Trying to pass unapply types

TestingUnapply.scala

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

Compiler error is:

[error] /tmp/proj1/TestUnapply.scala:10: type mismatch;
[error]  found   : AnyRef{def unapply(thing: TestingUnapply.ThingA): Option[String]}
[error]  required: AnyRef{def unapply[T <: TestingUnapply.Thing](thing: T): Option[String]}
[error]   process(x, new { def unapply(thing: ThingA) = ThingA.unapply(thing)})
[error]              ^
[error] /tmp/proj1/TestUnapply.scala:11: type mismatch;
[error]  found   : AnyRef{def unapply(thing: TestingUnapply.ThingB): Option[String]}
[error]  required: AnyRef{def unapply[T <: TestingUnapply.Thing](thing: T): Option[String]}
[error]   process(y, new { def unapply(thing: ThingB) = ThingB.unapply(thing).map(_._2.a)})
[error]              ^