Recoverable fatal error when trying to run hook_query_TAG_alter() I used the approach provided here to reverse comments order in Drupal 8:

    /** Implements hook_query_TAG_alter().
 *
 * Alter comments query to order by DESC as well as the default ASC.
 */
function MYMODULENAME_query_comment_filter_alter(QueryAlterableInterface $query) {
  $orderby = &amp;$query-&gt;getOrderBy();

  // Sorting for threaded comments.
  if (isset($orderby['torder'])) {
    // Sort by root parent first, then normal threaded.
    $query-&gt;addExpression("SUBSTRING_INDEX(c.thread, '.', 1)", 'rparent');
    $orderby = array('rparent' =&gt; 'DESC') + $orderby;
  }
  // Sorting for flat comments.
  else if (isset($orderby['c.cid'])) {
    $direction = 'DESC';

    $orderby['c.cid'] = $direction;
    $orderby = array('c.created' =&gt; $direction) + $orderby;
  }
}


but I receive the followig error when run the module:


  Recoverable fatal error: Argument 1 passed to
  mymd_query_comment_filter_alter() must be an instance of
  QueryAlterableInterface, instance of
  Drupal\Core\Database\Query\PagerSelectExtender given, called in
  D:\wamp95\www\drupal83\core\lib\Drupal\Core\Extension\ModuleHandler.php
  on line 501 and defined in mymd_query_comment_filter_alter()


what is the problem and how should I solve it?
I used Drupal\Core\Database\Query\AlterableInterface $query as argument.

It solved the problem.