import stainless.annotation._

trait Immutable[@mutable T] {
  def compare(t1: T, t2: T): Boolean
}

case class Box(var x: BigInt)

case object ImmutableObject extends Immutable[Box] {
  def compare(t1: Box, t2: Box): Boolean = true
}

Add benchmark where a class with a mutable type parameter is not considered mutable
Add benchmark where a class with a mutable type parameter is not considered mutable
