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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 - 7.3.26, 7.4.0 - 7.4.14, 8.0.0 - 8.0.3
bool(true)