试图避免使用隐式类扩展特定的文字类型：

implicit class keepAsListOfInt(val listOfInt: List[Int]) extends AnyVal {
  def :+(long: Long): List[Int] = listOfInt :+ long.toInt
}

// Won't compile - already widened to List[AnyVal]
val listOfInt: List[Int] = List(1) :+ 2L

但是由于编译器已经将表达式List(1) :+ 2L扩展为List[AnyVal]，所以从不调用隐式转换。我可以以某种方式隐式地强制执行转换吗？

更新-感谢sachav的答复和Alexey的有效关注，以下代码似乎可以解决此问题：

import scala.language.implicitConversions

implicit def listAnyValToListInt(l: List[AnyVal]): List[Int] = l.map {
  case n: Int                      => n
  case n: Long if n < Int.MinValue =>
    throw new IllegalArgumentException("Can't cast too small Long to Int: " + n)
  case n: Long if n > Int.MaxValue =>
    throw new IllegalArgumentException("Can't cast too big Long to Int: " + n)
  case n: Long                     => n.toInt
  case v                           =>
    throw new IllegalArgumentException("Invalid value: " + v)
}

val valid: List[Int] = List(1) :+ 2
val invalid: List[Int] = List(1) :+ 30000000000L // fails at runtime

尽管有一个编译时解决方案，它仍然会很好。