custom error message for missing default constructor

[stephanos]

I recently forgot to define a default constructor (when using reflection) and had a hard time discovering what I did wrong. The error message was "next on empty iterator" coming from:

def newInstance[T](clazz: Class[T])(op: T => Unit): T = {
    val constructor =
      clazz.getDeclaredConstructors.filter(_.getParameterTypes.length == 0).head

Maybe you could turn it into something like:

def newInstance[T](clazz: Class[T])(op: T => Unit): T = {
    val constructor =
            clazz.getDeclaredConstructors.filter(_.getParameterTypes.length == 0)
                    .headOption.getOrElse(sys.error("no default constructor found on " + clazz))

This way it would be much easier to find the reason for the exception!

Cheers!

[debasishg]

Fixed on master ..