Scala, scopt: using a custom class in command option


  • Scala: 2.13.1
  • scopt: 4.0.0-RC2

According to the scopt documentation, a command option can be defined as opt[A](‘o’, “option”) (or opt[A](‘o’)), where A is any type that is an instance of Read typeclass.

In this example, we will add a mode command option of type ServerMode:

1. Create an object ServerMode extending Enumeration class, which contains the option possible values:

object ServerMode extends Enumeration {
  type ServerMode = Value
  val ECHO, HELLO = Value

2. In Config case class, define the mode option of type ServerMode with the default value:

mode: ServerMode = ServerMode.HELLO

3. Add mode option as a command child:

opt[ServerMode]('m', "serverMode").action((x, c) => c.copy(mode = x)).text("Server mode").required()

A command mode option value can be specified in the following way:

command ... -m ECHO