Memoized Fibonacci

My:
object Sol {
def fib(n: Int): BigInt = {
  @annotation.tailrec
  def getTailRec(index: Int, prev: BigInt, current: BigInt): BigInt = {
    if (index <= 0) {
      current
    } else {
      getTailRec(index - 1, prev = prev + current, current = prev)
    }
  }
  getTailRec(n, prev = 1, current = 0)
}
}

Other:
import scala.collection.mutable.Map
object Sol {
  val cached: Map[Int, BigInt] = Map(0 -> 0, 1 -> 1)
  def fib(n: Int): BigInt =
    cached.getOrElseUpdate(n, fib(n-1) + fib(n-2))
}