Chapter5-2.scala

package chapter5

/**
  * Created by hoshi on 1/22/16.
  */
object MainObj2 {
  def main(args: Array[String]) {
    // a pattern match down to a PartialFunction[A,B]
    val list = List("A", 2, 3, "D")
    var tmp = list.filter(a => a match {
      case s: String => true
      case _ => false
    })
    println(tmp)
    // It reduces this code snippet
    tmp = list.filter {
      case s: String => true
      case _ => false
    }
    println(tmp)

    // Pattern Matching As Functions
    def handleRequest(req: List[String])(exceptions: PartialFunction[List[String], String]): String =
    if ( exceptions.isDefinedAt(req) ) exceptions(req) else "Handling URL " + req + " in the normal way"

    def doApi(call: String, params: List[String]): String = "Doing API call " + call

    println("foo " + handleRequest("foo" :: Nil) {
      case "api" :: call :: params => doApi(call, params)
    })

    val f1: PartialFunction[List[String], String] = {
      case "stuff" :: Nil => "Got some stuff"
    }
    val f2: PartialFunction[List[String], String] = {
      case "other" :: params => "Other:" + params
    }
    val f3 = f1 orElse f2
    println("F3 " + handleRequest("other" :: "b" :: Nil)(f3))
    println("F3 " + handleRequest("stuff" :: Nil)(f3))
  }
}

----

package chapter5

/**
  * Object-Oriented and Functional Tensions
  */
case class Circle(radius: Double) extends Shape
case class Square(length: Double) extends Shape
case class Rectangle(h: Double, w: Double) extends Shape

class Shape {}

object ShapeMain extends App {
  // It's easy to add common functions
  def area(shape: Shape): Double = shape match {
    case Circle(r) => r * r * Math.PI
    case Square(l) => l * l
    case Rectangle(h, w) => h * w
  }

  val c = Circle(5)
  val s = Square(4)
  val r = Rectangle(3, 2)
  println(area(c))
  println(area(s))
  println(area(r))
}

----

package chapter5

/**
  * Example of visitor pattern with pattern-matching version
  * No need "accept" method
  */
trait CarElement
case class Wheel(name: String) extends CarElement
case class Engine() extends CarElement
case class Body() extends CarElement
case class Car(elements: List[CarElement]) extends CarElement

object CarElementMain {
  def doSomething(in: CarElement): Unit = in match {
    case Wheel(name) => println(s"W $name")
    case Engine() => println("E")
    case Body() => println("B")
    case Car(e) => e.foreach(doSomething)
  }

  def main(args: Array[String]) {
    val elems = Car(List(new Engine, new Body, new Wheel("FR"), new Wheel("FL")))
    doSomething(elems)
  }
}