The SitePoint PHP blog has a new tutorial posted today showing the interaction between Drupal 8 hooks and the Symfony dispatcher in the last part of their series showing how to build a custom Drupal 8 module.
With the incorporation of many Symfony components into Drupal in its 8th version, we are seeing a shift away from many Drupalisms towards more modern PHP architectural decisions. For example, the both loved and hated hook system is getting slowly replaced. Plugins and annotations are taking away much of the need for info hooks and the Symfony Event Dispatcher component is replacing some of the invoked hooks. Although they remain strong in Drupal 8, it’s very possible that with Drupal 9 (or maybe 10) hooks will be completely removed.
He starts off with a brief introduction to what the event dispatcher is and how it currently interacts with the Drupal 8 system. He uses a simple form example with two text fields and how to hook in the dispatcher to fire a "demo_form.save" event when the user submits the form. He ties this into a DemoEvent and sets up a simple subscriber. He ends the article with a look at using hooks to achieve the same kind of goal.