trait A {
  implicit def toB: B
}

sealed trait B
case class B1() extends B
case class B2() extends B

object Main {

  implicit class AOps(a: A) {
    implicit def toB: B = a.toB
  }

  val a: A = new A() {
    override implicit def toB: B = B2()
  }

  // How to make the following to compile without change?
  val name: String = a match {
    case B1() => "B1"
    case B2() => "B2"
  }
}