The stackable traits design pattern is based on mixin composition—something we became familiar with in the early chapters of this book. We usually have an abstract class or a trait that defines an interface, a base implementation, and traits that extend the abstract class to stack modifications on it.
For our example, let's implement the following diagram:
The preceding diagram is of a really simple application. We have a base StringWriter class, which has a basic implementation (BasicStringWriter) that just returns a message containing the string. On the right-hand side, we have traits that can add stackable modifications ...
