Implicits.scala

package example

object Hello {
  def main(args: Array[String]): Unit =
    println("Hello")
  
  // 1 implicit conversions
  // NEVER USE THIS
  {
    import scala.language.implicitConversions
    case class MyThing(n: Int)
    case class TheirThing(n: Int)
    
    implicit def convertThings(theirThing: TheirThing): MyThing =
      MyThing(theirThing.n)
    
    def incMyThing(myThing: MyThing): MyThing = {
      //myThing.copy(n = myThing.n + 1)
      MyThing(myThing.n + 1)
    }
    val x: MyThing = incMyThing(MyThing(2))
    val y = incMyThing(TheirThing(2))
    //                 ^^^^^^^^^^
  }
  
  // 2 implicit extensions
  implicit class RichString(string: String) {
    def happy(): String = string ++ " LOL"
  }
  
  "hello".happy() // -> "hello LOL"

  // 3 implicit parameters
  case class Metadata(string: String)
  implicit val metadata = Metadata("abc")

  def addOneWithMetadata(n: Int, metadata: Metadata): Int = n + 1
  addOneWithMetadata(5, metadata)

  def addOneWithMetadataImplicit(n: Int)(implicit metadata: Metadata): Int = n + 1
  addOneWithMetadataImplicit(5)
  
  // 4 typeclasses
  trait Show[A] {
    def show(a: A): String
  }
  
  def show[A](a: A)(implicit showInstance: Show[A]): String =
    showInstance.show(a)
    
  def show2[A: Show](a: A): String = {
    implicitly[Show[A]].show(a)
  }

  implicit val stringShow: Show[String] = new Show[String] {
    override def show(a: String): String = a
  }
  
  implicit val intShow: Show[Int] = new Show[Int] {
    override def show(a: Int): String = a.toString
  }
  
  show("abc")
  show2(123)
  
  
  
}