lift, squeryl record, and scala implicits: adding new method to record, extending AnyVal

Question

I would like to add additional method for Squeryl Record (Lift web framework). The method is named validateTry. See the code below

import scala.language.postfixOps
import scala.util._

import net.liftweb.record._

package object code {
  implicit class RecordOps[T <: Record[T]](r: T) {
    def validateTry(): Try[T] = {
      r.validate match {
        case Nil => Success(r)
        case errs => Failure(new Exception("Error(s) during validation " + r.getClass() + ": " + errs.mkString(", ")))
      }
    }
  }
}

and it works as expected. But I would like to extend AnyVal, like this

  implicit class RecordOps[T <: Record[T]](r: T) extends AnyVal {

because as I see it will be "right" (as I see it should have influence on performance). But after I have added "extends AnyVal", I received error "value class needs to have exactly one public val parameter". What is this and how to fix? (And do I really need to fix?)

Thanks.

UPD. I added "val" to constructor definition and it started work. Thanks to the link Vasya Novikov gave me. Right peace of code looks like this:

implicit class RecordOps[T <: Record[T]](val r: T) extends AnyVal {

And it works as expected. Documentation says it should avoid instantiation of class as I see. The link is http://docs.scala-lang.org/overviews/core/value-classes.html