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Bug #66237 Mutating __toString causes array_intersect to return empty
Submitted: 2013-12-04 21:53 UTC Modified: 2013-12-11 20:55 UTC
From: simon at simon dot geek dot nz Assigned:
Status: Not a bug Package: Unknown/Other Function
PHP Version: 5.5Git-2013-12-04 (Git) OS:
Private report: No CVE-ID: None
 [2013-12-04 21:53 UTC] simon at simon dot geek dot nz
Description:
------------
Hopefully the test script is self-explanatory. When running array_intersect on arrays that contains an object that mutates itself and the return value in its __toString() method, the result is an empty array even if there are literal values in the arrays that intersect.

Test script:
---------------
<?php

class A {
	protected $i = 0;

	public function __toString() {
		$this->i++;
		return "$this->i";
	}
}

$a = new A;

$b = ['100', $a];

var_dump(array_intersect($b, $b));


Expected result:
----------------
array(1) {
  [0]=>
  string(3) "100"
}


Actual result:
--------------
array(0) {
}


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 [2013-12-11 20:55 UTC] aharvey@php.net
-Status: Open +Status: Not a bug
 [2013-12-11 20:55 UTC] aharvey@php.net
Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

array_intersect() is documented as comparing the string form of each element — if that's unstable, then bad things may happen.
 
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