CODEWITHSUNDEEP
scalametaprogramming
Illiax
Illiax

Reputation: 992

class as argument, scala.

as a simplified version of my code:

abstract class GenX
case class X1 extends GenX
case class X2 extends GenX
...

class A {
 val ab : LinkedList[X1] = LinkedList()
 val ac : LinkedList[X2] = LinkedList()
 ...
 def addX[T <: GenX]( x : GenX, clazz : T) =
   getList(clazz) append LinkedList(x) // HERE complains

 def getList(T <: GenX) (clazz : T) : LinkedList[_<: GenX] = clazz match {
  case X1 => ab
  case X2 => ac
  ...
  }
}

my intention is that when a GenX needs to be added to A, it can pass its class as argument for a generic addition like 

case class X1 extends GenX{
 def addToA(a : A) = a.addX(this, this getClass)
}

the problem now is that compiler complains bout x being of GenX type and not _$1 <: GenX type

I dont get it.

Upvotes: 1

Views: 75

Answers (1)

Shadowlands
Shadowlands

Reputation: 15074

First, with regard to appending, I would suggest using something like a ListBuffer rather than a LinkedList, it has a much friendlier API for appending.

Next, your declaration of the clazz argument declares it to be of type T (subtype of GenX), not Class[T]. You are better off just matching on x, anyway.

Finally, x is declared as of type GenX, and for all the compiler can tell is potentially a different subclass of GenX from clazz or the subclass type of the selected list, hence the actual compilation error you would have received.

Here is a version of A that should achieve what you are trying for:

import scala.collection.mutable.ListBuffer

class A {
  val ab : ListBuffer[X1] = ListBuffer()
  val ac : ListBuffer[X2] = ListBuffer()
  // ...

  def addX(x: GenX) = x match {
    case x1: X1 => ab += x1
    case x2: X2 => ac += x2
    // ...
  }         
}

Upvotes: 4

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