Changing Scala version in existing SBT project.

Question

How can I change Scala version in existing Simple Build Tool project?
I would like SBT to check whether the system's Scala version is correct and if it is not the case then download it.

Answer 1

As mentioned in RunningSBT, you can:

You can temporarily switch to another version of Scala using ++<version>.
This version does not have to be listed in your build.scala.versions property, but it does have to be in a repository or be a local Scala version you have defined.

But the CrossBuild page is more suited for what you want, as it shows in action how to change the build.scala.versions property.

So you should be able to

set build.scala.versions 2.7.7
reload
set build.scala.versions 2.8.0.RC2
reload

and each time trigger a compilation with a different Scala version.