Callback api for SwiftUI based on React's useEffect hook

Example.swift

struct Child: View {
    var count: Int
    
    var body: some View {
        Text("Child: \(count)")
            .useEffect(Int(floor(Double(count) / 2))) { source in
                // this only gets called when the source changes
                print("onAppear \(source)")
            }
    }
}

struct ContentView: View {
    @State var count: Int = 0
    
    @ViewBuilder var body: some View {
        Child(count: count)
        Stepper("Count: \(count)", value: $count)
    }
}

useEffect.swift

struct AsyncEffectView<Source: Hashable>: View {
    @State var observer: AnyCancellable? = nil
    var source: Source
    var action: (Source) -> AnyCancellable
    
    var body: some View {
        EmptyView()
            .onAppear {
                self.observer = self.action(self.source)
            }
            .onDisappear {
                self.observer?.cancel()
            }
            .id(source)
    }
}

extension View {
    func useEffect<Source: Hashable>(_ source: Source, perform action: @escaping (Source) -> Void) -> some View {
        return self
            .overlay(
                EmptyView().onAppear {
                    action(source)
                }
                .id(source)
            )
    }
    
    func useEffect<Source: Hashable>(_ source: Source, perform action: @escaping (Source) -> AnyCancellable) -> some View {
        return self
            .overlay(
                AsyncEffectView(source: source, action: action)
            )
    }
}