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RxDart vs FxDart › #15 · Report only status changes

Report only status changes

Toss-up

• fx
• uniqAdjacent
• uniq
• map

Requirement

A health-check feed reports ok, ok, warn, warn, ok, ok, ok — mostly repetition. Print one status now line per run (three lines), then a single statuses seen: line listing every distinct status in first-seen order. The data is in the code; both versions must print the lines shown under Expected output.

status now: ok
status now: warn
status now: ok
statuses seen: ok, warn

Side by side

Why they differ

Adjacent deduplication — "tell me when the value changes" — is one value of remembered state in either model, and the two sides are line-for-line twins. The only trap is naming, and it cuts in opposite directions. On the stream side, plain Stream.distinct is already adjacent-only — RxDart adds distinctUnique for the global version many people expect distinct to be. FxDart names it the other way around: uniq is global, like every collection library's uniq, and uniqAdjacent says the adjacent-ness out loud.

Both pairs are shown above on purpose: run-collapsing with distinct / uniqAdjacent, the seen-anywhere summary with distinctUnique / uniq. Note what the global versions cost in each model — a growing "seen" set either way, but the stream one must hold it for the (potentially unbounded) life of a subscription, which is why RxDart makes the global form the opt-in. On a finite feed like this the models don't separate at all: a tie.