self.scala

package com.michal

trait A[+Self <: A[_]] {
  def a: Int
  def b: Int
  def addToA(plus: Int): Self = makeCopy(a + plus, b)
  def makeCopy(newA: Int, newB: Int): Self
}

case class B(a: Int, b: Int) extends A[B] {
  def makeCopy(a: Int = a, b: Int = b): B = copy(a = a, b = b)
  def bMethod = s"$a, $b"
}

case class C(a: Int, b: Int, c: Int) extends A[C] {
  def makeCopy(a: Int = a, b: Int = b): C = copy(a = a, b = b)
  def cMethod = s"$a, $b, $c"
}

object MyApp extends App {
  println(B(7, 4).makeCopy(a = 3).addToA(7).bMethod)
  println(C(7, 4, 7).makeCopy(a = 3).addToA(7).cMethod)
}