Scala example source code file (ListBuffer.scala)

This example Scala source code file (ListBuffer.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.

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Scala tags/keywords

a, annotation, boolean, builder, int, iterator, list, listbuffer, listserializeend, nil, traversableonce

The ListBuffer.scala Scala example source code

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

package scala
package collection
package mutable

import generic._
import immutable.{List, Nil, ::}
import java.io._
import scala.annotation.migration

/** A `Buffer` implementation back up by a list. It provides constant time
 *  prepend and append. Most other operations are linear.
 *
 *  @author  Matthias Zenger
 *  @author  Martin Odersky
 *  @version 2.8
 *  @since   1
 *  @see [[http://docs.scala-lang.org/overviews/collections/concrete-mutable-collection-classes.html#list_buffers "Scala's Collection Library overview"]]
 *  section on `List Buffers` for more information.
 *
 *  @tparam A    the type of this list buffer's elements.
 *
 *  @define Coll `ListBuffer`
 *  @define coll list buffer
 *  @define thatinfo the class of the returned collection. In the standard library configuration,
 *    `That` is always `ListBuffer[B]` because an implicit of type `CanBuildFrom[ListBuffer, B, ListBuffer[B]]`
 *    is defined in object `ListBuffer`.
 *  @define bfinfo an implicit value of class `CanBuildFrom` which determines the
 *    result class `That` from the current representation type `Repr`
 *    and the new element type `B`. This is usually the `canBuildFrom` value
 *    defined in object `ListBuffer`.
 *  @define orderDependent
 *  @define orderDependentFold
 *  @define mayNotTerminateInf
 *  @define willNotTerminateInf
 */
@SerialVersionUID(3419063961353022662L)
final class ListBuffer[A]
      extends AbstractBuffer[A]
         with Buffer[A]
         with GenericTraversableTemplate[A, ListBuffer]
         with BufferLike[A, ListBuffer[A]]
         with Builder[A, List[A]]
         with SeqForwarder[A]
         with Serializable
{
  override def companion: GenericCompanion[ListBuffer] = ListBuffer

  import scala.collection.Traversable
  import scala.collection.immutable.ListSerializeEnd

  /** Expected invariants:
   *  If start.isEmpty, last0 == null
   *  If start.nonEmpty, last0 != null
   *  If len == 0, start.isEmpty
   *  If len > 0, start.nonEmpty
   */
  private var start: List[A] = Nil
  private var last0: ::[A] = _
  private var exported: Boolean = false
  private var len = 0

  protected def underlying: List[A] = start

  private def writeObject(out: ObjectOutputStream) {
    // write start
    var xs: List[A] = start
    while (!xs.isEmpty) { out.writeObject(xs.head); xs = xs.tail }
    out.writeObject(ListSerializeEnd)

    // no need to write last0

    // write if exported
    out.writeBoolean(exported)

    // write the length
    out.writeInt(len)
  }

  private def readObject(in: ObjectInputStream) {
    // read start, set last0 appropriately
    var elem: A = in.readObject.asInstanceOf[A]
    if (elem == ListSerializeEnd) {
      start = Nil
      last0 = null
    } else {
      var current = new ::(elem, Nil)
      start = current
      elem = in.readObject.asInstanceOf[A]
      while (elem != ListSerializeEnd) {
        val list = new ::(elem, Nil)
        current.tl = list
        current = list
        elem = in.readObject.asInstanceOf[A]
      }
      last0 = current
      start
    }

    // read if exported
    exported = in.readBoolean()

    // read the length
    len = in.readInt()
  }

  /** The current length of the buffer.
   *
   *  This operation takes constant time.
   */
  override def length = len

  // Don't use the inherited size, which forwards to a List and is O(n).
  override def size = length

  // Implementations of abstract methods in Buffer

  override def apply(n: Int): A =
    if (n < 0 || n >= len) throw new IndexOutOfBoundsException(n.toString())
    else super.apply(n)

  /** Replaces element at index `n` with the new element
   *  `newelem`. Takes time linear in the buffer size. (except the
   *  first element, which is updated in constant time).
   *
   *  @param n  the index of the element to replace.
   *  @param x  the new element.
   *  @throws Predef.IndexOutOfBoundsException if `n` is out of bounds.
   */
  def update(n: Int, x: A) {
    // We check the bounds early, so that we don't trigger copying.
    if (n < 0 || n >= len) throw new IndexOutOfBoundsException(n.toString)
    if (exported) copy()
    if (n == 0) {
      val newElem = new :: (x, start.tail)
      if (last0 eq start) {
        last0 = newElem
      }
      start = newElem
    } else {
      var cursor = start
      var i = 1
      while (i < n) {
        cursor = cursor.tail
        i += 1
      }
      val newElem = new :: (x, cursor.tail.tail)
      if (last0 eq cursor.tail) {
        last0 = newElem
      }
      cursor.asInstanceOf[::[A]].tl = newElem
    }
  }

  /** Appends a single element to this buffer. This operation takes constant time.
   *
   *  @param x  the element to append.
   *  @return   this $coll.
   */
  def += (x: A): this.type = {
    if (exported) copy()
    if (isEmpty) {
      last0 = new :: (x, Nil)
      start = last0
    } else {
      val last1 = last0
      last0 = new :: (x, Nil)
      last1.tl = last0
    }
    len += 1
    this
  }

  override def ++=(xs: TraversableOnce[A]): this.type = xs match {
    case x: AnyRef if x eq this      => this ++= (this take size)
    case _                           => super.++=(xs)

  }

  override def ++=:(xs: TraversableOnce[A]): this.type =
    if (xs.asInstanceOf[AnyRef] eq this) ++=: (this take size) else super.++=:(xs)

  /** Clears the buffer contents.
   */
  def clear() {
    start = Nil
    last0 = null
    exported = false
    len = 0
  }

  /** Prepends a single element to this buffer. This operation takes constant
   *  time.
   *
   *  @param x  the element to prepend.
   *  @return   this $coll.
   */
  def +=: (x: A): this.type = {
    if (exported) copy()
    val newElem = new :: (x, start)
    if (isEmpty) last0 = newElem
    start = newElem
    len += 1
    this
  }

  /** Inserts new elements at the index `n`. Opposed to method
   *  `update`, this method will not replace an element with a new
   *  one. Instead, it will insert a new element at index `n`.
   *
   *  @param  n     the index where a new element will be inserted.
   *  @param  seq   the iterable object providing all elements to insert.
   *  @throws Predef.IndexOutOfBoundsException if `n` is out of bounds.
   */
  def insertAll(n: Int, seq: Traversable[A]) {
    // We check the bounds early, so that we don't trigger copying.
    if (n < 0 || n > len) throw new IndexOutOfBoundsException(n.toString)
    if (exported) copy()
    var elems = seq.toList.reverse
    len += elems.length
    if (n == 0) {
      while (!elems.isEmpty) {
        val newElem = new :: (elems.head, start)
        if (start.isEmpty) last0 = newElem
        start = newElem
        elems = elems.tail
      }
    } else {
      var cursor = start
      var i = 1
      while (i < n) {
        cursor = cursor.tail
        i += 1
      }
      while (!elems.isEmpty) {
        val newElem = new :: (elems.head, cursor.tail)
        if (cursor.tail.isEmpty) last0 = newElem
        cursor.asInstanceOf[::[A]].tl = newElem
        elems = elems.tail
      }
    }
  }

  /** Reduce the length of the buffer, and null out last0
   *  if this reduces the length to 0.
   */
  private def reduceLengthBy(num: Int) {
    len -= num
    if (len <= 0)   // obviously shouldn't be < 0, but still better not to leak
      last0 = null
  }

  /** Removes a given number of elements on a given index position. May take
   *  time linear in the buffer size.
   *
   *  @param n         the index which refers to the first element to remove.
   *  @param count     the number of elements to remove.
   */
  @migration("Invalid input values will be rejected in future releases.", "2.11")
  override def remove(n: Int, count: Int) {
    if (n >= len)
      return
    if (count < 0)
      throw new IllegalArgumentException(s"removing negative number ($count) of elements")
    if (exported) copy()
    val n1 = n max 0
    val count1 = count min (len - n1)
    if (n1 == 0) {
      var c = count1
      while (c > 0) {
        start = start.tail
        c -= 1
      }
    } else {
      var cursor = start
      var i = 1
      while (i < n1) {
        cursor = cursor.tail
        i += 1
      }
      var c = count1
      while (c > 0) {
        if (last0 eq cursor.tail) last0 = cursor.asInstanceOf[::[A]]
        cursor.asInstanceOf[::[A]].tl = cursor.tail.tail
        c -= 1
      }
    }
    reduceLengthBy(count1)
  }

// Implementation of abstract method in Builder

  def result: List[A] = toList

  /** Converts this buffer to a list. Takes constant time. The buffer is
   *  copied lazily, the first time it is mutated.
   */
  override def toList: List[A] = {
    exported = !isEmpty
    start
  }

// New methods in ListBuffer

  /** Prepends the elements of this buffer to a given list
   *
   *  @param xs   the list to which elements are prepended
   */
  def prependToList(xs: List[A]): List[A] = {
    if (isEmpty) xs
    else {
      if (exported) copy()
      last0.tl = xs
      toList
    }
  }

// Overrides of methods in Buffer

  /** Removes the element on a given index position. May take time linear in
   *  the buffer size.
   *
   *  @param  n  the index which refers to the element to delete.
   *  @return n  the element that was formerly at position `n`.
   *  @note      an element must exists at position `n`.
   *  @throws Predef.IndexOutOfBoundsException if `n` is out of bounds.
   */
  def remove(n: Int): A = {
    if (n < 0 || n >= len) throw new IndexOutOfBoundsException(n.toString())
    if (exported) copy()
    var old = start.head
    if (n == 0) {
      start = start.tail
    } else {
      var cursor = start
      var i = 1
      while (i < n) {
        cursor = cursor.tail
        i += 1
      }
      old = cursor.tail.head
      if (last0 eq cursor.tail) last0 = cursor.asInstanceOf[::[A]]
      cursor.asInstanceOf[::[A]].tl = cursor.tail.tail
    }
    reduceLengthBy(1)
    old
  }

  /** Remove a single element from this buffer. May take time linear in the
   *  buffer size.
   *
   *  @param elem  the element to remove.
   *  @return      this $coll.
   */
  override def -= (elem: A): this.type = {
    if (exported) copy()
    if (isEmpty) {}
    else if (start.head == elem) {
      start = start.tail
      reduceLengthBy(1)
    }
    else {
      var cursor = start
      while (!cursor.tail.isEmpty && cursor.tail.head != elem) {
        cursor = cursor.tail
      }
      if (!cursor.tail.isEmpty) {
        val z = cursor.asInstanceOf[::[A]]
        if (z.tl == last0)
          last0 = z
        z.tl = cursor.tail.tail
        reduceLengthBy(1)
      }
    }
    this
  }

  /** Returns an iterator over this `ListBuffer`.  The iterator will reflect
   *  changes made to the underlying `ListBuffer` beyond the next element;
   *  the next element's value is cached so that `hasNext` and `next` are
   *  guaranteed to be consistent.  In particular, an empty `ListBuffer`
   *  will give an empty iterator even if the `ListBuffer` is later filled.
   */
  override def iterator: Iterator[A] = new AbstractIterator[A] {
    // Have to be careful iterating over mutable structures.
    // This used to have "(cursor ne last0)" as part of its hasNext
    // condition, which means it can return true even when the iterator
    // is exhausted.  Inconsistent results are acceptable when one mutates
    // a structure while iterating, but we should never return hasNext == true
    // on exhausted iterators (thus creating exceptions) merely because
    // values were changed in-place.
    var cursor: List[A] = if (ListBuffer.this.isEmpty) Nil else start

    def hasNext: Boolean = cursor ne Nil
    def next(): A =
      if (!hasNext) throw new NoSuchElementException("next on empty Iterator")
      else {
        val ans = cursor.head
        cursor = cursor.tail
        ans
      }
  }

  @deprecated("The result of this method will change along with this buffer, which is often not what's expected.", "2.11.0")
  override def readOnly: List[A] = start

  // Private methods

  /** Copy contents of this buffer */
  private def copy() {
    if (isEmpty) return
    var cursor = start
    val limit = last0.tail
    clear()
    while (cursor ne limit) {
      this += cursor.head
      cursor = cursor.tail
    }
  }

  override def equals(that: Any): Boolean = that match {
    case that: ListBuffer[_] => this.readOnly equals that.readOnly
    case _                   => super.equals(that)
  }

  /** Returns a clone of this buffer.
   *
   *  @return a `ListBuffer` with the same elements.
   */
  override def clone(): ListBuffer[A] = (new ListBuffer[A]) ++= this

  /** Defines the prefix of the string representation.
   *
   *  @return the string representation of this buffer.
   */
  override def stringPrefix: String = "ListBuffer"
}

/** $factoryInfo
 *  @define Coll `ListBuffer`
 *  @define coll list buffer
 */
object ListBuffer extends SeqFactory[ListBuffer] {
  implicit def canBuildFrom[A]: CanBuildFrom[Coll, A, ListBuffer[A]] = ReusableCBF.asInstanceOf[GenericCanBuildFrom[A]]
  def newBuilder[A]: Builder[A, ListBuffer[A]] = new GrowingBuilder(new ListBuffer[A])
}