scala.collection.TraversableLike.scala Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of scala-library Show documentation
Show all versions of scala-library Show documentation
Standard library for the Scala Programming Language
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2013, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.collection
import generic._
import mutable.{ Builder }
import scala.annotation.{tailrec, migration, bridge}
import scala.annotation.unchecked.{ uncheckedVariance => uV }
import parallel.ParIterable
import scala.language.higherKinds
/** A template trait for traversable collections of type `Traversable[A]`.
*
* $traversableInfo
* @define mutability
* @define traversableInfo
* This is a base trait of all kinds of $mutability Scala collections. It
* implements the behavior common to all collections, in terms of a method
* `foreach` with signature:
* {{{
* def foreach[U](f: Elem => U): Unit
* }}}
* Collection classes mixing in this trait provide a concrete
* `foreach` method which traverses all the
* elements contained in the collection, applying a given function to each.
* They also need to provide a method `newBuilder`
* which creates a builder for collections of the same kind.
*
* A traversable class might or might not have two properties: strictness
* and orderedness. Neither is represented as a type.
*
* The instances of a strict collection class have all their elements
* computed before they can be used as values. By contrast, instances of
* a non-strict collection class may defer computation of some of their
* elements until after the instance is available as a value.
* A typical example of a non-strict collection class is a
* [[scala.collection.immutable.Stream]].
* A more general class of examples are `TraversableViews`.
*
* If a collection is an instance of an ordered collection class, traversing
* its elements with `foreach` will always visit elements in the
* same order, even for different runs of the program. If the class is not
* ordered, `foreach` can visit elements in different orders for
* different runs (but it will keep the same order in the same run).'
*
* A typical example of a collection class which is not ordered is a
* `HashMap` of objects. The traversal order for hash maps will
* depend on the hash codes of its elements, and these hash codes might
* differ from one run to the next. By contrast, a `LinkedHashMap`
* is ordered because it's `foreach` method visits elements in the
* order they were inserted into the `HashMap`.
*
* @author Martin Odersky
* @version 2.8
* @since 2.8
* @tparam A the element type of the collection
* @tparam Repr the type of the actual collection containing the elements.
*
* @define Coll Traversable
* @define coll traversable collection
*/
trait TraversableLike[+A, +Repr] extends Any
with HasNewBuilder[A, Repr]
with FilterMonadic[A, Repr]
with TraversableOnce[A]
with GenTraversableLike[A, Repr]
with Parallelizable[A, ParIterable[A]]
{
self =>
import Traversable.breaks._
/** The type implementing this traversable */
protected type Self = Repr
/** The collection of type $coll underlying this `TraversableLike` object.
* By default this is implemented as the `TraversableLike` object itself,
* but this can be overridden.
*/
def repr: Repr = this.asInstanceOf[Repr]
final def isTraversableAgain: Boolean = true
/** The underlying collection seen as an instance of `$Coll`.
* By default this is implemented as the current collection object itself,
* but this can be overridden.
*/
protected[this] def thisCollection: Traversable[A] = this.asInstanceOf[Traversable[A]]
/** A conversion from collections of type `Repr` to `$Coll` objects.
* By default this is implemented as just a cast, but this can be overridden.
*/
protected[this] def toCollection(repr: Repr): Traversable[A] = repr.asInstanceOf[Traversable[A]]
/** Creates a new builder for this collection type.
*/
protected[this] def newBuilder: Builder[A, Repr]
protected[this] def parCombiner = ParIterable.newCombiner[A]
/** 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
*
* Note: this method underlies the implementation of most other bulk operations.
* It's important to implement this method in an efficient way.
*
*/
def foreach[U](f: A => U): Unit
/** Tests whether this $coll is empty.
*
* @return `true` if the $coll contain no elements, `false` otherwise.
*/
def isEmpty: Boolean = {
var result = true
breakable {
for (x <- this) {
result = false
break
}
}
result
}
/** Tests whether this $coll is known to have a finite size.
* All strict collections are known to have finite size. For a non-strict
* collection such as `Stream`, the predicate returns `'''true'''` if all
* elements have been computed. It returns `'''false'''` if the stream is
* not yet evaluated to the end.
*
* Note: many collection methods will not work on collections of infinite sizes.
*
* @return `'''true'''` if this collection is known to have finite size,
* `'''false'''` otherwise.
*/
def hasDefiniteSize = true
def ++[B >: A, That](that: GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
val b = bf(repr)
if (that.isInstanceOf[IndexedSeqLike[_, _]]) b.sizeHint(this, that.seq.size)
b ++= thisCollection
b ++= that.seq
b.result
}
/** As with `++`, returns a new collection containing the elements from the left operand followed by the
* elements from the right operand.
*
* It differs from `++` in that the right operand determines the type of
* the resulting collection rather than the left one.
* Mnemonic: the COLon is on the side of the new COLlection type.
*
* @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: TraversableOnce[B]): $Coll[B]
* @inheritdoc
*
* Example:
* {{{
* scala> val x = List(1)
* x: List[Int] = List(1)
*
* scala> val y = LinkedList(2)
* y: scala.collection.mutable.LinkedList[Int] = LinkedList(2)
*
* scala> val z = x ++: y
* z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)
* }}}
*
* @return a new $coll which contains all elements of this $coll
* followed by all elements of `that`.
*/
def ++:[B >: A, That](that: TraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
val b = bf(repr)
if (that.isInstanceOf[IndexedSeqLike[_, _]]) b.sizeHint(this, that.size)
b ++= that
b ++= thisCollection
b.result
}
/** As with `++`, returns a new collection containing the elements from the
* left operand followed by the elements from the right operand.
*
* It differs from `++` in that the right operand determines the type of
* the resulting collection rather than the left one.
* Mnemonic: the COLon is on the side of the new COLlection type.
*
* Example:
* {{{
* scala> val x = List(1)
* x: List[Int] = List(1)
*
* scala> val y = LinkedList(2)
* y: scala.collection.mutable.LinkedList[Int] = LinkedList(2)
*
* scala> val z = x ++: y
* z: scala.collection.mutable.LinkedList[Int] = LinkedList(1, 2)
* }}}
*
* This overload exists because: for the implementation of `++:` we should
* reuse that of `++` because many collections override it with more
* efficient versions.
*
* Since `TraversableOnce` has no `++` method, we have to implement that
* directly, but `Traversable` and down can use the overload.
*
* @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`.
*/
def ++:[B >: A, That](that: Traversable[B])(implicit bf: CanBuildFrom[Repr, B, That]): That =
(that ++ seq)(breakOut)
def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = {
def builder = { // extracted to keep method size under 35 bytes, so that it can be JIT-inlined
val b = bf(repr)
b.sizeHint(this)
b
}
val b = builder
for (x <- this) b += f(x)
b.result
}
def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
def builder = bf(repr) // extracted to keep method size under 35 bytes, so that it can be JIT-inlined
val b = builder
for (x <- this) b ++= f(x).seq
b.result
}
/** Selects all elements of this $coll which satisfy a predicate.
*
* @param p the predicate used to test elements.
* @return a new $coll consisting of all elements of this $coll that satisfy the given
* predicate `p`. The order of the elements is preserved.
*/
def filter(p: A => Boolean): Repr = {
val b = newBuilder
for (x <- this)
if (p(x)) b += x
b.result
}
/** Selects all elements of this $coll which do not satisfy a predicate.
*
* @param p 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`. The order of the elements is preserved.
*/
def filterNot(p: A => Boolean): Repr = filter(!p(_))
def collect[B, That](pf: PartialFunction[A, B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
val b = bf(repr)
for (x <- this) if (pf.isDefinedAt(x)) b += pf(x)
b.result
}
/** Builds a new collection by applying an option-valued function to all
* elements of this $coll on which the function is defined.
*
* @param f the option-valued 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 option-valued function
* `f` to each element and collecting all defined results.
* The order of the elements is preserved.
*
* @usecase def filterMap[B](f: A => Option[B]): $Coll[B]
* @inheritdoc
*
* @param pf the partial function which filters and maps the $coll.
* @return a new $coll resulting from applying the given option-valued function
* `f` to each element and collecting all defined results.
* The order of the elements is preserved.
def filterMap[B, That](f: A => Option[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
val b = bf(repr)
for (x <- this)
f(x) match {
case Some(y) => b += y
case _ =>
}
b.result
}
*/
/** Partitions this $coll in two ${coll}s according to a predicate.
*
* @param p 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
* is the same as in the original $coll.
*/
def partition(p: A => Boolean): (Repr, Repr) = {
val l, r = newBuilder
for (x <- this) (if (p(x)) l else r) += x
(l.result, r.result)
}
def groupBy[K](f: A => K): immutable.Map[K, Repr] = {
val m = mutable.Map.empty[K, Builder[A, Repr]]
for (elem <- this) {
val key = f(elem)
val bldr = m.getOrElseUpdate(key, newBuilder)
bldr += elem
}
val b = immutable.Map.newBuilder[K, Repr]
for ((k, v) <- m)
b += ((k, v.result))
b.result
}
/** Tests whether a predicate holds for all elements of this $coll.
*
* $mayNotTerminateInf
*
* @param p the predicate used to test elements.
* @return `true` if the given predicate `p` holds for all elements
* of this $coll, otherwise `false`.
*/
def forall(p: A => Boolean): Boolean = {
var result = true
breakable {
for (x <- this)
if (!p(x)) { result = false; break }
}
result
}
/** Tests whether a predicate holds for some of the elements of this $coll.
*
* $mayNotTerminateInf
*
* @param p the predicate used to test elements.
* @return `true` if the given predicate `p` holds for some of the
* elements of this $coll, otherwise `false`.
*/
def exists(p: A => Boolean): Boolean = {
var result = false
breakable {
for (x <- this)
if (p(x)) { result = true; break }
}
result
}
/** Finds the first element of the $coll satisfying a predicate, if any.
*
* $mayNotTerminateInf
* $orderDependent
*
* @param p the predicate used to test elements.
* @return an option value containing the first element in the $coll
* that satisfies `p`, or `None` if none exists.
*/
def find(p: A => Boolean): Option[A] = {
var result: Option[A] = None
breakable {
for (x <- this)
if (p(x)) { result = Some(x); break }
}
result
}
def scan[B >: A, That](z: B)(op: (B, B) => B)(implicit cbf: CanBuildFrom[Repr, B, That]): That = scanLeft(z)(op)
def scanLeft[B, That](z: B)(op: (B, A) => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = {
val b = bf(repr)
b.sizeHint(this, 1)
var acc = z
b += acc
for (x <- this) { acc = op(acc, x); b += acc }
b.result
}
@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 = {
var scanned = List(z)
var acc = z
for (x <- reversed) {
acc = op(x, acc)
scanned ::= acc
}
val b = bf(repr)
for (elem <- scanned) b += elem
b.result
}
/** 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 = {
var result: () => A = () => throw new NoSuchElementException
breakable {
for (x <- this) {
result = () => x
break
}
}
result()
}
/** 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] = if (isEmpty) None else Some(head)
/** 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.
*/
override def tail: Repr = {
if (isEmpty) throw new UnsupportedOperationException("empty.tail")
drop(1)
}
/** Selects the last element.
* $orderDependent
* @return The last element of this $coll.
* @throws NoSuchElementException If the $coll is empty.
*/
def last: A = {
var lst = head
for (x <- this)
lst = x
lst
}
/** 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] = if (isEmpty) None else Some(last)
/** 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 = {
if (isEmpty) throw new UnsupportedOperationException("empty.init")
var lst = head
var follow = false
val b = newBuilder
b.sizeHint(this, -1)
for (x <- this.seq) {
if (follow) b += lst
else follow = true
lst = x
}
b.result
}
def take(n: Int): Repr = slice(0, n)
def drop(n: Int): Repr =
if (n <= 0) {
val b = newBuilder
b.sizeHint(this)
(b ++= thisCollection).result
}
else sliceWithKnownDelta(n, Int.MaxValue, -n)
def slice(from: Int, until: Int): Repr =
sliceWithKnownBound(scala.math.max(from, 0), until)
// Precondition: from >= 0, until > 0, builder already configured for building.
private[this] def sliceInternal(from: Int, until: Int, b: Builder[A, Repr]): Repr = {
var i = 0
breakable {
for (x <- this.seq) {
if (i >= from) b += x
i += 1
if (i >= until) break
}
}
b.result
}
// Precondition: from >= 0
private[scala] def sliceWithKnownDelta(from: Int, until: Int, delta: Int): Repr = {
val b = newBuilder
if (until <= from) b.result
else {
b.sizeHint(this, delta)
sliceInternal(from, until, b)
}
}
// Precondition: from >= 0
private[scala] def sliceWithKnownBound(from: Int, until: Int): Repr = {
val b = newBuilder
if (until <= from) b.result
else {
b.sizeHintBounded(until - from, this)
sliceInternal(from, until, b)
}
}
def takeWhile(p: A => Boolean): Repr = {
val b = newBuilder
breakable {
for (x <- this) {
if (!p(x)) break
b += x
}
}
b.result
}
def dropWhile(p: A => Boolean): Repr = {
val b = newBuilder
var go = false
for (x <- this) {
if (!go && !p(x)) go = true
if (go) b += x
}
b.result
}
def span(p: A => Boolean): (Repr, Repr) = {
val l, r = newBuilder
var toLeft = true
for (x <- this) {
toLeft = toLeft && p(x)
(if (toLeft) l else r) += x
}
(l.result, r.result)
}
def splitAt(n: Int): (Repr, Repr) = {
val l, r = newBuilder
l.sizeHintBounded(n, this)
if (n >= 0) r.sizeHint(this, -n)
var i = 0
for (x <- this) {
(if (i < n) l else r) += x
i += 1
}
(l.result, r.result)
}
/** Iterates over the tails of this $coll. The first value will be this
* $coll and the final one will be an empty $coll, with the intervening
* values the results of successive applications of `tail`.
*
* @return an iterator over all the tails of this $coll
* @example `List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)`
*/
def tails: Iterator[Repr] = iterateUntilEmpty(_.tail)
/** Iterates over the inits of this $coll. The first value will be this
* $coll and the final one will be an empty $coll, with the intervening
* values the results of successive applications of `init`.
*
* @return an iterator over all the inits of this $coll
* @example `List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)`
*/
def inits: Iterator[Repr] = iterateUntilEmpty(_.init)
/** Copies elements of this $coll to an array.
* Fills the given array `xs` with at most `len` elements of
* this $coll, starting at position `start`.
* Copying will stop once either the end of the current $coll is reached,
* or the end of the array is reached, or `len` elements have been copied.
*
* @param xs the array to fill.
* @param start the starting index.
* @param len the maximal number of elements to copy.
* @tparam B the type of the elements of the array.
*
*
* @usecase def copyToArray(xs: Array[A], start: Int, len: Int): Unit
* @inheritdoc
*
* $willNotTerminateInf
*/
def copyToArray[B >: A](xs: Array[B], start: Int, len: Int) {
var i = start
val end = (start + len) min xs.length
breakable {
for (x <- this) {
if (i >= end) break
xs(i) = x
i += 1
}
}
}
def toTraversable: Traversable[A] = thisCollection
def toIterator: Iterator[A] = toStream.iterator
def toStream: Stream[A] = toBuffer.toStream
// Override to provide size hint.
override def to[Col[_]](implicit cbf: CanBuildFrom[Nothing, A, Col[A @uV]]): Col[A @uV] = {
val b = cbf()
b.sizeHint(this)
b ++= thisCollection
b.result
}
/** Converts this $coll to a string.
*
* @return a string representation of this collection. By default this
* string consists of the `stringPrefix` of this $coll, followed
* by all elements separated by commas and enclosed in parentheses.
*/
override def toString = mkString(stringPrefix + "(", ", ", ")")
/** 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 $coll.
*/
def stringPrefix : String = {
var string = repr.getClass.getName
val idx1 = string.lastIndexOf('.' : Int)
if (idx1 != -1) string = string.substring(idx1 + 1)
val idx2 = string.indexOf('$')
if (idx2 != -1) string = string.substring(0, idx2)
string
}
/** Creates a non-strict view of this $coll.
*
* @return a non-strict view of this $coll.
*/
def view = new TraversableView[A, Repr] {
protected lazy val underlying = self.repr
override def foreach[U](f: A => U) = self foreach f
}
/** Creates a non-strict view of a slice of this $coll.
*
* Note: the difference between `view` and `slice` is that `view` produces
* a view of the current $coll, whereas `slice` produces a new $coll.
*
* Note: `view(from, to)` is equivalent to `view.slice(from, to)`
* $orderDependent
*
* @param from the index of the first element of the view
* @param until the index of the element following the view
* @return a non-strict view of a slice of this $coll, starting at index `from`
* and extending up to (but not including) index `until`.
*/
def view(from: Int, until: Int): TraversableView[A, Repr] = view.slice(from, until)
/** Creates a non-strict filter of this $coll.
*
* Note: the difference between `c filter p` and `c withFilter p` is that
* the former creates a new collection, whereas the latter only
* restricts the domain of subsequent `map`, `flatMap`, `foreach`,
* and `withFilter` operations.
* $orderDependent
*
* @param p the predicate used to test elements.
* @return an object of class `WithFilter`, which supports
* `map`, `flatMap`, `foreach`, and `withFilter` operations.
* All these operations apply to those elements of this $coll
* which satisfy the predicate `p`.
*/
def withFilter(p: A => Boolean): FilterMonadic[A, Repr] = new WithFilter(p)
/** A class supporting filtered operations. Instances of this class are
* returned by method `withFilter`.
*/
class WithFilter(p: A => Boolean) extends FilterMonadic[A, Repr] {
/** Builds a new collection by applying a function to all elements of the
* outer $coll containing this `WithFilter` instance that satisfy predicate `p`.
*
* @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 the outer $coll
* that satisfies predicate `p` 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 the outer $coll that satisfies
* predicate `p` and collecting the results.
*/
def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That = {
val b = bf(repr)
for (x <- self)
if (p(x)) b += f(x)
b.result
}
/** Builds a new collection by applying a function to all elements of the
* outer $coll containing this `WithFilter` instance that satisfy
* predicate `p` and concatenating the results.
*
* @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 the outer $coll that satisfies predicate `p` and
* concatenating the results.
*
* @usecase def flatMap[B](f: A => TraversableOnce[B]): $Coll[B]
* @inheritdoc
*
* The type of the resulting collection will be guided by the static type
* of the outer $coll.
*
* @return a new $coll resulting from applying the given
* collection-valued function `f` to each element of the
* outer $coll that satisfies predicate `p` and concatenating
* the results.
*/
def flatMap[B, That](f: A => GenTraversableOnce[B])(implicit bf: CanBuildFrom[Repr, B, That]): That = {
val b = bf(repr)
for (x <- self)
if (p(x)) b ++= f(x).seq
b.result
}
/** Applies a function `f` to all elements of the outer $coll containing
* this `WithFilter` instance that satisfy predicate `p`.
*
* @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 =
for (x <- self)
if (p(x)) f(x)
/** Further refines the filter for this $coll.
*
* @param q the predicate used to test elements.
* @return an object of class `WithFilter`, which supports
* `map`, `flatMap`, `foreach`, and `withFilter` operations.
* All these operations apply to those elements of this $coll which
* satisfy the predicate `q` in addition to the predicate `p`.
*/
def withFilter(q: A => Boolean): WithFilter =
new WithFilter(x => p(x) && q(x))
}
// A helper for tails and inits.
private def iterateUntilEmpty(f: Traversable[A @uV] => Traversable[A @uV]): Iterator[Repr] = {
val it = Iterator.iterate(thisCollection)(f) takeWhile (x => !x.isEmpty)
it ++ Iterator(Nil) map (x => (newBuilder ++= x).result)
}
}