Publishes the first element of a stream, then finishes.
- iOS 13.0+Beta
- macOS 10.15+Beta
- Mac Catalyst 13.0+Beta
- tvOS 13.0+Beta
- watchOS 6.0+Beta
- Xcode 11.0+Beta
A publisher that only publishes the first element of a stream.
If this publisher doesn’t receive any elements, it finishes without publishing.