title: php event system implementation
body: <p>I would like to implement an Event system in my custom MVC framework, to allow decoupling
  of classes that need to interact with each other. Basically, the ability for any class to trigger an event and any other class that listens for this event to be able to hook into it.</p>
  
  <p>However, I cannot seem to find a correct implementation given the nature of php's share nothing architecture.</p>
  
  <p>For instance, let's say that I have a User model that each time that it is updated, it triggers a userUpdate event. Now, this event is useful for class A (for instance) as it needs to apply its own logic when a user is updated. 
  However, class A is not loaded when a user is updated, so it cannot bind to any events triggered by the User object.</p>
  
  <p>How can you get around such a scenario? 
  Am I approaching it wrongly?</p>
  
  <p>Any ideas would be greatly appreciated</p>