[wffurr]

How is that bad code style? That's exactly what virtual method dispatch does.

The authors in the article even address this point, stating that some operations might make sense as instance methods if they are instrinsic to the type hierarchy, but others, especially ad-hoc queries, are extrinsic to the types and best expressed as pattern matching.

Simply calling this "bad code style" sounds a lot like a justification for only having a verbose way to use an alternative to virtual method dispatch.

[zerr]

Enumerating and testing for type equality each derived classes in one place (i.e. manual type switch) is certainly a bad code practice in OO languages. Yes, the better way is to let virtual method dispatch mechanism decide.

[TeMPOraL]

Depends. It's useful when you want to have all dispatch code in one place (as opposed to it being scattered across numerous files). Doubly so if your language (like most languages) lacks multimethods. Triply so, if you need to dispatch on built-in types you can't extend, which sometimes happens in e.g. Java.