/**
* @param array|\stekycz\collections\ICollection $items
* @return \stekycz\collections\ArrayObject
*/
public function addAll($items)
{
Collections::checkValidType($items);
$items = Collections::isArrayType($items) ? $items : $items->toArray();
$this->items = array_merge($this->items, $items);
return $this;
}