The Scala team pulled out all the stops with Dotty. It's a real tour de force, on a par with the sea change of C++11. Even with the plaudits he's earned, Martin Odersky is for me in the top three language designers of our time. (I'm sure I'm being unfair to other members of his team with this comment, though.) Dotty's union types are a thing of beauty, its implicits are really second to none, and _so_ damn useful. Th…
* True intersections and union types -- use them sometimes, not something you can't live without though.
* Trait parameters -- slightly easier life for OOP, ok I guess.
* Function types and implicit function types -- right, will make your code even harder to read (subjective).
* Generic tuples -- again, I can't remember we ever had problems with tuples in Scala.
* Opaque types -- another small OOP improvement.
* Type lambdas -- I've never seen them used.
* Erased parameters -- probably useful if it improves performance even at the cost of readability right?
* Enums -- finally something practical, good.
And that's all about major changes in Scala 3. Ah, yes, we get a new compiler. Are you excited?
These changes look like a quarterly release than a major version shift. Now, imagine a project manager who's estimating the migration downtime for Scala 2 for the sake of the above.