code: func (nrt *NRTCachingDirectory) FileExists(name string) bool {
  	nrt.Lock() // synchronized
  	defer nrt.Unlock()
  	return nrt._fileExists(name)
  }
docs: // Returns how many bytes are being used by the RAMDirectory cache
  // func (nrt *NRTCachingDirectory) sizeInBytes() int64 {
  // 	return nrt.cache.sizeInBytes
  // }