如何在Scala中解决模式匹配和类型擦除

Question

I'm working on an existing piece of code :

def f(s: Option[String]) = …
def matchAny(a: Any) = a match { case s: Option[String] => f(s) }

And the compiler warns me (it's normal because it's not typesafe).

def matchAny(a: Any) = a match { case s: Option[_] => f(s.asInstanceOf[Option[String]] }

I know it's still not typesafe, but we gain the warning and the risk appears now explicitly in the code. But it's more verbose…

So, what do you think about this workaround ? And is there a better way ?

Answer 1

Slightly less verbose syntax that suppresses warning:

def matchAny(a: Any) = a match { case s: Option[String@unchecked] => f(s) }

In this case ( Option[String] matching), you can also have safer version which will fail immediately if something else than String is in the Option :

def matchAny(a: Any) = a match { case s@(None | Some(_: String)) => f(s) }

Answer 2

I would recommend use shapeless instead:

import shapeless._
def f(s: Option[String]) = Some("hello world")
val optionType: TypeCase[Option[String]] = TypeCase[Option[String]]
def matchAny(a: Any) = a match { case optionType(s) => f(s) }