Scala强制转换为选项[T]

Question

Something like:

  def cast[T](o: Any): Option[T] = o match {
    case v: T => Some(v)
    case _ => None
  }

or:

  def cast[T](c: Class[T], o: Any): Option[T] = o match {
    case v: T => Some(v)
    case _ => None
  }

Is this a good idea? Is there a standard library equivalent?

Why do I get and how do I resolve the following Scala compiler warning:

Warning:(7, 13) abstract type pattern T is unchecked since it is eliminated by erasure
    case v: T => Some(v)

Answer 1

Use class tag. Type information gets lost during runtime.So, you need provide type information which can be done using class tag.

import scala.reflect.ClassTag

def cast[T: ClassTag](o: Any): Option[T] = o match {
 case v: T => Some(v)
 case _ => None
}

Scala REPL

scala> cast[String]("hello")
res2: Option[String] = Some(hello)

scala> cast[Int]("scala")
res3: Option[Int] = None