Detecting whether a PHP variable is a reference / referenced

Question

Is there a way in PHP to determine whether a given variable is a reference to another variable and / or referenced by another variable? I appreciate that it might not be possible to separate detecting "reference to" and "reference from" given the comment on php.net that setting $a=& $b means "$a and $b are completely equal here. $a is not pointing to $b or vice versa. $a and $b are pointing to the same place."

If it's not possible to determine whether a given variable is a reference / referenced, is there a generalised way of determining if two variables are references of each other? Again, a comment on php.net supplies a function for doing such a comparison - although it is one that involves editing one of the variables and seeing if the other variable is similarly effected. I'd rather avoid doing this if possible since some of the variables I'm considering make heavy use of magic getters / setters.

The background to the request in this instance is to write a debugging function to help view structures in detail.

Answer 1

Full working example:

function EqualReferences(&$first, &$second){
    if($first !== $second){
        return false;
    } 
    $value_of_first = $first;
    $first = ($first === true) ? false : true; // modify $first
    $is_ref = ($first === $second); // after modifying $first, $second will not be equal to $first, unless $second and $first points to the same variable.
    $first = $value_of_first; // unmodify $first
    return $is_ref;
}

$a = array('foo');
$b = array('foo');
$c = &$a;
$d = $a;

var_dump(EqualReferences($a, $b)); // false
var_dump(EqualReferences($b, $c)); // false
var_dump(EqualReferences($a, $c)); // true
var_dump(EqualReferences($a, $d)); // false
var_dump($a); // unmodified
var_dump($b); // unmodified