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<?php $ar = [[1, 2, 3, 4], [1, 2, 3, 4]]; foreach ($ar as &$v) { foreach ($v as $v1) { $v1 = 0; } } unset($v); var_dump($ar);
Output for 7.0.0 - 7.0.20, 7.1.0 - 7.1.20, 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 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
array(2) { [0]=> array(4) { [0]=> int(1) [1]=> int(2) [2]=> int(3) [3]=> int(4) } [1]=> array(4) { [0]=> int(1) [1]=> int(2) [2]=> int(3) [3]=> int(4) } }

preferences:
137.26 ms | 404 KiB | 169 Q