Reference detection in array from another function

Question

So I\'m using the pin method, but the reference is detected one level too late:

$pin = time();

function wrap($arr){
  test($arr);
}

function test(&$arr         


        

Answer 1

I think you are over-complicating things. I solved this by looping over the array and checking if the current value in the array is equivalent (===) with the array.

function wrap( $arr){
    test($arr);
}

function test( $arr){
    foreach( $arr as $v) {
        if( $v === $arr) { 
            print 'ref, ';
        } else {
            if( is_array( $v)) { 
                test( $v); 
            } else {
                print $v . ', ';
            }
        }
    }
}

I used the following test cases:

echo "Array 1:\n";
$array1 = array(1, 2, 3);
$array1[4] = &$array1;
wrap( $array1);

echo "\nArray 2:\n";
$array2 = array(1, 2, 3, array(1, 2, 3));
$array2[2] = &$array2;
wrap( $array2);

Which produced this output:

Array 1: 
1, 2, 3, ref 
Array 2: 
1, 2, ref, 1, 2, 3, 

However, the above method will fail for nested references. If nested references are possible, as in the following test case:

echo "\nArray 3:\n";
$array3 = array(1, 2, 3, array(1, 2, 3));
$array3[3][2] = &$array3;
wrap( $array3);

Then we need to keep track of all the array references we've seen, like this:

function wrap( $arr){
    test( $arr);
}

function test( $arr){
    $refs = array(); // Array of references that we've seen

    $f = function( $arr) use( &$refs, &$f) {
        $refs[] = $arr;
        foreach( $arr as $v) {
            if( in_array( $v, $refs)) { 
                print 'ref, ';
            } else {
                if( is_array( $v)) {
                    $f( $v); 
                } else {
                    print $v . ', ';
                }
            }
        }
    };
    $f( $arr);
}

Using the above test case, this outputs:

Array 3: 
1, 2, 3, 1, ref, 3,

Edit: I've updated the final function that keeps track of all references to eliminate the global dependencies.

Answer 2

Introduction

I think a better approach would be to create a copy of the array and compare modification rather than use global pin and it can still be a 100% Recursive

Example 1

This is from your example above :

$array = array(1,2,3);
$array[4] = &$array;
wrap($array);

Output

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [4] => ref
)

Example 2

Are we really sure its detecting reference or just a copy of the array

//Case 1 : Expect no modification
$array = array(1, 2, 3, array(1, 2, 3));
wrap( $array);

//Case 2 : Expect Modification in Key 2
$array = array(1, 2, 3, array(1, 2, 3));
$array[2] = &$array;
wrap( $array);

Output

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
        )

)
Array
(
    [0] => 1
    [1] => 2
    [2] => ref
    [3] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
        )

)

Example 3

Is this really recursive ?

$array = array(1, 2, 3, array(1, 2, 3));
$array[4][4][2][6][1] = array(1,2,3=>&$array);
wrap( $array);

Output

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
        )

    [4] => Array
        (
            [4] => Array
                (
                    [2] => Array
                        (
                            [6] => Array
                                (
                                    [1] => Array
                                        (
                                            [0] => 1
                                            [1] => 2
                                            [3] => ref   <-- GOT YOU
                                        )

                                )

                        )

                )

        )

)

Your Modified Function

/**
 * Added printf since test now returns array
 * @param array $arr
 */
function wrap(array $arr) {
    printf("<pre>%s<pre>", print_r(test($arr), true));
}


/**
 * - Removed Top Refrence
 * - Removed Global
 * - Add Recursion
 * - Returns array
 * @param array $arr
 * @return array
 */
function test(array $arr) {
    $temp = $arr;
    foreach ( $arr as $key => &$v ) {
        if (is_array($v)) {
            $temp[$key]['_PIN_'] = true;
            $v = isset($arr[$key]['_PIN_']) ? "ref" : test($v);
        }
    }
    unset($temp); // cleanup
    return $arr;
}

Answer 3

function wrap($arr){ test($arr); }
/// ...
wrap($array);

Your wrap() function allocates new memory block for $arr. When you calling test() function within wrap()s body, it takes reference of $arr memory block, but not an $arrays memory block, because $arr is a copy of $array and PHP memory management system stores them separately.

---

There is a universal reference spotting function:

function is_equal_refs(&$a, &$b){
    $buffer = $a;          // saving current value in temporary variable

    $a = md5(time());      // assigning new value to memory block, pointed by reference

    $result = ($a === $b); // if they're still equal, then they're point to the same place.

    $a = $buffer;          // restoring value

    return $result;        // returning result
}

So, lets do some testing:

<?php
header('Content-Type: text/plain');

function is_equal_refs(&$a, &$b){
    $buffer = $a;

    $a = md5(time());

    $result = ($a === $b);

    $a = $buffer;

    return $result;
}

function wrap($arr){ test($arr); }

function test(&$arr){
    foreach($arr as &$v){

        if(is_equal_refs($arr, $v)){
            print_r('ref');
            echo PHP_EOL;
            break;
        }

        if(is_array($v))return test($v);

        print_r($v);
        echo PHP_EOL;
    }
}

$array   = array(1, 2, 3);
$array[] = &$array;

wrap($array);
?>

Shows:

1   // < $arr
2
3
1   // < $array
2
3
ref // < $array doubled -> reference found

The reason of such behavior is $arr[3] contains reference for $arrays memory block, but not reference of itself's memory block.

Lets remove a $array[] = &$array; row, and modify wrap() function to check:

function wrap($arr){
    $arr[] = &$arr;

    test($arr);
}

And result would be:

1   // < $arr
2
3
ref // < $arr doubled -> reference found

Because $arr not points to $array, but to itself in $arr[3]. So, in your code there are different references you want to spot.

---

CONCLUSION: What you want to achieve is breaking out PHP memory management rules.

---

UPDv1:

Need to seek a workaround, to restore $array reference in a wrap() function scope.

1) A "bad" / "globals" practice:

<?php
header('Content-Type: text/plain');

function is_equal_refs(&$a, &$b){
    $buffer = $a;

    $a = md5(time());

    $result = ($a === $b);

    $a = $buffer;

    return $result;
}

function wrap($array){
    global $check; // <- THIS

    test(empty($check) ? $array : $check); // <- THIS
}

function test(&$arr){
    foreach($arr as &$v){

        if(is_equal_refs($v, $arr)){
            print_r('ref');
            echo PHP_EOL;
            break;
        }

        if(is_array($v)){
            test($v);
        } else {
            print $v . ' ';
            echo PHP_EOL;
        }
    }
}

$array   = array(1, 2, 3);
$array[] = &$array;
$check   = &$array; // <- and THIS

wrap($array);
?>

Which shows:

1
2
3
ref

---

2) A "wrap everything in array or object" practice: (prefered and reliable)

<?php
header('Content-Type: text/plain');

define('REF_MARKER', 'x-my-tr!cky-ref'); // trick key definition

function is_equal_refs(&$a, &$b){
        $buffer = $a;

        $a = md5(time());

        $result = ($a === $b);

        $a = $buffer;

        return $result;
    }

function wrap(array $arr){
        // restore reference, if trick.
        // it might be moved to the top part of test() function (might affect performance).
        if(isset($arr[REF_MARKER]))$arr = &$arr[REF_MARKER];

        test($arr);
    }

// $array - subject to test;
// $refs  - internal ref list of all `subjects`;
function test(&$array, $refs = array()){
        $refs[] = &$array;

        foreach($array as &$value){

            foreach($refs as &$ref){
                if(is_equal_refs($ref, $value))return print 'ref ';
            }

            if(is_array($value)){
                $refs[] = &$value;

                test($value, $refs);
            } else {
                print $value . ' ';
            }
        }
    }

$array   = array(1, 2, 3);
$array[] = &$array;

wrap(array(REF_MARKER => &$array)); // trick

print PHP_EOL;

$ring      = array(1, 2, 3, array(4, 5, 6));
$ring[3][] = &$ring;

wrap(array(REF_MARKER => &$ring)); // trick

print PHP_EOL;

$test = array('a', 'b', 'c');
$ring = array(1, 2, 3);

$ring[] = &$test;
$test[] = &$ring;

wrap(array(REF_MARKER => &$ring)); // trick

print PHP_EOL;

wrap(range(1, 5)); // normal

print PHP_EOL;

$test = array(1, 2, 3, array(1, 2, 3), 4, array(5, 2, 3), array(6, array(1, 2, 3), 7), array(1, 2, 3));

wrap($test); // normal

print PHP_EOL;

$test[]    = &$test;
$test[3][] = &$test;
$test[5][] = &$test[3];

wrap(array(REF_MARKER => &$test)); // trick
?>

Shows:

1 2 3 ref
1 2 3 4 5 6 ref
1 2 3 a b c ref
1 2 3 4 5
1 2 3 1 2 3 4 5 2 3 6 1 2 3 7 1 2 3
1 2 3 1 2 3 ref 4 5 2 3 ref 6 1 2 3 7 1 2 3 ref