func IsNotFound(err error) bool {
	return isErrCode(err, ErrCodeKeyNotFound)
}

// IsExist returns true if and only if err is "key" already exists error.
func IsExist(err error) bool {
	return isErrCode(err, ErrCodeKeyExists)
}

// IsUnreachable returns true if and only if err indicates the server could not be reached.
func IsUnreachable(err error) bool {
	return isErrCode(err, ErrCodeUnreachable)
}