anchor.diff:        });
         return completer.future;
       };
  -    if (_isClosed) return _completeWithClosedException(completer);
  +    if (closed) return _completeWithClosedException(completer);
       List request = new List(3);
       request[0] = _FileUtils.READ_LIST_REQUEST;
       request[1] = _id;
  
positive.code:   Future<int> position() {
      _ensureFileService();
      Completer<int> completer = new Completer<int>();
      if (_isClosed) return _completeWithClosedException(completer);
      List request = new List(2);
      request[0] = _FileUtils.POSITION_REQUEST;
      request[1] = _id;
  
negative.code:     }
    }
  
    bool get closed() => _id == 0;
  
    void _checkNotClosed() {
      if (closed) {
        throw new FileIOException("File closed '$_name'");
      }
    }
  