code: func getMode(s string) (int, error) {
  	switch {
  	case strings.HasPrefix(s, "$argon2d"):
  		return ModeArgon2d, nil
  	case strings.HasPrefix(s, "$argon2id"):
  		return ModeArgon2id, nil
  	case strings.HasPrefix(s, "$argon2i"):
  		return ModeArgon2i, nil
  	default:
  		return -1, ErrDecodingFail
  	}
  }
docs: // getMode tries to extract the mode from an Argon2 encoded string.