dart-lang/stream_transform

Dart utility methods to create StreamTransfomer instances to manipulate Streams

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
​		asyncMapSample
​		buffer
​		sample
​		debounceBuffer
​		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)));