code: func (t *TxStructure) GetInt64(key []byte) (int64, error) {
  	v, err := t.Get(key)
  	if err != nil || v == nil {
  		return 0, errors.Trace(err)
  	}
  
  	n, err := strconv.ParseInt(string(v), 10, 64)
  	return n, errors.Trace(err)
  }
docs: // GetInt64 gets the int64 value of a key.