How to write “asInstanceOfOption” in Scala

Question

Is it possible to write an \"asInstanceOfOption\" method that would do what is intended by the following (bogus) code?

def asInstanceOfOption[T](o: Any): Option[         


        

Answer 1

Here's an elaboration on oxbow_lake's updated answer, further updated to require Scala 2.10:

// Implicit value class
implicit class Castable(val obj: AnyRef) extends AnyVal {
  def asInstanceOfOpt[T <: AnyRef : ClassTag] = {
    obj match {
      case t: T => Some(t)
      case _ => None
    }
  }
}

This can be used by doing:

"Hello".asInstanceOfOpt[String] == Some("Hello") // true
"foo".asInstanceOfOpt[List[_]] == None // true

However as mentioned in other answers this doesn't work for primitives because of boxing issues, nor does it handle generics because of erasure. To disallow primitives, I restricted obj and T to extend AnyRef. For a solution that handles primitives, refer to the answer for Matt R's followup question:

How to write asInstanceOfOpt[T] where T <: Any

Or use shapeless's Typeable, which handles primitives as well as many erasure cases:

Type casting using type parameter