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@ 2021-01-16T22:59:28Z

<?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";
}

Output for git.master, git.master_jit, rfc.property-hooks: 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) } } }

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2020-03-21 RFC: Is_Literal - declined
2020-12-04 Enumerations - included in PHP 8.1
2018-06-15 Typed Properties v2 - implemented in PHP 7.4
2016-08-12 Object typehint - included in PHP 7.2
2016-08-14 Arrow functions - withdrawn
2016-05-29 array_change_keys() - withdrawn
2016-04-19 Lexical scope support for anonymous classes - suspended
2016-04-17 Functional Interfaces - declined
2016-03-16 Typed Properties - superseded in favor of Typed Properties 2.0
2015-08-27 Callable Prototypes - declined
2015-05-01 Short Closures - declined / withdrawn in favor of Arrow Functions
2015-02-18 Scalar type hints v5 - included in PHP 7
2015-02-14 Union Types - declined
2013-09-22 Anonymous classes - included in PHP 7

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