Scala example source code file (GenTraversableFactory.scala)

This example Scala source code file (GenTraversableFactory.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, canbuildfrom, cc, genericcanbuildfrom, gentraversable, gentraversablefactory, int, integral, reusablecbfinstance, t

The GenTraversableFactory.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2006-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */


package scala
package collection
package generic

import scala.language.higherKinds

/** A template for companion objects of `Traversable` and subclasses thereof.
 *  This class provides a set of operations to create `$Coll` objects.
 *  It is typically inherited by companion objects of subclasses of `Traversable`.
 *
 *  @since 2.8
 *
 *  @define coll collection
 *  @define Coll `Traversable`
 *  @define factoryInfo
 *    This object provides a set of operations to create `$Coll` values.
 *    @author Martin Odersky
 *    @version 2.8
 *  @define canBuildFromInfo
 *    The standard `CanBuildFrom` instance for $Coll objects.
 *    @see CanBuildFrom
 *  @define genericCanBuildFromInfo
 *    The standard `CanBuildFrom` instance for $Coll objects.
 *    The created value is an instance of class `GenericCanBuildFrom`,
 *    which forwards calls to create a new builder to the
 *    `genericBuilder` method of the requesting collection.
 *    @see CanBuildFrom
 *    @see GenericCanBuildFrom
 */
abstract class GenTraversableFactory[CC[X] <: GenTraversable[X] with GenericTraversableTemplate[X, CC]]
extends GenericCompanion[CC] {

  private[this] val ReusableCBFInstance: GenericCanBuildFrom[Nothing] = new GenericCanBuildFrom[Nothing] {
    override def apply() = newBuilder[Nothing]
  }
  def ReusableCBF: GenericCanBuildFrom[Nothing] = ReusableCBFInstance

  /** A generic implementation of the `CanBuildFrom` trait, which forwards
   *  all calls to `apply(from)` to the `genericBuilder` method of
   *  $coll `from`, and which forwards all calls of `apply()` to the
   *  `newBuilder` method of this factory.
   */
  class GenericCanBuildFrom[A] extends CanBuildFrom[CC[_], A, CC[A]] {
    /** Creates a new builder on request of a collection.
     *  @param from  the collection requesting the builder to be created.
     *  @return the result of invoking the `genericBuilder` method on `from`.
     */
    def apply(from: Coll) = from.genericBuilder[A]

    /** Creates a new builder from scratch
     *  @return the result of invoking the `newBuilder` method of this factory.
     */
    def apply() = newBuilder[A]
  }

  /** Concatenates all argument collections into a single $coll.
   *
   *  @param xss the collections that are to be concatenated.
   *  @return the concatenation of all the collections.
   */
  def concat[A](xss: Traversable[A]*): CC[A] = {
    val b = newBuilder[A]
    // At present we're using IndexedSeq as a proxy for "has a cheap size method".
    if (xss forall (_.isInstanceOf[IndexedSeq[_]]))
      b.sizeHint(xss.map(_.size).sum)

    for (xs <- xss.seq) b ++= xs
    b.result()
  }

  /** Produces a $coll containing the results of some element computation a number of times.
   *  @param   n  the number of elements contained in the $coll.
   *  @param   elem the element computation
   *  @return  A $coll that contains the results of `n` evaluations of `elem`.
   */
  def fill[A](n: Int)(elem: => A): CC[A] = {
    val b = newBuilder[A]
    b.sizeHint(n)
    var i = 0
    while (i < n) {
      b += elem
      i += 1
    }
    b.result()
  }

  /** Produces a two-dimensional $coll containing the results of some element computation a number of times.
   *  @param   n1  the number of elements in the 1st dimension
   *  @param   n2  the number of elements in the 2nd dimension
   *  @param   elem the element computation
   *  @return  A $coll that contains the results of `n1 x n2` evaluations of `elem`.
   */
  def fill[A](n1: Int, n2: Int)(elem: => A): CC[CC[A]] =
    tabulate(n1)(_ => fill(n2)(elem))

  /** Produces a three-dimensional $coll containing the results of some element computation a number of times.
   *  @param   n1  the number of elements in the 1st dimension
   *  @param   n2  the number of elements in the 2nd dimension
   *  @param   n3  the number of elements in the 3nd dimension
   *  @param   elem the element computation
   *  @return  A $coll that contains the results of `n1 x n2 x n3` evaluations of `elem`.
   */
  def fill[A](n1: Int, n2: Int, n3: Int)(elem: => A): CC[CC[CC[A]]] =
    tabulate(n1)(_ => fill(n2, n3)(elem))

  /** Produces a four-dimensional $coll containing the results of some element computation a number of times.
   *  @param   n1  the number of elements in the 1st dimension
   *  @param   n2  the number of elements in the 2nd dimension
   *  @param   n3  the number of elements in the 3nd dimension
   *  @param   n4  the number of elements in the 4th dimension
   *  @param   elem the element computation
   *  @return  A $coll that contains the results of `n1 x n2 x n3 x n4` evaluations of `elem`.
   */
  def fill[A](n1: Int, n2: Int, n3: Int, n4: Int)(elem: => A): CC[CC[CC[CC[A]]]] =
    tabulate(n1)(_ => fill(n2, n3, n4)(elem))

  /** Produces a five-dimensional $coll containing the results of some element computation a number of times.
   *  @param   n1  the number of elements in the 1st dimension
   *  @param   n2  the number of elements in the 2nd dimension
   *  @param   n3  the number of elements in the 3nd dimension
   *  @param   n4  the number of elements in the 4th dimension
   *  @param   n5  the number of elements in the 5th dimension
   *  @param   elem the element computation
   *  @return  A $coll that contains the results of `n1 x n2 x n3 x n4 x n5` evaluations of `elem`.
   */
  def fill[A](n1: Int, n2: Int, n3: Int, n4: Int, n5: Int)(elem: => A): CC[CC[CC[CC[CC[A]]]]] =
    tabulate(n1)(_ => fill(n2, n3, n4, n5)(elem))

  /** Produces a $coll containing values of a given function over a range of integer values starting from 0.
   *  @param  n   The number of elements in the $coll
   *  @param  f   The function computing element values
   *  @return A $coll consisting of elements `f(0), ..., f(n -1)`
   */
  def tabulate[A](n: Int)(f: Int => A): CC[A] = {
    val b = newBuilder[A]
    b.sizeHint(n)
    var i = 0
    while (i < n) {
      b += f(i)
      i += 1
    }
    b.result()
  }

  /** Produces a two-dimensional $coll containing values of a given function over ranges of integer values starting from 0.
   *  @param   n1  the number of elements in the 1st dimension
   *  @param   n2  the number of elements in the 2nd dimension
   *  @param   f   The function computing element values
   *  @return A $coll consisting of elements `f(i1, i2)`
   *          for `0 <= i1 < n1` and `0 <= i2 < n2`.
   */
  def tabulate[A](n1: Int, n2: Int)(f: (Int, Int) => A): CC[CC[A]] =
    tabulate(n1)(i1 => tabulate(n2)(f(i1, _)))

  /** Produces a three-dimensional $coll containing values of a given function over ranges of integer values starting from 0.
   *  @param   n1  the number of elements in the 1st dimension
   *  @param   n2  the number of elements in the 2nd dimension
   *  @param   n3  the number of elements in the 3nd dimension
   *  @param   f   The function computing element values
   *  @return A $coll consisting of elements `f(i1, i2, i3)`
   *          for `0 <= i1 < n1`, `0 <= i2 < n2`, and `0 <= i3 < n3`.
   */
  def tabulate[A](n1: Int, n2: Int, n3: Int)(f: (Int, Int, Int) => A): CC[CC[CC[A]]] =
    tabulate(n1)(i1 => tabulate(n2, n3)(f(i1, _, _)))

  /** Produces a four-dimensional $coll containing values of a given function over ranges of integer values starting from 0.
   *  @param   n1  the number of elements in the 1st dimension
   *  @param   n2  the number of elements in the 2nd dimension
   *  @param   n3  the number of elements in the 3nd dimension
   *  @param   n4  the number of elements in the 4th dimension
   *  @param   f   The function computing element values
   *  @return A $coll consisting of elements `f(i1, i2, i3, i4)`
   *          for `0 <= i1 < n1`, `0 <= i2 < n2`, `0 <= i3 < n3`, and `0 <= i4 < n4`.
   */
  def tabulate[A](n1: Int, n2: Int, n3: Int, n4: Int)(f: (Int, Int, Int, Int) => A): CC[CC[CC[CC[A]]]] =
    tabulate(n1)(i1 => tabulate(n2, n3, n4)(f(i1, _, _, _)))

  /** Produces a five-dimensional $coll containing values of a given function over ranges of integer values starting from 0.
   *  @param   n1  the number of elements in the 1st dimension
   *  @param   n2  the number of elements in the 2nd dimension
   *  @param   n3  the number of elements in the 3nd dimension
   *  @param   n4  the number of elements in the 4th dimension
   *  @param   n5  the number of elements in the 5th dimension
   *  @param   f   The function computing element values
   *  @return A $coll consisting of elements `f(i1, i2, i3, i4, i5)`
   *          for `0 <= i1 < n1`, `0 <= i2 < n2`, `0 <= i3 < n3`, `0 <= i4 < n4`, and `0 <= i5 < n5`.
   */
  def tabulate[A](n1: Int, n2: Int, n3: Int, n4: Int, n5: Int)(f: (Int, Int, Int, Int, Int) => A): CC[CC[CC[CC[CC[A]]]]] =
    tabulate(n1)(i1 => tabulate(n2, n3, n4, n5)(f(i1, _, _, _, _)))

  /** Produces a $coll containing a sequence of increasing of integers.
   *
   *  @param start the first element of the $coll
   *  @param end   the end value of the $coll (the first value NOT contained)
   *  @return  a $coll with values `start, start + 1, ..., end - 1`
   */
  def range[T: Integral](start: T, end: T): CC[T] = range(start, end, implicitly[Integral[T]].one)

  /** Produces a $coll containing equally spaced values in some integer interval.
   *  @param start the start value of the $coll
   *  @param end   the end value of the $coll (the first value NOT contained)
   *  @param step  the difference between successive elements of the $coll (must be positive or negative)
   *  @return      a $coll with values `start, start + step, ...` up to, but excluding `end`
   */
  def range[T: Integral](start: T, end: T, step: T): CC[T] = {
    val num = implicitly[Integral[T]]
    import num._

    if (step == zero) throw new IllegalArgumentException("zero step")
    val b = newBuilder[T]
    b sizeHint immutable.NumericRange.count(start, end, step, isInclusive = false)
    var i = start
    while (if (step < zero) end < i else i < end) {
      b += i
      i += step
    }
    b.result()
  }

  /** Produces a $coll containing repeated applications of a function to a start value.
   *
   *  @param start the start value of the $coll
   *  @param len   the number of elements contained inthe $coll
   *  @param f     the function that's repeatedly applied
   *  @return      a $coll with `len` values in the sequence `start, f(start), f(f(start)), ...`
   */
  def iterate[A](start: A, len: Int)(f: A => A): CC[A] = {
    val b = newBuilder[A]
    if (len > 0) {
      b.sizeHint(len)
      var acc = start
      var i = 1
      b += acc

      while (i < len) {
        acc = f(acc)
        i += 1
        b += acc
      }
    }
    b.result()
  }
}