/**
* return a proxied SortList
*/
public function sort($sortList = null)
{
if (is_null($sortList)) {
if (is_null($this->sortList)) {
$this->sortList = new \ESQ\Sort\SortList();
}
} elseif ($sortList instanceof \ESQ\Sort\SortList) {
$this->sortList = $sortList;
} else {
throw new \InvalidArgumentException('first argument must be instance of SortList or null');
}
$proxy = new Proxy($this->sortList);
$search = $this;
return $proxy->register('back', function () use($search) {
return $search;
});
}