Case Classes

Case classes are the first way of constructing data that we'll look at. From the denotational perspective, a case class represents a logical and. For example, we're already worked with Vec. It represents a two-dimensional vector as an x and y coordinate, using a case class. From the operational perspective. Well, it's more complicated and we'll see the details.

An Example

We'll get started with an example of a case class in an animation.

import doodle.core._
import doodle.image._
import doodle.reactor._
import doodle.java2d._

final case class Circle(radius: Int)

val animation =
    .withRender(circle => Image
    .withOnTick(circle => if(circle.radius > 200) Circle(20) else Circle(circle.radius + 10)), 400))

Run the animation and see what happens. Now read the code and try to understand how it works. You might need to know that the function passed to withRender determines how a Circle is transformed into an Image, and the function passed to withOnTick determines how the Circle is updated each clock tick. The animation is updated each clock tick.

Declaring and Using Case Classes

We're now going to look at how we can declare case classes, and some of the ways we can use them.

We've seen an example of declaring a case class:

final case class Circle(radius: Int)

This declares a case class called Circle. It has a single field called radius with the type Int.

A case class is not a value. It declares a type. To create a value---an object---of type Circle we can write, for example,


In this case the field radius has the value 20.

A bit of terminology.

The terminology "instance" and "constructor" comes from the field of object-oriented programming.