scala.collection.mutable.MapBuilder.scala Maven / Gradle / Ivy

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Standard library for the Scala Programming Language

There is a newer version: 2.13.13

/*
 * Scala (https://www.scala-lang.org)
 *
 * Copyright EPFL and Lightbend, Inc.
 *
 * Licensed under Apache License 2.0
 * (http://www.apache.org/licenses/LICENSE-2.0).
 *
 * See the NOTICE file distributed with this work for
 * additional information regarding copyright ownership.
 */

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 ReusableBuilder[(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
}