ActiveObject.scala

@active
class A {
  // all non-@active locals
  // will be made private
  var y = 0
  def bar(x: Int) = x + 5
  
  @active // should return Unit
  def foo(x: Int) = {
    y = bar(x)
  }
}

// -------- ↓ --------

class A {
  private val executor$ = Executors.newFixedThreadPool(1)
  
  private var y = 0
  private def bar(x: Int) = x + 5
  
  def foo(x: Int) = {
    executor$.submit(new Runnable {
      def run = {
        y = bar(x)
      }
    }
    ()
  }
}

// -------- or --------

trait ActiveObject {
  private lazy val executor = Executors.newFixedThreadPool(1)
  def active(code: ⇒ Unit) = {
    executor.submit(new Runnable { def run() = code })
    ()
  }
}