For https://medium.com/@pavarnos/lazy-event-dispatching-with-symfony-1fc8813c44e1

ConfigureLazyEventDispatcher.php

<?php 

/**
 * Add this to your container builder with
 * $containerBuilder->addCompilerPass(new ConfigureLazyEventDispatcher(new LazyEventDispatcher($containerBuilder));
 */
class ConfigureLazyEventDispatcher implements CompilerPassInterface
{
    /** @var LazyEventDispatcher */
    private $dispatcher;

    /**
     * @param LazyEventDispatcher $dispatcher
     */
    public function __construct(LazyEventDispatcher $dispatcher)
    {
        $this->dispatcher = $dispatcher;
    }

    /**
     * @param ContainerBuilder $container
     */
    public function process(ContainerBuilder $container)
    {
        $container->addResource(new FileResource(__FILE__));

        foreach ($container->getDefinitions() as $serviceName => $definition) {
            $reflection = new \ReflectionClass($definition->getClass());
            if (!$reflection->isInstantiable()) {
                continue;
            }
            if (!$reflection->hasMethod('getSubscribedEvents')) {
                // you could check here for handlers that you forgot to connect to events
                continue;
            }
            foreach ($this->getSubscribedEvents($reflection->getName()) as $event) {
                $this->dispatcher->addLazyListener($event['name'], $serviceName, $event['method'], $event['priority']);
            }
        }
        $this->dispatcher->saveLazyListeners();
    }

    /**
     * traverse the tricky structure returned by getSubscribedEvents() and make it nice and linear
     * @param string $className
     * @return array [event name, method name, priority]
     */
    private function getSubscribedEvents($className)
    {
//        * array('eventName' => 'methodName')
//        * array('eventName' => array('methodName', $priority))
//        * array('eventName' => array(array('methodName1', $priority), array('methodName2'))
        $method    = [];
        $rawEvents = call_user_func($className . '::getSubscribedEvents');
        foreach ($rawEvents as $eventName => $params) {
            if (is_string($params)) {
                $method[] = ['name' => $eventName, 'method' => $params, 'priority' => 0];
            } elseif (is_string($params[0])) {
                $method[] = [
                    'name'     => $eventName,
                    'method'   => $params[0],
                    'priority' => isset($params[1]) ? $params[1] : 0,
                ];
            } else {
                foreach ($params as $listener) {
                    $method[] = [
                        'name'     => $eventName,
                        'method'   => $listener[0],
                        'priority' => isset($listener[1]) ? $listener[1] : 0,
                    ];
                }
            }
        }
        return $method;
    }
}