Better Config

Config.scala

import scala.util.control.NonFatal
import better.files.Scanner.Read

/**
  * Extend this trait to create your application config
  *
  * Pros of this approach:
  * 1) Library free approach - only 15 lines of dependency free "library" (four one-line defs for you to override)
  * 2) Failures happen when the Config object is loaded instead of when a config value is accessed
  * 3) Strongly typed
  * 4) Overrides can be provided using both system properties and/or environment variables
  * 5) No more config file DSL - your configs are in plain old Scala
  * 6) Easily understandable error messages
  * 7) You can define your own Read instances to read complex objects as configs
  */
trait Config {
  protected def configValue(key: String): Option[String] =
    sys.props.get(key) orElse sys.env.get(key)

  protected def config[A](key: String)(implicit read: Read[A]): Option[A] =
    configValue(key) map {c =>
      try {
        read(c)
      } catch {
        case NonFatal(e) => throw new IllegalArgumentException(s"Could not parse config value=$c for key=$key", e)
      }
    }

  protected def config[A: Read](key: String, defaultValue: => A): A =
    config(key).getOrElse(defaultValue)

  protected def configOrError[A: Read](key: String, errorMsgPrefix: String = "Missing config"): A =
    config(key, throw new NoSuchElementException(s"$errorMsgPrefix key=$key"))
}

MyConfig.scala

// usage

object MyConfig extends Config {
  object db {
    val host: String = config("db.host", "postgres.rds.com")
    val port: Int    = config("db.port", 9099)
    val pass: String = configOrError("db.password")
  }

  object aws {
    val secret: String = config("aws.secret").getOrElse(new AWSPasswordManager().load().getPassword())
  }
}

// access
val driver = new PsqlDriver(host = MyConfig.db.host, host = MyConfig.db.port)

hey nice, but its not library free if it imports, well, a library

@alwins0n: It just imports a Read typeclass which many common libraries like cats and better-files have it. You can just implement the Read typeclass yourself then if you want truly library free - it will be 15 more lines of code then...