import SwiftUI struct ContentView2: View { @ObservedObject private var counter: Counter = .shared var body: some View { print("ContentView2.body") return VStack { HStack { Text("\(counter.count)") Button("+") { self.counter.increment() } } AView(value: Integer(42)) .padding() .border(Color.gray, width: 1) .padding() } } } private struct AView<Value: CustomStringConvertible>: View { let value: Value var body: some View { print("AView.body") return VStack { HStack { Text("\(Counter.shared.count), \(value.description)") Button("+") { Counter.shared.increment() } } BView(value: value) .padding() .border(Color.gray, width: 1) .padding() } } } private struct BView<Value: CustomStringConvertible>: View { let value: Value var body: some View { print("BView.body") return HStack { Text("\(Counter.shared.count), \(value.description)") Button("+") { Counter.shared.increment() } } } } private final class Counter: ObservableObject { @Published private(set) var count: Int = 0 func increment() { count += 1 } static let shared: Counter = .init() } final class Integer: Hashable, CustomStringConvertible { let value: Int init(_ value: Int) { self.value = value } static func == (lhs: Integer, rhs: Integer) -> Bool { lhs.value == rhs.value } func hash(into hasher: inout Hasher) { value.hash(into: &hasher) } var description: String { value.description } }
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