Scala 2.10 TypeTag usage

Question

I\'m digging new scala reflection api and can\'t figure out why the following snippet doesn\'t work as expected. Given hierarchy (tried to simplify as much as I can):

Answer 1

actually you don't check the type of msg here, compiler will warn you that msg: T is erased, so all you are left checking is that type defined on TFilter is the same as a type defined on function f.

I looks like pattern matching is "assisted" by Manifest and ClassTag, so msg: T is indeed a correct type. If you try it with primitives or List[T] it will not work correctly.

val mFilter = new MFilter[Int]
messages collect mFilter.f[Int] // res31: Seq[Int] = List()

val messages = List(List(1), List("a"))
val mFilter = new MFilter[List[Int]]
messages collect mFilter.f[List[Int]] // res32: List[List[Int]] = List(List(1), List(a))

Look at this discussion: http://grokbase.com/t/gg/scala-user/126p8eh1w0/how-to-make-typetag-work-in-a-pattern

bug "Use TypeTags when pattern-matching otherwise erased types": here