Basic PHP Class doesn't recognized !!!

Hello,

I made my own Library in /App/Libraries directory, in my Lib, i inherited from basic php class. 

They are Iterator and Countable, but inside CI4 there are not recognized ! 

Code:

15 namespace app\Libraries;

...

22 class MasterCollection implements Iterator, Countable {
23     
24     protected $Items = array();
25  
26     public function count(): int 
27     {
28         return count($this->Items);     
29     }


Thanks !

\Iterator, \Countable
or
use Iterator;
use Countable;

Thanks ! it works...