Is best way to exchange variable?

Exchange-Variable.php

<?php
/*
 * Code A
 * ----
 * It also create temp variable, but not see in coding?
 */
list($a, $b) = array($b, $a);


/* 
 *Code B
 * ----
 * Not temp variable, better than Code A?
 */
$a = 7;
$b = 3;

$a = $a + $b; // a = (10)
$b = $a - $b; // b = (7)
$a = $a - $b; // a = (3)

/*
So:
---------
   $a = 3
   $b = 7
*/


/*
 * Reference: http://www.laruence.com/2011/03/24/858.html
 */
?>