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<?php function is_cyclic(array &$array) { $lastKey = array_key_last($array); if ($lastKey === null) { // Array is empty return false; } static $marker; if ($marker === null) { $marker = new stdClass(); } if ($array[$lastKey] === $marker) { return true; } $array[] = $marker; foreach ($array as &$item) { if (is_array($item) && is_cyclic($item)) { array_pop($array); return true; } } array_pop($array); return false; } // Contains reference to itself $v = [1, 2, 3]; $v[1] = &$v; // Contains nested array with reference to $x $x = [1, [2, 3]]; $x[1][1] = &$x; // Contains nested array with reference to an ancestor $y = [1, [2, [3, 4]]]; $y[1][1][1] = &$y[1]; // Nested array contains reference to itself $z = [1, [2, 3]]; $z[1][1] = &$z[1]; // This array is not recursive $p = [1, 2, [3, 4, [5, 6, 7]]]; foreach (['v', 'x', 'y', 'z', 'p'] as $var) { $arr = &${$var}; echo "Array \$$var | Cyclic: "; var_export(is_cyclic($arr)); echo "\n"; echo "----------------\n"; var_dump($arr); echo "\n\n"; }
based on 2XYFM
Output for 8.0.0 - 8.0.3
Array $v | Cyclic: true ---------------- array(3) { [0]=> int(1) [1]=> *RECURSION* [2]=> int(3) } Array $x | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> array(2) { [0]=> int(2) [1]=> *RECURSION* } } Array $y | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> array(2) { [0]=> int(3) [1]=> *RECURSION* } } } Array $z | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> *RECURSION* } } Array $p | Cyclic: false ---------------- array(3) { [0]=> int(1) [1]=> int(2) [2]=> array(3) { [0]=> int(3) [1]=> int(4) [2]=> array(3) { [0]=> int(5) [1]=> int(6) [2]=> int(7) } } }
Output for 7.3.0 - 7.3.26, 7.4.0 - 7.4.14
Array $v | Cyclic: true ---------------- array(3) { [0]=> int(1) [1]=> &array(3) { [0]=> int(1) [1]=> *RECURSION* [2]=> int(3) } [2]=> int(3) } Array $x | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> array(2) { [0]=> int(2) [1]=> &array(2) { [0]=> int(1) [1]=> *RECURSION* } } } Array $y | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> array(2) { [0]=> int(3) [1]=> *RECURSION* } } } Array $z | Cyclic: true ---------------- array(2) { [0]=> int(1) [1]=> &array(2) { [0]=> int(2) [1]=> *RECURSION* } } Array $p | Cyclic: false ---------------- array(3) { [0]=> int(1) [1]=> int(2) [2]=> array(3) { [0]=> int(3) [1]=> int(4) [2]=> array(3) { [0]=> int(5) [1]=> int(6) [2]=> int(7) } } }