Functional dynamic dispatch

FpDynamicDispatch.scala

case class Circle(radius: Double)
case class Rectangle(x: Double, y: Double)
case class Square(x: Double)

trait ShapeOps[T] {
  def perimter(t: T): Double
  def area(t: T): Double
}

object ShapeOps {
  val circleShapeOps: ShapeOps[Circle] = new ShapeOps[Circle] {
    override def perimter(t: Circle): Double = 2 * Math.PI * t.radius
    override def area(t: Circle): Double = Math.PI * t.radius * t.radius
  }

  val recangleShapeOps: ShapeOps[Rectangle] = new ShapeOps[Rectangle] {
    override def perimter(t: Rectangle): Double = 2 * (t.x + t.y)
    override def area(t: Rectangle): Double = t.x * t.y
  }
}

trait Shape {
  type T
  def ops: ShapeOps[T]
  def t: T
  override def toString: String = t.toString
}

object Shape extends ShapeOps[Shape] {

  //Smart constructors
  def circle(radius: Double): Shape = new Shape {
    override type T = Circle
    override def ops: ShapeOps[Circle] = ShapeOps.circleShapeOps
    override def t: T = Circle(radius)
  }

  def rectangle(x: Double, y: Double): Shape = new Shape {
    override type T = Rectangle
    override def ops: ShapeOps[Rectangle] = ShapeOps.recangleShapeOps
    override def t: Rectangle = Rectangle(x, y)
  }

  override def perimter(t: Shape): Double = t.ops.perimter(t.t)
  override def area(t: Shape): Double = t.ops.area(t.t)

}

val shapes: Seq[Shape] = List(
  Shape.circle(22),
  Shape.rectangle(34, 56)
)

val totalArea = shapes.map(Shape.area).sum

println(s"Total area $totalArea")