dart: stop future with CancelableOperation

main.dart

import 'package:async/async.dart';

void main() async  {
  final cancellableOperation = CancelableOperation.fromFuture(operation());
  cancellableOperation.then((p0) => print('cancelable operation finished normally'),
      onCancel: () => print('cancelable operation was canceled'));
  await Future.delayed(Duration(seconds: 1)).then((_) {
    cancellableOperation.cancel();
    print('operation cancelled');
  });
}

Future<void> operation() async {
  await Future.delayed( Duration(seconds: 1));
  print('1');
  await Future.delayed( Duration(seconds: 1));
  print('2');
  await Future.delayed( Duration(seconds: 1));
  print('3');
  await Future.delayed( Duration(seconds: 1));
  print('4');
  await Future.delayed( Duration(seconds: 1));
  print('5');
}

you can't stop function execution with CancelableOperation