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

    public function setPreviousItem(ProxySourceItem $item = null)
    {
        $lastPreviousItem = $this->previousItem;
        $this->previousItem = $item;
        if ($lastPreviousItem) {
            // We did have a item before...
            if (!$item || $item->id() !== $lastPreviousItem->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 setPreviousItem(ProxySourceItem $item = null)
 {
     parent::setPreviousItem($item);
     // expose additional metadata
     $this->data()->set('previous_project', $item);
 }