The state pattern is a clear example of reification in software design, making the concept of our domain problem an explicit object rather than just a side value.
In Chapter 8, Unit Testing and Refactoring, we had an object that represented a merge request, and it had a state associated with it (open, closed, and so on). We used an enum to represent those states because, at that point, they were just data holding a value the string representation of that particular state. If they had to have some behavior, or the entire merge request had to perform some actions depending on its state and transitions, this would not have been enough.
The fact that we are adding behavior, a runtime structure, to a part of the code has to make us think ...
