Type class

Type class is a tool used in functional programming to enable ad-hoc polymorphism.

Type class consists of:

• The type class itself;
• Instances for particular types;
• The interface methods that we expose to users. The ways of specifying an interface: Interface Objects and Interface Syntax.

Type class

trait Base64Writer[A] {
  def toBase64(value: A): String
}

Instances

object Base64Instances {

  implicit val stringWriter: Base64Writer[String] =
    new Base64Writer[String] {
      def toBase64(value: String): String = {
        val message = value.getBytes
        java.util.Base64.getEncoder.encodeToString(message)
      }
    }

  implicit val integerWriter: Base64Writer[Int] =

    new Base64Writer[Int] {
      def toBase64(value: Int): String = {
        val message = value.toString.getBytes
        java.util.Base64.getEncoder.encodeToString(message)
      }
    }

}

Interface object

object Base64 {
  def toBase64[A](value: A)(implicit w: Base64Writer[A]): String =
    w.toBase64(value)
}

import Base64Instances._

Base64.toBase64("Hello world!")
// res0: String = SGVsbG8gd29ybGQh

Base64.toBase64(42)
// res1: String = NDI=

Interface syntax

object Base64WriterSyntax {

  implicit class Base64WriterOps[A](value: A) {
    def toBase64(implicit w: Base64Writer[A]): String =
      w.toBase64(value)
  }

import Base64Instances._
import Base64WriterSyntax._

"Hello world!".toBase64
// res0: String = SGVsbG8gd29ybGQh

42.toBase64
// res1: String = NDI=