Foo[A, F[_ <: A]] doesn't compile #10185Description
sealed trait Foo[A, F[_ <: A]]
case class Bar[A, F[_ <: A]]() extends Foo[A, F]
class F[S <: String]
object Test {
def f(foo: Foo[String, F]): Unit = foo match {
case Bar() => ()
}
}REPL output:
$ ~/scala-2.12.1/bin/scala
Welcome to Scala 2.12.1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_102).
Type in expressions for evaluation. Or try :help.
scala> :paste
// Entering paste mode (ctrl-D to finish)
import scala.language.higherKinds
sealed trait Foo[A, F[_ <: A]]
case class Bar[A, F[_ <: A]]() extends Foo[A, F]
class F[S <: String]
object Test {
def f(foo: Foo[String, F]): Unit = foo match {
case Bar() => ()
}
}
// Exiting paste mode, now interpreting.
<console>:20: error: constructor cannot be instantiated to expected type;
found : Bar[A,F(in class Bar)]
required: Foo[String,F(in object $iw)]
case Bar() => ()
^
scala> This might be related to #9394, but this one is more complicated (involves a higher-kinded type parameter with upper bounded parameter) and workarounds proposed in #9394 do not apply.