Foo

foo.java

// uni
public interface Uni<T> {
  static Uni<T> fromCompletionStage(CompletionStage<T> foo);
  CompletionStage<T> subscribeToCompletionStage(); // start the execution eagerly (should it be named subscribeAndComplete)
  U to(Class<U> clazz); // converts to whatever like Mono
  U more(Class<U> clazz); // converts to whatever like Mono
  ...
  // add operators
}

public class UniImpl extends CompletionStageImp implements Uni {
  ..
}

class SomeMPAPI {
  CompletionStage<Foo> bar();
}

class SomeQuarkusAPI {
  Uni<Foo> baz() { } ;
}

class SomeUserCode {
  void someMethod() {
     fromCompletionStage(someMPAPI.bar()).uniWizbang();
     someQuarkusAPI.baz().to(Single.class).rxWizbang();
     someQuarkusAPI.more(ExtraOperators.class).extraOperatorWizbang();
     
     // alternative of parallel classes from MP
     someMPApi.unwrap(SomeQuarkusMPApi.class).bar().uniWizbang();
  }
}
     
//options
// [ ] Add a unwrap() on Uni to allow "more" operators

interface Multi extends Flow.Publisher {
  // add operators
  static Multi<T> fromPublisher(Flow.Publisher<T> foo);
  U to(Class<U> clazz); // converts to whatever like Flux
}