detecting infinite array recursion in PHP?

Question

i\'ve just reworked my recursion detection algorithm in my pet project dump_r()

https://github.com/leeoniya/dump_r.php

detecting object recursion is not too diff

Answer 1

Someone will correct me if I am wrong, but PHP is actually detecting recursion at the right moment. Your assignation simply creates the additional cycle. The example should be:

$arr    = array();
$arr    = array(&$arr);

Which will result in

array(1) { [0]=> &array(1) { [0]=> *RECURSION* } } 

As expected.

---

Well, I got a bit curious myself how to detect recursion and I started to Google. I found this article http://noteslog.com/post/detecting-recursive-dependencies-in-php-composite-values/ and this solution:

function hasRecursiveDependency($value)
{
    //if PHP detects recursion in a $value, then a printed $value 
    //will contain at least one match for the pattern /\*RECURSION\*/
    $printed = print_r($value, true);
    $recursionMetaUser = preg_match_all('@\*RECURSION\*@', $printed, $matches);
    if ($recursionMetaUser == 0)
    {
        return false;
    }
    //if PHP detects recursion in a $value, then a serialized $value 
    //will contain matches for the pattern /\*RECURSION\*/ never because
    //of metadata of the serialized $value, but only because of user data
    $serialized = serialize($value);
    $recursionUser = preg_match_all('@\*RECURSION\*@', $serialized, $matches);
    //all the matches that are user data instead of metadata of the 
    //printed $value must be ignored
    $result = $recursionMetaUser > $recursionUser;
    return $result;
}