Scala 2.8 adds specialized type parameters. A specialized type parameter instructs the compiler to generate a generic version and a number of specialized versions of the given definition, and use the most specific version whenever the static type information at a call site allows it.
Links:
[1] http://www.scala-lang.org/sites/default/files/sids/dragos/Thu, 2010-05-06, 17:56/sid-spec.pdf
[2] http://www.scala-lang.org/sites/default/files/sids/dragos/Thu, 2010-05-06, 17:55/sid-spec.tex