Question

I’m using integer coordinates for hex grids as follows:

object Cood
{ 
  val up = Cood(0, 2)
  val upRight = Cood(1, 1)
  val downRight = Cood(1, -1)
  val down = Cood(0, - 2)
  val downLeft = Cood(-1, -1)
  val upLeft = Cood(- 1, 1)    
  val dirns: List[Cood] = List[Cood](up, upRight, downRight, down, downLeft, upLeft) 
}
case class Cood(x: Int, y: Int)
{
  def +(operand: Cood): Cood = Cood(x + operand.x, y + operand.y)
  def -(operand: Cood): Cood = Cood(x - operand.x, y - operand.y)
  def *(operand: Int): Cood = Cood(x * operand, y * operand)
}

Hexs and Sides both have coordinate values. Every Hex has 6 sides but some sides will be shared by 2 Hexs. Eg Hex(2, 2) and its upper neighbour Hex(2, 6) share Side(2, 4). So I want to apply set operations something like this:

val hexCoods: Set[Cood] = ... some code
val sideCoods: Set[Cood] = hexCoods.flatMap(i => Cood.dirns.map(_ + i).toSet)

But if I do this Cood will be treated as a reference type and the duplicate co-ordinates won’t be stripped out. Is there any way round this?

Answer 1

Did you try it?

scala> Set.empty + Cood(1,1) + Cood(1,2) + Cood(1,1)
res0: scala.collection.immutable.Set[Cood] = Set(Cood(1,1), Cood(1,2))

Like @sschaef pointed out in the comments, case classes have automatically-generated equals and hashCode methods, which implement structural equality rather than just comparing identity. This means that you shouldn’t get duplicates in your set, and sure enough the set in my test didn’t have a duplicate entry.