implicts.scala

/*
The default error message is:

  /home/se/tmp/implicit.scala:41: error: could not find implicit value for parameter c: this.Converter[String]
  println(view[String](1))
                      ^

We could change this to something better..., e.g.,

  /home/se/tmp/implicit.scala:41: error: No implicit `Converter` for type String found in scope. Did you forget to import it?
  println(view[String](1))
                      ^

 */

import scala.annotation.implicitNotFound

@implicitNotFound("No implicit `Converter` for type ${T} found in scope. Did you forget to import it?")
trait Converter[T] {
  def convert(x: Int): T
}

def view[T](x: Int)(implicit c: Converter[T]): T = c.convert(x)

object IntConverter {
  implicit object IntView extends Converter[Int] {
    def convert(x: Int) = x
  }
}

object StringConverter {
  implicit object StringView extends Converter[String] {
    def convert(x: Int) = "hello"
  }
}

import IntConverter._
// import StringConverter._

println(view[Int](1))
println(view[String](1))