<?php
$array = array_fill(0, 10000, 1);

function by_reference(&$array) {
    echo "Inner by_reference: ", memory_get_usage(true), "\n";
    foreach ($array as $var) {
        echo "Inner foreach: ", memory_get_usage(true), "\n";
        break;
    }
}

function by_value($array) {
    echo "Inner by_value: ", memory_get_usage(true), "\n";
    foreach ($array as $var) {
        echo "Inner foreach: ", memory_get_usage(true), "\n";
        break;
    }
}

echo "Start: ", memory_get_usage(true), "\n";

by_reference($array);

echo "After by_reference: ", memory_get_usage(true), "\n";

by_value($array);

echo "After by_value: ", memory_get_usage(true), "\n";