Case classes, pattern matching and varargs

Question

Let\'s say I have such class hierarchy:

abstract class Expr
case class Var(name: String) extends Expr
case class ExpList(listExp: List[Expr]) extends Expr
         


        

Answer 1

Just as a comment to Dan's solution: If you have this inside a function it does, due to the bug in Scala not work https://issues.scala-lang.org/browse/SI-3772. You get something like:

scala> :paste
// Entering paste mode (ctrl-D to finish)
    def g(){
        class Expr {}
        case class ExpList(listExp: List[Expr]) extends Expr
        object ExpList {
          def apply(listExp: Expr*) = new ExpList(listExp.toList)
        }
    }
// Exiting paste mode, now interpreting.

:10: error: ExpList is already defined as (compiler-generated) case cla
ss companion object ExpList
                    object ExpList {
                           ^

For now the workaround is simply to put the object first.

scala> :paste
// Entering paste mode (ctrl-D to finish)
    def g(){
        class Expr {}
        object ExpList {
          def apply(listExp: Expr*) = new ExpList(listExp.toList)
        }
        case class ExpList(listExp: List[Expr]) extends Expr
    }

// Exiting paste mode, now interpreting.
g: ()Unit

I hope that will prevent people from stumbling over this bug as I did.