I have tried the memory usage of some simple variables and encounter unexpected results, please see this code:

        $datetimes = [];
        $memory_before = memory_get_usage();

        for ($x = 0; $x < 1000; $x++) {
            $datetimes[] = new \DateTime();
        }
        var_dump('DateTimes: ' . (memory_get_usage() - $memory_before));


        $ints = [];
        $memory_before = memory_get_usage();

        for ($x = 0; $x < 1000; $x++) {
            $ints[] = $x;
        }
        var_dump('Integers: ' . (memory_get_usage() - $memory_before));

I get this output (on PHP 7.4, 64bit):

string(17) "DateTimes: 350504"
string(15) "Integers: 37160"

37 KB memory for 1000 ints does not make sense to me, right? I'd expect 8000 byte plus some array overhead.

My experiment scales: for a million ints, I get 33558808 byte memory usage.

I have disabled xdebug.