Freek Lijten has a new post to his site today today talking about a concept of good OOP design, separation of concerns, and how the use of events can help make it "even better". In it he converts some code from a decently structure state into something even driven, splitting out the work from the handling code.
At PHP Benelux 2015 I witnessed a talk by Matias Noback about events. It was a great talk so if you have chance to see it yourself somewhere, do so! In a very tiny nutshell he took us from what most would consider already decent code to better code. Lets start with "decent".
His "decent" code handles user management, executing certain business rules once the user is successfully registered. In the first version of is code, the User is passed into the "saveUser" function and several actions are performed (is the username in use? can they be saved?) including the sending of the email as requested once a user registers. This code is primarily procedural, all in one place and Freek updates it using events to make it a bit more well-contained. He extracts the piece sending the email and translates that into an event. This is then pushed into a set of handlers and executed allowing for greater flexibility if additional actions are needed in the future.