public number Ds\Deque::sum( void )

<?php 
   deque = new \Ds\Deque([5, 8, 1, 7, 3, 1]);   echo("The elements in deque: \n");   print_r(deque); 

   echo("The sum of all deque elements: "); 
   var_dump($deque->sum()); 
?>