵͢Δ • ͢΂ͯͷࣜΛ·ͱΊͯҾ਺ͱͯ͠ड͚औΔ • ՄมҾ਺ •

   ϝιου overload Ͱෳ਺࣮૷ let _v0 = Image(uiImage: profile.image) let _v1 = Spacer() let _v2 = Text(profile.name) return ViewBuilder.buildBlock(_v0, _v1, _v2)

9. buildExpression • ࣜ୯ҐͰม׵͢Δ͜ͱ͕Մೳ • ݱࡏ͸ར༻ෆՄ let _v0 = ViewBuilder.buildExpression(Image(uiImage: profile.image))

   let _v1 = ViewBuilder.buildExpression(Spacer()) let _v2 = ViewBuilder.buildExpression(Text(profile.name)) return ViewBuilder.buildBlock(_v0, _v1, _v2)

10. buildOptional • ࣮૷͢Ε͹ if จ͕࢖͑ΔΑ͏ʹͳΔ • Ҿ਺͸ Optional ܕʹ͢Δඞཁ͕͋Δ •

    ϝιου໊ʹ͍ͭͯٞ࿦த • beta 2 Ͱ͸ڍಈ͕࢓༷ͱҟͳΔ

11. if isEnabled { "hoge" } else { 42 }

12. var _v0Opt: String? var _v1Opt: Int? if isEnabled { _v0

    = "hoge" } else { _v1 = 42 } let _v0 = MyBuilder.buildOptional(_v0Opt) let _v1 = MyBuilder.buildOptional(_v1Opt)

13. buildEither • ৚݅ʹΑΒͣܕΛ֬ఆ͢Δ͜ͱ͕Ͱ͖Δ • first/second ύϥϝʔλϥϕϧͰ෼ذ͕ද͞ΕΔ • ݱࡏ͸ར༻ෆՄ let _v0:

    String if languageCode == "ja" { _v0 = MyBuilder.buildEither(first: "hoge") } else if languageCode == "en" { _v0 = MyBuilder.buildEither(second: MyBuilder.buildEither(first: "foo")) } else { _v0 = MyBuilder.buildEither(second: MyBuilder.buildEither(second: "")) }

14. ͦͷଞͷϝιου buildDo • do จͰಛఆͷڍಈΛಋೖ͢Δ৔߹ʹ༻͍Δ • buildBlockͷ୅ΘΓʹݺ͹ΕΔ buildFunction • ฦΓ஋ͷܕΛ࠷ޙʹม׵͢Δ৔߹ʹ༻͍Δ

    • Ұ൪࠷ޙʹbuildBlockͷ୅ΘΓʹݺ͹ΕΔ

15. ޚਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠