Question

I think I stumbled across a bug in PHP. However, to be sure, I am asking here first.

$k=0;
echo preg_replace_callback('/./', function($groups) use ($k) {
    return $k++;
}, 'xxxxxx');

Script output: 000000

Expected output: 012345

Am I missing something?

Answer 1

$k is bound to the closure by value, not by reference. So it will always be the same between multiple closure calls.

You can also pass it by reference using &$k. Note that this will also modify the $k value outside the closure.