public function get_key_list() {
        $keys = array();
        foreach ($this->collection as $node) {
            $keys[] = $node->key;
        }
        return $keys;
    }
public function get_key_list() {
        $keys = array();
        foreach ($this->collection as $node) {
            $keys[] = $node->key;
        }
        return $keys;
    }
public function get_key_list ( ) { $ keys = array ( ) ; foreach ( $ this -> collection as $ node ) { $ keys [ ] = $ node -> key ; } return $ keys ; }
Return a list of all the keys of all the nodes.
@return array the keys.
Return a list of all the keys of all the nodes .