Scala 没有为类型参数推断任何内容

调用

get[A]

的类型参数怎么可能在这个代码段中是

Nothing

？如果在没有显式类型参数的情况下调用

get

，如何强制编译器产生错误

case class User(email: String)

object Hello {
  def main(args: Array[String]): Unit = {
    val store = new ObjectStore
    store.get
  }
}

class ObjectStore {
  def get[A: Manifest]: Option[A] = {
    println(manifest[A].toString())
    None
  }
}

基于此，应采取以下措施：

@implicitNotFound("Nothing was inferred")
sealed trait NotNothing[-T]
object NotNothing {
  implicit object notNothing extends NotNothing[Any]
  implicit object `\n The error is because the type parameter was resolved to Nothing` extends NotNothing[Nothing]
}

class ObjectStore {
  def get[T](implicit evManifest: Manifest[T], evNotNothing: NotNothing[T]): Option[T] = {
    println(manifest[T].toString())
    None
  }
}

object X {
  val oo = new ObjectStore().get[Any]
  //fails to compile
  //val o = new ObjectStore().get
}