Zero. People are actively aware of what happened in Python 2/3.

The good thing is that Scala is a typed language, so they can

a) provide tooling for migrating code

b) compile things and get clear information about how much differences there are

I think somebody said that necessary lines of change from Scala 2 -> Scala 3 should be below 0.1% to be acceptable.

Oh you. Our codebase uses scala xml and macros; migration will be a major PITA.

Author of Scala macros here. Here's a recent discussion on the future of macros in the brave new world of Dotty: https://www.reddit.com/r/scala/comments/4our5m/keynote_scala....

You will most likely get a chance of upgrading your macros into scala.meta before dotty comes out.

Also xml support as the scala-xml library will continue. Though as the xml literals are removed you have to use string interpolation (xml"<your><xml/>here</your>") which isn't as nice to use. (hopefully someone comes up with a nice DSL or something instead)

By the time this becomes an issue hopefully there will be a library that acts as a drop-in replacement for scala xml, at least.

You will want to rewrite your macro's soon.

Odersky gave some details of language features being removed for Scala 3 in his talk and it seemed to be really obscure features I don't use anyway.

Never give 0 for a statistical prediction.

Python may not be statically typed, but they still have an automated tool for migrating from 2 to 3.

...which covers only a subset of conversion issues and offers no guarantees.

... and that is different from Scala how?

Unlike Scala, you can't figure out what Python code means correctly and statically — you have little idea what will be called by a function without running the code up to that point, so it's hard to do semantics-preserving refactorings.

But Python changed Strings to use Unicode, and that's something everybody uses and that is insanely hard to refactor automatically even with types.

For Dotty, instead, there are some hard-to-refactor-for changes, but they're in really advanced Scala things, so I expect they'll affect fewer users — mostly the kind of users who can write shapeless-like stuff.

How much money are you willing to lay down, at what odds?