Description:
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By creating an array structure in the following format:

$a=[];
$a['ref']=&$a;
$a['val']=$a;

Any PHP-only attempt at discovering this recursion will fail. Also, structures like RecursiveIterators will loop infinitely, unserialize(serialize($a)) also drops out the val part.

Generally PHP behaves very weird and unexpectedly. I have not traced this in the Zend engine to see what is causing it, but my hypothesis is that accessing $a['val'] is creating a new copy of it every time (and my PHP-side tests confirm this).


Test script:
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$a=['ref'=>&$a];
$a['val']=$a;
var_dump($a); //normal, as expected

var_dump(unserialize(serialize($a))); //half-arsed

foreach (new RecursiveIteratorIterator(new RecursiveArrayIterator($a)) as $k=>$v)
	echo $k,"=>",@$v,PHP_EOL; //infinite loop


Expected result:
----------------
At least RecursiveIterators should be able to distinguish this behavior, if serialize can not handle it. Or PHP internals should be changed in a way that this does not happen.
Or these examples be marked as dangerous because they can possibly break applications.

Actual result:
--------------
Infinite Loop