trait DateTimeDayTrait in Date time day 8

trait DateTimeDayTrait {

  /**
   * {@inheritdoc}
   */
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $elements = [];
    $day_separator = $this
      ->getSetting('day_separator');
    $time_separator = $this
      ->getSetting('time_separator');
    foreach ($items as $delta => $item) {
      $elements[$delta]['date'] = $this
        ->buildDateWithIsoAttribute($item->date);
      if (!empty($item->start_time)) {
        $elements[$delta]['day_separator'] = [
          '#plain_text' => $day_separator,
        ];
        $elements[$delta]['start_time'] = $this
          ->buildTimeWithAttribute($item->start_time);
        if (!empty($item->end_time)) {
          $elements[$delta]['time_separator'] = [
            '#plain_text' => $time_separator,
          ];
          $elements[$delta]['end_time'] = $this
            ->buildTimeWithAttribute($item->end_time);
        }
      }
    }
    return $elements;
  }

}