How do you define a local var/val in the primary constructor in Scala?

Question

In Scala, a class\'s primary constructor has no explicit body, but is defined implicitly from the class body. How, then, does one distinguish between fields and local values

Answer 1

Another option we have is to make the primary object constructor private and use a companion object's apply method as a builder. If we apply (pun is not intended) this approach to your example it will look like this:

class R private (val x: Int, val y: Int);

object R {
  def apply(n: Int, d: Int): R = {
    val g = myfunc;
    new R(n / g, d / g);
  }
}

To create an R instance instead of:

val r = new R(1, 2);

write:

val r = R(1, 2);

This is a little bit verbose, but it could be worse, I think :). Let's hope that private[this] vals will be treated as temporary variables in future releases of Scala. Martin himself hinted that.