Swift Combine and iOS version limitations?

Question

For example AppTrackingTransparency exists in iOS 14+ but an app supports iOS 13+.

I used the following code:

@available(iOS 14, *)
    func requestATTPermissions() ->
    Future<ATTrackingManager.AuthorizationStatus, Never> {
    ...
}

if #available(iOS 14, *) {
            requestATTPermissions()
                .sink { [weak self] _ in
                    self?.completion?()
                }
                .store(in: &combineSubscriptionCollector.subscriptions)
        } else {
            completion?()
        }

But is it possible to move if #available(iOS 14, *) { into Future/AnyPublisher which in iOS 13 works like Just(()) and in iOS14+ requests ATT? Somehow like this:

Just(()).map {
  if #available(iOS 14, *) {
    return requestATTPermissions()
       .map { status in ... }
  } else {
    return Just(())
  }
}
.sink { [weak self] _ in
    self?.completion?()
}
.store(in: &combineSubscriptionCollector.subscriptions)

Answer 1

If I understand correctly, you just need to use flatMap instead of map:

Just(()).flatMap { _ in
    if #available(iOS 14, *) {
        return requestATTPermisions().map { status in
            // do not return anything here...
        }.eraseToAnyPublisher()
    } else {
        return Just(()).eraseToAnyPublisher()
    }
}
// .sink and .store...

Though I think this is easier to read and understand:

let publisher: AnyPublisher<(), Never>
if #available(iOS 14, *) {
    publisher = requestATTPermisions().map { status in
        // ...
    }.eraseToAnyPublisher()
} else {
    publisher = Just(()).eraseToAnyPublisher()
}
publisher.sink { ... }.store(in: ...)