Ejemplos meetup de Scala, 12 de julio de 2018

ejemplos.scala

case class Point(x: Double, y: Double) {
  def +(p: Point)  = Point(x + p.x, y + p.y)
  def *(a: Double) = Point(a * x, a * y)

  def distTo(that: Point) = {
    val Point(dx, dy) = this + that * -1
    math.sqrt(dx * dx + dy * dy)
  }
}

trait Shape
case class Circle(center: Point, radius: Double) extends Shape
case class Polygon(vertices: Seq[Point]) extends Shape {

  def edges: Seq[(Point, Point)] =
    (vertices.init zip vertices.tail) :+ (vertices.last, vertices.head)

  // Pattern match to extract the points.
  def perimeter: Double =
    edges.map { case (p1, p2) ⇒ p1 distTo p2 }.sum

  // Pattern match to extract xy coordinates.
  def area: Double =
    edges.map {
      case (Point(x1, y1), Point(x2, y2)) ⇒ (x2 - x1) * (y2 + y1)
    }.sum / 2

}

def name(p: Point): String = p match {
  case Point(0, 0) ⇒ "origen"
  case Point(x, y) ⇒ s"el punto $x $y"
}

val triangle = Polygon(List(Point(0, 0), Point(0, 4), Point(3, 4)))
val myShapes = List(
  Circle(Point(3, 0), 5),
  triangle,
  Circle(triangle.vertices.head, 20)
)


assert(triangle.area == 6)
assert(triangle.perimeter == 12)

myShapes.map {
  case Circle(Point(0, 0), r) ⇒ "Un circulo en el origen"
  case Circle(c, r) if r < 10 ⇒ "Un circulo chico"
  case Circle(c, r)           ⇒ "Un circulo grande"
  case Polygon(vs)            ⇒ s"Un poligono de ${vs.length} lados"
}

val n = 20
List(11, 22, 33).map { x ⇒ 2 * x } // no es un closure
List(11, 22, 33).map { x ⇒ n * x } // sí es un closure (captura variables de afuera)

val persons = List("Alicia", "Bernardo", "Claudio")
val ns = List(66, 22, 77, 44, 22)
val hola = Stream.continually("Hola")

persons zip ns zip hola