MyAppWithFlags.scala

import com.twitter.app.App

object MyApp extends App {
  
  // parses an integer from the "-port" flag.
  // Finagle already provides an implicit Flaggable typeclass for Int
  // usage: -port 9000
  val port = flag[Int]("port", 8080, "port this server should use")
  
  // parses an Env trait. See typeclass below
  val env = flag[Env]("env", Env.Dev, "environment this server runs")
  
  sealed trait Env
  case object Prod extends Env
  case object Dev extends Env
  implicit val flaggableEnv = new Flaggable[Env] {
    override def parse(env: String): Env = env match {
      case "prod" => Prod
      case "dev" => Dev
    }
  }
  
  // best practice to turn this on. 
  // The app won't start if parameters are wrong or missing
  override def failfastOnFlagsNotParsed: Boolean = true
  
  def main() {
    // access the port simply with the apply method.
    // There are also other ways (get, getWithDefault)
    println(s"Hello, World ${port()}")
  }
}