vvviiimmm

// Our generic interface
trait Animal {
  def voice: String
}

// Implementation 1
class Dog extends Animal {
  override def voice: String = "woof!"
}

vvviiimmm

// Our generic interface
trait Animal {
  def voice: String
}

// Pure definitions
case class Dog()
case class Cat()

// Implementation 1

vvviiimmm

// Our generic inteface
trait Shape {
  def area: Double
}

// Implementation 1
class Circle(radius: Double) extends Shape {
  override def area: Double = math.Pi * math.pow(radius, 2)
}

vvviiimmm

trait Shape {
  def area: Double
}

// Shape definition data structures, should be in a diffrent file/namespace
case class Circle(radius: Double)
case class Rectangle(width: Double, length: Double)

// Implementation 1
class CircleShape(radius: Double) extends Shape {

vvviiimmm

trait Shape {
  def area: Double
}

case class Circle(radius: Double)
case class Rectangle(width: Double, length: Double)

//               v  (no constructor parameters)
class CircleShape extends Shape {
  override def area : Double = ??? // radius?

vvviiimmm

// Won't compile
trait Shape {
  //       vvv (hmm)
  def area(???): Double
}

case class Circle(radius: Double)
case class Rectangle(width: Double, length: Double)

class CircleShape extends Shape {

vvviiimmm

// Shape is now a parametrized trait
// 'A' is placeholder for `Circle`, `Rectangle` or other shape representation
trait Shape[A] {
  def area(a: A): Double
}

case class Circle(radius: Double)
case class Rectangle(width: Double, length: Double)

// We have to extend with Shape[Circle] because we have to pass 'Circle' to `area`

vvviiimmm

def areaOf[A](shape: A, shapeImpl: Shape[A]): Double = shapeImpl.area(shape)

areaOf(Circle(10), new CircleShape)

vvviiimmm

//                      vvvvvvvv
def areaOf[A](shape: A)(implicit shapeImpl: Shape[A]): Double = shapeImpl.area(shape)

// No more implementation objects
areaOf(Circle(10))

vvviiimmm

implicit val circleShape = new CircleShape
implicit val rectangleShape = new RectangleShape

areaOf(Circle(10))
areaOf(Rectangle(5, 5))