typeclass-sugar.scala

  trait Serialiser[A]{
    def toJson(x: A): String
  }

  // [A: Serialiser] means the compiler expects an implicit Serialiser 
  // needs to be available for A
  def writeJsonToDisk[A: Serialiser](item: A){
    def writeToDisk(x:String){println(s"I saved [$x] to disk, honest!")}
    
    // Access the parameter with implicity
    writeToDisk(implicitly[Serialiser[A]].toJson(item))
  }

typeclass.scala

// Pretend this is your awesome library code that you want others to use freely
object MyAmazingSerialisationLib{
  
  trait Serialiser[A]{
    def toJson(x: A): String
  }

  def writeJsonToDisk[A](item: A)(implicit serialiser: Serialiser[A]){
    def writeToDisk(x: String) {println(s"I saved [$x] to disk, honest!")}
    writeToDisk(serialiser.toJson(item))
  }
}

object TypeClasses extends App {
  
  import MyAmazingSerialisationLib._

  case class Dog(name: String)

  case class ComputerMachine(id: Int, complexity: Int)

  implicit val dogSerialiser = new Serialiser[Dog] {
    def toJson(dog: Dog) = s"""{"name":"${dog.name}"}"""
  }

  // compiles because we have evidence of serialiser
  writeJsonToDisk(Dog("Spot"))  

  // doesn't compile because we dont have a serialiser in scope
  writeJsonToDisk(ComputerMachine(2, 20)) 
}