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RxDart vs FxDart › #45 · Sample the gauge on each poll tick

Sample the gauge on each poll tick

Toss-up async

• fxEvents
• sampleOn

Requirement

A pressure gauge emits readings 1..8, one every 50 ms. A dashboard polls three times — at 125, 275 and 425 ms — and each poll should show the latest reading at that instant: 2, 5, then 8. Print the three polled readings after the streams close. Both schedules are simulated in the code; both versions must print the lines shown under Expected output.

poll 1: reading 2
poll 2: reading 5
poll 3: reading 8

Side by side

Why they differ

They don't. "The latest value at this instant" only exists in the push model — it presumes things arrive on their own — and both panels express it as the same one-operator sentence: the gauge stream, sampled by the poll stream. RxDart writes gauge().sample(polls()); fxdart writes fxEvents(gauge()).sampleOn(polls()). In both, the "what is current?" state lives inside the operator, each trigger emits the newest reading since the last one, and unsampled readings are simply dropped.

The pull pipelines still have no clock and no "current value" — that refusal stands. Instead, fxdart absorbs the Rx approach in a dedicated events layer: fxEvents is a thin wrapper chain over plain Streams (never an extension, so it collides with nothing) that owns the push-native verbs the pull side would not. RxDart's operator catalog remains far larger; this verb, fxdart speaks natively. And if each sampled reading were the start of real downstream work, .pull() hands the samples to the typed FxAsync pipeline, pulled on demand.