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run code in 300+ PHP versions simultaneously
<?php $arr = array(); $arr["a"] = "A"; $arr["b"] = "B"; $str = array_filter($arr, function($e1, $e2){ echo $e1." :: ".$e2."<br>"; return $e1; }); var_dump($str);

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40.19 ms | 402 KiB | 5 Q