anchor.diff:  }
   
   /// Enforces a *quiet* wait period between events.
  -class Debouncer<T> implements StreamTransformer {
  +class Debouncer<T> implements StreamTransformer<T, T> {
   
     final Duration _wait;
     final Duration _maxWait;
  
positive.code:             controller = new StreamController<T>(
                onListen: () {
                  subscription = input.listen((data) {
                
                    addData = _trailing;
                    lastData = data;
                    bool setTimer = false;
  
negative.code:       throw new ArgumentError('`maxWait` cannot be less than `wait`.');
      }
    }
  
    StreamTransformer<T, T> get _transformer =>
        new StreamTransformer<T, T>(
            (Stream<T> input, bool cancelOnError) {
  