Is there any trick to use macros in the same file they are defined?

Question

I have the following code:

object Macros {

  import scala.language.experimental.macros
  import scala.reflect.macros.blackbox

  def hello(): Unit = macro hello_impl

  def hello_impl(c: blackbox.Context)(): c.Expr[Unit] = {
    import c.universe._
    reify {
      println("Hello World!")
    }
  }
}


object Main {

  def main(args: Array[String]): Unit = {
    Macros.hello()
  }

}

It throws the following compilation error:

Error:(21, 17) macro implementation not found: hello
(the most common reason for that is that you cannot use macro implementations in the same compilation run that defines them)
    Macros.hello()
                ^

My question is: is there a way to "fool" the compiler in order to use macro expansions in the same file they are defined? My motivation is the following: I like to code in Scala, and lately I was submitting some problems in online judge Codeforces and some Scala constructions turned out to be very slow. So, I want to create some macro expansions in order to execute those constructions fast. But I cannot submit more than one file.

Thanks!

Answer 1

At the moment, this is not possible in production releases of Scala 2.10 and 2.11. We might be able to achieve this with scala.meta, but that's well in the future.