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