what is the use of the ampersand added to the front of the function call

[eluser]Unknown[/eluser]
Hi，
I read the CodeIgniter source code，found the is_loaded function defined in the Common.php file，as follow
function is_loaded($class = '')

And that function is called in Controller.php file：
$this->load->_base_classes =& is_loaded();
my question is why add the ampersand to is_loaded()，i think it is useless

[eluser]InsiteFX[/eluser]
It creates a reference to that object.

PHP.net - Passing by Reference

InsiteFX