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Extension methods on Stream adding common transform 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.


Like where but allows an asynchronous predicate.


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


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.


Appends the values of a stream after another stream finishes.

merge, mergeAll, concurrentAsyncExpand

Interleaves events from multiple streams into a single stream.


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


Let values through until a Future fires.


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


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


Like Iterable.whereType for a stream.

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)));