ObservableOptional.swift

import Combine

final class ObservableOptional<Wrapped: ObservableObject>: ObservableObject {
    let objectWillChange = ObservableObjectPublisher()
    var value: Wrapped? {
        willSet {
            objectWillChange.send()
            updateSubscription(newValue)
        }
    }

    private var subscriber: AnyCancellable?

    init(_ value: Wrapped? = nil) {
        self.value = value
        updateSubscription(value)
    }

    private func updateSubscription(_ value: Wrapped?) {
        subscriber?.cancel()
        if let publisher = value?.objectWillChange {
            subscriber = publisher.sink { [weak self] _ in
                self?.objectWillChange.send()
            }
        }
    }
}

// MARK: Example

import SwiftUI

class ThingsResult: ObservableObject {
    let initial: String
    @Published var later: String? = nil
    init(_ initial: String) {
        self.initial = initial
    }
}

func doThings() -> ThingsResult {
    let rv = ThingsResult("some stuff")
    Timer.scheduledTimer(withTimeInterval: 2, repeats: false) { [weak rv] _ in
        rv?.later = "more stuff"
    }
    return rv
}

class ResultsProxy: ObservableObject {
    var objectWillChange = ObservableObjectPublisher()
    var value: ThingsResult? {
        willSet {
            objectWillChange.send()
            if let childPublisher = newValue?.objectWillChange {
                objectWillChange = childPublisher
            }
        }
    }
}

struct ContentView: View {
    @ObservedObject var result = ObservableOptional<ThingsResult>()

    var body: some View {
        VStack {
            if self.result.value != nil {
                Text("Result").bold()
                Text(self.result.value!.initial)
                Text(self.result.value!.later ?? "waiting for more stuff...")
            } else {
                Button(action: {
                    self.result.value = doThings()
                }) {
                    Text("Do things")
                }
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}