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final class Parent: ObservableObject { @Published var child: Child init(child: Child) { self.child = child } } final class Child: ObservableObject { @Published var age: Int init(age: Int) { self.age = age } func haveBirthday() { age += 1 } } /FTUFE0CTFSWBCMF0CKFDU 3FQSPEVDFUIFJTTVFPG0CTFSWBCMF0CKFDU

/FTUFE0CTFSWBCMF0CKFDU 3FQSPEVDFUIFJTTVFPG0CTFSWBCMF0CKFDU final class Parent: ObservableObject { @Published var child: Child init(child: Child) { self.child = child } } final class Child: ObservableObject { @Published var age: Int init(age: Int) { self.age = age } func haveBirthday() { age += 1 } } struct BirthdayView: View { @StateObject var parent = Parent(child: Child(age: 1)) var body: some View { Text("child is \(parent.child.age) years old") Button("Have Birthday", action: { parent.child.haveBirthday() }) } }

final class Parent: ObservableObject { @Published var child: Child private var cancellables = Set() init(child: Child) { self.child = child child.objectWillChange.sink { [weak self] in self?.objectWillChange.send() } .store(in: &cancellables) } } final class Child: ObservableObject { @Published var age: Int init(age: Int) { self.age = age } func haveBirthday() { age += 1 } } /FTUFE0CTFSWBCMF0CKFDU 'JYUIFJTTVFPG0CTFSWBCMF0CKFDU

final class Parent: ObservableObject { @Published var child: Child private var cancellables = Set() init(child: Child) { self.child = child child.objectWillChange.sink { [weak self] in self?.objectWillChange.send() } .store(in: &cancellables) } } final class Child: ObservableObject { @Published var age: Int init(age: Int) { self.age = age } func haveBirthday() { age += 1 } } struct BirthdayView: View { @StateObject var parent = Parent(child: Child(age: 1)) var body: some View { Text("child is \(parent.child.age) years old") Button("Have Birthday", action: { parent.child.haveBirthday() }) } } /FTUFE0CTFSWBCMF0CKFDU 'JYUIFJTTVFPG0CTFSWBCMF0CKFDU

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@Observable final class Parent { var child: Child init(child: Child) { self.child = child } } @Observable final class Child { var age: Int init(age: Int) { self.age = age } func haveBirthday() { age += 1 } } /FTUFE!0CTFSWBCMF 8JMMUIFJTTVFCFSFQSPEVDFE

5IFJTTVFJTSFTPMWFE @Observable final class Parent { var child: Child init(child: Child) { self.child = child } } @Observable final class Child { var age: Int init(age: Int) { self.age = age } func haveBirthday() { age += 1 } } struct BirthdayView: View { @State var parent = Parent(child: Child(age: 1)) var body: some View { Text("child is \(parent.child.age) years old") Button("Have Birthday", action: { parent.child.haveBirthday() }) } } /FTUFE!0CTFSWBCMF

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*OMJOF!0CTFSWBCMF.BDSP final class Child { @ObservationTracked var age: Int init(age: Int) { self.age = age } func haveBirthday() { age += 1 } @ObservationIgnored private let _$observationRegistrar = Observation.ObservationRegistrar() internal nonisolated func access( keyPath: KeyPath ) { _$observationRegistrar.access(self, keyPath: keyPath) } internal nonisolated func withMutation( keyPath: KeyPath, _ mutation: () throws -> MutationResult ) rethrows -> MutationResult { try _$observationRegistrar.withMutation(of: self, keyPath: keyPath, mutation) } } extension Child: Observation.Observable { }

*OMJOF!0CTFSWBUJPO5SBDLFE.BDSP final class Child { var age: Int{ @storageRestrictions(initializes: _age) init(initialValue) { _age = initialValue } get { access(keyPath: \.age) return _age } set { withMutation(keyPath: \.age) { _age = newValue } } } … }

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