1. Type Class Polymorphism
In Scala
Mayank Bairagi
Sr. Software Consultant
Knoldus

2. Polymorphism
Same Operation Working on different type of
values
Type of Polymorphism
1. Parametric
2. ad hoc

3. Polymorphism By
●Overloading
●Inheritance
●Pattern Matching
●Trait/ Interface
●Type parameters and Generic types

4. Type Classes
Type Classes are Introduce first in haskell language
Scala Type Classes are Pattern instead of language feature
Example:
scala.math.Numaric, scala.math.Ordering
Every Thing in Scalaz is Type class ( monoids, monads,
applicative , functors )

5. OverLoading
case class Book(title:String,author:String)
case class Movie(title:String,director:String)
object OverLoading {
def serialize(book:Book)= "Book("
+book.title+","+book.author+")"
def serialize(movie:Movie)= "Book("
+movie.title+","+movie.director+")"
}

6. OverLoading
case class Book(title:String,author:String)
case class Movie(title:String,director:String)
object OverLoading {
def serialize(book:Book)= "Book("
+book.title+","+book.author+")"
def serialize(movie:Movie)= "Book("
+movie.title+","+movie.director+")"
}

7. Interface
trait Serializable {
def serialize:String
}
class Book(title:String,author:String) extends Serializable{
override def serialize= "Book(" +this.title+","+this.author+")"
}
class Movie(title:String,director:String) extends Serializable{
override def serialize= "Movie("
+this.title+","+this.director+")"
}

8. Problem With Interface
We Have Coupling Problem Here , How each class
is serialize , this information has to be in the class.
In order to add more trait and override the methods
I need to have control on these classes. I should be
allowed to view and modify the source code.

9. Pattern Matching
object Serialize {
def serialize(x:Any)
{
x match {
case b:Book => "Book(" +b.title+","+b.author+")"
case m:Movie => "Movie(" +m.title+","+m.director+")"
}
}
}

10. Problem With Pattern Matching
● Both the Movie and Book classes are unaware how
actually there serialized.
● If I need more than one type of serialization than I need
more serialize method with it's own case match block.
● Now we have fixed the coupling problem, but
unfortunatly we have introduce new coupling
● Method serialize need to know about all the classes
which need to be serialize.
● Problem of control and source code is still exist

11. Type Class
case class Book(title:String,author:String)
case class Movie(title:String,director:String)
trait Serializable[T] {
def ser(t:T):String
}
object Serializable{
def serialize[T](t:T, s:Serializable[T])=s.ser(t)
}
object BookIsSerialzabel extends Serializable[Book]
{
def ser(book:Book)= "Book(" +book.title+","+book.author+")"
}
object MovieIsSerialzabel extends Serializable[Movie]
{
def ser(movie:Movie)= "Movie(" +movie.title+","+movie.director+")"
}

12. Type Class With Implicit
case class Book(author:String) extends Card[Book]
case class Movie(director:String) extends Card[Movie]
trait Serializable[T] {
def ser(t:T):String=t.asInstanceOf[Card[T]].title
}
object Serializable{
def serialize[T](t:T)(implicit s:Serializable[T])=s.ser(t)
implicit object BookIsSerialzabel extends Serializable[Book]
{override def ser(book:Book)= "Book(" +book.title+","+book.author+")"}
implicit object MovieIsSerialzabel extends Serializable[Movie]
{ override def ser(movie:Movie)= "Movie("
+movie.title+","+movie.director+")"}
}

13. Type Variances and Context Bound
Co variance +T
Contra variance -T

14. Thank you