How to maintan backwards compatibility?

Let's say you have a case class MyConfig(url: String).
Now you need to add another property: port: Int, but without breaking existing serialized values.

You have 2 options:

  1. use an Option[Int], and set a default value later if it is missing
  2. use a Int = MyDefaultValue to avoid Option gymnastics

Using Option

Using Option[T] is handy when you don't have a default value.
But it is a bit cumbersome to handle:


          case class MyConfig(url: String, port: Option[Int]) derives JsonRW
          parsedConfig.port.getOrElse(...)

Using default value

If you do have a default value for a particular property, by all means do use it.
It will make your life much easier, you can pretend it was always there:


          case class MyConfig(url: String, port: Int = 1234) derives JsonRW