Returns a publisher as a class instance.
- iOS 13.0+
- macOS 10.15+
- Mac Catalyst 13.0+
- tvOS 13.0+
- watchOS 6.0+
- Xcode 11.0+
A class instance that republishes its upstream publisher.
The downstream subscriber receieves elements and completion states unchanged from the upstream publisher. Use this operator when you want to use reference semantics, such as storing a publisher instance in a property.