RxDart vs FxDart › #8 · Drop the nulls, keep the values

Drop the nulls, keep the values

Toss-up

• fx
• compact
• map

Requirement

A battery monitor produced nine voltage samples, three of which the sensor dropped (null). Discard the failures, print each surviving sample formatted to one decimal, then report how many were dropped. The data is in the code; both versions must print the lines shown under Expected output.

3.4 V
3.9 V
4.1 V
3.7 V
4.4 V
4.0 V
Dropped 3 empty samples

Side by side

Why they differ

whereNotNull is compact — the same operator wearing each library's naming convention. Both do the thing that matters beyond filtering: they narrow the static type, turning a double? element type into double, so the toStringAsFixed call downstream needs no null checks and no !. Filter and promote in one word, on both sides.

So the verdict is a tie on vocabulary — and the honest remainder is only the delivery model. The stream version lifts a list it already holds into a Stream and awaits the collection back out; the pull version finishes before the stream version's first await would have run. On a nine-element fixed list that overhead is small enough to shrug at, which is exactly the difference between this example and the verdict-carrying aggregation in Total the valid even amounts: here the point is that the two libraries agree, right down to the type promotion.