Method startWith

src/main/java/io/reactivex/rxjava3/core/Flowable.java:15763–15770

Returns a Flowable which first runs the other CompletableSource then the current Flowable if the other completed normally. Ba

(@NonNull CompletableSource other)

     * @since 3.0.0
     */
    @CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    @BackpressureSupport(BackpressureKind.FULL)
    public final Flowable<T> startWith(@NonNull CompletableSource other) {
        Objects.requireNonNull(other, "other is null");
        return Flowable.concat(Completable.wrap(other).<T>toFlowable(), this);
    }

    /**
     * Returns a {@code Flowable} which first runs the other {@link SingleSource}