Scala Programming Projects

Contravariant encoder

Now, we would like to model the opposite of decoding a string to an object—encoding an object to a string! We make our Encoder contravariant by adding a - sign in front of the A type parameter, as shown in the following code:

trait Encoder[-A] {  def encode(a: A): String}

The following code is an instance of this Encoder:

object AnimalEncoder extends Encoder[Animal] {  def encode(a: Animal): String = a.toString}

We have the Cat <:< Animal relationship, and Encoder is contravariant on its argument. This implies that Encoder[Animal] <:< Encoder[Cat], and I can, therefore, assign Encoder[Animal] to a variable of type Encoder[Cat], as shown in the following code:

val catEncoder: Encoder[Cat] = AnimalEncodercatEncoder.encode( ...