如何编写 asInstanceOfOpt[T] 其中 T <: Any [英] How to write asInstanceOfOpt[T] where T &lt;: Any

问题描述

asInstanceOfOpt 有一个方便的实现，它是 asInstanceOf 的安全版本，在 如何编写asInstanceOfOption"；在 Scala 中.看来，Scala 2.9.1，这个解决方案现在只适用于 AnyRef:

There's a handy implementation of asInstanceOfOpt, a safe version of asInstanceOf, given in the answer to How to write "asInstanceOfOption" in Scala. It appears that, Scala 2.9.1, this solution now only works with AnyRef:

class WithAsInstanceOfOpt(obj: AnyRef) {
  def asInstanceOfOpt[B](implicit m: Manifest[B]): Option[B] =
    if (Manifest.singleType(obj) <:< m)
      Some(obj.asInstanceOf[B])
    else
      None
}

可以重写以支持 Any 吗?

Can this be rewritten to support Any?

推荐答案

你可以使用 shapeless's 可从 Miles Sabin 输入:

You could use shapeless's Typeable from Miles Sabin:

使用类型参数进行类型转换

它处理原语和装箱:

scala> import shapeless._; import syntax.typeable._
import shapeless._
import syntax.typeable._

scala> 1.cast[Int]
res1: Option[Int] = Some(1)

scala> 1.cast[String]
res2: Option[String] = None

scala> "hello".cast[String]
res4: Option[String] = Some(hello)

scala> "foo".cast[Int]
res5: Option[Int] = None

您可以在此处查看源代码以了解其编写方式:

You can see the source here to see how it's written:

https://github.com/milessabin/shapeless/blob/master/core/src/main/scala/shapeless/typeable.scala

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