Question

I’m trying to achieve something like this:

def a(b: Any) = {
  b match {
     case x: Seq[String] => println("x")
  }
}

// somewhere else

a(List("b"))

As a result I’d love to see “x” being printed, and I don’t.

Basically I want to match against a type/trait and cover all of the objects whose types derive from/implement such type/trait, with the trait being Seq and the type parameter being known in advance.
Since I’m a scala novice I’m quite stuck, however.

Ideas?

Answer 1

You can’t check against parameterized types because of type erasure. See this question why there will be a warning: Warning about an unchecked type argument in this Scala pattern match?

Another question and its answers tell you how to get around that: How do I get around type erasure on Scala? Or, why can’t I get the type parameter of my collections?

Nevertheless your code works fine, when you don’t check against type parameters:

scala> List("a") match { case _: Seq[_] => 1 case _ => 2 }
res0: Int = 1