Scala 2.10 macro varargs examples

macro-varargs.scala

/**
* Related to this question: http://stackoverflow.com/q/13663216/334519
*
* Unhelpful error message:
* scala> MacroExample.foo(List(1, 2, 3): _*)
* <console>:8: error: no `: _*' annotation allowed here
* (such annotations are only allowed in arguments to *-parameters)
*               MacroExample.foo(List(1, 2, 3): _*)
*                                             ^
*
* And downright strange:
* scala> MacroExample.bar(List(1, 2, 3): _*)
* res0: List[Int] = List(1, 2, 3)
*
* scala> MacroExample.bar(1, 2, 3)
* res1: Int = 1
**/

import language.experimental.macros
import scala.reflect.macros.Context

object MacroExample {
  def foo(xs: Int*): Any = macro foo_impl
  def foo_impl(c: Context)(xs: c.Expr[Int]*) = xs.head

  def bar(xs: Int*): Any = macro bar_impl
  def bar_impl(c: Context)(xs: c.Expr[Int]*) = {
    import c.universe._

    xs.head.tree match {
      case Typed(e, _) => c.Expr(e)
      case i           => c.Expr(i)
    }
  }
}