code: func (f StructField) PutInBatch(batch *leveldb.Batch, val interface{}) (err error) {
  	b, err := rlp.EncodeToBytes(val)
  	if err != nil {
  		return err
  	}
  	batch.Put(f.key, b)
  	return nil
  }
docs: // PutInBatch marshals provided val and puts it into the batch.