Is Scala incompatible with itself? [duplicate]

Question

Why is Scala binary incompatible between different releases?

Answer 1

It has to do with the way traits are compiled, because traits are kind of like interfaces but they can contain implementation. This makes it so it is VERY easy to make changes that don't break source compatibility but break binary compatibility, because when you add a new method to a trait along with an implementation, you have to recompile everything that implements that trait so that they will pickup that implementation. There's probably other issues, too, but I think they're mostly along the same lines.

Answer 2

Lack of JVM support for Scala-specific features, such as traits mentioned, and the fact that it is actively evolving.