Tells the subscriber that a publisher of void elements is ready to receive further requests.
- iOS 13.0+
- macOS 10.15+
- Mac Catalyst 13.0+
- tvOS 13.0+
- watchOS 6.0+
- Xcode 11.0+
A Subscribers.Demand instance indicating how many more elements the subscriber expects to receive.
Void inputs and outputs when you want to signal that an event has occurred, but don’t need to send the event itself.