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Bringing OOP functionality into WordPress

So if, like me, you’re an object orientated programmer and are suddenly asked to build functionality into WordPress it can feel like you’re trapped into procedural code and functions. Consequently; I thought I would whip up a little tutorial of how to work within WordPress, whilst maintaining your OOP integrity. The reason this is important is quite simple, if you’re building complex functionality into WordPress, you want to be able to use OOP principles and methodologies.

Don’t worry or get confused, themes vs plugins

Essentially, these are the same thing! They use the same library of code, the APIs you can use within WordPress are the same. You could be asked to implement the code in either, and you’ll do it the same way. The real difference is whether you want the functionality to be exposed if the website changes theme, if that’s the case you’ll move the code into a WordPress.

PSR-4 Autoloading

The first thing you’ll want to do is get some PSR-4 autoloading running so that you can use your classes without having a huge set of require, require_once or include statements which can be a nightmare to maintain. If you’re working in a theme put this code into your functions.php – if you’re in a plugin then I would advise you do this in the registration file which might be wp-contents/plugins/yourplugin.php or it might be wp-contents/plugins/yourplugin/functions.php. If in doubt, look for the declaration of the plugin – which will be a PHP code comment as seen here.

I will use JohnoTheCoder as my vendor name and PluginTutorial as the project namespace. The file we’re putting this code into is called whenever WordPress is loaded (because the theme is initialised, as are the plugins) – so you’ll want something like this

    Declare the autoloading - you can repeat this for all your different namespaces if you wish, for example if you're bringing in code from other repositories
spl_autoload_register(function ($class) {

    // The classes I want to autoload are within the JohnoTheCoder\PluginTutorial namespace
    $prefix = 'JohnoTheCoder\\PluginTutorial\\';

    // The class being loaded is not within my namesapce, return early
    if (strncmp($prefix, $class, strlen($prefix)) !== 0) {

    // All we're doing here is saying that your namespace classes are found within the src subdirectory
    $file = __DIR__ . '/src/' . str_replace('\\', '/', str_replace($prefix, "", $class) . '.php';

    // If the file does not exist - throw an exception with a helpful message
    if (!file_exists($file)) {
        Throw new Exception("Class [$class] not found in expected location [$file]");

    // The file does exist, so require the file


What this means now is that you can reference JohnoTheCoder\PluginTutorial classes, and they will be looked for within your plugin, for example JohnoTheCoder\PluginTutorial\Subspace\MyClass would be found in plugin-directory/src/Subspace/MyClass.php – of course you can modify this to follow the naming conventions you have in place.

That’s it for this short tutorial – I’ll do some more “OOP in WP” tutorials in the future, to enhance maintainability and help encourage true OOP development within WordPress plugins and themes.

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I'd love to hear your opinion on what I've written. Anecdotes are always welcome.

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