byRef vs byVal vs byRet, Php

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<?php

function byRef(&$arr){
    $arr[] = '';
}
function byVal($arr){
    $arr[] = '';
    return $arr;
}
function byRet(){
    $arr = [];
    $arr[] = '';
    return $arr;
}

//
$times = 4; // Cantidad de veces para promediar
$max = 1000000; // Cantidad de veces a ejecutar la funcion

//
$avg = [];
for ($x = 0; $x < $times; $x++) {
    $time_start = microtime(true);
    for ($i = 0; $i < $max; $i++) {
        $ref = [];
        byRef($ref);
    }
    $time_end = microtime(true);
    $avg[] = $time_end - $time_start;
}
echo "byRef: ~". number_format(array_sum($avg) / $times, 10) . " segs<br>\n";

//
$avg = [];
for ($x = 0; $x < $times; $x++) {
    $time_start = microtime(true);
    for ($i = 0; $i < $max; $i++) {
        $in = [];
        $out = byVal($in);
    }
    $time_end = microtime(true);
    $avg[] = $time_end - $time_start;
}
echo "byVal: ~". number_format(array_sum($avg) / $times, 10) . " segs<br>\n";

//
$avg = [];
for ($x = 0; $x < $times; $x++) {
    $time_start = microtime(true);
    for ($i = 0; $i < $max; $i++) {
        $ret = byRet();
    }
    $time_end = microtime(true);
    $avg[] = $time_end - $time_start;
}
echo "byRet: ~". number_format(array_sum($avg) / $times, 10) . " segs<br>\n";

[ + ] Show input
Absolute running time: 1.96 sec, cpu time: 3.23 sec, memory peak: 8 Mb, absolute service time: 1,97 sec