DepCells.scala

// Cells that depend on their handler context.

object HandlerCtx {

  def apply(): HandlerCtx = {
    new HandlerCtx
  }

}

class HandlerCtx private {
  self =>

  type Group

  def register(cell: Cell { type Group = self.Group }): Unit = println("OK")

}

object Cell {

  def apply()(implicit ctx: HandlerCtx): Cell { type Group = ctx.Group } = {
    new CellImpl { type Group = ctx.Group }
  }

}

trait Cell {

  type Group

}

private class CellImpl extends Cell {
}

object Test {
  def main(args: Array[String]): Unit = {
    implicit val ctx = HandlerCtx()
    val cell = Cell()
    ctx.register(cell)

    val ctx2 = HandlerCtx()
    ctx2.register(cell)
  }
}