public function next($t) {
        if ($t !== NULL) array_push($this->front, $t);
        return empty($this->back) ? NULL : array_pop($this->back);
    }
public function next($t) {
        if ($t !== NULL) array_push($this->front, $t);
        return empty($this->back) ? NULL : array_pop($this->back);
    }
public function next ( $ t ) { if ( $ t !== NULL ) array_push ( $ this -> front , $ t ) ; return empty ( $ this -> back ) ? NULL : array_pop ( $ this -> back ) ; }
Move hole to the next element.
@param $t Element to fill hole with
@return Original contents of new hole.
Move hole to the next element .