What are the limitations of Scala's Manifests?

Scala's Manifests are a way to get around some type erasure problems due to the JVM's lack of reified generics.

They are discussed in several other questions; here are a few:

• What is a Manifest in Scala and when do you need it?
• How does Scala's (2.8) Manifest work?
• How do I get around type erasure on Scala? Or, why can't I get the type parameter of my collections?
• How can I use Scala's Manifest class to instantiate the erased class at runtime?
• Manifest vs ClassManifest. What does this Scala error mean?

One of the comments mentions that “This feature is experimental, and there are cas开发者_Go百科es in which it doesn't work. Still, it can go a long way.” (Daniel Sobral)

What are the cases where the Manifest approach breaks down and why?

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The most important case should be open Tickets in the Scala teams bug tracking system. I found the following:

• manifests + intersection types violate val-binding abstraction
• Compiler cannot determine implicit Manifest for type constructor
• ClassManifest.typeArguments returns empty list on array manifests
• manifests need to account for variance

I believe the general idea is, that Manifests will be part of the planned/upcomming Scala reflection library and apart from using them in the context of Arrays is "on your own risk" ( see ).

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One more:

    scala> class C;
    defined class C

    scala> trait T;
    defined trait T

    scala> manifest[C] <:< manifest[C with T]
    res0: Boolean = true

I've not even reported it since, according to this, manifests are deprecated in 2.10 so they are not fixing bugs with them.