src/main/java/io/reactivex/internal/operators/flowable/FlowableScalarXMap.java
public static <T, U> Flowable<U> scalarXMap(final T value, final Function<? super T, ? extends Publisher<? extends U>> mapper) {
        return RxJavaPlugins.onAssembly(new ScalarXMapFlowable<T, U>(value, mapper));
    }
public static <T, U> Flowable<U> scalarXMap(final T value, final Function<? super T, ? extends Publisher<? extends U>> mapper) {
        return RxJavaPlugins.onAssembly(new ScalarXMapFlowable<T, U>(value, mapper));
    }
public static < T , U > Flowable < U > scalarXMap ( final T value , final Function < ? super T , ? extends Publisher < ? extends U > > mapper ) { return RxJavaPlugins . onAssembly ( new ScalarXMapFlowable < T , U > ( value , mapper ) ) ; }
Maps a scalar value into a Publisher and emits its values.

@param <T> the scalar value type
@param <U> the output value type
@param value the scalar value to map
@param mapper the function that gets the scalar value and should return
a Publisher that gets streamed
@return the new Flowable instance
Maps a scalar value into a Publisher and emits its values .