What is the equivalent of Kotlin's Flow.flatMapLatest in Dart Stream?

Question

In Kotlin there is Flow.flatMapLatest() function that:

Returns a flow that switches to a new flow produced by transform function every time the original flow emits a value. When the original flow emits a new value, the previous flow produced by transform block is cancelled.

Is there an equivalent function for Dart's Stream?

Answer 1

Nothing existing, but it should be fairly easy to write.

import "dart:async";

extension StreamExpandLatest<S> on Stream<S> {
  Stream<T> expandLatest<T>(Stream<T> expand(S value)) {
    var result = StreamController<T>(sync: true);
    result.onListen = () {
      StreamSubscription<T>? current;
      StreamSubscription<S> sourceSubscription = this.listen((S data) {
        current?.cancel();
        try {
          current = expand(data).listen(result.add, onError: result.addError);
        } catch (e, s) {
          result.addError(e, s);
        }
      }, onError: (Object e, StackTrace s) {
        current?.cancel();
        result.addError(e, s);
      }, onDone: () {
        current?.cancel();
        result.close();
      });
      result
        ..onPause = () {
          sourceSubscription.pause();
          current?.pause();
        }
        ..onResume = () {
          current?.resume();
          sourceSubscription.resume();
        }
        ..onCancel = () {
          current?.cancel();
          sourceSubscription.cancel();
        };
    };
    return result.stream;
  }
}