I've recently started playing with Scala (2.8) and noticed the I can write the following code (in the Scala Interpreter):
scala> var x : Unit = 10 x : Unit = () It's not obvious what's going on there. I really didn't expect to see any implicit conversion to Unit.
See section "6.26.1 Value Conversions" in the Scala Language Specification version 2.8:
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Value Discarding. If e has some value type and the expected type is Unit, e is converted to the expected type by embedding it in the term { e; () }.
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scalacOptions += "-Ywarn-value-discard" in SBT configuration.Anything can be converted to Unit. This is mostly necessary to support side-effecting methods which nonetheless return values, but where the return value is often ignored. For instance
import java.util.{List =>JList} def remove2[A](foo: JList[A], a1:A, a2:A):Unit = { foo.remove(a1) foo.remove(a2) //if you couldn't convert the (usually pointless) return value of remove to Unit, this wouldn't type } 
Well, anything can be converted to unit (which is its purpose). You can think of Unit as unit in the lattice of (sub)types, which means it is a supertype of everything. See Wikipedia article.
