castObject.php

<?php

$foo = castObject($bar, '\\My\\FooObject');

function castObject($obj, $toClass) {
  if (is_callable("$toClass::__cast")) {
    return call_user_func("$toClass::__cast", $obj);
  }
  if ($obj instanceof $toClass) {
    return $obj;
  }
  // some default behavior here
}