Match parameterized type using Scala's pattern matching

Question

I have a class Operator[T: TypeTag : ClassTag] and in of it's methods, I want to use Scala's pattern matching on the parameterized type T. I know how pattern matching works and so tried the following in Scala's repl and got an error.

scala> def matchTest() = T match {
     | case x: String => "abcd"
     | case _ => null
     | }
<console>:11: error: not found: value T
       def matchTest() = T match {
                            ^

maybe this helps: http://stackoverflow.com/questions/20125975/scala-match-type-argument-for-an-object — Rado Buransky, Jan 02 '15 at 07:59
@RadoBuransky: I did add `TypeTag` and `ClassTag` just for tackling type erasure. — Kamal Banga, Jan 02 '15 at 08:06

score 5 · Answer 1 · answered Jan 02 '15 at 08:09

5

T is a type, not a value. You can only match on values.

You can get an implicitly[ClassTag[T]] or implicitly[TypeTag[T]], which are values, and do matching on those.

answered Jan 02 '15 at 08:09

Daniel C. Sobral

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And `classTag[T]` and `typeTag[T]` are shorthands for these. :) – Jan 02 '15 at 08:16
Can you give me full example, I still get some error on doing `def matchTest[T: TypeTag: ClassTag]() = typeTag[T] match { case typeTag[String] => "abcd" case _ => null }` – Kamal Banga Jan 02 '15 at 08:42
@KamalBanga Because you can call functions on a case matching. Assign `typeTag[String]` to a variable first, and then match on that. – Daniel C. Sobral Jan 03 '15 at 23:50

Match parameterized type using Scala's pattern matching

1 Answers1