code: func newStandardDirectoryReader(directory store.Directory, readers []AtomicReader,
  	sis *SegmentInfos, termInfosIndexDivisor int, applyAllDeletes bool) *StandardDirectoryReader {
  	// log.Printf("Initializing StandardDirectoryReader with %v sub readers...", len(readers))
  	ans := &StandardDirectoryReader{segmentInfos: sis}
  	ans.DirectoryReaderImpl = newDirectoryReader(ans, directory, readers)
  	return ans
  }
docs: // TODO support IndexWriter