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Scala example source code file (GenTraversableLike.scala)

This example Scala source code file (GenTraversableLike.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, annotation, b, boolean, canbuildfrom, gentraversableonce, int, option, repr, that, the

The GenTraversableLike.scala Scala example source code

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

package scala
package collection


import generic._
import scala.annotation.migration


/** A template trait for all traversable collections upon which operations
 *  may be implemented in parallel.
 *
 *  @define thatinfo the class of the returned collection. Where possible, `That` is
 *    the same class as the current collection class `Repr`, but this
 *    depends on the element type `B` being admissible for that class,
 *    which means that an implicit instance of type `CanBuildFrom[Repr, B, That]`
 *    is found.
 *  @define bfinfo an implicit value of class `CanBuildFrom` which determines
 *    the result class `That` from the current representation type `Repr` and
 *    and the new element type `B`.
 *  @define orderDependent
 *
 *    Note: might return different results for different runs, unless the
 *    underlying collection type is ordered.
 *  @define orderDependentFold
 *
 *    Note: might return different results for different runs, unless the
 *    underlying collection type is ordered.
 *    or the operator is associative and commutative.
 *  @define mayNotTerminateInf
 *
 *    Note: may not terminate for infinite-sized collections.
 *  @define willNotTerminateInf
 *
 *    Note: will not terminate for infinite-sized collections.
 *
 *  @define traversableInfo
 *  This is a base trait of all kinds of Scala collections.
 *
 *  @define Coll `GenTraversable`
 *  @define coll general collection
 *  @define collectExample
 *  @tparam A    the collection element type.
 *  @tparam Repr the actual type of the element container.
 *
 *  @author Martin Odersky
 *  @author Aleksandar Prokopec
 *  @since 2.9
 */
trait GenTraversableLike[+A, +Repr] extends Any with GenTraversableOnce[A] with Parallelizable[A, parallel.ParIterable[A]] {

  def repr: Repr

  def size: Int

  /** Selects the first element of this $coll.
   *  $orderDependent
   *  @return  the first element of this $coll.
   *  @throws `NoSuchElementException` if the $coll is empty.
   */
  def head: A

  /** Optionally selects the first element.
   *  $orderDependent
   *  @return  the first element of this $coll if it is nonempty,
   *           `None` if it is empty.
   */
  def headOption: Option[A]

  /** Tests whether this $coll can be repeatedly traversed.
   *  @return   `true`
   */
  def isTraversableAgain: Boolean

  /** Selects all elements except the first.
   *  $orderDependent
   *  @return  a $coll consisting of all elements of this $coll
   *           except the first one.
   *  @throws `UnsupportedOperationException` if the $coll is empty.
   */
  def tail: Repr

  /** Selects the last element.
    * $orderDependent
    * @return The last element of this $coll.
    * @throws NoSuchElementException If the $coll is empty.
    */
  def last: A

  /** Optionally selects the last element.
   *  $orderDependent
   *  @return  the last element of this $coll$ if it is nonempty,
   *           `None` if it is empty.
   */
  def lastOption: Option[A]

  /** Selects all elements except the last.
   *  $orderDependent
   *  @return  a $coll consisting of all elements of this $coll
   *           except the last one.
   *  @throws `UnsupportedOperationException` if the $coll is empty.
   */
  def init: Repr

  /** Computes a prefix scan of the elements of the collection.
   *
   *  Note: The neutral element `z` may be applied more than once.
   *
   *  @tparam B         element type of the resulting collection
   *  @tparam That      type of the resulting collection
   *  @param z          neutral element for the operator `op`
   *  @param op         the associative operator for the scan
   *  @param cbf        combiner factory which provides a combiner
   *
   *  @return           a new $coll containing the prefix scan of the elements in this $coll
   */
  def scan[B >: A, That](z: B)(op: (B, B) => B)(implicit cbf: CanBuildFrom[Repr, B, That]): That

  /** Produces a collection containing cumulative results of applying the
   *  operator going left to right.
   *
   *  $willNotTerminateInf
   *  $orderDependent
   *
   *  @tparam B      the type of the elements in the resulting collection
   *  @tparam That   the actual type of the resulting collection
   *  @param z       the initial value
   *  @param op      the binary operator applied to the intermediate result and the element
   *  @param bf      $bfinfo
   *  @return        collection with intermediate results
   */
  def scanLeft[B, That](z: B)(op: (B, A) => B)(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Produces a collection containing cumulative results of applying the operator going right to left.
   *  The head of the collection is the last cumulative result.
   *  $willNotTerminateInf
   *  $orderDependent
   *
   *  Example:
   *  {{{
   *    List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)
   *  }}}
   *
   *  @tparam B      the type of the elements in the resulting collection
   *  @tparam That   the actual type of the resulting collection
   *  @param z       the initial value
   *  @param op      the binary operator applied to the intermediate result and the element
   *  @param bf      $bfinfo
   *  @return        collection with intermediate results
   */
  @migration("The behavior of `scanRight` has changed. The previous behavior can be reproduced with scanRight.reverse.", "2.9.0")
  def scanRight[B, That](z: B)(op: (A, B) => B)(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Applies a function `f` to all elements of this $coll.
   *
   *  @param  f   the function that is applied for its side-effect to every element.
   *              The result of function `f` is discarded.
   *
   *  @tparam  U  the type parameter describing the result of function `f`.
   *              This result will always be ignored. Typically `U` is `Unit`,
   *              but this is not necessary.
   *
   *  @usecase def foreach(f: A => Unit): Unit
   *    @inheritdoc
   */
  def foreach[U](f: A => U): Unit

  /** Builds a new collection by applying a function to all elements of this $coll.
   *
   *  @param f      the function to apply to each element.
   *  @tparam B     the element type of the returned collection.
   *  @tparam That  $thatinfo
   *  @param bf     $bfinfo
   *  @return       a new collection of type `That` resulting from applying the given function
   *                `f` to each element of this $coll and collecting the results.
   *
   *  @usecase def map[B](f: A => B): $Coll[B]
   *    @inheritdoc
   *    @return       a new $coll resulting from applying the given function
   *                  `f` to each element of this $coll and collecting the results.
   */
  def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Builds a new collection by applying a partial function to all elements of this $coll
   *  on which the function is defined.
   *
   *  @param pf     the partial function which filters and maps the $coll.
   *  @tparam B     the element type of the returned collection.
   *  @tparam That  $thatinfo
   *  @param bf     $bfinfo
   *  @return       a new collection of type `That` resulting from applying the partial function
   *                `pf` to each element on which it is defined and collecting the results.
   *                The order of the elements is preserved.
   *
   *  @usecase def collect[B](pf: PartialFunction[A, B]): $Coll[B]
   *    @inheritdoc
   *
   *    $collectExample
   *
   *    @return       a new $coll resulting from applying the given partial function
   *                  `pf` to each element on which it is defined and collecting the results.
   *                  The order of the elements is preserved.
   */
  def collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Builds a new collection by applying a function to all elements of this $coll
   *  and using the elements of the resulting collections.
   *
   *  @param f      the function to apply to each element.
   *  @tparam B     the element type of the returned collection.
   *  @tparam That  $thatinfo
   *  @param bf     $bfinfo
   *  @return       a new collection of type `That` resulting from applying the given collection-valued function
   *                `f` to each element of this $coll and concatenating the results.
   *
   *  @usecase def flatMap[B](f: A => GenTraversableOnce[B]): $Coll[B]
   *    @inheritdoc
   *
   *    For example:
   *
   *    {{{
   *      def getWords(lines: Seq[String]): Seq[String] = lines flatMap (line => line split "\\W+")
   *    }}}
   *
   *    The type of the resulting collection is guided by the static type of $coll. This might
   *    cause unexpected results sometimes. For example:
   *
   *    {{{
   *      // lettersOf will return a Seq[Char] of likely repeated letters, instead of a Set
   *      def lettersOf(words: Seq[String]) = words flatMap (word => word.toSet)
   *
   *      // lettersOf will return a Set[Char], not a Seq
   *      def lettersOf(words: Seq[String]) = words.toSet flatMap (word => word.toSeq)
   *
   *      // xs will be an Iterable[Int]
   *      val xs = Map("a" -> List(11,111), "b" -> List(22,222)).flatMap(_._2)
   *
   *      // ys will be a Map[Int, Int]
   *      val ys = Map("a" -> List(1 -> 11,1 -> 111), "b" -> List(2 -> 22,2 -> 222)).flatMap(_._2)
   *    }}}
   *
   *    @return       a new $coll resulting from applying the given collection-valued function
   *                  `f` to each element of this $coll and concatenating the results.
   */
  def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Returns a new $coll containing the elements from the left hand operand followed by the elements from the
   *  right hand operand. The element type of the $coll is the most specific superclass encompassing
   *  the element types of the two operands.
   *
   *  @param that   the traversable to append.
   *  @tparam B     the element type of the returned collection.
   *  @tparam That  $thatinfo
   *  @param bf     $bfinfo
   *  @return       a new collection of type `That` which contains all elements
   *                of this $coll followed by all elements of `that`.
   *
   *  @usecase def ++[B](that: GenTraversableOnce[B]): $Coll[B]
   *    @inheritdoc
   *
   *    Example:
   *    {{{
   *      scala> val a = List(1)
   *      a: List[Int] = List(1)
   *      
   *      scala> val b = List(2)
   *      b: List[Int] = List(2)
   *      
   *      scala> val c = a ++ b
   *      c: List[Int] = List(1, 2)
   *      
   *      scala> val d = List('a')
   *      d: List[Char] = List(a)
   *      
   *      scala> val e = c ++ d
   *      e: List[AnyVal] = List(1, 2, a)
   *    }}}
   *
   *    @return       a new $coll which contains all elements of this $coll
   *                  followed by all elements of `that`.
   */
  def ++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That

  /** Selects all elements of this $coll which satisfy a predicate.
   *
   *  @param pred  the predicate used to test elements.
   *  @return      a new $coll consisting of all elements of this $coll that satisfy the given
   *               predicate `p`. Their order may not be preserved.
   */
  def filter(pred: A => Boolean): Repr

  /** Selects all elements of this $coll which do not satisfy a predicate.
   *
   *  @param pred  the predicate used to test elements.
   *  @return      a new $coll consisting of all elements of this $coll that do not satisfy the given
   *               predicate `p`. Their order may not be preserved.
   */
  def filterNot(pred: A => Boolean): Repr

  /** Partitions this $coll in two ${coll}s according to a predicate.
   *
   *  @param pred the predicate on which to partition.
   *  @return     a pair of ${coll}s: the first $coll consists of all elements that
   *              satisfy the predicate `p` and the second $coll consists of all elements
   *              that don't. The relative order of the elements in the resulting ${coll}s
   *              may not be preserved.
   */
  def partition(pred: A => Boolean): (Repr, Repr)

  /** Partitions this $coll into a map of ${coll}s according to some discriminator function.
   *
   *  Note: this method is not re-implemented by views. This means
   *        when applied to a view it will always force the view and
   *        return a new $coll.
   *
   *  @param f     the discriminator function.
   *  @tparam K    the type of keys returned by the discriminator function.
   *  @return      A map from keys to ${coll}s such that the following invariant holds:
   *               {{{
   *                 (xs groupBy f)(k) = xs filter (x => f(x) == k)
   *               }}}
   *               That is, every key `k` is bound to a $coll of those elements `x`
   *               for which `f(x)` equals `k`.
   *
   */
  def groupBy[K](f: A => K): GenMap[K, Repr]

  /** Selects first ''n'' elements.
   *  $orderDependent
   *  @param  n    the number of elements to take from this $coll.
   *  @return a $coll consisting only of the first `n` elements of this $coll,
   *          or else the whole $coll, if it has less than `n` elements.
   */
  def take(n: Int): Repr

  /** Selects all elements except first ''n'' ones.
   *  $orderDependent
   *  @param  n    the number of elements to drop from this $coll.
   *  @return a $coll consisting of all elements of this $coll except the first `n` ones, or else the
   *          empty $coll, if this $coll has less than `n` elements.
   */
  def drop(n: Int): Repr

  /** Selects an interval of elements.  The returned collection is made up
   *  of all elements `x` which satisfy the invariant:
   *  {{{
   *    from <= indexOf(x) < until
   *  }}}
   *  $orderDependent
   *
   *  @param unc_from   the lowest index to include from this $coll.
   *  @param unc_until  the lowest index to EXCLUDE from this $coll.
   *  @return  a $coll containing the elements greater than or equal to
   *           index `from` extending up to (but not including) index `until`
   *           of this $coll.
   */
  def slice(unc_from: Int, unc_until: Int): Repr

  /** Splits this $coll into two at a given position.
   *  Note: `c splitAt n` is equivalent to (but possibly more efficient than)
   *         `(c take n, c drop n)`.
   *  $orderDependent
   *
   *  @param n the position at which to split.
   *  @return  a pair of ${coll}s consisting of the first `n`
   *           elements of this $coll, and the other elements.
   */
  def splitAt(n: Int): (Repr, Repr)

  /** Takes longest prefix of elements that satisfy a predicate.
   *  $orderDependent
   *  @param   pred  The predicate used to test elements.
   *  @return  the longest prefix of this $coll whose elements all satisfy
   *           the predicate `p`.
   */
  def takeWhile(pred: A => Boolean): Repr

  /** Splits this $coll into a prefix/suffix pair according to a predicate.
   *
   *  Note: `c span p`  is equivalent to (but possibly more efficient than)
   *  `(c takeWhile p, c dropWhile p)`, provided the evaluation of the
   *  predicate `p` does not cause any side-effects.
   *  $orderDependent
   *
   *  @param pred the test predicate
   *  @return  a pair consisting of the longest prefix of this $coll whose
   *           elements all satisfy `p`, and the rest of this $coll.
   */
  def span(pred: A => Boolean): (Repr, Repr)

  /** Drops longest prefix of elements that satisfy a predicate.
   *  $orderDependent
   *  @param   pred  The predicate used to test elements.
   *  @return  the longest suffix of this $coll whose first element
   *           does not satisfy the predicate `p`.
   */
  def dropWhile(pred: A => Boolean): Repr

  /** Defines the prefix of this object's `toString` representation.
   *
   *  @return  a string representation which starts the result of `toString`
   *           applied to this $coll. By default the string prefix is the
   *           simple name of the collection class $coll.
   */
  def stringPrefix: String

}

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