Sculpin\Contrib\ProxySourceCollection\ProxySourceItem::setNextItem PHP Method

    public function setNextItem(ProxySourceItem $item = null)
    {
        $lastNextItem = $this->nextItem;
        $this->nextItem = $item;
        if ($lastNextItem) {
            // We did have a item before...
            if (!$item || $item->id() !== $lastNextItem->id()) {
                // But we no longer have a item or the item we
                // were given does not have the same ID as the
                // last one we had...
                $this->reprocess();
            }
        } elseif ($item) {
            // We didn't have a item before but we do now...
            $this->reprocess();
        }
    }

 public function setNextItem(ProxySourceItem $item = null)
 {
     parent::setNextItem($item);
     // expose additional metadata
     $this->data()->set('next_project', $item);
 }