Server Config Object (hypothetical implementation and usage)

ServerConfig.scala

package local

import scalaz.Monoid._

object ServerConfig {

  case class Port(get: Int = 8080)
  case class Zookeeper(get: String = "default_zookeeper")
  case class Environemnt(get: String = "default_env")

  case class ServerConfig(
    port: Port = Port(),
    zookeeper: Zookeeper = Zookeeper(),
    environment: Environment = Environment(),
  )

  implicit object MonoidPort extends Monoid[Port] {
    def zero: Port = Port()

    // left-biased overriding
    // if either argument is the default, then the other argument "wins"
    // if neither argument is the default, then the left argument "wins"
    def append(x: Port, y: Port): Port = (x, y) match {
      case (zero, _) => y
      case (_, zero) => x
      case _ => x
    }
  }

  implicit object MonoidZookeeper extends Monoid[Zookeeper] {
    def zero: Zookepper = Zookeeper()

    // left-biased overriding
    def append(x: Zookeeper, y: Zookeeper) = (x, y) match {
      case (zero, _) => y
      case (_, zero) => x
      case _ => x
    }
  }

  implicit object MonoidEnvironment extends Monoid[Environment] {
    def zero: Environment = Environment("default_env")

    // left-biased overriding
    def append(x: Zookeeper, y: Zookeeper) = (x, y) match {
      case (zero, _) => y
      case (_, zero) => x
      case _ => x
    }
  }

  implicit object MonoidServerConfig extends Monoid[ServerConfig] {
    def zero: ServerConfig = ServerConfig()

    // left-biased overriding
    def append(x: ServerConfig, y: ServerConfig) = (x, y) match {
      (ServerConfig(x1, x2, x3), ServerConfig(y1, y2, y3)) =>
        ServerConfig(
          append(x1, y1),
          append(x2, y2),
          append(x3, y3)
        )
    }
  }
}

object Usage {

  import local.ServerConfig._

  val commandlineServerConfig = ServerConfig(
    port = Port(22),
    environment = Environment("dev")
  )

  val oroborosServerConfig = ServerConfig(
    zookeeper = Zookeeper("something_or_other")
  )

  val ansibleServerConfig = ServerConfig(
    zookeeper = Zookeeper("this_not_that"),
    port = Port(88)
  )

  // cascading configs, giving commandlineServerConfig highest priority.
  // |+| is a method of `Monoid`, it's just infix `append`.
  // any args that are unset in any of the configs will be set to default
  // values
  val realServerConfig =
    commandlineServerConfig |+|
    oroborosServerConfig |+|
    ansibleServerConfig

  val server = new Server(realServerConfig)
  server.run()
}