I have recently started to create video clips for the lectures I deliver in my professional courses. So far, this try goes very well. Students find these video clips highly useful when going over the material in between the meetings. Most likely this try will evolve and become permanent. The video clips are avilable through secret private facebook groups I created for my courses. Students who participated in previous rounds of my courses can join these secret private groups and continuously enjoy professional updates.
The Visitor Design Pattern
The visitor design pattern allows us to add operations to objects that already exist without modifying their classes and without extending them.