What visitor buys you here is merely the fact that you don’t have to put an abstract method plus implementations for each distinct type-based desicion (bloating a single file), but create those implementations externally (out of the itinerary source files). I.e. you just managed to avoid putting the type-based code in the types themselves, but somewhere else. Good for you. Where would we be without patterns!

Btw, Scala supports the switch you describe (where the compiler notifies you of missed cases).

It is the incident you remember, finally I had some time to publish the drafts.

I remember that sed tidbit – is this something new, or something that you only now wrote about?