[RESOLVED] how to determine if one array is reference to another?

sneakyimp

so if you use strict equality to compare two separate arrays, you get true if all their keys and values are the same:

$arr1 = array('a', 'b', 'c');
$arr2 = array('a', 'b', 'c');
echo ($arr1 === $arr2) ? "EQUAL\n" : "NOT EQUALj\n"; // outputs 'EQUAL'

Is there any way to discern whether one array is a reference to another array, and not just a separate array with identical keys and values?

function is_ref($a1, $a2) {
  // returns TRUE if $a1 =& $a2;
}

$arr1 = array('a', 'b', 'c');
$arr2 = array('a', 'b', 'c');
$ref =& $arr1;

echo (is_ref($arr1, $arr2)) ? "REF\n" : "NOT A REF\n"; // should say NOT A REF
echo (is_ref($arr1, $ref)) ? "REF\n" : "NOT A REF\n"; // should say REF

NogDog

I don't think there's a programmatic way to tell. In reality, both variables are references to the same "thing"; it's not a case of $ref being a reference to $arr1, but rather $ref refers to the same array entity in memory that $arr1 does. For instance:

<pre><?php
$foo = array(1,2,3);
$bar =& $foo;
var_dump($foo);
var_dump($bar);
unset($foo);
var_dump($foo);
var_dump($bar);
?></pre>

Outputs:

array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}
array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}


Notice:  Undefined variable: foo in C:\wamp\www\test\test.php on line 7

NULL
array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}

laserlight

This hack seems to work:

function is_ref(&$a1, &$a2) {
    if ($a1 === $a2) {
        $t = $a1;
        $a1 = !$a1;
        $result = $a2 == $a1;
        $a1 = $t;
        return $result;
    } else {
        return false;
    }
}

$arr1 = array('a', 'b', 'c');
$arr2 = array('a', 'b', 'c');
$ref =& $arr1;

echo (is_ref($arr1, $arr2)) ? "REF\n" : "NOT A REF\n"; // should say NOT A REF
echo (is_ref($arr1, $ref)) ? "REF\n" : "NOT A REF\n"; // should say REF

sneakyimp

Hmmmm...I see the skill in the hack and it does work. Pretty awkward though, eh? So I guess there's no non-hax way to do it?

bradgrafelman

Sounds like you're trying to see if two memory pointers are equal in that they both point to the same memory location (talking about C++, for example)? In PHP, no, I'm not sure that there's an easier or more straight-forward way of doing it.

sneakyimp

Very well then, thread resolved! thanks!