Is there a way to use pattern matching in build.sbt? - scala

Question

I'm trying to play with Scala's PlayFramework and am running into an issue with my build.sbt file. Specifically:
Pattern matching in val statements is not supported
Which is from the obvious:
val env = sys.props.getOrElse("ENV", default = "local")
val (someVal, otherVal) = env match {
case "local" => ("x","a")
case _ => //etc
}
Is there a way to use a match statement in the build.sbt file at all? The error says that it's not supported in val statements. Where is it actually supported?
Edit:
I've tried adding a method to a build.scala object as well, but even when I use plain if statements I still get the same "Pattern matching in val statements is not supported"
Build.scala:
import sbt._
import Keys._
object ExampleBuild extends Build {
def getEnvData(env: String) = {
if(env == "local") {
("c","q")
} else if (env == "other") {
("b","v")
} else {
("x","a")
}
}
}
And updated build.sbt:
val env = sys.props.getOrElse("ENV", default = "local")
val (someVar, otherVar) = ExampleBuild.getEnvData(env)
But to no avail.

Answer 1

The error is not caused by the match statement, but from this:
val (someVar, otherVar) = ...
which is a form of pattern matching (on tuples) not supported by sbt.
Here's a relevant comment from the SbtParser implementation
// Check No val (a,b) = foo or val a,b = foo as these are problematic to range positions and the WHOLE architecture.
You can work around this limitation by using a case class instead of a tuple.
in Build.scala
case class EnvData(someVar: String, otherVar: String)
in build.sbt
val envData = env match {
case "local" => EnvData("x", "a")
case _ => //etc
}
and then use it like envData.someVar, envData.otherVar and so on.