class LayoutSectionItemList

class LayoutSectionItemList extends FieldItemList implements SectionListInterface {
    use SectionListTrait;
    
    /**
     * Numerically indexed array of field items.
     *
     * @var \Drupal\layout_builder\Plugin\Field\FieldType\LayoutSectionItem[]
     */
    protected $list = [];
    
    /**
     * {@inheritdoc}
     */
    public function getSections() {
        $sections = [];
        foreach ($this->list as $delta => $item) {
            $sections[$delta] = $item->section;
        }
        return $sections;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function setSections(array $sections) {
        $this->list = [];
        $sections = array_values($sections);
        
        /** @var \Drupal\layout_builder\Plugin\Field\FieldType\LayoutSectionItem $item */
        foreach ($sections as $section) {
            $item = $this->appendItem();
            $item->section = $section;
        }
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getEntity() {
        $entity = parent::getEntity();
        // Ensure the entity is updated with the latest value.
        $entity->set($this->getName(), $this->getValue());
        return $entity;
    }
    
    /**
     * {@inheritdoc}
     */
    public function preSave() {
        parent::preSave();
        // Loop through each section and reconstruct it to ensure that all default
        // values are present.
        foreach ($this->list as $item) {
            $item->section = Section::fromArray($item->section
                ->toArray());
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function equals(FieldItemListInterface $list_to_compare) {
        if (!$list_to_compare instanceof LayoutSectionItemList) {
            return FALSE;
        }
        // Convert arrays of section objects to array values for comparison.
        $convert = function (LayoutSectionItemList $list) {
            return array_map(function (Section $section) {
                return $section->toArray();
            }, $list->getSections());
        };
        return $convert($this) === $convert($list_to_compare);
    }
    
    /**
     * Overrides \Drupal\Core\Field\FieldItemListInterface::defaultAccess().
     *
     * @ingroup layout_builder_access
     */
    public function defaultAccess($operation = 'view', AccountInterface $account = NULL) {
        // @todo Allow access in https://www.drupal.org/node/2942975.
        return AccessResult::forbidden();
    }

}