class C { implicit this =>
  def f(implicit c: C) = ???
  def g = f // ok
}
class C(x: X, y: Y) { self(implicit x) =>
  def f(implicit z: X) = ???
  def g = f // ok
}
// C.x needn't be a field as in:
class C(implicit x: X, y: Y) { ... }  // don't want implicit param section
class C(x: X, y: Y) {
  implicit private val x1: X = x   // incurs a field
}