ColorAndShape.scala

case class Color(red: Double, green: Double, blue: Double) {
  def isLight: Boolean =
    (red + green + blue) / 3.0 >= 0.5

  def toGreyscale: Color = {
    val avg = (red + green + blue) / 3.0
    Color(avg, avg, avg)
  }
}

sealed trait Shape {
  def area: Double
}

case class Circle(radius: Double, color: Color) extends Shape {
  def area: Double =
    radius * radius * math.Pi
}

case class Rect(width: Double, height: Double, color: Color) extends Shape {
  def area: Double =
    width * height
}

object otherLibrary {
  def perimeterOf(shape: Shape): Double = {
    shape match {
      case Circle(r, c)  => 2 * math.Pi * r
      case Rect(w, h, c) => 2 * w + 1 * h
    }
  }
}