DynamicImpl.scala

class DynamicImpl(x: AnyRef) extends Dynamic {
  def _select_(name: String): DynamicImpl = {
    new DynamicImpl(x.getClass.getMethod(name).invoke(x))
  }
  def _invoke_(name: String)(args: Any*) = {
    new DynamicImpl(x.getClass.getMethod(name, args.map(_.asInstanceOf[AnyRef].getClass) : _*).invoke(x, args.map(_.asInstanceOf[AnyRef]) : _*))
  }
  override def typed[T] = x.asInstanceOf[T]
  override def toString = "Dynamic(" + x.toString + ")"
}

implicit def toDynamic(x: Any): Dynamic = new DynamicImpl(x.asInstanceOf[AnyRef])

class Duck {
  def quack = "Quack!"
}

class QuackingSwan {
  def quack = "Swack!"
}

def makeQuack(d: Dynamic) {
  println(d.quack.typed[String])
}

makeQuack(new Duck)
makeQuack(new QuackingSwan)

val s: Dynamic = "Hello, world!"
s.toLowerCase
s.length
s.isEmpty.typed[Boolean]

DynamicXML.scala

import scala.xml.{NodeSeq, XML}

class DynamicXML(n: NodeSeq) extends Dynamic {
  def _select_(name: String) = {
    new DynamicXML(n \ name)
  }
  def _invoke_(name: String)(args: Any*) = {
    error("unsupported")
  }
  override def typed[T] = n.asInstanceOf[T]
  override def toString = "DynamicXML(" + n.toString + ")"
}

// A string, to prove I'm not cheating!
val s: String = ("""
  <book>
    <author>
      <firstName>William</firstName>
      <lastName>Shakespeare</lastName>
    </author>
    <title>Hamlet</title>
  </book>""")

val book = new DynamicXML(XML.loadString(s))

book.author.lastName
book.title.typed[NodeSeq].text