Sylvain Lorinet Divi

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:

	<?xml version="1.0" encoding="UTF-8"?>
	<opml version="1.0">
	<head>
	<title>Subscriptions - [email protected]</title>
	</head>
	<body>
	<outline text="PHP" title="PHP">
	<outline htmlUrl="http://frederickvanbrabant.com" title="frederickvanbrabant.com" xmlUrl="http://frederickvanbrabant.com/feed.xml" type="rss" text="frederickvanbrabant.com"/>
	<outline htmlUrl="http://mattallan.org" title="mattallan.org" xmlUrl="http://mattallan.org/feed.xml" type="rss" text="mattallan.org"/>
	<outline title="asked.io" xmlUrl="https://asked.io/rss" type="rss" text="asked.io"/>

	---
	- hosts: all
	user: root
	sudo: true

	tasks:
	- name: update apt
	command: apt-get update

	- name: update bash

	<?php
	/**
	* Magnet links library for PHP
	*
	* @link http://stackoverflow.com/questions/6634059/magnet-links-library-for-php
	*/

	$magnetUri = 'magnet:?xt=urn:sha1:YNCKHTQCWBTRNJIV4WNAE52SJUQCZO5C';

	echo 'Magnet URI demo: ', $magnetUri, "\n\n";