Example.php

<?php

$collection = new Doctrine\Common\Collection\ArrayCollection();

// add objects to the collection that contain a getCreated method returning a DateTime instance

$iterator = $collection->getIterator();

$iterator->uasort(function ($first, $second) {
    if ($first === $second) {
        return 0;
    }

    return (float) $first->getCreated()->format("U.u") < (float) $second->getCreated()->format("U.u") ? -1 : 1;
});