How to use PHP’s namespaces and constants within your WordPress plugins

Recently I switched from using a class to emulate a namespace in my WordPress plugins to actually using PHP’s namespace, which is available in PHP 5.3.0 or greater. I’m going to demonstrate some things that all my plugins thus far have in common.

1. Create a namespace

Right before your plugin meta data comment, you must lead with your namespace (otherwise PHP will complain):

namespace CompanyName\PluginName;

I use a master namespace for everything I do (CompanyName) and a sub-namespace for the specific plugin I’m working on (PluginName).

2. Define a namespace constant

After the plugin meta data comment I define a constant, in other words, a shortcut to reference my namespace within WordPress hooks. It’s just less to type in the future and I can change my namespace without affecting plugin functionality.

define(__NAMESPACE__ . '\NS', __NAMESPACE__ . '\\');

What this allows me to do is use a constant called NS to render CompanyName\PluginName\ so that after leading with NS in a WordPress hook callback, all I need to provide is my function name.

To create additional constants within your namespace, you can do that like so:

define(NS . 'PS', 'plugin-slug');

3. Use your namespace constant in a WordPress hook

Here is what a function and a hook looks like in a namespaced environment:

function initialize_plugin() {


  NS . 'initialize_plugin'

It’s really not that much different compared to not using a namespace and it certainly looks a lot cleaner than if you were using a class.

4. Use core WordPress functions

There are times where you need to use WordPress functions like the register_activation_hook, for example. It’s important to remember to change the namespace back to the global namespace for those functions.

The way to do that is to precede the function with a backslash:

\register_activation_hook(__FILE__, NS . 'register_activation_hook');

This should get you started and if you have any questions, leave them in the comments below.

15 thoughts on “How to use PHP’s namespaces and constants within your WordPress plugins

  1. Elium

    Even if it work like that, I would have declared my namespace right before plugin meta data comment.
    According to php manual : “A namespace definition is the first statement the PHP interpreter should encounter in a PHP file. The only statement allowed to occur above a namespace declaration is a declare statement, and then again, only if it declares the encoding of the script.”

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  3. violacase

    Very nice article. You helped me get on the road.
    I REALLY LOVE your trick for creating a spacename constant.

    One thing: since comments are not interpreted by the PHP engine you may have comment before the namespace declaration I should think.

    1. Ryan Sechrest Post author

      I was able to add a comment before the namespace, but like Elium mentioned, PHP’s documentation says:

      A file containing a namespace must declare the namespace at the top of the file before any other code – with one exception: the declare keyword.

      It comes down to whether a comment is considered code or not.

      A little further down, it does narrow it down to a code construct:

      The only code construct allowed before a namespace declaration is the declare statement, for defining encoding of a source file. In addition, no non-PHP code may precede a namespace declaration, including extra whitespace.

      At the end of the day, it’s no problem to stay on the cautious side 🙂

    1. Ryan Sechrest Post author

      I don’t think so, because when WordPress queues and executes hooks, it would take the namespace and function name literally, i.e., it would have no knowledge of the alias in that context. The constant, on the other hand, provides WordPress with the full namespace. If you get it working though, I’d be interested in seeing how you did it!

  4. Bruno

    Thank you for the trick.
    I am a beginner.
    Why adding '__NAMESPACE__' to the constant name ?

    Why not like so:
    define('NS', __NAMESPACE__ . '\\'); ?

    Thank you.


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