Creating an object from a type parameter in Scala

问题

I want to create a method that takes a type parameter, obviously with no parameters on its constructor, and returns a dummy object constructed with that constructor. Basically some kind of factory pattern.

• Is that even possible in Scala?
• Is that a good idea? Any better pattern if it is not?
• Is there a way to achieve this at compile-time only (i.e. without reflection)?

Code example :

trait Model
class A extends Model
class B extends Model

def dummy[T <: Model] = new T   // Fails compilation with "class type required but T found"

dummy[A]  // Returns an instance of A
dummy[B]  // Returns an instance of B

回答1:

This can be done using ClassManifests, which are designed to overcome erasure:

def dummy[T <: Model : ClassManifest] = classManifest[T].erasure.newInstance

As for doing it at compile time without reflection, I guess that it could be done using scala 2.10 macros.

来源：https://stackoverflow.com/questions/15861441/creating-an-object-from-a-type-parameter-in-scala