gistfile1.php

<?php

function function_pass_by_value($a) {
    // Will trigger copy-on-write! WOW!
    $a[] = 101; 
}

function function_pass_by_reference($a) {
    // Readonly. Will not trigger copy-on-write!
    // $a is passed by reference.
    $b = $a[101];
}

$array = array_fill(0, 100000, 123);

$x = microtime(true);
for ($i = 0; $i < 1000; $i++) {
    function_pass_by_reference($array);
}
$diff = microtime(true) - $x;
echo count($array) . " : pass by reference : $diff\n";

$x = microtime(true);
for ($i = 0; $i < 1000; $i++) {
    function_pass_by_value($array);
}
$diff = microtime(true) - $x;
echo count($array) . " : pass by value : $diff\n";