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Haskell totally erased types and has a mechanism to recover that information as values. Both are way safer and easier to use than Java's versions.



Scala follows a similar route. It erases types, but lets you reify on demand in form of TypeTags.


Except not:

    x match {
      case _: List[Int] => 1
      case _: List[Char] => 2
      case _: String => 3
    }
This used java's semi-erased class tags and doesn't report a TypeTag constraint in its type. It will also return 1 when x is of type List[Char] since partial erasure means that the first two patterns end up being identical. The compiler will warn you about this situation, but generally it shows up all the time for various reasons. Super bad news.

That all said, the TypeTag system could be very nice someday. Especially if asInstanceOf were dropped eventually or, better, relied upon TypeTag.




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