anchor.diff:    @override
     void dispose() {
       final Iterable<StreamSubscription<Store>> subscriptions =
  -        _streamSubscriptions.values;
  +      _streamSubscriptions.values;
       for (final StreamSubscription<Store> subscription in subscriptions)
         subscription.cancel();
       _streamSubscriptions.clear();
  
positive.code: }
  
  /// State for a [StoreWatcher] widget.
  class StoreWatcherState extends State<StoreWatcher>
      with StoreWatcherMixin<StoreWatcher> {
    // If you get these errors from the analyzer, then you need to add a file
    // analysis_options.yaml like you find in the root of this repo.
    // [error] The class 'StoreWatcherMixin' cannot be used as a mixin because it
    // extends a class other than Object.
    // [error] The class 'StoreWatcherMixin' cannot be used as a mixin because it
    // references 'super'
  
    final Map<StoreToken, Store> _storeTokens = <StoreToken, Store>{};
  
  
negative.code: /// Listens to changes in a number of different stores.
  ///
  /// Used by [StoreWatcher] to track which stores the widget is listening to.
  abstract class StoreWatcherMixin <T extends StatefulWidget> implements State<T>{
    final Map<Store, StreamSubscription<Store>> _streamSubscriptions = <Store, StreamSubscription<Store>>{};
  
    /// Start receiving notifications from the given store, optionally routed
    /// to the given function.
  