1. Configure and use Scala

Configure and use Scala 

Set the Scala version used for building the project 

The scalaVersion configures the version of Scala used for compilation. By default, sbt also adds a dependency on the Scala library with this version. See the next section for how to disable this automatic dependency. If the Scala version is not specified, the version sbt was built against is used. It is recommended to explicitly specify the version of Scala.

For example, to set the Scala version to “2.11.1”,

scalaVersion := "2.11.1"

Disable the automatic dependency on the Scala library 

sbt adds a dependency on the Scala standard library by default. To disable this behavior, set the autoScalaLibrary setting to false.

autoScalaLibrary := false

Temporarily switch to a different Scala version 

To set the Scala version in all scopes to a specific value, use the ++ command. For example, to temporarily use Scala 2.10.4, run:

> ++ 2.10.4

Use a local Scala installation for building a project 

Defining the scalaHome setting with the path to the Scala home directory will use that Scala installation. sbt still requires scalaVersion to be set when a local Scala version is used. For example,

scalaVersion := "2.10.0-local"

scalaHome := Some(file("/path/to/scala/home/"))

Build a project against multiple Scala versions 

See cross building.

Enter the Scala REPL with a project’s dependencies on the classpath, but not the compiled project classes 

The consoleQuick action retrieves dependencies and puts them on the classpath of the Scala REPL. The project’s sources are not compiled, but sources of any source dependencies are compiled. To enter the REPL with test dependencies on the classpath but without compiling test sources, run test:consoleQuick. This will force compilation of main sources.

Enter the Scala REPL with a project’s dependencies and compiled code on the classpath 

The console action retrieves dependencies and compiles sources and puts them on the classpath of the Scala REPL. To enter the REPL with test dependencies and compiled test sources on the classpath, run test:console.

Enter the Scala REPL with plugins and the build definition on the classpath 

> consoleProject

For details, see the consoleProject page.

Define the initial commands evaluated when entering the Scala REPL 

Set initialCommands in console to set the initial statements to evaluate when console and consoleQuick are run. To configure consoleQuick separately, use initialCommands in consoleQuick. For example,

initialCommands in console := """println("Hello from console")"""

initialCommands in consoleQuick := """println("Hello from consoleQuick")"""

The consoleProject command is configured separately by initialCommands in consoleProject. It does not use the value from initialCommands in console by default. For example,

initialCommands in consoleProject := """println("Hello from consoleProject")"""

Define the commands evaluated when exiting the Scala REPL 

Set cleanupCommands in console to set the statements to evaluate after exiting the Scala REPL started by console and consoleQuick. To configure consoleQuick separately, use cleanupCommands in consoleQuick. For example,

cleanupCommands in console := """println("Bye from console")"""

cleanupCommands in consoleQuick := """println("Bye from consoleQuick")"""

The consoleProject command is configured separately by cleanupCommands in consoleProject. It does not use the value from cleanupCommands in console by default. For example,

cleanupCommands in consoleProject := """println("Bye from consoleProject")"""

Use the Scala REPL from project code 

sbt runs tests in the same JVM as sbt itself and Scala classes are not in the same class loader as the application classes. This is also the case in console and when run is not forked. Therefore, when using the Scala interpreter, it is important to set it up properly to avoid an error message like:

Failed to initialize compiler: class scala.runtime.VolatileBooleanRef not found.
** Note that as of 2.8 scala does not assume use of the java classpath.
** For the old behavior pass -usejavacp to scala, or if using a Settings
** object programmatically, settings.usejavacp.value = true.

The key is to initialize the Settings for the interpreter using embeddedDefaults. For example:

val settings = new Settings
settings.embeddedDefaults[MyType]
val interpreter = new Interpreter(settings, ...)

Here, MyType is a representative class that should be included on the interpreter’s classpath and in its application class loader. For more background, see the original proposal that resulted in embeddedDefaults being added.

Similarly, use a representative class as the type argument when using the break and breakIf methods of ILoop, as in the following example:

def x(a: Int, b: Int) = {
  import scala.tools.nsc.interpreter.ILoop
  ILoop.breakIf[MyType](a != b, "a" -> a, "b" -> b )
}