Foreach loop with value by reference and using `unset` and set to array creates overflow memory.

[Tomanhez]

Description

The following code:

$array = [
	new stdClass(),
	new stdClass(),
	new stdClass(),
	new stdClass(),
	new stdClass(),
	new stdClass(),
	new stdClass(),
	new stdClass(),
	new stdClass(),
	new stdClass(),
	new stdClass(),
	new stdClass(),
];

foreach ($array as $key => &$value) {
	unset($array[$key]);
	$array[] = $value;// the same situation with $array[$key] = $value;
}

Resulted in this output:

If array elements are light there is possible to get 'Process exited with code 137.'
But if are higher than stdClass it kill all application. 

Using foreach without using $key: `foreach ($array as &$value)`
generates: `Fatal error: Allowed memory size of...` - IMO this is better message for debugging what is wrong 

But I expected this output instead:

Better message to be able to debug it, or possibility to use above construction :]

PHP Version

8.2

Operating System

Ubuntu 22

[iluuu1994]

For reference: https://wiki.php.net/rfc/php7_foreach#foreach_by_reference_over_arrays

Your example is supposed to loop forever, because on every iteration you're adding a next element to the array, leading to more iterations. Is that what you expected? If not, you need to explicitly create a copy of the array you're iterating (e.g. by creating a new temporary variable).

I did find a bug while looking at this though:

$array = ['foo'];

foreach ($array as $key => &$value) {
    unset($array[$key]);
    $array[] = 'foo';
    var_dump($array);
}

Details

array(1) {
  [1]=>
  string(3) "foo"
}
array(1) {
  [2]=>
  string(3) "foo"
}
array(1) {
  [3]=>
  string(3) "foo"
}
array(1) {
  [4]=>
  string(3) "foo"
}
array(1) {
  [5]=>
  string(3) "foo"
}
array(1) {
  [6]=>
  string(3) "foo"
}
array(1) {
  [7]=>
  string(3) "foo"
}
array(1) {
  [8]=>
  string(3) "foo"
}

This should also be looping forever, but stops after 8 iterations due to incorrect array-separation.

[iluuu1994]

@Tomanhez Regarding the 137 exit code: This is a SIGKILL, which could possibly have been issued by your OS because your process was consuming too much memory. What is your memory_limit INI setting? If this is too high, and the process consumed a lot of memory, the OS might kill the process to prevent the system from crashing.

[Tomanhez]

@iluuu1994 Thanks for describing loop forever. Its my mistake. Generally I will try to avoid using iteration by reference in favour to create and return new array. For me everything is clear, we can close this issue. Thanks!

[iluuu1994]

@Tomanhez Let's keep this open for the issue described in #13178 (comment) :)