Solution for propagating changes from nested ObservableObjects

Example.swift

class TrackViewModel {
    private let nestedViewModel: PlaybackViewModel
    
    private var propagation: Any?
    
    init(nestedViewModel: PlaybackViewModel) {
        self.nestedViewModel = nestedViewModel
        
        propagation = nestedViewModel.propagateWeakly(to: self)
    }
    
    ...
}

Publisher+propagateWeakly.swift

import Combine

extension ObservableObject {
    public func propagateWeakly<InputObservableObject>(
        to inputObservableObject: InputObservableObject
    ) -> AnyCancellable where
        InputObservableObject: ObservableObject,
        InputObservableObject.ObjectWillChangePublisher == ObservableObjectPublisher
    {
        objectWillChange.propagateWeakly(to: inputObservableObject)
    }
}

extension Publisher where Failure == Never {
    public func propagateWeakly<InputObservableObject>(
        to inputObservableObject: InputObservableObject
    ) -> AnyCancellable where
        InputObservableObject: ObservableObject,
        InputObservableObject.ObjectWillChangePublisher == ObservableObjectPublisher
    {
        sink { [weak inputObservableObject] _ in
            inputObservableObject?.objectWillChange.send()
        }
    }
}