<?php
$t = memory_get_usage();

for ($i=0; $i<999999; $i++) {
    $a = [];
}

echo memory_get_usage() - $t . "\n";


$t = memory_get_usage();

for ($i=0; $i<999999; $i++) {
    $a = new stdClass();
}

echo memory_get_usage() - $t;

// 488
// 402