trait ConfigFormBaseTrait in Drupal 9

trait ConfigFormBaseTrait {

  /**
   * Retrieves a configuration object.
   *
   * @param string $name
   *   The name of the configuration object to retrieve. The name corresponds to
   *   a configuration file. For @code \Drupal::config('book.admin') @endcode,
   *   the config object returned will contain the contents of book.admin
   *   configuration file.
   *
   * @return \Drupal\Core\Config\Config|\Drupal\Core\Config\ImmutableConfig
   *   An editable configuration object if the given name is listed in the
   *   getEditableConfigNames() method or an immutable configuration object if
   *   not.
   */
  protected function config($name) {

    /** @var \Drupal\Core\Config\ConfigFactoryInterface $config_factory */
    if (method_exists($this, 'configFactory')) {
      $config_factory = $this
        ->configFactory();
    }
    elseif (property_exists($this, 'configFactory')) {
      $config_factory = $this->configFactory;
    }
    if (!isset($config_factory) || !$config_factory instanceof ConfigFactoryInterface) {
      throw new \LogicException('No config factory available for ConfigFormBaseTrait');
    }
    if (in_array($name, $this
      ->getEditableConfigNames())) {

      // Get a mutable object from the factory.
      $config = $config_factory
        ->getEditable($name);
    }
    else {
      $config = $config_factory
        ->get($name);
    }
    return $config;
  }

  /**
   * Gets the configuration names that will be editable.
   *
   * @return array
   *   An array of configuration object names that are editable if called in
   *   conjunction with the trait's config() method.
   */
  protected abstract function getEditableConfigNames();

}