class CommentFieldItemList

class CommentFieldItemList extends FieldItemList {
    
    /**
     * {@inheritdoc}
     */
    public function get($index) {
        // The Field API only applies the "field default value" to newly created
        // entities. In the specific case of the "comment status", though, we need
        // this default value to be also applied for existing entities created
        // before the comment field was added, which have no value stored for the
        // field.
        if ($index == 0 && empty($this->list)) {
            $field_default_value = $this->getFieldDefinition()
                ->getDefaultValue($this->getEntity());
            return $this->appendItem($field_default_value[0]);
        }
        return parent::get($index);
    }
    
    /**
     * {@inheritdoc}
     */
    public function offsetExists($offset) {
        // For consistency with what happens in get(), we force offsetExists() to
        // be TRUE for delta 0.
        if ($offset === 0) {
            return TRUE;
        }
        return parent::offsetExists($offset);
    }
    
    /**
     * {@inheritdoc}
     */
    public function access($operation = 'view', AccountInterface $account = NULL, $return_as_object = FALSE) {
        if ($operation === 'edit') {
            // Only users with administer comments permission can edit the comment
            // status field.
            $result = AccessResult::allowedIfHasPermission($account ?: \Drupal::currentUser(), 'administer comments');
            return $return_as_object ? $result : $result->isAllowed();
        }
        if ($operation === 'view') {
            // Only users with "post comments" or "access comments" permission can
            // view the field value. The formatter,
            // Drupal\comment\Plugin\Field\FieldFormatter\CommentDefaultFormatter,
            // takes care of showing the thread and form based on individual
            // permissions, so if a user only has ‘post comments’ access, only the
            // form will be shown and not the comments.
            $result = AccessResult::allowedIfHasPermission($account ?: \Drupal::currentUser(), 'access comments')->orIf(AccessResult::allowedIfHasPermission($account ?: \Drupal::currentUser(), 'post comments'));
            return $return_as_object ? $result : $result->isAllowed();
        }
        return parent::access($operation, $account, $return_as_object);
    }

}