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sealed abstract class Super[+A] {
def f[B >: A](mem: List[B]) : List[B]
def g(mem: List[_]) = ???
}
// This one should fail, target is a supertype
class Bop1[+A](val element: A) extends Super[A] {
@annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = (null: Super[A]).f(mem)
@annotation.tailrec final def f1[B >: A](mem: List[B]): List[B] = this.g(mem)
}
// These succeed
class Bop2[+A](val element: A) extends Super[A] {
@annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = (null: Bop2[A]).f(mem)
}
object Bop3 extends Super[Nothing] {
@annotation.tailrec final def f[B](mem: List[B]): List[B] = (null: Bop3.type).f(mem)
}
class Bop4[+A](val element: A) extends Super[A] {
@annotation.tailrec final def f[B >: A](mem: List[B]): List[B] = Other.f[A].f(mem)
}
object Other {
def f[T] : Bop4[T] = sys.error("")
}
object Bop {
def m1[A] : Super[A] = sys.error("")
def m2[A] : Bop2[A] = sys.error("")
}
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