What's faster in PHP, a big switch statement, or an array key lookup where the array initialisation is paid every time?

I did some tests:

File array_gen.php

<?
    echo '<?
        $a = 432;
        $hash = array(
    ';

    for($i = 0; $i < 10000; $i++)
        echo "$i => $i,\n";

    echo ');
        echo $hash[$a];
    ';

File switch_gen.php:

<?
    echo '<?
        $a = 432;
        switch($a) {
    ';
    for($i = 0; $i < 10000; $i++)
        echo "case $i: echo $i; break;\n";

    echo '}';

Then:

php array_gen.php > array_.php
php switch_gen.php > switch.php

time tcsh -c 'repeat 1000 php array.php > /dev/null'
19.297u 4.791s 0:25.16 95.7%
time tcsh -c 'repeat 1000 php switch.php > /dev/null'
25.081u 5.543s 0:31.66 96.7%

Then I modified the loop to:

for($i = 'a'; $i < 'z'; $i++)
  for($j = 'a'; $j < 'z'; $j++)
    for($k = 'a'; $k < 'z'; $k++)

To create 17576, 3 letter combinations.

time tcsh -c 'repeat 1000 php array.php > /dev/null'
30.916u 5.831s 0:37.85 97.0%
time tcsh -c 'repeat 1000 php switch.php > /dev/null'
36.257u 6.624s 0:43.96 97.5%

The array method wins every time, even once you include setup time. But not by a lot. So I think I will ignore this optimization and go with whatever is easier.

It sort of depends on the array size, but for most practical purposes, you can consider that the array is faster. The reason is simple; a switch statement must compare sequentially against each entry in the switch statement, but the array approach simply takes the hash and finds that entry. When you have so few entries in your switch that the sequential comparisons are faster than the hashing, it's faster to use a switch, but the array approach becomes more efficient quickly. In computer science terms, it's a question of O(n) vs. O(1).