Closure Question

closure.php

<?php

/**
*  What will the following code output? (No cheating!)
*/

class Test {
	private $a;
	private $b;
	public function getFunction()
	{
		$a = $this->a;
		$b = $this->b;
		return function() use ($a, $b) {
			return isset($a) && isset($b) ? $a + $b : 11;
		};
	}
	public function __set($name, $value) {
		$this->$name = $value + 20;
	}
}

$obj = new Test();
$a = 10;
$b = 20;

$function = $obj->getFunction();

$obj->a = $a;
$obj->b = $b;

echo call_user_func($function);

$function = $obj->getFunction();

echo call_user_func($function);

?>