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<?php $one = [1]; $two = [42]; $arr1 = ['k' => &$one]; $arr2 = ['k' => &$two]; var_dump(current($one), current($two)); print_r(array_merge_recursive($arr1, $arr2)); var_dump(current($one), current($two));
Output for 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 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 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
int(1) int(42) Array ( [k] => Array ( [0] => 1 [1] => 42 ) ) int(1) int(42)

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226.43 ms | 404 KiB | 330 Q