3v4l.org

run code in 300+ PHP versions simultaneously
<?php $arr = [ 1 => ["key" => "a"], 2 => ["key" => "b"] ]; foreach ($arr as $key => &$val) { $arr[$val["key"]] = $val; unset($arr[$key]); } var_dump($arr);
Output for 5.4.2 - 5.4.45, 5.5.24 - 5.5.35, 5.6.8 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.10, 7.2.0 - 7.2.33, 7.3.16 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.7
array(0) { }
preferences:
186.22 ms | 404 KiB | 225 Q