TestingUnapply2.scala

Updating the code to:

```scala
import scala.reflect.ClassTag

object TestingUnapply {

  sealed trait Thing
  case class ThingA(a: String) extends Thing
  case class ThingB(b: String, thingA: ThingA) extends Thing

  val x: Thing = ThingA("hello")
  val y: Thing = ThingB("goodbye", ThingA("maybe"))

  process(x, new { def unapply(thing: ThingA) = ThingA.unapply(thing)})
  process(y, new { def unapply(thing: ThingB) = ThingB.unapply(thing).map(_._2.a)})

  def process[T <: Thing: ClassTag](thing: Thing, extract: { def unapply(thing: T): Option[String]}) = thing match {
    case extract(a) => s"The value of a is: $a"
  }
}
```

Now results in the compiler error:

[error] /tmp/TestUnapply.scala:18: Parameter type in structural refinement may not refer to an abstract type defined outside that refinement
[error]   def process[T <: Thing: ClassTag](thing: Thing, extract: { def unapply(thing: T): Option[String]}) = thing match {