```scala
object TypeClasses5 {

  trait Show[A] {
    def show(a: A): String
  }

  object Show {
    private def instance[A](f: A => String): Show[A] = new Show[A] {
      def show(a: A): String = f(a)
    }

    implicit val intCanShow: Show[Int] = instance(int => s"int $int")
    implicit val stringCanShow: Show[String] = instance(str => s"string $str")

    implicit class ShowOps[A: Show](val a: A) {
      def show = Show[A].show(a)
    }

    def apply[A](implicit sh: Show[A]): Show[A] = sh

    def show[A:Show](a: A) = Show[A].show(a)
  }

  def main(args: Array[String]): Unit = {
    import Show._
    println( show(20) )
    println( show("Hello") )

    println( 40.show )
    println( "Hello world".show )
  }

}
```