在Scala中，如何在TypeTag可用时转换值

Question

Given

• a value of type Any
• a TypeTag corresponding to the desired type

How can I cast the value

Unfortunately, the following snippet doesn't compile

val v: Any = 123
val tag    = typeTag[Int]
val i      = v.asInstanceOf[t.tpe]

Answer 1

Use this

import scala.reflect.ClassTag

def getTypedArg[T: ClassTag](any: Any): Option[T] = {
      any match {
        case t: T => Some(t)
        case invalid =>
          None
      }
}

---

Usage

scala> getTypedArg[Int](5)
res1: Option[Int] = Some(5)

scala> getTypedArg[Int]("str")
res2: Option[Int] = None

---

Source: Retrieve class-name from ClassTag

---

EDIT-1

As asked by @Aki , it can be made to work with TypeTag s too, with this hack

import reflect.runtime.universe._
import scala.reflect.ClassTag

def typeToClassTag[T: TypeTag]: ClassTag[T] = {
  ClassTag[T]( typeTag[T].mirror.runtimeClass( typeTag[T].tpe ) )
}

def getTypedArg2[T: TypeTag](any: Any): Option[T] = {
  implicit val c: ClassTag[T] = typeToClassTag[T]
  any match {
    case t: T => Some(t)
    case invalid =>
      None
  }
}

Reference: How to get ClassTag form TypeTag, or both at same time?

Answer 2

You could write your own method that does the casting.
(note that this method will never throw ClassCastExceptions)

def cast[A](a: Any, tag: TypeTag[A]): A = a.asInstanceOf[A]