I have recently developed a collection of video clips that explain various topics related to defining and using functions in the Scala programming language. These video clips, as well as many others, are available as part of the ‘Scala Fundamentals’ course, available for free personal and academic usage at www.abelski.com.
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.