Can't get PHPStorm's generic style notation support to work :(

generics-style-notation-support.php

<?php

/**
 * @return ArrayObject<int, Result>
 */
function getResults() {
    $results = new ArrayObject();
    $results[] = new Result();

    return $results;
}

$results = getResults();
foreach ($results as $key => $result) {
    // PHPStorm 2018.3 still thinks $result is mixed :(
    $result->value;
}