DifferencesFromCore3.md

How are Core 4 HookEvents different from Core 3 Hooks?

1. HookEvents are not required to be placed in an extension (Theme, Module).
   • They can be placed in the App namespace for example.
2. Hook names, types, areas and categories are all eliminated.
   • Generic contracts are enforced through inheritance.
   • Locations and IDs are unique because the classname is unique.
3. Hooks now use more standard terminology: HookEvent and HookEventListener instead of Subscriber and Provider (which were reversed from Symfony and therefore confusing).
4. The admin User Interface is MUCH simpler.
5. HookEvents use the Symfony EventDispatcher instead of a custom HookDispatcher.
6. Zikula-specific dependencies have been removed so the bundle becomes useful within the Symfony ecosystem.
7. The persistent object (Connection) is simplified to only three properties: hookEventClass, listenerClass, priority.

This new hook system is completely incompatible with the old Hooks system. In Zikula Core 3.1 the new system is introduced as a Forward-Compatibility layer. This allows either system to be used, but they cannot connect to each other. E.g. a new HookEvent cannot trigger nor connect to an old Provider and a new HookEvenntListener cannot listen to nor respond to an old Subscriber.

The old system is deprecated and will all be removed in Core 4.0.0.