Scala Option? Why does Some not inherit AnyVal and why is it not a value type?

Question

Why does Scala Some not inherit from AnyVal so that it uses the value type feature and save the boxing costs?

Something like:

sealed trait TestOption[+A] extends Any {
  def isEmpty: Boolean
  def get: A
}

final case class TestSome[+A](val x: A) extends AnyVal with TestOption[A] {
  def isEmpty = false
  def get = x
} 

case object TestNone extends TestOption[Nothing] {
  def isEmpty = true
  def get = throw new NoSuchElementException("None.get")
}

Answer 1

From the documentation for Value Classes:

Summary of Limitations

A value class

• must have only a primary constructor with exactly one public, val parameter whose type is not a value class. (From Scala 2.11.0, the parameter may be non-public.)
• may not have specialized type parameters.
• may not have nested or local classes, traits, or objects
• may not define a equals or hashCode method.
• must be a top-level class or a member of a statically accessible object
• can only have defs as members. In particular, it cannot have lazy vals, vars, or vals as members.
• cannot be extended by another class.

The bold ones excludes Some from being a Value Class as currently written. The second of these could probably be addressed by a slight change but the former kills it. You'd not be able to wrap another Value Class in Some if Some were made a Value Class itself.