Simple macro-based wrapper example

wrapper.scala

import scala.language.experimental.macros
import scala.reflect.macros.Context

object WrapperExample {
  def wrap[A](a: A): A = macro wrap_impl[A]

  def wrap_impl[A: c.WeakTypeTag](c: Context)(a: c.Expr[A]) = {
    import c.universe._

    val wrapped = weakTypeOf[A]
    val f = Select(reify(Predef).tree, "println")

    val methods = wrapped.declarations.collect {
      case m: MethodSymbol if !m.isConstructor => DefDef(
        Modifiers(Flag.OVERRIDE),
        m.name,
        Nil, Nil,
        TypeTree(),
        Block(
          Apply(f, c.literal("Calling: " + m.name.decoded).tree :: Nil),
          Select(a.tree, m.name)
        )
      )
    }.toList

    val constructor = DefDef(
      Modifiers(), nme.CONSTRUCTOR, Nil, Nil :: Nil, TypeTree(),
      Block(
        Apply(
          Select(Super(This(tpnme.EMPTY), tpnme.EMPTY), nme.CONSTRUCTOR), Nil
        ) :: Nil,
        c.literalUnit.tree
      )
    )

    val anon = c.fresh

    c.Expr(Block(
      ClassDef(Modifiers(Flag.FINAL), newTypeName(anon), Nil,
        Template(
          List(Ident(wrapped.typeSymbol.name)),
          emptyValDef,
          constructor :: methods
        )
      ) :: Nil,
      Apply(Select(New(Ident(newTypeName(anon))), nme.CONSTRUCTOR), Nil)
    ))
  }
}

See http://stackoverflow.com/questions/13767582/creating-a-method-definition-tree-from-a-method-symbol-and-a-body for an explanation and related dicsussion.

A discussion of a subtle error in this code: http://groups.google.com/group/scala-internals/browse_thread/thread/492560d941b315cc