Reuse property with version number when adding a dependency in sbt - scala

Question

I have a project built with sbt 0.11.
I'm trying to create a simple UI with Scala Swing, so first thing is to add a dependency on scala-swing in my build.sbt:
libraryDependencies += "org.scala-lang" % "scala-swing" % "2.9.1-1"
But I have a SettingKey scalaVersion defined:
scalaVersion := "2.9.1-1"
How can I reference that property? If I try to use it like
libraryDependencies += "org.scala-lang" % "scala-swing" % scalaVersion
Compiler complains that it found sbt.SettingKey[String] while String is expected. There are methods get(...) and evaluate(...) on SettingKey but they require some Setting[Scope] parameter to be passed in.
What is the simplest way to just reference this property?

Answer 1

You need to tell the system that libraryDependencies now depends on scalaVersion:
libraryDependencies <+= (scalaVersion) { sv => "org.scala-lang" % "scala-swing" % sv }
(that's my preferred formatting; it's actually invoking the apply method on scalaVersion so you could write it a few different ways, e.g., scalaVersion("org.scala-lang" % "scala-swing" % _).)
If you had multiple settings you wanted to depend on simultaneously, you'd apply on the tuple of them:
foo <<= (scalaVersion, organization) { (sv, o) => o + " uses Scala " + sv }

Answer 2

libraryDependencies <+= scalaVersion("org.scala-lang" % "scala-swing" % _)
The < tells SBT that your setting has a dependency on another setting.
The + tells SBT that you want to add another value, not replace the existing ones (also, it indicates the the contents of the setting are a sequence, and you are adding one element to it).
The syntax setting(function) is the same as function(setting), where function takes a setting evaluated at the proper context as parameter. I don't even know how to write that, and it would be very verbose, so the shortcut is very helpful.
One can also use (setting 1, setting 2)((a, b) => ... ) to make dependencies on multiple settings.
PS: The following might works as well, and it is a bit shorter, but it has been deprecated without special compiler flags as of 2.10.0.
libraryDependencies <+= scalaVersion("org.scala-lang" % "scala-swing" %)

Answer 3

Realising this is old - adding an answer in case anyone else comes across it.
Just add .value to the scalaVersion variable to get the string value:
libraryDependencies += "org.scala-lang" % "scala-swing" % scalaVersion.value

Answer 4

Something like
libraryDependencies <+= scalaVersion { v => "org.scala-lang" % "scala-swing" % v}
should work.