have been happily pattern matching and doing data driven design in Scala since around 2007... 20 years after and it's still only fully available in Java 22(!). Probably another 10 years before 8 and 17 go out of business. A feature gap of 30 years is huge, that's an entire generation of new developers who never had a chance to use these principles. I still don't get why Scala couldn't make it on JVM (despite the usual controversy)

You're joking of course. Acton says "solve for transforming the data you have given the constraints of the platform [by which he means the Hardware] and nothing else." The fundamental principle upon which Java was founded is WORA: "write once, run anywhere". Mobile code. Acton does not use Java, and cannot, because it is fundamentally hardware independent. He programs games for consoles. Acton's obsession is with performance so he is concerned only with the fantasy world within his program without any concern for its relation to the real outside world, so he has no use for abstraction.

"This guy" here. Can you point at a few of those things? I want to make sure not to mislead new Java devs. 😉

Why this modafukas aren't clear? Why they want to show that they knows google knowledge?😅

I hope my comment serves as a good guide for beginners, assuming that your comment is satirical!: Dynamic dispatch _is_ polymorphism, fellow internet stranger! You see, C++ programmers don't get this feature without an extra keyword (which notifies them that this feature is going to be used, which can sometimes be a bad thing for performance, hence it is a language feature). Imagine making an instance (an object!) of a subclass (so, a class that extends another) and calling a method on it. If this method was overridden by the subclass, then, _no matter_ what the type of the variable was, the method called would be the overridden version from the subclass. This happens because the compiler stores an extra table (called the "V-table", or in Java's case, the "I-table") along with EVERY OBJECT[!], to keep track of what version of a method should be called. Method calls that need the V-table are called "virtual calls" (because... we make the concept of an object "virtual", and go on to call methods that were not defined in the class the object is from, but were defined in other classes, because we used inheritance). Virtual calls are often avoided in data-oriented design (as shown in this talk, in the form of the separation of processing methods), because looking into a table is simply extra work we can avoid using a data-oriented design. To answer those wondering why a hierarchy for `Page` was used, well, please recall the fact that `Page` is a `record`, which means that the compiler is already making some optimizations for when they are used, and that the hierarchy exists only for pattern-matching, since we're using a sealed interface. _I hope this helps someone!_

First Nicholai defined Polymorphism as Runtime Polymorphism (method overriding) in Java which is what most people mean by it. He proceeded to show a new concise alternative using switch on Types, gave a good example, and explained its limitations and when you might want to use it (to maintain separation of concerns when adding an ancilliary feature - my interpretation). I had some concerns during the presentation but by the end I was very satisfied with the talk as a whole and got his message.