3v4l.org

run code in 300+ PHP versions simultaneously
<?php $array = ['a' => 1, 'b' => 2, 0, 'f' => 4, '-f' => 5]; ksort($array); /** Array ( [-f] => 5 [0] => 0 [a] => 1 [b] => 2 [f] => 4 ) */ ?>

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