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<?php declare(strict_types=1); function foo(int $x, ?int &$y = null) { var_dump($y); if ($y != null) { $y = $x ** 2; } return $x * 2; } var_dump([foo(5, $a), $a]);
Output for 8.2.0 - 8.2.29, 8.3.0 - 8.3.25, 8.4.1 - 8.4.12
NULL array(2) { [0]=> int(10) [1]=> NULL }

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