magnetic.scala

  trait Magnetic[T] {
    protected sealed trait TagMag
    type Magnet = T @@ TagMag
    protected implicit def tag(value: T) = Tag[T, TagMag](value)
    def apply(mag: Magnet): T = mag
  }

  object CreateDescriptor extends Magnetic[CreateDescriptor] {
    implicit def default(unit: Unit): Magnet = CreateDescriptor(None, AssetDescriptorRecord())
    implicit def fromUser(user: ProfilePair): Magnet = CreateDescriptor(Some(user), AssetDescriptorRecord())
  }