code: func (w *DataFileWriter) Write(v interface{}) error {
  	w.blockCount++
  	err := w.datumWriter.Write(v, w.blockEnc)
  	return err
  }
docs: // Write out a single datum.
  //
  // Encoded datums are buffered internally and will not be written to the
  // underlying io.Writer until Flush() is called.