Scala example source code file (App.scala)

This example Scala source code file (App.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

app, array, collection, delayedinit, listbuffer, long, mutable, the, unit

The App.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2010-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala

import scala.compat.Platform.currentTime
import scala.collection.mutable.ListBuffer

/** The `App` trait can be used to quickly turn objects
 *  into executable programs. Here is an example:
 *  {{{
 *  object Main extends App {
 *    Console.println("Hello World: " + (args mkString ", "))
 *  }
 *  }}}
 *  Here, object `Main` inherits the `main` method of `App`.
 *
 *  `args` returns the current command line arguments as an array.
 *
 *  ==Caveats==
 *
 *  '''''It should be noted that this trait is implemented using the [[DelayedInit]]
 *  functionality, which means that fields of the object will not have been initialized
 *  before the main method has been executed.'''''
 *
 *  It should also be noted that the `main` method should not be overridden:
 *  the whole class body becomes the “main method”.
 *
 *  Future versions of this trait will no longer extend `DelayedInit`.
 *
 *  @author  Martin Odersky
 *  @version 2.1, 15/02/2011
 */
trait App extends DelayedInit {

  /** The time when the execution of this program started, in milliseconds since 1
    * January 1970 UTC. */
  @deprecatedOverriding("executionStart should not be overridden", "2.11.0")
  val executionStart: Long = currentTime

  /** The command line arguments passed to the application's `main` method.
   */
  @deprecatedOverriding("args should not be overridden", "2.11.0")
  protected def args: Array[String] = _args

  private var _args: Array[String] = _

  private val initCode = new ListBuffer[() => Unit]

  /** The init hook. This saves all initialization code for execution within `main`.
   *  This method is normally never called directly from user code.
   *  Instead it is called as compiler-generated code for those classes and objects
   *  (but not traits) that inherit from the `DelayedInit` trait and that do not
   *  themselves define a `delayedInit` method.
   *  @param body the initialization code to be stored for later execution
   */
  @deprecated("The delayedInit mechanism will disappear.", "2.11.0")
  override def delayedInit(body: => Unit) {
    initCode += (() => body)
  }

  /** The main method.
   *  This stores all arguments so that they can be retrieved with `args`
   *  and then executes all initialization code segments in the order in which
   *  they were passed to `delayedInit`.
   *  @param args the arguments passed to the main method
   */
  @deprecatedOverriding("main should not be overridden", "2.11.0")
  def main(args: Array[String]) = {
    this._args = args
    for (proc <- initCode) proc()
    if (util.Properties.propIsSet("scala.time")) {
      val total = currentTime - executionStart
      Console.println("[total " + total + "ms]")
    }
  }
}