public void Ds\Deque::allocate( int $capacity )

<?php 
   deque = new \Ds\Deque();    var_dump(deque->capacity()); 

   deque->allocate(20);    var_dump(deque->capacity()); 
?>

<?php 
   deque = new \Ds\Deque();    var_dump(deque->capacity());  

   deque->allocate(50);   var_dump(deque->capacity());  

   deque->allocate(60);   var_dump(deque->capacity()); 
?>