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Getting started

Metaconfig is a library to manage configuration options for Scala applications with the following goals:

  • Model configuration as Scala data structures: Metaconfig allows you to manage all user configuration options as immutable case classes and sealed traits.
  • Limit boilerplate where possible: Metaconfig provides automatic configuration decoders and encoders to help you avoid copy-pasting the same setting name in multiple places like the application implementation, configuration parser and configuration documentation. Copy-pasting strings is both cumbersome and it also increases the risk of making mistakes resulting in a bad end-user experience.
  • Evolve configuration without breaking changes: it's normal that configuration options change as your application evolves (naming is hard). Metaconfig supports several ways to evolve user configuration options in a backwards compatible way so that your existing users have an easier time to upgrade to the latest versions of your application.
  • Report helpful error messages: Metaconfig reports errors using source positions in the user-written configuration files, similar to how a compiler reports errors.
  • Treat command-line arguments as configuration: Metaconfig provides a command-line parser with automatic generation of --help messages, tab completions for bash/zsh and more. Command-line arguments map into Scala case classes, just like HOCON and JSON configuration.

Quick start

libraryDependencies += "org.scalameta" %% "metaconfig-typesafe-config" % "0.13.0-46-f07f0607-SNAPSHOT"

Next, write a case class for your user configuration.

import metaconfig._
import metaconfig.generic._

case class HelloConfig(
  verbose: Boolean = false,
  name: String = "Susan"
)
object HelloConfig {
  lazy val default = HelloConfig()
  implicit lazy val surface: Surface[HelloConfig] = deriveSurface[HelloConfig]
  implicit lazy val decoder: ConfDecoder[HelloConfig] = deriveDecoder[HelloConfig](default)
  implicit lazy val encoder: ConfEncoder[HelloConfig] = deriveEncoder[HelloConfig]
}

Next, parse HOCON into your case class

metaconfig.Hocon.parseString[HelloConfig](
  """
  verbose = true
  name = John
  """
).get
// res0: HelloConfig = HelloConfig(verbose = true, name = "John")
metaconfig.Hocon.parseString[HelloConfig](
  """
  verrbose = true # typo is ignored
  name = John
  """
).get
// res1: HelloConfig = HelloConfig(verbose = false, name = "John")
metaconfig.Hocon.parseString[HelloConfig](
  """
  verrbose = true # typo is an error
  name = John
  """
)(HelloConfig.decoder.noTypos)
// res2: Configured[HelloConfig] = NotOk(
//   error = <input>:2:0 error: found option 'verrbose' which wasn't expected, or isn't valid in this context.
//  Did you mean 'verbose'?
//   verrbose = true # typo is an error
// ^
// 
// )

Use parseCommandLine to parse command-line arguments.

metaconfig.Conf.parseCliArgs[HelloConfig](
  List("--verbose", "--name", "Amelie")
).andThen(_.as[HelloConfig]).get
// res3: HelloConfig = HelloConfig(verbose = true, name = "Amelie")
metaconfig.Conf.parseCliArgs[HelloConfig](
  List("--verbose", "--names", "Amelie")
).andThen(_.as[HelloConfig])
// res4: Configured[HelloConfig] = NotOk(
//   error = found argument '--names' which wasn't expected, or isn't valid in this context.
//  Did you mean '--name'?
// )
Reference →