Scala example source code file (IsTraversableOnce.scala)

This example Scala source code file (IsTraversableOnce.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

a, a0, c, char, gentraversableonce, istraversableonce, repr

The IsTraversableOnce.scala Scala example source code

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

package scala
package collection
package generic

/** Type class witnessing that a collection representation type `Repr` has
 *  elements of type `A` and has a conversion to `GenTraversableOnce[A]`.
 *
 *  This type enables simple enrichment of `GenTraversableOnce`s with extension
 *  methods which can make full use of the mechanics of the Scala collections
 *  framework in their implementation.
 *
 *  Example usage,
 * {{{
 *    class FilterMapImpl[A, Repr](val r: GenTraversableOnce[A]) {
 *      final def filterMap[B, That](f: A => Option[B])(implicit cbf: CanBuildFrom[Repr, B, That]): That = {
 *        val b = cbf()
 *        for(e <- r.seq) f(e) foreach (b +=)
 *        b.result
 *      }
 *    }
 *    implicit def filterMap[Repr, A](r: Repr)(implicit fr: IsTraversableOnce[Repr]): FilterMapImpl[fr.A,Repr] =
 *      new FilterMapImpl[fr.A, Repr](fr.conversion(r))
 *
 *    val l = List(1, 2, 3, 4, 5)
 *    List(1, 2, 3, 4, 5) filterMap (i => if(i % 2 == 0) Some(i) else None)
 *    // == List(2, 4)
 * }}}
 *
 * @author Miles Sabin
 * @author J. Suereth
 * @since 2.10
 */
trait IsTraversableOnce[Repr] {
  /** The type of elements we can traverse over. */
  type A
  /** A conversion from the representation type `Repr` to a `GenTraversableOnce[A]`. */
  val conversion: Repr => GenTraversableOnce[A]
}

object IsTraversableOnce {
  import scala.language.higherKinds

  implicit val stringRepr: IsTraversableOnce[String] { type A = Char } =
    new IsTraversableOnce[String] {
      type A = Char
      val conversion = implicitly[String => GenTraversableOnce[Char]]
    }

  implicit def genTraversableLikeRepr[C[_], A0](implicit conv: C[A0] => GenTraversableOnce[A0]): IsTraversableOnce[C[A0]] { type A = A0 } =
    new IsTraversableOnce[C[A0]] {
      type A = A0
      val conversion = conv
    }
}