Can't extend Edges in case class in scala 3

[TomLous]

For the 2.0.0 release with Scala 3.3.1

I'm aware that the library was build for 2.13, but I'm using it with scala 3 and seems to work for the most part

The main issue was with using a case class for creating a labeled Edge

private case class LocationEdge(source: String, target: String, label: Direction) extends LDiEdge[String, Direction]

Which gives the error:

error overriding method _1 in trait AnyDiEdge of type => String;
method _1 of type => String cannot override final member method _1 in trait AnyDiEdge
..
error overriding method _2 in trait AnyDiEdge of type => String;
method _2 of type => String cannot override final member method _2 in trait AnyDiEdge

The workaround was to use a normal class, like

 private case class LocationEdge(override val source: String, override val target: String, override val label: Direction) extends LDiEdge[String, Direction]:
    override def equals(obj: Any): Boolean =
      super.equals(obj) && obj.isInstanceOf[LocationEdge] && obj.asInstanceOf[LocationEdge].label == label

But that also meant I had to override the equals method if I didn't want Edges with the same spurce/target but different labels to be deduplicated

[TomLous]

Also minor note, but accessing label information only works if I define the Graph from a list of edges like:

val graph = DefaultGraphImpl.from(Nil, edges)

If I use

val graph = Graph.from(edges)

I get an error If I try to access the label

graph.get(currentNode).outgoing.find(_.label == Direction.Left)

value label is not a member of graph.EdgeT

[spamegg1]

@TomLous I think we're both trying to use this library for Advent of Code Day 08?

I have the same issue, using the code for the MyLDiEdge example in the docs:

Adding the override val modifiers does not help:

It seems to me that the final modifiers in AnyDiEdge should be removed.

[TomLous]

Ha indeed. Pretty overkill for day 8, but I like the graph library and wanted to give the 2.0.0 version a spin.
Got it working with the workaround.
https://github.com/TomLous/advent-of-code/blob/main/2023/src/main/scala/aoc2023/day8/Day8.scala

[spamegg1]

Thanks for the workaround!

I'm quite disappointed I can't use this library as it currently is. I really wanted to make it work, I even added infix syntactic sugar for adding labels with +: with a Scala 3 extension method (screw the Scala 2 implicit classes, they make no sense):

  // for infix sugar n1 ~> n2 +: l ; ~> is given by DiEdgeImplicits.
  extension (e: DiEdge[Node])
    def +:(move: Move) = new LDiEdge[Node, Move]:
      def label: Move = move
      def source: Node = e.source
      def target: Node = e.target

so I could do cool stuff like this:

wasteland += node.label ~> node.left +: Direction.Left
wasteland += node.label ~> node.right +: Direction.Right

but eventually I needed a multi-graph with multi edges...

[peter-empen]

Thanks for reporting! To sum up, when defining a case class in Scala 3, there are two issues:

1. error overriding getter for source and target. This can be resolved by spelling out override val in the case class definition.
2. error overriding method for _1 and _2 is reported because the library used _1 and _2 in Scala 2 but Scala 3, inspired by Graph for Scala 😉, also added these methods to case classes. This is why you had to fall back to a plain class. We are going to resolve the conflicting methods in the library.

@spamegg1 Your current implementation takes care of equal but not hashCode. So yes, you better extend multilabeled.LDiEdge.

@TomLous

graph.get(currentNode).outgoing.find(_.label == Direction.Left)

value label is not a member of graph.EdgeT

Sure, you inspect the inner edge but label is a member of your outer edge.

[spamegg1]

@peter-empen

We are going to resolve the conflicting methods in the library.

Thanks a lot! 🙏 (I can finally solve Day 08 properly)

[peter-empen]

Does 2.0.1 work for you?

[spamegg1]

Does 2.0.1 work for you?

Seems to be working, yeah!
I'm trying to create this graph (with multiple edges between same pair of nodes):

I have stuff like this:

  // for infix sugar n1 ~> n2 +: l ; ~> is given by DiEdgeImplicits.
  extension (e: DiEdge[Node])
    def +:(move: Move) = new LDiEdge[Node, Move]:
      def label: Move = move
      def source: Node = e.source
      def target: Node = e.target

And then populate with stuff like:

  def populate(bonds: Seq[Bond]): Wasteland =
    val wasteland: Wasteland = Graph.empty
    bonds.foreach(bond =>
      wasteland += bond.label
      wasteland += bond.left
      wasteland += bond.right
      wasteland += bond.label ~> bond.left +: Left
      wasteland += bond.label ~> bond.right +: Right
    )
    wasteland

The result is:

res0: Graph[Node, LDiEdge[Node, Move]] = Graph(
  NodeSet(AAA, BBB, CCC, DDD, EEE, GGG, ZZZ), 
  EdgeSet(
    AAA ~> BBB :++ Left, 
    AAA ~> CCC :++ Right, 
    BBB ~> DDD :++ Left, 
    BBB ~> EEE :++ Right, 
    CCC ~> GGG :++ Left, 
    CCC ~> ZZZ :++ Right, 
    DDD ~> DDD :++ Left, 
    DDD ~> DDD :++ Right, 
    EEE ~> EEE :++ Left, 
    EEE ~> EEE :++ Right, 
    GGG ~> GGG :++ Left, 
    GGG ~> GGG :++ Right, 
    ZZZ ~> ZZZ :++ Left, 
    ZZZ ~> ZZZ :++ Right
  )
)

Looks right!

So am I doing this correctly? The output :++ looks different than what I defined +:.

[peter-empen]

Great, So the compiler issue is resolved.
Let's discuss any remaining question separately.

[TomLous]

Thanks @peter-empen 👍🏻