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A collection of utilities to transform and manipulate streams.

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Extension methods on Stream adding common transform operators.

Operators #

asyncMapBuffer, asyncMapSample, concurrentAsyncMap #

Alternatives to asyncMap. asyncMapBuffer prevents the callback from overlapping execution and collects events while it is executing. asyncMapSample prevents overlapping execution and discards events while it is executing. concurrentAsyncMap allows overlap and removes ordering guarantees for higher throughput.

Like asyncMap but events are buffered in a List until previous events have been processed rather than being called for each element individually.

asyncWhere #

Like where but allows an asynchronous predicate.

audit #

Waits for a period of time after receiving a value and then only emits the most recent value.

buffer #

Collects values from a source stream until a trigger stream fires and the collected values are emitted.

combineLatest, combineLatestAll #

Combine the most recent event from multiple streams through a callback or into a list.

debounce, debounceBuffer #

Prevents a source stream from emitting too frequently by dropping or collecting values that occur within a given duration.

followedBy #

Appends the values of a stream after another stream finishes.

merge, mergeAll, concurrentAsyncExpand #

Interleaves events from multiple streams into a single stream.

scan #

Scan is like fold, but instead of producing a single value it yields each intermediate accumulation.

startWith, startWithMany, startWithStream #

Prepend a value, an iterable, or a stream to the beginning of another stream.

switchMap, switchLatest #

Flatten a Stream of Streams into a Stream which forwards values from the most recent Stream

takeUntil #

Let values through until a Future fires.

tap #

Taps into a single-subscriber stream to react to values as they pass, without being a real subscriber.

throttle #

Blocks events for a duration after an event is successfully emitted.

whereType #

Like Iterable.whereType for a stream.

Comparison to Rx Operators #

The semantics and naming in this package have some overlap, and some conflict, with the ReactiveX suite of libraries. Some of the conflict is intentional - Dart Stream predates Observable and coherence with the Dart ecosystem semantics and naming is a strictly higher priority than consistency with ReactiveX.

Rx Operator Category variation stream_transform
sample sample/throttleLast(Duration) sample(Stream.periodic(Duration), longPoll: false)
throttleFirst(Duration) throttle
sample(Observable) sample(trigger, longPoll: false)
debounce debounce/throttleWithTimeout(Duration) debounce
debounce(Observable) No equivalent
buffer buffer(boundary), bufferWithTime,bufferWithCount No equivalent
buffer(boundaryClosingSelector) buffer(trigger, longPoll: false)
RxJs extensions audit(callback) No equivalent
auditTime(Duration) audit
exhaustMap No equivalent
throttleTime(trailing: true) throttle(trailing: true)
throttleTime(leading: false, trailing: true) No equivalent
No equivalent? asyncMapBuffer
debounce(leading: true, trailing: false)
debounce(leading: true, trailing: true)

Getting a StreamTransformer instance #

It may be useful to pass an instance of StreamTransformer so that it can be used with stream.transform calls rather than reference the specific operator in place. Any operator on Stream that returns a Stream can be modeled as a StreamTransformer using the fromBind constructor.

final debounce = StreamTransformer.fromBind(
    (s) => s.debounce(const Duration(milliseconds: 100)));
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A collection of utilities to transform and manipulate streams.

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