- print_r: documentation ( source)
<?php
/* Function to reverse
$arr from start to end*/
function reverseArray(&$arr, $start=0): void
{
$end = count($arr)-1;
while ($start < $end)
{
[$arr[$start],$arr[$end]] = [$arr[$end],$arr[$start]];
$start++;
$end--;
}
}
$a = [1,2,3,4];
reverseArray($a);
print_r($a);