typeclasses

typeclasses.scala

// Start with a typed trait, which will form a small "concept"
trait Concept[T]{
  def describe : String
}
  
// Then the idea is to create models implementing this concept
// for the various types we want to use it
implicit class IntModel(n: Int) extends Concept[Int]{
  def describe : String = "The integer " + n
}
  
// Now we can use our model on integers like so
4 describe                                      //> res0: String = The integer 4

// 4.0 describe //This doesnt compile since we dont have a model in scope for Double
	 
// We can also create models for other types like a list doubles etc
implicit class ListModel(l: List[Int]) extends Concept[List[Int]]{
  def describe : String = l mkString("A list of integers ", ", ", ".")
}
   
List(1,2,3,4,5) describe                  //> res1: String = A list of integers 1, 2, 3, 4, 5.
	 
// Create another scope
{
  // Shadows the previous model
  implicit class ListModel(l: List[Int]) extends Concept[List[Int]]{
    def describe : String = l mkString("My description of the integer list ", ", ", ".")
  }
  		
  List(1,2,3,4,5) describe
}                                         //> res2: String = My description of the integer list 1, 2, 3, 4, 5.
	
// One more scope
{
  // Shadows the previous model
  implicit class IntModel(n: Int) extends Concept[Int]{
    def describe : String = "<p>" + n + "</p>"
  }
    
  5 describe
}                                         //> res3: String = <p>5</p>