A thought on inheritance...

inheritance.kt

interface Data<T: Data> {
  companion object {
    abstract fun decode(encoded: Encoded): T
  }
}

class Coords2D : Data<Coords2D> {
  companion object {
    fun decode(encoded: Encoded): Coords2D {
      ...
    }
  }
}

class Coords3D : Data<Coords3D> {
  companion object {
    fun decode(encoded: Encoded): Coords3D {
      ...
    }
  }
}