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/*
* 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.collection
import scala.annotation.tailrec
import scala.collection.mutable.{ArrayBuffer, Builder}
import scala.collection.immutable.LazyList
/** Views are collections whose transformation operations are non strict: the resulting elements
* are evaluated only when the view is effectively traversed (e.g. using `foreach` or `foldLeft`),
* or when the view is converted to a strict collection type (using the `to` operation).
* @define coll view
* @define Coll `View`
*/
trait View[+A] extends Iterable[A] with IterableOps[A, View, View[A]] with IterableFactoryDefaults[A, View] with Serializable {
override def view: View[A] = this
override def iterableFactory: IterableFactory[View] = View
override def empty: scala.collection.View[A] = iterableFactory.empty
override def toString: String = className + "()"
override protected[this] def stringPrefix: String = "View"
@deprecated("Views no longer know about their underlying collection type; .force always returns an IndexedSeq", "2.13.0")
@`inline` def force: IndexedSeq[A] = toIndexedSeq
}
/** This object reifies operations on views as case classes
*
* @define Coll View
* @define coll view
*/
@SerialVersionUID(3L)
object View extends IterableFactory[View] {
/**
* @return A `View[A]` whose underlying iterator is provided by the `it` parameter-less function.
*
* @param it Function creating the iterator to be used by the view. This function must always return
* a fresh `Iterator`, otherwise the resulting view will be effectively iterable only once.
*
* @tparam A View element type
*/
def fromIteratorProvider[A](it: () => Iterator[A]): View[A] = new AbstractView[A] {
def iterator = it()
}
/**
* @return A view iterating over the given `Iterable`
*
* @param it The `IterableOnce` to view. A proper `Iterable` is used directly. If it is really only
* `IterableOnce` it gets memoized on the first traversal.
*
* @tparam E View element type
*/
def from[E](it: IterableOnce[E]): View[E] = it match {
case it: View[E] => it
case it: Iterable[E] => View.fromIteratorProvider(() => it.iterator)
case _ => LazyList.from(it).view
}
def empty[A]: View[A] = Empty
def newBuilder[A]: Builder[A, View[A]] = ArrayBuffer.newBuilder[A].mapResult(from)
override def apply[A](xs: A*): View[A] = new Elems(xs: _*)
/** The empty view */
@SerialVersionUID(3L)
case object Empty extends AbstractView[Nothing] {
def iterator = Iterator.empty
override def knownSize = 0
override def isEmpty: Boolean = true
}
/** A view with exactly one element */
@SerialVersionUID(3L)
class Single[A](a: A) extends AbstractView[A] {
def iterator: Iterator[A] = Iterator.single(a)
override def knownSize: Int = 1
override def isEmpty: Boolean = false
}
/** A view with given elements */
@SerialVersionUID(3L)
class Elems[A](xs: A*) extends AbstractView[A] {
def iterator = xs.iterator
override def knownSize = xs.knownSize
override def isEmpty: Boolean = xs.isEmpty
}
/** A view containing the results of some element computation a number of times. */
@SerialVersionUID(3L)
class Fill[A](n: Int)(elem: => A) extends AbstractView[A] {
def iterator = Iterator.fill(n)(elem)
override def knownSize: Int = 0 max n
override def isEmpty: Boolean = n <= 0
}
/** A view containing values of a given function over a range of integer values starting from 0. */
@SerialVersionUID(3L)
class Tabulate[A](n: Int)(f: Int => A) extends AbstractView[A] {
def iterator: Iterator[A] = Iterator.tabulate(n)(f)
override def knownSize: Int = 0 max n
override def isEmpty: Boolean = n <= 0
}
/** A view containing repeated applications of a function to a start value */
@SerialVersionUID(3L)
class Iterate[A](start: A, len: Int)(f: A => A) extends AbstractView[A] {
def iterator: Iterator[A] = Iterator.iterate(start)(f).take(len)
override def knownSize: Int = 0 max len
override def isEmpty: Boolean = len <= 0
}
/** A view that uses a function `f` to produce elements of type `A` and update
* an internal state `S`.
*/
@SerialVersionUID(3L)
class Unfold[A, S](initial: S)(f: S => Option[(A, S)]) extends AbstractView[A] {
def iterator: Iterator[A] = Iterator.unfold(initial)(f)
}
/** An `IterableOps` whose collection type and collection type constructor are unknown */
type SomeIterableOps[A] = IterableOps[A, AnyConstr, _]
/** A view that filters an underlying collection. */
@SerialVersionUID(3L)
class Filter[A](val underlying: SomeIterableOps[A], val p: A => Boolean, val isFlipped: Boolean) extends AbstractView[A] {
def iterator = underlying.iterator.filterImpl(p, isFlipped)
override def knownSize: Int = if (underlying.knownSize == 0) 0 else super.knownSize
override def isEmpty: Boolean = iterator.isEmpty
}
object Filter {
def apply[A](underlying: Iterable[A], p: A => Boolean, isFlipped: Boolean): Filter[A] =
underlying match {
case filter: Filter[A] if filter.isFlipped == isFlipped => new Filter(filter.underlying, a => filter.p(a) && p(a), isFlipped)
case _ => new Filter(underlying, p, isFlipped)
}
}
/** A view that removes the duplicated elements as determined by the transformation function `f` */
@SerialVersionUID(3L)
class DistinctBy[A, B](underlying: SomeIterableOps[A], f: A => B) extends AbstractView[A] {
def iterator: Iterator[A] = underlying.iterator.distinctBy(f)
override def knownSize: Int = if (underlying.knownSize == 0) 0 else super.knownSize
override def isEmpty: Boolean = underlying.isEmpty
}
@SerialVersionUID(3L)
class LeftPartitionMapped[A, A1, A2](underlying: SomeIterableOps[A], f: A => Either[A1, A2]) extends AbstractView[A1] {
def iterator = new AbstractIterator[A1] {
private[this] val self = underlying.iterator
private[this] var hd: A1 = _
private[this] var hdDefined: Boolean = false
def hasNext = hdDefined || {
@tailrec
def findNext(): Boolean =
if (self.hasNext) {
f(self.next()) match {
case Left(a1) => hd = a1; hdDefined = true; true
case Right(_) => findNext()
}
} else false
findNext()
}
def next() =
if (hasNext) {
hdDefined = false
hd
} else Iterator.empty.next()
}
}
@SerialVersionUID(3L)
class RightPartitionMapped[A, A1, A2](underlying: SomeIterableOps[A], f: A => Either[A1, A2]) extends AbstractView[A2] {
def iterator = new AbstractIterator[A2] {
private[this] val self = underlying.iterator
private[this] var hd: A2 = _
private[this] var hdDefined: Boolean = false
def hasNext = hdDefined || {
@tailrec
def findNext(): Boolean =
if (self.hasNext) {
f(self.next()) match {
case Left(_) => findNext()
case Right(a2) => hd = a2; hdDefined = true; true
}
} else false
findNext()
}
def next() =
if (hasNext) {
hdDefined = false
hd
} else Iterator.empty.next()
}
}
/** A view that drops leading elements of the underlying collection. */
@SerialVersionUID(3L)
class Drop[A](underlying: SomeIterableOps[A], n: Int) extends AbstractView[A] {
def iterator = underlying.iterator.drop(n)
protected val normN = n max 0
override def knownSize = {
val size = underlying.knownSize
if (size >= 0) (size - normN) max 0 else -1
}
override def isEmpty: Boolean = iterator.isEmpty
}
/** A view that drops trailing elements of the underlying collection. */
@SerialVersionUID(3L)
class DropRight[A](underlying: SomeIterableOps[A], n: Int) extends AbstractView[A] {
def iterator = dropRightIterator(underlying.iterator, n)
protected val normN = n max 0
override def knownSize = {
val size = underlying.knownSize
if (size >= 0) (size - normN) max 0 else -1
}
override def isEmpty: Boolean =
if(knownSize >= 0) knownSize == 0
else iterator.isEmpty
}
@SerialVersionUID(3L)
class DropWhile[A](underlying: SomeIterableOps[A], p: A => Boolean) extends AbstractView[A] {
def iterator = underlying.iterator.dropWhile(p)
override def knownSize: Int = if (underlying.knownSize == 0) 0 else super.knownSize
override def isEmpty: Boolean = iterator.isEmpty
}
/** A view that takes leading elements of the underlying collection. */
@SerialVersionUID(3L)
class Take[+A](underlying: SomeIterableOps[A], n: Int) extends AbstractView[A] {
def iterator = underlying.iterator.take(n)
protected val normN = n max 0
override def knownSize = {
val size = underlying.knownSize
if (size >= 0) size min normN else -1
}
override def isEmpty: Boolean = iterator.isEmpty
}
/** A view that takes trailing elements of the underlying collection. */
@SerialVersionUID(3L)
class TakeRight[+A](underlying: SomeIterableOps[A], n: Int) extends AbstractView[A] {
def iterator = takeRightIterator(underlying.iterator, n)
protected val normN = n max 0
override def knownSize = {
val size = underlying.knownSize
if (size >= 0) size min normN else -1
}
override def isEmpty: Boolean =
if(knownSize >= 0) knownSize == 0
else iterator.isEmpty
}
@SerialVersionUID(3L)
class TakeWhile[A](underlying: SomeIterableOps[A], p: A => Boolean) extends AbstractView[A] {
def iterator: Iterator[A] = underlying.iterator.takeWhile(p)
override def knownSize: Int = if (underlying.knownSize == 0) 0 else super.knownSize
override def isEmpty: Boolean = iterator.isEmpty
}
@SerialVersionUID(3L)
class ScanLeft[+A, +B](underlying: SomeIterableOps[A], z: B, op: (B, A) => B) extends AbstractView[B] {
def iterator: Iterator[B] = underlying.iterator.scanLeft(z)(op)
override def knownSize: Int = {
val size = underlying.knownSize
if (size >= 0) size + 1 else -1
}
override def isEmpty: Boolean = iterator.isEmpty
}
/** A view that maps elements of the underlying collection. */
@SerialVersionUID(3L)
class Map[+A, +B](underlying: SomeIterableOps[A], f: A => B) extends AbstractView[B] {
def iterator = underlying.iterator.map(f)
override def knownSize = underlying.knownSize
override def isEmpty: Boolean = underlying.isEmpty
}
/** A view that flatmaps elements of the underlying collection. */
@SerialVersionUID(3L)
class FlatMap[A, B](underlying: SomeIterableOps[A], f: A => IterableOnce[B]) extends AbstractView[B] {
def iterator = underlying.iterator.flatMap(f)
override def knownSize: Int = if (underlying.knownSize == 0) 0 else super.knownSize
override def isEmpty: Boolean = iterator.isEmpty
}
/** A view that collects elements of the underlying collection. */
@SerialVersionUID(3L)
class Collect[+A, B](underlying: SomeIterableOps[A], pf: PartialFunction[A, B]) extends AbstractView[B] {
def iterator = underlying.iterator.collect(pf)
}
/** A view that concatenates elements of the prefix collection or iterator with the elements
* of the suffix collection or iterator.
*/
@SerialVersionUID(3L)
class Concat[A](prefix: SomeIterableOps[A], suffix: SomeIterableOps[A]) extends AbstractView[A] {
def iterator = prefix.iterator ++ suffix.iterator
override def knownSize = {
val prefixSize = prefix.knownSize
if (prefixSize >= 0) {
val suffixSize = suffix.knownSize
if (suffixSize >= 0) prefixSize + suffixSize
else -1
}
else -1
}
override def isEmpty: Boolean = prefix.isEmpty && suffix.isEmpty
}
/** A view that zips elements of the underlying collection with the elements
* of another collection.
*/
@SerialVersionUID(3L)
class Zip[A, B](underlying: SomeIterableOps[A], other: Iterable[B]) extends AbstractView[(A, B)] {
def iterator = underlying.iterator.zip(other)
override def knownSize = {
val s1 = underlying.knownSize
if (s1 == 0) 0 else {
val s2 = other.knownSize
if (s2 == 0) 0 else s1 min s2
}
}
override def isEmpty: Boolean = underlying.isEmpty || other.isEmpty
}
/** A view that zips elements of the underlying collection with the elements
* of another collection. If one of the two collections is shorter than the other,
* placeholder elements are used to extend the shorter collection to the length of the longer.
*/
@SerialVersionUID(3L)
class ZipAll[A, B](underlying: SomeIterableOps[A], other: Iterable[B], thisElem: A, thatElem: B) extends AbstractView[(A, B)] {
def iterator = underlying.iterator.zipAll(other, thisElem, thatElem)
override def knownSize = {
val s1 = underlying.knownSize
if(s1 == -1) -1 else {
val s2 = other.knownSize
if(s2 == -1) -1 else s1 max s2
}
}
override def isEmpty: Boolean = underlying.isEmpty && other.isEmpty
}
/** A view that appends an element to its elements */
@SerialVersionUID(3L)
class Appended[+A](underlying: SomeIterableOps[A], elem: A) extends AbstractView[A] {
def iterator: Iterator[A] = new Concat(underlying, new View.Single(elem)).iterator
override def knownSize: Int = {
val size = underlying.knownSize
if (size >= 0) size + 1 else -1
}
override def isEmpty: Boolean = false
}
/** A view that prepends an element to its elements */
@SerialVersionUID(3L)
class Prepended[+A](elem: A, underlying: SomeIterableOps[A]) extends AbstractView[A] {
def iterator: Iterator[A] = new Concat(new View.Single(elem), underlying).iterator
override def knownSize: Int = {
val size = underlying.knownSize
if (size >= 0) size + 1 else -1
}
override def isEmpty: Boolean = false
}
@SerialVersionUID(3L)
class Updated[A](underlying: SomeIterableOps[A], index: Int, elem: A) extends AbstractView[A] {
def iterator: Iterator[A] = new AbstractIterator[A] {
private[this] val it = underlying.iterator
private[this] var i = 0
def next(): A = {
val value = if (i == index) { it.next(); elem } else it.next()
i += 1
value
}
def hasNext: Boolean =
if(it.hasNext) true
else if(index >= i) throw new IndexOutOfBoundsException(index.toString)
else false
}
override def knownSize: Int = underlying.knownSize
override def isEmpty: Boolean = iterator.isEmpty
}
@SerialVersionUID(3L)
private[collection] class Patched[A](underlying: SomeIterableOps[A], from: Int, other: IterableOnce[A], replaced: Int) extends AbstractView[A] {
def iterator: Iterator[A] = underlying.iterator.patch(from, other.iterator, replaced)
override def knownSize: Int = if (underlying.knownSize == 0 && other.knownSize == 0) 0 else super.knownSize
override def isEmpty: Boolean = if (knownSize == 0) true else iterator.isEmpty
}
@SerialVersionUID(3L)
class ZipWithIndex[A](underlying: SomeIterableOps[A]) extends AbstractView[(A, Int)] {
def iterator: Iterator[(A, Int)] = underlying.iterator.zipWithIndex
override def knownSize: Int = underlying.knownSize
override def isEmpty: Boolean = underlying.isEmpty
}
@SerialVersionUID(3L)
class PadTo[A](underlying: SomeIterableOps[A], len: Int, elem: A) extends AbstractView[A] {
def iterator: Iterator[A] = underlying.iterator.padTo(len, elem)
override def knownSize: Int = {
val size = underlying.knownSize
if (size >= 0) size max len else -1
}
override def isEmpty: Boolean = underlying.isEmpty && len <= 0
}
private[collection] def takeRightIterator[A](it: Iterator[A], n: Int): Iterator[A] = {
val k = it.knownSize
if(k == 0 || n <= 0) Iterator.empty
else if(n == Int.MaxValue) it
else if(k > 0) it.drop((k-n) max 0)
else new TakeRightIterator[A](it, n)
}
private final class TakeRightIterator[A](private[this] var underlying: Iterator[A], maxlen: Int) extends AbstractIterator[A] {
private[this] var len: Int = -1
private[this] var pos: Int = 0
private[this] var buf: ArrayBuffer[AnyRef] = _
def init(): Unit = if(buf eq null) {
buf = new ArrayBuffer[AnyRef](maxlen min 256)
len = 0
while(underlying.hasNext) {
val n = underlying.next().asInstanceOf[AnyRef]
if(pos >= buf.length) buf.addOne(n)
else buf(pos) = n
pos += 1
if(pos == maxlen) pos = 0
len += 1
}
underlying = null
if(len > maxlen) len = maxlen
pos = pos - len
if(pos < 0) pos += maxlen
}
override def knownSize = len
def hasNext: Boolean = {
init()
len > 0
}
def next(): A = {
init()
if(len == 0) Iterator.empty.next()
else {
val x = buf(pos).asInstanceOf[A]
pos += 1
if(pos == maxlen) pos = 0
len -= 1
x
}
}
override def drop(n: Int): Iterator[A] = {
init()
if (n > 0) {
len = (len - n) max 0
pos = (pos + n) % maxlen
}
this
}
}
private[collection] def dropRightIterator[A](it: Iterator[A], n: Int): Iterator[A] = {
if(n <= 0) it
else {
val k = it.knownSize
if(k >= 0) it.take(k - n)
else new DropRightIterator[A](it, n)
}
}
private final class DropRightIterator[A](private[this] var underlying: Iterator[A], maxlen: Int) extends AbstractIterator[A] {
private[this] var len: Int = -1 // known size or -1 if the end of `underlying` has not been seen yet
private[this] var pos: Int = 0
private[this] var buf: ArrayBuffer[AnyRef] = _
def init(): Unit = if(buf eq null) {
buf = new ArrayBuffer[AnyRef](maxlen min 256)
while(pos < maxlen && underlying.hasNext) {
buf.addOne(underlying.next().asInstanceOf[AnyRef])
pos += 1
}
if(!underlying.hasNext) len = 0
pos = 0
}
override def knownSize = len
def hasNext: Boolean = {
init()
len != 0
}
def next(): A = {
if(!hasNext) Iterator.empty.next()
else {
val x = buf(pos).asInstanceOf[A]
if(len == -1) {
buf(pos) = underlying.next().asInstanceOf[AnyRef]
if(!underlying.hasNext) len = 0
} else len -= 1
pos += 1
if(pos == maxlen) pos = 0
x
}
}
}
}
/** Explicit instantiation of the `View` trait to reduce class file size in subclasses. */
@SerialVersionUID(3L)
abstract class AbstractView[+A] extends scala.collection.AbstractIterable[A] with View[A]
