array_push & array_udiff with custom class objects

Question

I am pushing class objects onto two different arrays an then want to take the different of these arrays. However, when I use array push with array_udiff I cannot get array_udiff to output anything other than null. Here's the barebones of the code.

Class definition:

class follower
{
    public $friend;
    public $newposts;

    }

Data assignment: for loop containing:

        $holder = new follower();
....put data in $holder....
        array_push($object_array1, $holder);

second for loop doing the same thing...

       $holder = new follower();
....put data in $holder....
    array_push($object_array2, $holder);

Function to compare objects in the object arrays:

function compare_followers($f1, $f2)
{
    $s1 = $f1->friend;
    $s2 = $f2->friend;
    return strcmp($s1, $s2);
}

And finally unsuccessful attempt to compare these two arrays (the arrays look as they should, arrays of follower objects)

$object_array = array_udiff($object_array2, $object_array1, 'compare_followers');

$object_array is null. In addition to the code above, I tried playing around with the comparison function - making it a static function within the class or declaring it as an unnamed function in the array_udiff call, but neither of those things worked.

If I apply compare_followers to individual class members, that works fine. Similarly, if I push the following object onto my $object_array1 and $object_array2 the array_udiff works fine:

    $holderA = array(
            'friend' =>$holder->friend,
            'newposts' => $holder->newposts
            );

        array_push($object_array2, $holder); (and same for $object_array1)

$object_array = array_udiff($object_array2, $object_array1, 'compare_followers');

The problem with this latter, working apprpoach is that it gives a dictionary of objects rather than an array of objects - I need an array.

Here are some of the stackoverflow questions that are relevant but don't address this: array_udiff not working as expected, How does array_udiff() work?, array intersect for object array php. Here's the documentation for this class (http://php.net/manual/en/function.array-udiff.php

What am I doing wrong?

Thanks for any suggestions.

Answer 1

Try this. Careful of what the arrays actually contain.

<?php

class follower {
    public $friend;
    public $newposts;

    public function __construct($friend, $newpost) {
        $this->friend = $friend;
        $this->newposts = $newpost;
    }
}

$object_array1 = array();
$holder = new follower('me', 'first');
array_push($object_array1, $holder);

$object_array2 = array();
$holder = new follower('you', 'second');
array_push($object_array2, $holder);

function compare_followers($f1, $f2) {
    $s1 = $f1->friend;
    $s2 = $f2->friend;
    return strcmp($s1, $s2);
}

$object_array = array_udiff($object_array2, $object_array1, 'compare_followers');

var_dump($object_array);