nikic

Why objects (usually) use less memory than arrays in PHP

This is just a small post in response to [this tweet][tweet] by Julien Pauli (who by the way is the release manager for PHP 5.5). In the tweet he claims that objects use more memory than arrays in PHP. Even though it can be like that, it's not true in most cases. (Note: This only applies to PHP 5.4 or newer.)

The reason why it's easy to assume that objects are larger than arrays is because objects can be seen as an array of properties and a bit of additional information (like the class it belongs to). And as array + additional info > array it obviously follows that objects are larger. The thing is that in most cases PHP can optimize the array part of it away. So how does that work?

The key here is that objects usually have a predefined set of keys, whereas arrays don't:

nikic

<?php error_reporting(E_ALL);

function test() {}

$nIter = 1000000;
$argNums = [0, 1, 2, 3, 4, 5, 100];

$func = 'test';

foreach ($argNums as $argNum) {

nikic

<?php

error_reporting(E_ALL);

function xrange($start, $end, $step = 1) {
    for ($i = $start; $i < $end; $i += $step) {
        yield $i;
    }
}

nikic

<?php

/*
 * Note: This script will directly modify the .php files in the given directory.
 * It is assumed that the code is under version control, so you can easily review
 * the changes using `git diff` or similar.
 */

function usageError() {
    die("Usage: php -d asp_tags=1 portAlternativeTags.php dir/\n");

nikic

<?php

error_reporting(E_ALL);

/* Data can be send to coroutines using `$coroutine->send($data)`. The sent data will then
 * be the result of the `yield` expression. Thus it can be received using a code like
 * `$data = yield;`.
 */

/* What we're building in this script is a coroutine-based streaming XML parser. The PHP

nikic

<?php ini_set('memory_limit', -1);

if ($argc != 3) die("error\n");

$file = $argv[1];
$num = $argv[2];

$startTime = microtime(true);
for ($i = 0; $i < $num; ++$i) {
    require $file;

nikic

Order of evaluation in PHP

Yesterday I found some people on my [favorite reddit][lolphp] wonder about the output of the following code:

<?php

$a = 1;
$c = $a + $a++;

nikic

<?php

use PhpParser\Node;
use PhpParser\Node\Expr;

error_reporting(E_ALL);

ini_set('memory_limit', -1);

//$dir = __DIR__ . '/../../Symfony_2.3';

nikic

New features in PHP 5.5

This is only a summary. For a full list of changes see the NEWS file.

Feature	RFC / announcement	Author
Bundled ZendOptimizer+ as OPcache	https://wiki.php.net/rfc/optimizerplus	zeev

nikic

rackspace/php-opencloud/lib/OpenCloud/Common/Metadata.php:40
    In method __set():
    return $this->setProperty($property, $value);
kub-at/php-simple-html-dom-parser/src/KubAT/PhpSimple/lib/simple_html_dom.php:989
    In method __set():
    return $this->_[HDOM_INFO_OUTER] = $value;
kub-at/php-simple-html-dom-parser/src/KubAT/PhpSimple/lib/simple_html_dom.php:992
    In method __set():
    return $this->_[HDOM_INFO_TEXT] = $value;
kub-at/php-simple-html-dom-parser/src/KubAT/PhpSimple/lib/simple_html_dom.php:994