assignmentHelper.php

<?php

function incrementDeep(&$array, $value) {
    $array += $value;
}

$test['foo']['bar']['test'] = 5;

incrementDeep($test['foo']['bar']['test'], 5);
incrementDeep($test['foo']['bar']['test2'], 5);

print_r($test);
die();

/* Result:

Array
(
    [foo] => Array
        (
            [bar] => Array
                (
                    [test] => 10
                    [test2] => 5
                )

        )

)
 */