In Scala, how can i declare right type in base abstract class to access by index in this situation

Question

I'm sorry, I'm very new to Scala.

My code looks like below.

abstract class A{
  val container: Any
  //Some other member and methods are hidden
}

class B extends A {
  val container: Vector(1,2)
  //Some other member and methods are hidden
}

class C extends A {
  val container: ArrayBuffer(1,2,3)
  //Some other member and methods are hidden
}

So, when i want use these function in main function like below, which means that i intend to access container by index.

val vector = new ArrayBuffer[A].empty
vector += new B
vector += new C
  
for( vec <- vector ){
  println(vec.container(0))
}

However, the compiler says "Any does not take parameters"

So, my problem is, how should i declare value container in base class to access input with index.

Help me, Thanks.

Answer 1

There are at least 2 variants:

import scala.collection.mutable.ArrayBuffer
import scala.collection.immutable.Vector
import scala.collection.IndexedSeq

// variant 1
trait A1[T] {
  def container: IndexedSeq[T]
}

class B1 extends A1[Int] {
  val container: Vector[Int] = Vector(1, 2)
}

class C1 extends A1[Long] {
  val container: Vector[Long] = Vector(1, 2)
}

// variant 2
trait A2 {
  def container: IndexedSeq[_]
}

class B2 extends A2 {
  val container: Vector[Int] = Vector(1, 2)
}

class C2 extends A2 {
  val container: ArrayBuffer[Long] = ArrayBuffer(1, 2)
}

object Main extends App {
  val coll1 = new ArrayBuffer[A1[_]]()
  coll1 += new B1()
  coll1 += new C1()
  val coll2 = new ArrayBuffer[A2]()
  coll2 += new B2()
  coll2 += new C2()
  
  for( vec <- coll1 ) {
    println(vec.container(0))
  }
  for( vec <- coll2 ) {
    println(vec.container(0))
  }
}

tested here on Scala 2.13.6