PHP array_map memory usage

gistfile1.php

<?php

// Memory benchmark related to http://stackoverflow.com/questions/11657835/how-to-get-a-one-dimensional-scalar-array-as-a-doctrine-dql-query-result

// Build an array of 50 MiB
$data = [];
for ($i = 0; $i < 1024; $i++) {
    $data[] = ['id' => str_repeat(' ', 1024 * 50)]; // store 50kb more
}

// Variant 1, will double memory usage to 100 MiB, if uncommented
$ids1 = [];
//$ids1 = array_map('current', $data);

// Variant 2, will stay at 50 MiB
$ids2 = [];
foreach ($data as $d) {
    $ids2[] = $d['id'];
}

echo 'peak memory: ' . (memory_get_peak_usage() / 1024 / 1024) . " MiB\n";