RemoteContentView.swift

struct RemoteContentView<Value, Empty, Progress, Failure, Content> : View where Empty : View,
                                                                             Progress : View,
                                                                              Failure : View,
                                                                              Content : View
{
    let empty: () -> Empty
    let progress: () -> Progress
    let failure: (_ error: Error, _ retry: @escaping () -> Void) -> Failure
    let content: (_ value: Value) -> Content

    init<R: RemoteContent>(remoteContent: R,
                           empty: @escaping () -> Empty,
                           progress: @escaping () -> Progress,
                           failure: @escaping (_ error: Error, _ retry: @escaping () -> Void) -> Failure,
                           content: @escaping (_ value: Value) -> Content) where R.ObjectWillChangePublisher == ObservableObjectPublisher,
                                                                                 R.Value == Value
    {
        self.remoteContent = AnyRemoteContent(remoteContent)

        self.empty = empty
        self.progress = progress
        self.failure = failure
        self.content = content
    }

    var body: some View {
        ZStack {
            switch remoteContent.loadingState {
                case .initial:
                    empty()

                case .inProgress:
                    progress()

                case .success(let value):
                    content(value)

                case .failure(let error):
                    failure(error) {
                        remoteContent.load()
                    }
            }
        }
        .onAppear {
            remoteContent.load()
        }
        .onDisappear {
            remoteContent.cancel()
        }
    }

    @ObservedObject private var remoteContent: AnyRemoteContent<Value>
}