Emulating separate compilation in Scala

link.scala

//Link testa and testz.
//To compile this file, testz.scala, testa.scala, and test.scala must be compiled.
//In this approach, we can select different implementation of test.A
object link extends test with testa with testz {
  class A extends super[testa].A with super[testz].A
  def main(args: Array[String]) {
    val a = new A
    println(a.aaa())
    println(a.aaa2())
    println(a.zzz())
    println(a.zzz2())
  }
}

test.scala

//Header file
trait test {
  trait A {
    def aaa(): Int
    def aaa2(): Int
    def zzz(): Int
    def zzz2(): Int
  }
}

testa.scala

//Partial implementation of header.A
//This file can be compiled only if test.scala is compiled
trait testa {header: test =>
  trait A extends header.A {
    def aaa() = zzz2
    def aaa2() = 100
  }
}

testz.scala

//Partial implementation of header.A
//This file can be compiled only if test.scala is compiled
trait testz {header: test =>
  trait A extends header.A {
    def zzz() = aaa2()
    def zzz2() = 22
  }
}