しくみから理解するSwiftUI

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͘͠Έ͔Βཧղ͢ΔSwiftUI 2019/09/18 iOSDC Reject Conference (Day. 2) twitter.com/kumamo_tone

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• iOS/AndroidΤϯδχΞ • Yahoo!ΧϨϯμʔ iOS։ൃ • ษڧձӡӦ • Bonﬁre iOSɺWWDC Extended ͳͲ • potatotips #65 ΋ΑΖ͘͠ • ϚΠϒʔϜ • ఱؾͷࢠ ۽ຊ ࿨ਖ਼ (@kumamo_tone)

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• ୈҰ෦: some View ΍ VStack/HStack Λ࣮ݱ͢Δػೳ • Implicit return from single expressions • Function Builder • Opaque Result Type • ୈೋ෦: @State ΍ @Binding Λ࣮ݱ͢Δػೳ • Property Wrappers • ૝ఆର৅ऀ • ؾܰʹཧղ͍ͨ͠ • SwiftUI ؾʹͳͬͯ͸͍Δ͚Ͳ͋·ΓखΛ෇͚Ε͍ͯͳ͍ TL;DR

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } }

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } public protocol View { associatedtype Body : View var body: Self.Body { get } } 7JFXϓϩτίϧͷ͜ͱ 7JFXϓϩτίϧͷఆٛ

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } TPNFͬͯԿʁ͆

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } TPNFͬͯԿʁ͆ ͜ͷதͰ͸ Կ͕ߦΘΕ͍ͯΔʁ

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } SFUVSOͲ͜ʹߦͬͨʁ ͜ͷதͰ͸ Կ͕ߦΘΕ͍ͯΔʁ TPNFͬͯԿʁ͆

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } SFUVSOͲ͜ʹߦͬͨʁ ʁ TPNFͬͯԿʁ͆ ͜ͷதͰ͸ Կ͕ߦΘΕ͍ͯΔʁ

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" Magic?

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" No.

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Swift5.1ʹ௥Ճ͞Εͨɺ3ͭͷ৽ػೳʹΑͬͯઆ໌Ͱ͖Δ • Implicit return from single expressions • Function builders • Opaque Result Type some View Λ࣮ݱ͢Δػೳ

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Swift5.1ʹ௥Ճ͞Εͨɺ3ͭͷ৽ػೳʹΑͬͯઆ໌Ͱ͖Δ • Swift Evolution: SE-0255 • Implicit return from single expressions • Swift Evolution: SE-XXXX • Function builders • Swift Evolution: SE-0244 • Opaque Result Type some View Λ࣮ݱ͢Δػೳ ͻͱͭΊʂ

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Implicit return from single expressions

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SE-0255: Implicit return from single expressions • ϝϦοτ • ͖ͬ͢Γ͢Δ ΫϩʔδϟͰ͸લ͔Βɺ͕ࣜͻͱ͔ͭ͠ͳ͍ͱ͖returnΛলུͰ͖ͨ let names = persons.map { $0.name }

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SE-0255: Implicit return from single expressions struct Rectangle { var width = 0.0, height = 0.0 var area: Double { width * height } } ؔ਺΍ Computed Property Ͱ΋OK ΫϩʔδϟͰ͸લ͔Βɺ͕ࣜͻͱ͔ͭ͠ͳ͍ͱ͖returnΛলུͰ͖ͨ • ϝϦοτ • ͖ͬ͢Γ͢Δ let names = persons.map { $0.name }

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } }

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struct ContentView: View { var body: some View { return VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } SFUVSO͕লུ͞Ε͍ͯͨ

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• Swift Evolution: SE-0255 • Implicit return from single expressions • Swift Evolution: SE-XXXX • Function builders (draft proposal) • Swift Evolution: SE-0244 • Opaque Result Type some View Λ࣮ݱ͢Δػೳ ;ͨͭΊʂ

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Function builders (draft proposal)

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• վߦ۠੾Γͷཁૉ͔ͨͪΒɺม਺એݴͱؔ਺ݺͼग़͠Λੜ੒͢Δ • @_functionBuilderΛ͚ͭͨؔ਺͸ɺFunction builderʹͳΔ SE-XXXX: Function Builders

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• վߦ۠੾Γͷཁૉ͔ͨͪΒɺม਺એݴͱؔ਺ݺͼग़͠Λੜ੒͢Δ • @_functionBuilderΛ͚ͭͨstruct͸ɺFunction builderʹͳΔ SE-XXXX: Function Builders // @TupleBuilder͸ // @_functionBuilderͱͯ͠Ͳ͔͜Ͱఆٛ @TupleBuilder func build() -> (Int, Int, Int) { 1 2 3 } func build() -> (Int, Int, Int) { let _a = 1 let _b = 2 let _c = 3 return TupleBuilder .buildBlock(_a, _b, _c) } ίϯύΠϥ͕ม׵

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } ఆٛΛݟΔ

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public struct VStack : View where Content : View { @inlinable public init(  alignment: HorizontalAlignment = .center, spacing: CGFloat? = nil, @ViewBuilder content: () -> Content) public typealias Body = Never } ఆٛΛݟΔ

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@_functionBuilder public struct ViewBuilder { public static func buildBlock (_ content: Content) -> Content where Content : View } Ҿ਺1ݸͰɺͦΕͱಉ͡ܕͷViewΛฦ͍ͯ͠Δ

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extension ViewBuilder { public static func buildBlock (_ c0: C0, _ c1: C1) -> TupleView<(C0, C1)> where C0 : View, C1 : View } Ҿ਺2ݸͰɺͦΕͱಉ͡ܕͷTupleView<(C0, C1)>Λฦ͍ͯ͠Δ

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extension ViewBuilder { public static func buildBlock (_ c0: C0, _ c1: C1) -> TupleView<(C0, C1)> where C0 : View, C1 : View } Ҿ਺2ݸͰɺͦΕͱಉ͡ܕͷTupleView<(C0, C1)>Λฦ͍ͯ͠Δ ʹ74UBDLͷҾ਺ͷਖ਼ମ

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extension ViewBuilder { public static func buildBlock(_ c0: C0, _ c1: C1, _ c2: C2) -> TupleView<(C0, C1, C2)> where C0 : View, C1 : View, C2 : View } 3ݸ൛

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extension ViewBuilder { public static func buildBlock(_ c0: C0, _ c1: C1, _ c2: C2, _ c3: C3) -> TupleView<(C0, C1, C2, C3)> where C0 : View, C1 : View, C2 : View, C3 : View } 4ݸ൛…

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extension ViewBuilder { public static func buildBlock(_ c0: C0, _ c1: C1, _ c2: C2, _ c3: C3, _ c4: C4, _ c5: C5, _ c6: C6, _ c7: C7, _ c8: C8, _ c9: C9) -> TupleView<(C0, C1, C2, C3, C4, C5, C6, C7, C8, C9)> where C0 : View, C1 : View, C2 : View, C3 : View, C4 : View, C5 : View, C6 : View, C7 : View, C8 : View, C9 : View } 10ݸ൛·Ͱ͋Δ

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struct ContentView: View { var body: some View { return VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } ͭ·Γ͜ͷϒϩοΫ͸

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struct ContentView: View { var body: some View { return VStack { return ViewBuilder.buildBlock( Text(item.title), Text(item.subtitle) .foregroundColor(Color.gray) } } } } ͜͏ղऍ͞ΕΔ

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ฦΓ஋ͷܕ͸ $5FYU $5FYUͳͷͰɺ 5VQMF7JFX 5FYU 5FYU ʹͳΔ struct ContentView: View { var body: some View { return VStack { return ViewBuilder.buildBlock( Text(item.title), Text(item.subtitle) .foregroundColor(Color.gray) } } } }

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ฦΓ஋ͷܕ͸ɺ74UBDLͷܕύϥϝʔλ$POUFOUʹΑͬͯ 74UBDL5VQMF7JFX 5FYU 5FYU ʹͳΔ struct ContentView: View { var body: some View { return VStack { return ViewBuilder.buildBlock( Text(item.title), Text(item.subtitle) .foregroundColor(Color.gray) } } } }

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struct ContentView: View { var body: some View { let hoge = VStack { return ViewBuilder.buildBlock( Text(item.title), Text(item.subtitle) .foregroundColor(Color.gray) ) } return hoge } } ద౰ͳม਺ʹ୅ೖͯ͠ɺ PQU$MJDL͢Δͱɺ ܕΛ֬ೝ͢Δ͜ͱ͕Ͱ͖·͢

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@_functionBuilder public struct NumsBuilder { public static func buildBlock(_ nums: Int...) -> [Int] { nums } } func printNums(@NumsBuilder numsBuilder: () -> [Int]) { numsBuilder().forEach { print($0) } } printNums { 1 2 3 } ࣗ෼Ͱͭ͘Δ͜ͱ΋Ͱ͖Δ

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Opaque Result Type

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• δΣωϦΫεͷΑ͏ͳ΋ͷ • some Protocol ͷΑ͏ͳܕ͕ Opaque Result Type • some View ͸  ʮ۩ମతͳܕ͸ެ։͠ͳ͍͚ͲɺViewϓϩτίϧʹద߹ͨ͠ԿΒ͔ͷܕʯ  Ͱ͋Δ͜ͱΛද͢ SE-0244: Opaque Result Type

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struct ContentView: View { var body: some View { return VStack { return ViewBuilder.buildBlock( Text(item.title), Text(item.subtitle) .foregroundColor(Color.gray) ) } } } 74UBDL5VQMF7JFX 5FYU 5FYU ͷ࣮ࡍͷܕ͸ɺ ͨͱ͑͹ɺTPNF7JFX ͕ͩɺ֎ଆ͔Βݟͨͱ͖͸7JFXͱͯ͠ৼΔ෣͏

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struct ContentView: View { var body: VStack> { return VStack ( return ViewBuilder.buildBlock( Text(item.title), Text(item.subtitle) .foregroundColor(Color.gray) ) } } } ۩ମܕΛࢦఆͯ͠΋0,

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struct ContentView: View { var body: VStack> { return VStack ( return ViewBuilder.buildBlock( Text(item.title), Text(item.subtitle) .foregroundColor(Color.gray) ) } } } ۩ମܕΛࢦఆͯ͠΋0, ͜ͷܗͳΒɺ΋͸΍4XJGUະຬͷจ๏Ͱ΋ҙຯ͕௨Δ

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ϝϦοτ • ͖ͬ͢Γ͢Δ SE-0244: Opaque Result Type

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ϝϦοτ • ͖ͬ͢Γ͢Δ SE-0244: Opaque Result Type VStack> ͦΕ͚ͩͰ͸ͳ͍ ʢ˞Computed property ͸ܕએݴΛলུͰ͖ͳ͍ʣ

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• ίϯύΠϧ࣌ʹԿΒ͔ͷܕͰ͋Δ͜ͱ͕֬ఆ͢Δ • ίϯύΠϧ࣌ʹ෼͔ΔͷͰɺ࣮ߦ࣌ʹύϑΥʔϚϯεϩε͕ͳ͍ SE-0244: Opaque Result Type

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SE-0244: Opaque Result Type func map(l: List , _ f: A -> B) -> List { switch l { case .Nil: return .Nil case let .Cons(x, xs): return cons(f(x), map(xs, f)) } } [1,2].map { $0 * 2 } δΣωϦΫεͷܕ͸  ֎ଆ͔Β࣮ࡍͷܕΛ  ࢦఆͯ֬͠ఆ͢Δ Opaque Result Type Ͱ͸  ಺ଆ͔Β࣮ࡍͷܕ͕֬ఆ͢Δ *OU*OU struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } 74UBDL 5VQMF7JFX 5FYU 5FYU

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struct ContentView: View { var body: View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } 7JFX͸QSPUPDPMͰɺ BTTPDJBUFEUZQFΛ΋ͭͷͰɺ ͜͏͸ॻ͚ͳ͍

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struct ContentView: View { var body: AnyView { AnyView(VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) }) } } ܕফڈ͸Ͱ͖Δ͕ɺ ύϑΥʔϚϯεϩε͕͋Δ

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·ͱΊ

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } SFUVSO͸ ࣜͭͳΒলུՄೳ

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } SFUVSO͸ ࣜͭͳΒলུՄೳ 'VODUJPO#VJMEFSʹΑͬͯɺ 7JFX#VJMEFSCVJME#MPDL 5FYU 5FYU ͱղऍ͞ΕΔ ࣮ࡍͷܕ͸ɺ74UBDL5VQMF7JFX 5FYU 5FYU

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struct ContentView: View { var body: some View { VStack { Text(item.title) Text(item.subtitle) .foregroundColor(Color.gray) } } } TPNF7JFX͸ 7JFXʹద߹͢Δ ԿΒ͔ͷܕͰ͋Δ͜ͱΛࣔ͢ 'VODUJPO#VJMEFSʹΑͬͯɺ 7JFX#VJMEFSCVJME#MPDL 5FYU 5FYU ͱղऍ͞ΕΔ ࣮ࡍͷܕ͸ɺ74UBDL5VQMF7JFX 5FYU 5FYU SFUVSO͸ ࣜͭͳΒলུՄೳ

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ୈҰ෦ some Viewฤ ׬

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ୈೋ෦ Property Wrappers ฤ

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struct ContentView: View { @State var isOn: Bool var body: some View { Toggle(isOn: $isOn) { if self.isOn { Text("On") } else { Text("Off") } }.frame(width: 200) } } #PPMܕͷ ϓϩύςΟ

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struct ContentView: View { @State var isOn: Bool var body: some View { Toggle(isOn: $isOn) { if self.isOn { Text("On") } else { Text("Off") } }.frame(width: 200) } } #PPMܕͷ ϓϩύςΟ UPHHMFΛͻͱͭ ΋ͭ7JFX

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struct ContentView: View { @State var isOn: Bool var body: some View { Toggle(isOn: $isOn) { if self.isOn { Text("On") } else { Text("Off") } }.frame(width: 200) } } !4UBUF ͬͯԿʁ

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struct ContentView: View { @State var isOn: Bool var body: some View { Toggle(isOn: $isOn) { if self.isOn { Text("On") } else { Text("Off") } }.frame(width: 200) } } JT0O ͬͯԿʁ !4UBUF ͬͯԿʁ

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struct ContentView: View { @State var isOn: Bool var body: some View { Toggle(isOn: $isOn) { if self.isOn { Text("On") } else { Text("Off") } }.frame(width: 200) } } JT0O ͬͯԿʁ !4UBUF ͬͯԿʁ QSPKFDUFE7BMVFΛ ฦ͢ԋࢉࢠ 1SPQFSUZ8SBQQFS

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• Swift Evolution: SE-0258 • Property Wrappers ViewόΠϯσΟϯάΛ࣮ݱ͢Δػೳ

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• ϓϩύςΟʔͷϥούʔ • தʹਅͷ஋͕แ·Ε͍ͯΔΠϝʔδ • ϓϩύςΟͷsetterͱgetterΛݺΜͩͱ͖ʹ͍ͨ͠ॲཧΛɺ  ผΫϥεʹҠৡ͢ΔσβΠϯύλʔϯΛ  ίϯύΠϥʔϨϕϧͰఏڙͯ͘͠ΕΔػೳ • Kotlin ͷ Delegated Properties ͱࣅ͍ͯΔ Property Wrappers

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struct Foo { private var _foo: Int? var foo: Int { get { if let value = _foo { return value } let initialValue = 1738 _foo = initialValue return initialValue } set { _foo = newValue } } } ஗ԆධՁ͢Δ ܭࢉܕϓϩύςΟ MB[ZWBSGPP ͱ͓ͳ͡ ܭࢉܕϓϩύςΟʹ ౎౓ܭࢉͯ͠ ݁ՌΛฦͨ͠Γ HFU ઃఆͨ͠ΓʢTFUʣ ͢Δ΋ͷ

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struct Foo { private var _foo: Int? var foo: Int { get { if let value = _foo { return value } let initialValue = 1738 _foo = initialValue return initialValue } set { _foo = newValue } } } ௕͍͠ଟ͍

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@propertyWrapper enum Lazy { case uninitialized(() -> Value) case initialized(Value) init(wrappedValue: @autoclosure @escaping () -> Value) { self = .uninitialized(wrappedValue)} var wrappedValue: Value { mutating get { switch self { case .uninitialized(let initializer): let value = initializer() self = .initialized(value) return value case .initialized(let value): return value }} set { self = .initialized(newValue) } }} δΣωϦΫε൛Λ࡞ͬͯ TFUUFSͱHFUUFSɺ όοΩϯάϑΟʔϧυ ʢXSBQQFE7BMVFʣ ʹؔ͢Δ৘ใΛɺ 1SPQFSUZ8SBQQFS ʹԡ͠ࠐΊΕ͹ʜ

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class Foo { @Lazy var foo: Int = 1738 } ࢖͏ଆ͸͖ͬ͢Γʂ

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class Foo { @Lazy var foo: Int = 1738 } private var _foo: Lazy = Lazy(wrappedValue: 1738) var foo: Int { get { return _foo.wrappedValue } set { _foo.wrappedValue = newValue } } ࣮ࡍʹ͸͜Μͳײ͡ͷίʔυʹల։͞ΕΔ

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@propertyWrapper // ͱ͘ʹҙຯ͸ͳ͍ struct Nyan { ... var projectedValue: String { return "ʹΌʔΜ" } } QSPKFDUFE7BMVF͕͋Ε͹

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class Hoge { @Nyan var foo: Int = 1738 func meow() { print($foo) } } Hoge().meow() // ʹΌʔΜ ͰऔΓग़ͤΔ ※ projectedValue ͕ఆٛ͞Εͯͳ͚Ε͹ Use of unresolved identiﬁer ‘$foo’ ʹͳΓ·ͨ͠ (Xcode 11 GM Seed1)

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• Property wrapper Ͱ͸  ϓϩύςΟʹؔ͢ΔॲཧΛଞͷܕʹҠৡͰ͖Δ • @Hoge var foo: Int ͱॻ͘ͱ  var _foo: Hoge ͱ var foo: Int ʹల։͞ΕΔ • foo ͸ _foo.wrappedValue ͱ౳Ձ • $foo ͸ _foo.projectedValue ͱ౳Ձ • SwiftUIͰ͸Ͳ͏͍͏;͏ʹ࢖ΘΕ͍ͯΔͷ͔ʁ Property Wrapper ·ͱΊ

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struct ContentView: View { @State var isOn: Bool var body: some View { Toggle(isOn: $isOn) { if self.isOn { Text("On") } else { Text("Off") } }.frame(width: 200) } } ͜Ε͸ 1SPQFSUZ8SBQQFS

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struct ContentView: View { @State var isOn: Bool var body: some View { Toggle(isOn: $isOn) { if self.isOn { Text("On") } else { Text("Off") } }.frame(width: 200) } } ͜Ε͸ 1SPQFSUZ8SBQQFS ී௨ʹݺͿͱ XSBQQFE7BMVF͕औΕΔ

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มߋΛݕ஌ɾ௨஌͢Δ #JOEJOH7BMVF /// A linked View property that instantiates a persistent state /// value of type `Value`, allowing the view to read and update its /// value. @available(iOS 13.0, OSX 10.15, tvOS 13.0, watchOS 6.0, *) @propertyWrapper public struct State : DynamicProperty { /// Initialize with the provided initial value. public init(wrappedValue value: Value) /// Initialize with the provided initial value. public init(initialValue value: Value) /// The current state value. public var wrappedValue: Value { get nonmutating set } /// Produces the binding referencing this state value public var projectedValue: Binding { get } }

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• Property wrapperͰget/set࣌ʹΠϕϯτͷൃߦΛߦ͏͜ͱʹΑΓɺ  ஋ͷಉظ΍View΁ͷόΠϯσΟϯάΛՄೳʹ͍ͯ͠Δʢ˞ʣ • $ Ͱ Binding͕औΓग़ͤΔ • BindingΛViewʹ౉͢ͱɺViewʹόΠϯσΟϯά͞ΕΔ  ʢมߋͨ͠ͱ͖ʹΠϕϯτΛൃߦͨ͠Γɺ  ɹมߋΛݕ஌ͯ͠Viewʹ൓өͯ͘͠ΕͨΓ͢Δʣ SwiftUIͰ͍ͯ͠Δ͜ͱ ·ͱΊ ʢ˞ʣਪଌɻIF΍υΩϡϝϯτɺWWDCͷηογϣϯͷ಺༰ͳͲ͔Βਪଌ͢Δ͔͠ͳ͍

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• ެࣜ࡞ྫ • UserDefaults • Clamping • ϥΠϒϥϦ • ValidatedPropertyKit • DIAttribute ྫΛ৭ʑΈͯΠϝʔδΛ͔ͭ΋͏

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enum GlobalSettings { @UserDefault(key: "FOO_FEATURE_ENABLED", defaultValue: false) static var isFooFeatureEnabled: Bool @UserDefault(key: "BAR_FEATURE_ENABLED", defaultValue: false) static var isBarFeatureEnabled: Bool } User Defaults ม਺ʹॻ͘ϊϦͰӬଓԽ

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@propertyWrapper struct UserDefault { let key: String let defaultValue: T var wrappedValue: T { get { return UserDefaults.standard.object(forKey: key) as? T ?? defaultValue } set { UserDefaults.standard.set(newValue, forKey: key) } } } γϯϓϧ ʢγϯϓϧ͗ͯ͢ෆཁઆ΋͋Δʣ User Defaultsʢ࣮૷ʣ

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Clamping struct Color { @Clamping(min: 0, max: 255) var red: Int = 127 @Clamping(min: 0, max: 255) var green: Int = 127 @Clamping(min: 0, max: 255) var blue: Int = 127 @Clamping(min: 0, max: 255) var alpha: Int = 255 } ஋Λ ʹ·ΔΊͯ͘ΕΔ

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var wrappedValue: V { get { return value } set { if newValue < min { value = min } else if newValue > max { value = max } else { value = newValue } } } @propertyWrapper struct Clamping { var value: V let min: V let max: V init(wrappedValue: V, min: V, max: V) { value = wrappedValue self.min = min self.max = max assert(value >= min && value <= max) } Clampingʢ࣮૷ʣ

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• SvenTiigi/ValidatedPropertyKit • https://github.com/SvenTiigi/ValidatedPropertyKit • @Validated(.isEmail)Ͱ  EϝʔϧΞυϨεͷόϦσʔγϣϯ͕Ͱ͖ͨΓ͢Δ • γϯϓϧ SvenTiigi/ValidatedPropertyKit

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SvenTiigi/ValidatedPropertyKit @Validated(.nonEmpty) var username: String? @Validated(.isEmail) var email: String? @Validated(.range(8...)) var password: String? @Validated(.greaterOrEqual(1)) var friends: Int? @Validated(.isURL && .hasPrefix("https")) var avatarURL: String?

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• tattn/DIAttribute • https://github.com/tattn/DIAttribute • AndroidͷDaggerͷΑ͏ͳΞϊςʔγϣϯϕʔεͰDIΛ࣮ݱ͢ΔϥΠ ϒϥϦ • γϯϓϧ tattn/DIAttribute

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tattn/DIAttribute DIResolver.register(ViewController.self, keyPath: \.apiClient, value: ProductionAPIClient()) DIResolver.register(ViewController.self, keyPath: \.apiClient, value: MockAPIClient())

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tattn/DIAttribute final class ViewController: UIViewController { @Inject(Self.self) var apiClient: APIClientProtocol } %*3FTPMWFSSFHJTUFSͰ ొ࿥ͨ͠஋͕࢖ΘΕΔ

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import Foundation @propertyWrapper public struct Inject { public init(_ type: Target.Type) {} public var wrappedValue: Value { DIResolver.resolve(Target.self)! } } SFTPMWFΛୟ͍͍ͯΔ͚ͩ

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SFHJTUFSͨ͠ͱ͖ʹ%*3FTPMWFS͕ΫϩʔδϟΛอ͓࣋ͯ͠Γɺ SFTPMWFͰ͸ɺอ࣋ͨ͠ΫϩʔδϟΛධՁͯ͠ฦ͢ public struct DIResolver { private static var factories: [ObjectIdentifier: [ObjectIdentifier: Factory]] = [:] public static func resolve( _ target: Target.Type = Target.self, value: Value.Type = Value.self) -> Value? { factories[.init(target)]?[.init(value)]?() as? Value } }

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ୈೋ෦ Property Wrappers ฤ ׬

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SwiftUI ͸Swift5.1ͷػೳʹΑ͖ͬͯͬ͢Γॻ͚ΔΑ͏ʹͳ͍ͬͯΔ • Swift Evolution: SE-0255: Implicit return from single expressions • Swift Evolution: SE-XXXX :Function builders • Swift Evolution: SE-0244: Opaque Result Type • Swift Evolution: SE-0258: Property Wrappers • ܅΋܅͚ͩͷ  ࠷ڧͷFunction Builders / Property WrappersΛ࡞ͬͯಆ͓͏ʂ ·ͱΊ

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• Swift Evolution • https://github.com/apple/swift-evolution/blob/master/proposals/0255-omit-return.md • https://github.com/apple/swift-evolution/blob/9992cf3c11c2d5e0ea20bee98657d93902d5b174/proposals/XXXX- function-builders.md • https://github.com/apple/swift-evolution/blob/master/proposals/0244-opaque-result-types.md • https://github.com/apple/swift-evolution/blob/master/proposals/0258-property-wrappers.md# References

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• SwiftUIͷຐ๏Λ࣮ݱ͢Δ࢓૊Έ (Custom Attributes, Function Builder) • https://qiita.com/kentrino/items/dc6e77a0ddd21187cc55 • SwiftUIͷίʔυΛಡΈղ͘ • https://blog.personal-factory.com/2019/06/07/understand-swiftui-code/ • Swift 5.1 ʹಋೖ͞ΕΔ Opaque Result Type ͱ͸Կ͔ • https://qiita.com/koher/items/338d2f2d0c4731e3508f • Opaque Result Typeͷղઆ • https://qiita.com/omochimetaru/items/f13fe3e54fab01648ba4 • SwiftUIͰ࢖༻͞Ε͍ͯΔSwift5.1ͷ৽ػೳ - ΫοΫύου։ൃऀϒϩά • https://techlife.cookpad.com/entry/2019/06/25/120000Qa • SwiftUIͷProperty Wrappersͱσʔλ΁ͷΞΫηεํ๏ • https://qiita.com/shiz/items/6eaf87fa79499623306a See Also

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Enjoy SwiftUI!