Is it possible to override/replace an event subscriber?

Question

I would like to replace an event subscriber.

Can I write a class that implements EventSubscriberInterface which replaces another event subscriber?

Answer 1

Since an event subscriber is a service, you can achieve it by creating a class that implements ServiceModifierInterface.

Drupal doesn't have a class that alters an event subscriber (which isn't a class used in tests). Changing the class associated to an even subscriber isn't different from changing the class associated with a generic service, which is what the following code used from the CoreServiceProvider class does, in its alter() method.

$uuid_service = $container->getDefinition('uuid');

// Debian/Ubuntu uses the (broken) OSSP extension as their UUID
// implementation. The OSSP implementation is not compatible with the
// PECL functions.
if (function_exists('uuid_create') && !function_exists('uuid_make')) {
  $uuid_service->setClass('Drupal\\Component\\Uuid\\Pecl');
}
elseif (function_exists('com_create_guid')) {
  $uuid_service->setClass('Drupal\\Component\\Uuid\\Com');
}

$container->getDefinition() returns a Definition instance.