gistfile1.txt

$ scalac sample.scala
sample.scala:14: error: applyDynamic does not support passing a vararg parameter
  new Foo().foo(xs:_*).foobar(new Bar().bar)
                                        ^
one error found

sample.scala

import scala.language.dynamics

class Foo {
  def foo(xs: Int*): Foo = ???
  def foobar(b: Bar): Int = ???
}

class Bar extends Dynamic {
  def selectDynamic(name: String): Bar = ???
}

object Sample extends App {
  val xs = Seq(1, 2, 3)
  new Foo().foo(xs:_*).foobar(new Bar().bar)
}