Play Framework/Scala example source code file (Collections.scala)

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

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

Play Framework tags/keywords

a, api, b, collections, lib, library, list, none, option, play, play framework, seq, some

The Collections.scala Play Framework example source code

/*
 * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
 */
package play.api.libs

/**
 * Utilities functions for Collections
 */
object Collections {

  /**
   * Produces a Seq from a seed and a function.
   *
   * Example, produces a List from 0 to 100.
   *
   * {{{
   * unfoldLeft(0) { state match
   *   case a if a > 100 => None
   *   case a => (a + 1, a + 1)
   * }
   * }}}
   *
   * @tparam A Type of the final List elements.
   * @tparam B Seed type
   * @param seed Initial value.
   * @param f Function producing the List elements.
   */
  def unfoldLeft[A, B](seed: B)(f: B => Option[(B, A)]): Seq[A] = {
    def loop(seed: B)(ls: List[A]): List[A] = f(seed) match {
      case Some((b, a)) => loop(b)(a :: ls)
      case None => ls
    }
    loop(seed)(Nil)
  }

}