gistfile1.scala

miles@frege:~$ scala
Welcome to Scala version 2.11.0 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_55).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import scala.language.dynamics
import scala.language.dynamics

scala> case class Assoc[K, V](value: V)
defined class Assoc

scala> def mkAssoc[V](key: String)(value: V) = Assoc[key.type, V](value)
mkAssoc: [V](key: String)(value: V)Assoc[key.type,V]

scala> implicit def fooAssoc = mkAssoc("foo")(true)
fooAssoc: Assoc[String("foo"),Boolean]

scala> implicit def barAssoc = mkAssoc("bar")(23)
barAssoc: Assoc[String("bar"),Int]

scala> object SafeDynamic extends Dynamic {
     |   def selectDynamic[V](key: String)(implicit assoc: Assoc[key.type, V]): V = assoc.value
     | }
defined object SafeDynamic

scala> SafeDynamic.foo
res0: Boolean = true

scala> SafeDynamic.bar
res1: Int = 23

scala> SafeDynamic.baz
<console>:15: error: could not find implicit value for parameter assoc: Assoc[String("baz"),V]
              SafeDynamic.baz
              ^