Description:
------------
this should be definitely supported, probably with SORT_UNIQUE_STRICT constant.

currently, there is not simple way to remove same instance duplicates

Test script:
---------------
$d = new \DateTime('2000-1-1');
print_r(
    array_unique([$d, $d, new \DateTime('2000-1-1')], SORT_REGULAR)
);

Expected result:
----------------
array with 2 DateTime elements

Actual result:
--------------
remove same instance duplicates - not supported by array_unique