Question

In order to avoid Java exceptions I’m using Scala’s exception handling class.

However, when compiling the following snippet:

 import scala.util.control.Exception._

 val cls = classManifest[T].erasure

 // Invoke special constructor if it's available. Otherwise use default constructor.
 allCatch opt cls.getConstructor(classOf[Project]) match {
   case Some(con) =>
     con.newInstance(project) // use constructor with one Project param
   case None =>
     cls.newInstance // just use default constructor
 };

I receive the following error:

 error: type mismatch;
    [scalac]  found   : java.lang.reflect.Constructor[_]
    [scalac]  required: java.lang.reflect.Constructor[_$1(in method init)] where
              type _$1(in method init)
    [scalac]     allCatch opt cls.getConstructor(classOf[Project]) match {
    [scalac]                                    ^
    [scalac] one error found

What’s going on here and how can I fix it?

Answer 1

The type inference scheme has gotten confused by the types available–specifically, by the type of cls. If we write generic code:

def clser[A](cls: Class[A]) = allCatch opt cls.getConstructor(classOf[Project])

then it works perfectly okay. But you’re probably doing something else–I can’t tell what because you didn’t provide the code–and this results in a mismatch between the expected and actual types.