Base class for defining newtypes that have no type parameters.

This class does not define any "builder", or related HasBuilder instance, as you're expected to provide one yourself.

Usage sample:

type EmailAddress = EmailAddress.Type

object EmailAddress extends Newtype[String] { self =>
  def apply(value: String): Option[Type] =
    if (value.contains("@"))
      Some(unsafeCoerce(value))
    else
      None

  // Recommended instance, but not required;
  // use Newtype.Validated to get rid of this boilerplate ;-)
  implicit val builder: HasBuilder.Aux[EmailAddress, String] =
    new HasBuilder[EmailAddress] {
      type Source = String

      def build(v: String): Either[BuildFailure[Type], Type] =
        apply(v) match {
          case Some(r) =>
            Right(r)
          case None =>
            Left(BuildFailure[EmailAddress]("missing @"))
        }
    }
}