import scala.collection._
import scala.concurrent._
import ExecutionContext.global

object Ex1 {
  var x: List[Int] = null
  def foo() {
    val buffer = mutable.ListBuffer[Int]()
    buffer ++= (0 until 100)
    x = buffer.result
    Future {
      // not safe!
      // a non-immutable object is assigned to a non-final field
      println(x)
    }
  }
}

object Ex2 {
  val buffer = mutable.ListBuffer[Int]()
  buffer ++= (0 until 100)
  val x = buffer.result
  Future {
    // again not safe!
    // the reference to `Ex2.this` escaped to another thread during construction
    // so it does not matter that the field `x` is final
    println(x)
  }
}

class Ex3 {
  val buffer = mutable.ListBuffer[Int]()
  buffer ++= (0 until 100)
  val x = buffer.result
}

object Test extends App {
  val obj = new Ex3
  Future {
    // safe!
    // although the list is itself not an immutable object,
    // it is obtained by reading a final field in an immutable object `Ex3`,
    // so any modifications to the list prior to assignment to the field `x` become visible,
    // and the assignment of `x` cannot be reordered with the assignment to the field `obj`
    // (see Goetz book, page 350)
    obj.x
  }
}