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<?php $x = new stdclass; $x->{"whatever"} = 1337; $x = (array)$x; var_dump($x); //$x = array("42" => 1337); foreach ($x as $key => $value) { var_dump($key); if (!array_key_exists((string)$key, $x)) echo 'wtf'; } ?>
Output for 5.4.2 - 5.4.45, 5.5.24 - 5.5.35, 5.6.8 - 5.6.21, 7.0.0 - 7.0.20, 7.1.0 - 7.1.25, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
array(1) { ["whatever"]=> int(1337) } string(8) "whatever"

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188.83 ms | 404 KiB | 235 Q