Drill on how type class with implicit bring in polymorphism

ContextImplicitShow

trait Show[A] {
  def doShow(input : A) : String
}

// Value class apporach need more tune up
// Value class: Goal is to avoid a runtime overhead
//implicit class LetShowable[A](val a: A) extends AnyVal{
//  def letShow(implicit sh: Show[A]) = sh.doShow(a)
//}


object Show {
  def apply[A]()(implicit sa: Show[A]) : Show[A] = sa

  implicit class LetShowable[A: Show](val a: A) {
    def letShow = implicitly[Show[A]].doShow(a)
  }


  // using apply will avoid using implicitly
  def showUseApply[A: Show](a: A) : Unit = {
    println( Show.apply[A].doShow(a) )
    println(Show[A].doShow(a))
  }

  def showBetter[A: Show](a: A ) : Unit = {
    val impAInstance = implicitly[Show[A]]
    println(impAInstance.doShow(a))
  }
  def show[A](a: A)(implicit sa : Show[A]) : Unit = {
    println(sa.doShow(a))
  }


  implicit val intShow = new Show[Int] {
    override def doShow(input : Int): String = input.toString
  }
}

import Show._

show(12)
showBetter(23)
showUseApply(100)