I'm developing a Wordpress Woocommerce plugin. On my local environment it works fine but I have problems when adding the plugin to a replica of the prod environment. I am new to wordpress and not very familiar with web dev (I'm a Java programmer).

In the plugin file, I instantiate a class from the Woocommerce plugin package like this:

$coupon = new WC_Coupon($some_code);

In the local environment (php 5.4.10 , Woocommerce 2.0.13, Wordpress 3.6) it's fine. In the production environment (php 5.4.10 , Woocommerce, Wordpress 3.4.2) I have the following error:

Fatal error: Class 'WC_Coupon' not found

I have tried including the file where the WC_Coupon class is defined but then the error becomes

Fatal error: Cannot redeclare class WC_Coupon

So what is the proper way to use classes declared in another plugin?

Note: upgrading is not an option at the moment.

3 Answers 3


You have to check if the class exists, but before that you have to wait that all plugin are loaded: no one can assure that your plugin is loaded after WooCommerce.

For run a code from plugin when all plugin are loaded hook into plugins_loaded hook.

Be aware that you cannot use this hook in a theme, because when theme load that hook was already fired.

add_action('plugins_loaded', 'my_coupon_init');

function my_coupon_init() {
  if ( class_exists('WC_Coupon') ) {
    $coupon = new WC_Coupon($some_code);
    // some code here
  } else {
    add_action('admin_notices', 'wc_not_loaded');

function wc_not_loaded() {
      '<div class="error"><p>%s</p></div>',
      __('Sorry cannot create coupon because WooCommerce is not loaded')
  • Not sure if in that case plugins_loaded is the proper hook. One will have to search when exactly that class is available and hook in after that. Anyway +1
    – kaiser
    Commented Aug 19, 2013 at 13:48
  • In this particular case, I am hooking to the deactivation hook register_deactivation_hook( __FILE__, 'deactivate');. So I can't wait. Can I ask wordpress to load the class if it's not loaded yet?
    – znat
    Commented Aug 19, 2013 at 14:01
  • 2
    Thanks @kaiser. The WC_Coupon is loaded by __construct of the main WooCommerce class (really by includes() method directly called by __construct) and WooCommerce class is instanziate (as singleton) as soon as plugin is loaded. So plugins_loaded is proper hook in this case ;)
    – gmazzap
    Commented Aug 19, 2013 at 14:28
  • Anonymous before core loads? Well done Woo, well done.
    – kaiser
    Commented Aug 19, 2013 at 14:45
  • @NathanZ Check class_exists( 'WC_Coupon' ). Also please state that you're using this during deactivation... could have saved answering crowd tons of time...
    – kaiser
    Commented Aug 19, 2013 at 14:46

This is too late but I would like to share how to use woocommerce and its classes without having an error class not found.

First is to check if woocommerce is installed and use the woocommerce_loaded action hook.

 * Check if WooCommerce is active
if ( in_array( 'woocommerce/woocommerce.php', apply_filters( 'active_plugins', get_option( 'active_plugins' ) ) ) ) {
    // Put your plugin code here

    add_action('woocommerce_loaded' , function (){
         //Put your code here that needs any woocommerce class 
         //You can also Instantiate your main plugin file here 


I hope this helps someone.


The proper way would be :

 if( class_exists('WC_Coupon') ) $coupon = new WC_Coupon($some_code);

It's better to check if class exists before using it, it avoids fatal error if the plugin is disabled.

You can't redeclare a class it's not allowed in PHP.

You can also extend class :

class My_WC_Coupon extends WC_Coupon {
   //some code
   //some hook

But most of the time and in this case with WooCommerce you'd better find a hook in documentation that will handle the job.

  • 1
    If you extend your class via a hook, won't the new class only exist in the scope of the function hook?
    – alexg
    Commented Dec 29, 2015 at 18:05

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