Stream<T>.fromIterable constructor Null safety

Stream<T>.fromIterable(
  1. Iterable<T> elements
)

Creates a stream that gets its data from elements.

The iterable is iterated when the stream receives a listener, and stops iterating if the listener cancels the subscription, or if the Iterator.moveNext method returns false or throws. Iteration is suspended while the stream subscription is paused.

If calling Iterator.moveNext on elements.iterator throws, the stream emits that error and then it closes. If reading Iterator.current on elements.iterator throws, the stream emits that error, but keeps iterating.

Can be listened to more than once. Each listener iterates elements independently.

Example:

final numbers = [1, 2, 3, 5, 6, 7];
final stream = Stream.fromIterable(numbers);

Implementation

factory Stream.fromIterable(Iterable<T> elements) =>
    Stream<T>.multi((controller) {
      Iterator<T> iterator;
      try {
        iterator = elements.iterator;
      } catch (e, s) {
        controller.addError(e, s);
        controller.close();
        return;
      }
      var zone = Zone.current;
      var isScheduled = true;

      void next() {
        if (!controller.hasListener || controller.isPaused) {
          // Cancelled or paused since scheduled.
          isScheduled = false;
          return;
        }
        bool hasNext;
        try {
          hasNext = iterator.moveNext();
        } catch (e, s) {
          controller.addErrorSync(e, s);
          controller.closeSync();
          return;
        }
        if (hasNext) {
          try {
            controller.addSync(iterator.current);
          } catch (e, s) {
            controller.addErrorSync(e, s);
          }
          if (controller.hasListener && !controller.isPaused) {
            zone.scheduleMicrotask(next);
          } else {
            isScheduled = false;
          }
        } else {
          controller.closeSync();
        }
      }

      controller.onResume = () {
        if (!isScheduled) {
          isScheduled = true;
          zone.scheduleMicrotask(next);
        }
      };

      zone.scheduleMicrotask(next);
    });