How is it posible that while & list & each combination is so much faster than array_walk and foreach on PHP?

Question

I got this code:

<?php
// Test results
$array1 = test('array_walk');
$array2 = test('array_walk_list_each');
$array3 = test('array_walk_foreach1');
$array4 = test('array_walk_foreach2');

// Check arrays for equal
var_dump($array1 == $array2, $array1 == $array3, $array1 == $array4);

// Test function 1
function array_walk_list_each(&$array, $function, $userData = null) {
    while ( list($key, $value) = each($array) )
        $function($array[$key], $key, $userData);
}

// Test function 2
function array_walk_foreach1(&$array, $function, $userData = null) {
    foreach ($array as $key => &$value )
        $function($value, $key, $userData);
}

// Test function 3
function array_walk_foreach2(&$array, $function, $userData = null) {
    foreach ($array as $key => $value )
        $function($array[$key], $key, $userData);
}

function some_function(&$value, $key, $userData) {
    $value = "$key => $userData";
}

function test($function, $count = 10000, $arrayElements = 1000) {
    echo $function, ' ... ';
    $array = array_fill(0, $arrayElements, "some text value");

    $timer = microtime(true);
    for( $i = 0; ++$i < $count; )
        $function($array, 'some_function', 'some user data');
    printf("%.3f sec\n", microtime(true) - $timer);

    return $array;
}

The Output of this is very difficult for me to understand:

array_walk ... 1.024 sec
array_walk_list_each ... 0.002 sec
array_walk_foreach1 ... 1.135 sec
array_walk_foreach2 ... 1.359 sec
bool(true)
bool(true)
bool(true)

the performance difference between these functions it's almost a joke.

How is it possible? am I doing something wrong?

I am running the script from the terminal using PHP 7.0

Answer 1

Simply because each() needs to reset the array to iterate over it again. So you have a single execution within the loop function. While the others are iterating over it.

http://php.net/manual/en/function.each.php

Your result would produce only 1 iteration of 10000 rows, while the others would be 10000 iterations of 10000 rows.

$array = array_fill(0, 10000, uniqid('', false));
$fill = [];
$fill2 = [];
$timer = microtime(true);
for ($i = 0; $i < 10; $i++) {
    while (list($key, $value) = each($array)) {
        $fill[] = 'value';
    }
}
printf("While list each %.3f sec\n", microtime(true) - $timer);
$timer = microtime(true);
for ($i = 0; $i < 10; $i++) {
    foreach ($array as $key => $value) {
        $fill2[] = 'value';
    }
}
printf("Foreach %.3f sec\n", microtime(true) - $timer);
var_dump(count($fill), count($fill2));

Result: https://3v4l.org/bvNdO

---

To get identical results for all of the functions you would need to change the array_walk_list_each function.

 while ( list($key, $value) = each($array) ){
    $function($array[$key], $key, $userData);
 }
 reset($array);