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<?php function is_cyclic(array &$array) { json_encode($array); return json_last_error() === JSON_ERROR_RECURSION; } $array = [1, [2, 3]]; $array[1][1] = &$array; var_dump(is_cyclic($array));
Output for 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.30, 8.2.0 - 8.2.25, 8.3.0 - 8.3.14
bool(true)

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69.35 ms | 406 KiB | 5 Q