Scala example source code file (MapBuilder.scala)

This example Scala source code file (MapBuilder.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, b, builder, coll, mapbuilder

The MapBuilder.scala Scala example source code

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


package scala
package collection
package mutable

/** The canonical builder for immutable maps, working with the map's `+` method
 *  to add new elements.
 *  Collections are built from their `empty` element using this + method.
 *
 *  @tparam A      Type of the keys for the map this builder creates.
 *  @tparam B      Type of the values for the map this builder creates.
 *  @tparam Coll   The type of the actual collection this builder builds.
 *  @param empty   The empty element of the collection.
 *
 *  @since 2.8
 */
class MapBuilder[A, B, Coll <: scala.collection.GenMap[A, B] with scala.collection.GenMapLike[A, B, Coll]](empty: Coll)
extends Builder[(A, B), Coll] {
  protected var elems: Coll = empty
  def +=(x: (A, B)): this.type = {
    elems = (elems + x).asInstanceOf[Coll]
      // the cast is necessary because right now we cannot enforce statically that
      // for every map of type Coll, `+` yields again a Coll. With better support
      // for hk-types we might be able to enforce this in the future, though.
    this
  }
  def clear() { elems = empty }
  def result: Coll = elems
}