OptionParser

scopt.immutable.OptionParser is instantiated within your object, set up by an (ordered) sequence of invocations of the various builder methods such as opt method or arg method.

val parser = new scopt.OptionParser[Config]("scopt") {
 head("scopt", "4.x")

 opt[Int]('f', "foo").action( (x, c) =>
   c.copy(foo = x) ).text("foo is an integer property")

 opt[File]('o', "out").required().valueName("<file>").
   action( (x, c) => c.copy(out = x) ).
   text("out is a required file property")

 opt[(String, Int)]("max").action({
     case ((k, v), c) => c.copy(libName = k, maxCount = v) }).
   validate( x =>
     if (x._2 > 0) success
     else failure("Value <max> must be >0") ).
   keyValueName("<libname>", "<max>").
   text("maximum count for <libname>")

 opt[Seq[File]]('j', "jars").valueName("<jar1>,<jar2>...").action( (x,c) =>
   c.copy(jars = x) ).text("jars to include")

 opt[Map[String,String]]("kwargs").valueName("k1=v1,k2=v2...").action( (x, c) =>
   c.copy(kwargs = x) ).text("other arguments")

 opt[Unit]("verbose").action( (_, c) =>
   c.copy(verbose = true) ).text("verbose is a flag")

 opt[Unit]("debug").hidden().action( (_, c) =>
   c.copy(debug = true) ).text("this option is hidden in the usage text")

 help("help").text("prints this usage text")

 arg[File]("<file>...").unbounded().optional().action( (x, c) =>
   c.copy(files = c.files :+ x) ).text("optional unbounded args")

 note("some notes.".newline)

 cmd("update").action( (_, c) => c.copy(mode = "update") ).
   text("update is a command.").
   children(
     opt[Unit]("not-keepalive").abbr("nk").action( (_, c) =>
       c.copy(keepalive = false) ).text("disable keepalive"),
     opt[Boolean]("xyz").action( (x, c) =>
       c.copy(xyz = x) ).text("xyz is a boolean property"),
     opt[Unit]("debug-update").hidden().action( (_, c) =>
       c.copy(debug = true) ).text("this option is hidden in the usage text"),
     checkConfig( c =>
       if (c.keepalive && c.xyz) failure("xyz cannot keep alive")
       else success )
   )
}

// parser.parse returns Option[C]
parser.parse(args, Config()) match {
 case Some(config) =>
   // do stuff

 case None =>
   // arguments are bad, error message will have been displayed
}