The Author Online Book Forums are Moving

The Author Online Book Forums will soon redirect to Manning's liveBook and liveVideo. All book forum content will migrate to liveBook's discussion forum and all video forum content will migrate to liveVideo. Log in to liveBook or liveVideo with your Manning credentials to join the discussion!

Thank you for your engagement in the AoF over the years! We look forward to offering you a more enhanced forum experience.

kmeredith (23) [Avatar] Offline
#1
First off, thanks for writing another Scala book. I learned a lot from DSLs in Action - applying your teachings to building a DSL on my last job.

Chapter 2 mentions:

Encoding this type of implementation using OO and
subtyping will lead us to the path of the Visitor pattern [5], which, as we all know is fraught
with grave perils


As a reader with some Java/.NET experience, but working with Scala the past 1.5 years, I'm not aware of the "grave perils" of the Visitor Pattern.

I believe that it'd please be helpful to present a link or brief mention of the problems of the Visitor Pattern.
Debasish Ghosh (116) [Avatar] Offline
#2
Visitor is one of the most convoluted patterns in GoF. Every one has expressed lots of concerns over the complexity of using this pattern. Just google it and you will find lots of links. However a more interesting topic is to judge how pattern matching is a better alternative when structuring your code. Here are 2 links which you may find useful :-

1. In Defense of Pattern Matching by Martin Odersky (http://www.artima.com/weblogs/viewpost.jsp?thread=166742)
2. Matching Objects with Patterns (http://lampwww.epfl.ch/~emir/written/MatchingObjectsWithPatterns-TR.pdf)

The second paper gives a comparative analysis of the advantages of using pattern matching over the Visitor pattern in Scala.

Thanks.