CODEWITHSUNDEEP
scalainheritance
LaloInDublin
LaloInDublin

Reputation: 5449

Extending scala case class without constantly duplicating constructors vals?

Is there a way to extend a case class without constantly picking up new vals along the way?

For example this doesn't work:

case class Edge(a: Strl, b: Strl)
case class EdgeQA(a: Strl, b: Strl, right: Int, asked: Int) extends Edge(a, b)

"a" conflicts with "a", so I'm forced to rename to a1. But I don't want all kinds of extra public copies of "a" so I made it private. 

case class Edge(a: Strl, b: Strl)
case class EdgeQA(private val a1: Strl, private val b1: Strl, right: Int, asked: Int) extends Edge(a, b)

This just doesn't seem clean to me... Am I missing something?

Upvotes: 74

Views: 81979

Answers (4)

Xavier Guihot
Xavier Guihot

Reputation: 61666

Starting in Scala 3, traits can have parameters:

trait Edge(a: Strl, b: Strl)
case class EdgeQA(a: Strl, b: Strl, c: Int, d: Int) extends Edge(a, b)

Upvotes: 5

david.perez
david.perez

Reputation: 7012

This solution offers some advantages over the previous solutions:

trait BaseEdge {
  def a: Strl
  def b: Strl
}
case class Edge(a:Strl, b:Strl) extends BaseEdge
case class EdgeQA(a:Strl, b:Strl, right:Int, asked:Int ) extends BaseEdge

In this way:

  • you don't have redundant vals, and
  • you have 2 case classes.

Upvotes: 60

bajohns
bajohns

Reputation: 1296

As the previous commenter mentioned: case class extension should be avoided but you could convert your Edge class into a trait.

If you want to avoid the private statements you can also mark the variables as override 

trait Edge{
  def a:Strl
  def b:Strl
}

case class EdgeQA(override val a:Strl, override val b:Strl, right:Int, asked:Int ) extends Edge

Don't forget to prefer def over val in traits

Upvotes: 79

nickgroenke
nickgroenke

Reputation: 1502

Case classes can't be extended via subclassing. Or rather, the sub-class of a case class cannot be a case class itself.

Upvotes: 15

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