Scala example source code file (Breaks.scala)

This example Scala source code file (Breaks.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

breakcontrol, breaks, controlthrowable, nothing, t, tryblock, unit

The Breaks.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package util.control

/** A class that can be instantiated for the break control abstraction.
 *  Example usage:
 *  {{{
 *  val mybreaks = new Breaks
 *  import mybreaks.{break, breakable}
 *
 *  breakable {
 *    for (...) {
 *      if (...) break()
 *    }
 *  }
 *  }}}
 *  Calls to break from one instantiation of `Breaks` will never
 *  target breakable objects of some other instantiation.
 */
class Breaks {

  private val breakException = new BreakControl

  /**
   * A block from which one can exit with a `break`. The `break` may be
   * executed further down in the call stack provided that it is called on the
   * exact same instance of `Breaks`.
   */
  def breakable(op: => Unit) {
    try {
      op
    } catch {
      case ex: BreakControl =>
        if (ex ne breakException) throw ex
    }
  }

  sealed trait TryBlock[T] {
    def catchBreak(onBreak: =>T): T
  }

  /**
   * This variant enables the execution of a code block in case of a `break()`:
   * {{{
   * tryBreakable {
   *   for (...) {
   *     if (...) break()
   *   }
   * } catchBreak {
   *   doCleanup()
   * }
   * }}}
   */
  def tryBreakable[T](op: =>T) = new TryBlock[T] {
    def catchBreak(onBreak: =>T) = try {
      op
    } catch {
      case ex: BreakControl =>
        if (ex ne breakException) throw ex
        onBreak
    }
  }

  /**
   * Break from dynamically closest enclosing breakable block using this exact
   * `Breaks` instance.
   *
   * @note This might be different than the statically closest enclosing block!
   */
  def break(): Nothing = { throw breakException }
}

/** An object that can be used for the break control abstraction.
 *  Example usage:
 *  {{{
 *  import Breaks.{break, breakable}
 *
 *  breakable {
 *    for (...) {
 *      if (...) break
 *    }
 *  }
 *  }}}
 */
object Breaks extends Breaks

private class BreakControl extends ControlThrowable