Setter CLIs

We have the concept of a setter CLI, you may not need to use this on it’s own, but it’s handy to know how it works.

It’s a CLI parser that, in stead of parsing a T directly, parses a T => T, this allows you to parse a config.yml and override parts of it from CLI flags or env variables, which is useful for practical microservice use.

import com.monovore.decline._
import net.andimiller.recline.annotations._
import net.andimiller.recline.generic._

case class Configuration(name: String, port: Int)

val config = Configuration("abc", 123) // imagine we parsed this from a config file
// config: Configuration = Configuration(abc,123) // imagine we parsed this from a config file

val setterCli = deriveSetterOpts[Configuration]
// setterCli: Opts[Configuration => Configuration] = Opts([--name <string>] [--port <integer>])

Command("program", "")(setterCli).parse(List("--name", "real name")).map(f => f(config))
// res0: Either[Help, Configuration] = Right(Configuration(real name,123))

You’ll see that it transforms the configuration using our CLI flags as overrides.