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avoid-unassigned-stream-subscriptions

added in: 1.13.0
warning
Pro+
preset: recommended

Warns when a stream subscription is not assigned to a variable.

Not assigning a stream subscription to a variable and not calling the cancel method when the subscription is not longer needed can lead to a memory leak.

Example​

❌ Bad:

void fn() {
  final stream = Stream.fromIterable([1, 2, 3]);

  // LINT: This stream subscription is not assigned to a variable and may cause a memory leak.
  stream.listen((event) {
    print(event);
  });
}

✅ Good:

void fn() {
  final stream = Stream.fromIterable([1, 2, 3]);

  final savedSubscription = stream.listen((event) {
    print(event);
  });

  ...

  savedSubscription.cancel(); // Correct, assigned and later disposed
}

Additional Resources​