Scala: public getter with private setter?

How can I make a field that has a public getter but the setter is private, in Scala?

EDIT: too bad there is no one-liner way to do this like there is in Groovy. Those so开发者_Python百科lutions are all pretty clunky looking.

class Foo {
  private var _value: Int = 0
  def value = _value
}

class ExplicitProperty {
   private[this] var s: Int = _
   def size = s
   private def size_=(x: Int) {
      s = x
   }
}