I am wondering what the "&" sign does in this callback function.
array_walk($array, function (& $item) {
$item['new_key'] = $item['old_key'];
unset($item['old_key']);
});
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Bram Janssen
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It indicates 'pass by value'. – Elanochecer Mar 27 '19 at 10:07
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[Reference to `$item`](https://www.php.net/manual/en/language.references.pass.php). This means that the original variable `$item` will reflect any changes that occur to it within that callback. – Script47 Mar 27 '19 at 10:07