/**
  * The singleton method.
  *
  * @return Muut_Developer_Subscription The instance.
  * @author Paul Hughes
  * @since  3.0
  */
 public static function instance()
 {
     if (!is_a(self::$instance, __CLASS__)) {
         self::$instance = new self();
     }
     return self::$instance;
 }
 /**
  * Initializes the Developer Subscription class.
  *
  * @return void
  * @author Paul Hughes
  * @since 3.0
  */
 public function initDeveloperSubscription()
 {
     $class = 'Muut_Developer_Subscription';
     if (!in_array($class, $this->alreadyInit) && muut()->getOption('subscription_api_key', '') && muut()->getOption('subscription_secret_key', '')) {
         require_once muut()->getPluginPath() . 'lib/subscriber/developer-subscription.class.php';
         if (class_exists($class)) {
             Muut_Developer_Subscription::instance();
         }
         $this->alreadyInit[] = $class;
     }
 }