... without loop

spread_without_loop.php

<?php

function printMemory($start, $header) {
    printf(
        "%s - Time: %s | Memory (current): %s KB | Memory (max): %s KB" . PHP_EOL,
        $header,
        number_format(round((microtime(true) - $start) * 1000, 6), 6, ',', ''),
        number_format(round((memory_get_usage() / 1024), 2), 2, ',', ''),
        number_format(round((memory_get_peak_usage() / 1024), 2), 2, ',', '')
    );
}

$big1 = range(0, 100000);
$big2 = array_fill(100000, 100000, 'string');
$big3 = range(200000, 100000);

$start = microtime(true);
$result = [...$big1, ...$big2, ...$big3];
printMemory($start, '... without loop');