Scala DSL - Nested block referencing parent

Question

Playing about with a DSL in Scala, so lets say I have something like this:

house {
  floor {
    bedroom(\"kids)
    bedroom(\"master\")
  }
  floor {
    ki         


        

Answer 1

This approach uses mutable fields to set the child-to-parent relation after the involved objects have been created:

/* Data classes */

class House(val floors: Seq[Floor])
class Floor(val name: String, val bedrooms: Seq[Bedroom]) { var house: House = _}
class Bedroom(val name: String) { var floor: Floor = _ }

/* Factory methods */

def house(floors: Floor*) = {
  val house = new House(floors)
  floors foreach (_.house = house)
  house
}

def floor(name: String)(bedrooms: Bedroom*) = {
  val floor = new Floor(name, bedrooms)
  bedrooms foreach (_.floor = floor)
  floor
}

def bedroom(name: String) = new Bedroom(name)

This allows you to create house structures in a concise and type-safe way as follows:

val myHouse = 
  house(
    floor("first")(
      bedroom("joe")
    ),
    floor("second")(
      bedroom("anna"),
      bedroom("clara")
    )
  )

assert(myHouse.floors(0).house == myHouse)
assert(myHouse.floors(1).house == myHouse)
assert(myHouse.floors(0).bedrooms(0).floor == myHouse.floors(0))
assert(myHouse.floors(1).bedrooms(1).floor == myHouse.floors(1))

It should be fairly easy to factor out common behaviour into some base traits or methods, for example, iterating over the subcomponents to fix the relationships.