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RxDart vs FxDart › #5 · Unique visitors, first visit kept

Unique visitors, first visit kept

Toss-up

• fx
• uniqBy
• map

Requirement

Today's visit log holds eight visits by four accounts. Keep each user's first visit only — deduping across the whole log, not just adjacent entries — and print who they are, when they first arrived, and the unique count. The data is in the code; both versions must print the lines shown under Expected output.

ana — first visit 09:02
ben — first visit 09:15
cho — first visit 10:05
dee — first visit 11:01
4 unique visitors in 8 visits

Side by side

Why they differ

This is one of RxDart's best matches for an FxDart operator. Plain Stream.distinct only compares adjacent events (FxDart's uniqAdjacent is the same idea), so RxDart adds distinctUnique: dedup across the whole stream, first occurrence kept — exactly uniqBy's contract. Both maintain a seen-set for the stream's lifetime, both preserve arrival order, and ana's 09:40 and 11:48 revisits vanish identically on both sides.

The remaining difference is ergonomic, not semantic. "Same visitor" is one key function for uniqBy — (v) => v.user — while distinctUnique asks for a matched equals + hashCode pair, two closures that must agree with each other. That is a mild inconvenience, not a model gap, and the async main is the usual stream overhead on fixed data. Verdict: a tie — the global-dedup operator exists on both sides and behaves the same way.