php an array of reference

I have two arrays. one will be added with arrays as children, another one keeps references to the array being added to the first one.

$list=array();
$stack=array();

in a for loop:

$list[]=array('something');
$stack[]=& end($list); //errors: Only variables should be as开发者_开发百科signed by reference 

what am i doing wrong here? thanks for help.

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Edited

$stack[] = &$list[count($list)-1];  //> Assuming numeric index incremental

or

end($list);
$stack[] = &$list[key($list)];

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Objects will be always passed by reference in PHP 5.

EDITED

But if array is not a class then

$element = array();
$list[] = &$element;
$stack[] = &$element;