code: func (h *Hash) Scan(src interface{}) error {
  	srcB, ok := src.([]byte)
  	if !ok {
  		return fmt.Errorf("can't scan %T into Hash", src)
  	}
  	if len(srcB) != HashLength {
  		return fmt.Errorf("can't scan []byte of len %d into Hash, want %d", len(srcB), HashLength)
  	}
  	copy(h[:], srcB)
  	return nil
  }
docs: // Scan implements Scanner for database/sql.