scala.collection.Iterator.scala Maven / Gradle / Ivy
/*
* 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.collection.mutable.{ArrayBuffer, ArrayBuilder, Builder, ImmutableBuilder}
import scala.annotation.tailrec
import scala.annotation.unchecked.uncheckedVariance
import scala.runtime.Statics
/** Iterators are data structures that allow to iterate over a sequence
* of elements. They have a `hasNext` method for checking
* if there is a next element available, and a `next` method
* which returns the next element and advances the iterator.
*
* An iterator is mutable: most operations on it change its state. While it is often used
* to iterate through the elements of a collection, it can also be used without
* being backed by any collection (see constructors on the companion object).
*
* It is of particular importance to note that, unless stated otherwise, ''one should never
* use an iterator after calling a method on it''. The two most important exceptions
* are also the sole abstract methods: `next` and `hasNext`.
*
* Both these methods can be called any number of times without having to discard the
* iterator. Note that even `hasNext` may cause mutation -- such as when iterating
* from an input stream, where it will block until the stream is closed or some
* input becomes available.
*
* Consider this example for safe and unsafe use:
*
* {{{
* def f[A](it: Iterator[A]) = {
* if (it.hasNext) { // Safe to reuse "it" after "hasNext"
* it.next() // Safe to reuse "it" after "next"
* val remainder = it.drop(2) // it is *not* safe to use "it" again after this line!
* remainder.take(2) // it is *not* safe to use "remainder" after this line!
* } else it
* }
* }}}
*
* @define mayNotTerminateInf
* Note: may not terminate for infinite iterators.
* @define preservesIterator
* The iterator remains valid for further use whatever result is returned.
* @define consumesIterator
* After calling this method, one should discard the iterator it was called
* on. Using it is undefined and subject to change.
* @define consumesAndProducesIterator
* After calling this method, one should discard the iterator it was called
* on, and use only the iterator that was returned. Using the old iterator
* is undefined, subject to change, and may result in changes to the new
* iterator as well.
* @define consumesTwoAndProducesOneIterator
* After calling this method, one should discard the iterator it was called
* on, as well as the one passed as a parameter, and use only the iterator
* that was returned. Using the old iterators is undefined, subject to change,
* and may result in changes to the new iterator as well.
* @define consumesOneAndProducesTwoIterators
* After calling this method, one should discard the iterator it was called
* on, and use only the iterators that were returned. Using the old iterator
* is undefined, subject to change, and may result in changes to the new
* iterators as well.
* @define coll iterator
*/
trait Iterator[+A] extends IterableOnce[A] with IterableOnceOps[A, Iterator, Iterator[A]] { self =>
/** Check if there is a next element available.
*
* @return `true` if there is a next element, `false` otherwise
* @note Reuse: $preservesIterator
*/
def hasNext: Boolean
@deprecated("hasDefiniteSize on Iterator is the same as isEmpty", "2.13.0")
@`inline` override final def hasDefiniteSize = isEmpty
/** Return the next element and advance the iterator.
*
* @throws NoSuchElementException if there is no next element.
* @return the next element.
* @note Reuse: Advances the iterator, which may exhaust the elements. It is valid to
* make additional calls on the iterator.
*/
@throws[NoSuchElementException]
def next(): A
@inline final def iterator = this
/** Wraps the value of `next()` in an option.
*
* @return `Some(next)` if a next element exists, `None` otherwise.
*/
def nextOption(): Option[A] = if (hasNext) Some(next()) else None
/** Tests whether this iterator contains a given value as an element.
* $mayNotTerminateInf
*
* @param elem the element to test.
* @return `true` if this iterator produces some value that is
* is equal (as determined by `==`) to `elem`, `false` otherwise.
* @note Reuse: $consumesIterator
*/
def contains(elem: Any): Boolean = exists(_ == elem) // Note--this seems faster than manual inlining!
/** Creates a buffered iterator from this iterator.
*
* @see [[scala.collection.BufferedIterator]]
* @return a buffered iterator producing the same values as this iterator.
* @note Reuse: $consumesAndProducesIterator
*/
def buffered: BufferedIterator[A] = new AbstractIterator[A] with BufferedIterator[A] {
private[this] var hd: A = _
private[this] var hdDefined: Boolean = false
def head: A = {
if (!hdDefined) {
hd = next()
hdDefined = true
}
hd
}
override def knownSize = {
val thisSize = self.knownSize
if (thisSize >= 0 && hdDefined) thisSize + 1
else thisSize
}
def hasNext =
hdDefined || self.hasNext
def next() =
if (hdDefined) {
hdDefined = false
hd
} else self.next()
}
/** A flexible iterator for transforming an `Iterator[A]` into an
* `Iterator[Seq[A]]`, with configurable sequence size, step, and
* strategy for dealing with remainder elements which don't fit evenly
* into the last group.
*
* A `GroupedIterator` is yielded by `grouped` and by `sliding`,
* where the `step` may differ from the group `size`.
*/
class GroupedIterator[B >: A](self: Iterator[B], size: Int, step: Int) extends AbstractIterator[immutable.Seq[B]] {
require(size >= 1 && step >= 1, f"size=$size%d and step=$step%d, but both must be positive")
private[this] var buffer: Array[B] = null // current result
private[this] var prev: Array[B] = null // if sliding, overlap from previous result
private[this] var first = true // if !first, advancing may skip ahead
private[this] var filled = false // whether the buffer is "hot"
private[this] var partial = true // whether to emit partial sequence
private[this] var padding: () => B = null // what to pad short sequences with
private[this] def pad = padding != null // irrespective of partial flag
private[this] def newBuilder = {
val b = ArrayBuilder.make[Any]
val k = self.knownSize
if (k > 0) b.sizeHint(k min size) // if k < size && !partial, buffer will grow on padding
b
}
/** Specifies a fill element used to pad a partial segment
* so that all segments have the same size.
*
* Any previous setting of `withPartial` is ignored,
* as the last group will always be padded to `size` elements.
*
* The by-name argument is evaluated for each fill element.
*
* @param x The element that will be appended to the last segment, if necessary.
* @return The same iterator, and ''not'' a new iterator.
* @note This method mutates the iterator it is called on, which can be safely used afterwards.
* @note This method is mutually exclusive with `withPartial`.
* @group Configuration
*/
def withPadding(x: => B): this.type = {
padding = () => x
partial = true // redundant, as padding always results in complete segment
this
}
/** Specify whether to drop the last segment if it has less than `size` elements.
*
* If this flag is `false`, elements of a partial segment at the end of the iterator
* are not returned.
*
* The flag defaults to `true`.
*
* Any previous setting of `withPadding` is ignored,
* as the last group will never be padded.
* A partial segment is either retained or dropped, per the flag.
*
* @param x `true` if partial segments may be returned, `false` otherwise.
* @return The same iterator, and ''not'' a new iterator.
* @note This method mutates the iterator it is called on, which can be safely used afterwards.
* @note This method is mutually exclusive with `withPadding`.
* @group Configuration
*/
def withPartial(x: Boolean): this.type = {
partial = x
padding = null
this
}
/** Eagerly fetch `size` elements to buffer.
*
* If buffer is dirty and stepping, copy prefix.
* If skipping, skip ahead.
* Fetch remaining elements.
* If unable to deliver size, then pad if padding enabled, otherwise drop segment.
* Returns true if successful in delivering `count` elements,
* or padded segment, or partial segment.
*/
private def fulfill(): Boolean = {
val builder = newBuilder
var done = false
// keep prefix of previous buffer if stepping
if (prev != null) builder.addAll(prev)
// skip ahead
if (!first && step > size) {
var dropping = step - size
while (dropping > 0 && self.hasNext) {
self.next(): Unit
dropping -= 1
}
done = dropping > 0 // skip failed
}
var index = builder.length
if (!done) {
// advance to rest of segment if possible
while (index < size && self.hasNext) {
builder.addOne(self.next())
index += 1
}
// if unable to complete segment, pad if possible
if (index < size && pad) {
builder.sizeHint(size)
while (index < size) {
builder.addOne(padding())
index += 1
}
}
}
// segment must have data, and must be complete unless they allow partial
val ok = index > 0 && (partial || index == size)
if (ok) buffer = builder.result().asInstanceOf[Array[B]]
else prev = null
ok
}
// fill() returns false if no more sequences can be produced
private def fill(): Boolean = filled || { filled = self.hasNext && fulfill() ; filled }
def hasNext = fill()
@throws[NoSuchElementException]
def next(): immutable.Seq[B] =
if (!fill()) Iterator.empty.next()
else {
filled = false
// if stepping, retain overlap in prev
if (step < size) {
if (first) prev = buffer.drop(step)
else if (buffer.length == size) Array.copy(src = buffer, srcPos = step, dest = prev, destPos = 0, length = size - step)
else prev = null
}
val res = immutable.ArraySeq.unsafeWrapArray(buffer).asInstanceOf[immutable.ArraySeq[B]]
buffer = null
first = false
res
}
}
/** A copy of this $coll with an element value appended until a given target length is reached.
*
* @param len the target length
* @param elem the padding value
* @tparam B the element type of the returned $coll.
* @return a new $coll consisting of
* all elements of this $coll followed by the minimal number of occurrences of `elem` so
* that the resulting collection has a length of at least `len`.
*/
def padTo[B >: A](len: Int, elem: B): Iterator[B] = new AbstractIterator[B] {
private[this] var i = 0
override def knownSize: Int = {
val thisSize = self.knownSize
if (thisSize < 0) -1
else thisSize max (len - i)
}
def next(): B = {
val b =
if (self.hasNext) self.next()
else if (i < len) elem
else Iterator.empty.next()
i += 1
b
}
def hasNext: Boolean = self.hasNext || i < len
}
/** Partitions this iterator in two iterators according to a predicate.
*
* @param p the predicate on which to partition
* @return a pair of iterators: the iterator that satisfies the predicate
* `p` and the iterator that does not.
* The relative order of the elements in the resulting iterators
* is the same as in the original iterator.
* @note Reuse: $consumesOneAndProducesTwoIterators
*/
def partition(p: A => Boolean): (Iterator[A], Iterator[A]) = {
val (a, b) = duplicate
(a filter p, b filterNot p)
}
/** Returns an iterator which groups this iterator into fixed size
* blocks. Example usages:
* {{{
* // Returns List(List(1, 2, 3), List(4, 5, 6), List(7)))
* (1 to 7).iterator.grouped(3).toList
* // Returns List(List(1, 2, 3), List(4, 5, 6))
* (1 to 7).iterator.grouped(3).withPartial(false).toList
* // Returns List(List(1, 2, 3), List(4, 5, 6), List(7, 20, 25)
* // Illustrating that withPadding's argument is by-name.
* val it2 = Iterator.iterate(20)(_ + 5)
* (1 to 7).iterator.grouped(3).withPadding(it2.next).toList
* }}}
*
* @note Reuse: $consumesAndProducesIterator
*/
def grouped[B >: A](size: Int): GroupedIterator[B] =
new GroupedIterator[B](self, size, size)
/** Returns an iterator which presents a "sliding window" view of
* this iterator. The first argument is the window size, and
* the second argument `step` is how far to advance the window
* on each iteration. The `step` defaults to `1`.
*
* The returned `GroupedIterator` can be configured to either
* pad a partial result to size `size` or suppress the partial
* result entirely.
*
* Example usages:
* {{{
* // Returns List(ArraySeq(1, 2, 3), ArraySeq(2, 3, 4), ArraySeq(3, 4, 5))
* (1 to 5).iterator.sliding(3).toList
* // Returns List(ArraySeq(1, 2, 3, 4), ArraySeq(4, 5))
* (1 to 5).iterator.sliding(4, 3).toList
* // Returns List(ArraySeq(1, 2, 3, 4))
* (1 to 5).iterator.sliding(4, 3).withPartial(false).toList
* // Returns List(ArraySeq(1, 2, 3, 4), ArraySeq(4, 5, 20, 25))
* // Illustrating that withPadding's argument is by-name.
* val it2 = Iterator.iterate(20)(_ + 5)
* (1 to 5).iterator.sliding(4, 3).withPadding(it2.next).toList
* }}}
*
* @param size the number of elements per group
* @param step the distance between the first elements of successive
* groups
* @return A `GroupedIterator` producing `Seq[B]`s of size `size`, except the
* last element (which may be the only element) will be truncated
* if there are fewer than `size` elements remaining to be grouped.
* This behavior can be configured.
*
* @note Reuse: $consumesAndProducesIterator
*/
def sliding[B >: A](size: Int, step: Int = 1): GroupedIterator[B] =
new GroupedIterator[B](self, size, step)
def scanLeft[B](z: B)(op: (B, A) => B): Iterator[B] = new AbstractIterator[B] {
// We use an intermediate iterator that iterates through the first element `z`
// and then that will be modified to iterate through the collection
private[this] var current: Iterator[B] =
new AbstractIterator[B] {
override def knownSize = {
val thisSize = self.knownSize
if (thisSize < 0) -1
else thisSize + 1
}
def hasNext: Boolean = true
def next(): B = {
// Here we change our self-reference to a new iterator that iterates through `self`
current = new AbstractIterator[B] {
private[this] var acc = z
def next(): B = {
acc = op(acc, self.next())
acc
}
def hasNext: Boolean = self.hasNext
override def knownSize = self.knownSize
}
z
}
}
override def knownSize = current.knownSize
def next(): B = current.next()
def hasNext: Boolean = current.hasNext
}
@deprecated("Call scanRight on an Iterable instead.", "2.13.0")
def scanRight[B](z: B)(op: (A, B) => B): Iterator[B] = ArrayBuffer.from(this).scanRight(z)(op).iterator
def indexWhere(p: A => Boolean, from: Int = 0): Int = {
var i = math.max(from, 0)
val dropped = drop(from)
while (dropped.hasNext) {
if (p(dropped.next())) return i
i += 1
}
-1
}
/** Returns the index of the first occurrence of the specified
* object in this iterable object.
* $mayNotTerminateInf
*
* @param elem element to search for.
* @return the index of the first occurrence of `elem` in the values produced by this iterator,
* or -1 if such an element does not exist until the end of the iterator is reached.
* @note Reuse: $consumesIterator
*/
def indexOf[B >: A](elem: B): Int = indexOf(elem, 0)
/** Returns the index of the first occurrence of the specified object in this iterable object
* after or at some start index.
* $mayNotTerminateInf
*
* @param elem element to search for.
* @param from the start index
* @return the index `>= from` of the first occurrence of `elem` in the values produced by this
* iterator, or -1 if such an element does not exist until the end of the iterator is
* reached.
* @note Reuse: $consumesIterator
*/
def indexOf[B >: A](elem: B, from: Int): Int = {
var i = 0
while (i < from && hasNext) {
next()
i += 1
}
while (hasNext) {
if (next() == elem) return i
i += 1
}
-1
}
@inline final def length: Int = size
@deprecatedOverriding("isEmpty is defined as !hasNext; override hasNext instead", "2.13.0")
override def isEmpty: Boolean = !hasNext
def filter(p: A => Boolean): Iterator[A] = filterImpl(p, isFlipped = false)
def filterNot(p: A => Boolean): Iterator[A] = filterImpl(p, isFlipped = true)
private[collection] def filterImpl(p: A => Boolean, isFlipped: Boolean): Iterator[A] = new AbstractIterator[A] {
private[this] var hd: A = _
private[this] var hdDefined: Boolean = false
def hasNext: Boolean = hdDefined || {
if (!self.hasNext) return false
hd = self.next()
while (p(hd) == isFlipped) {
if (!self.hasNext) return false
hd = self.next()
}
hdDefined = true
true
}
def next() =
if (hasNext) {
hdDefined = false
hd
}
else Iterator.empty.next()
}
/** Creates an iterator over all the elements of this iterator that
* satisfy the predicate `p`. The order of the elements
* is preserved.
*
* '''Note:''' `withFilter` is the same as `filter` on iterators. It exists so that
* for-expressions with filters work over iterators.
*
* @param p the predicate used to test values.
* @return an iterator which produces those values of this iterator which satisfy the predicate `p`.
* @note Reuse: $consumesAndProducesIterator
*/
def withFilter(p: A => Boolean): Iterator[A] = filter(p)
def collect[B](pf: PartialFunction[A, B]): Iterator[B] = new AbstractIterator[B] with (A => B) {
// Manually buffer to avoid extra layer of wrapping with buffered
private[this] var hd: B = _
// Little state machine to keep track of where we are
// Seek = 0; Found = 1; Empty = -1
// Not in vals because scalac won't make them static (@inline def only works with -optimize)
// BE REALLY CAREFUL TO KEEP COMMENTS AND NUMBERS IN SYNC!
private[this] var status = 0/*Seek*/
def apply(value: A): B = Statics.pfMarker.asInstanceOf[B]
def hasNext = {
val marker = Statics.pfMarker
while (status == 0/*Seek*/) {
if (self.hasNext) {
val x = self.next()
val v = pf.applyOrElse(x, this)
if (marker ne v.asInstanceOf[AnyRef]) {
hd = v
status = 1/*Found*/
}
}
else status = -1/*Empty*/
}
status == 1/*Found*/
}
def next() = if (hasNext) { status = 0/*Seek*/; hd } else Iterator.empty.next()
}
/**
* Builds a new iterator from this one without any duplicated elements on it.
* @return iterator with distinct elements
*
* @note Reuse: $consumesIterator
*/
def distinct: Iterator[A] = distinctBy(identity)
/**
* Builds a new iterator from this one without any duplicated elements as determined by `==` after applying
* the transforming function `f`.
*
* @param f The transforming function whose result is used to determine the uniqueness of each element
* @tparam B the type of the elements after being transformed by `f`
* @return iterator with distinct elements
*
* @note Reuse: $consumesIterator
*/
def distinctBy[B](f: A => B): Iterator[A] = new AbstractIterator[A] {
private[this] val traversedValues = mutable.HashSet.empty[B]
private[this] var nextElementDefined: Boolean = false
private[this] var nextElement: A = _
def hasNext: Boolean = nextElementDefined || (self.hasNext && {
val a = self.next()
if (traversedValues.add(f(a))) {
nextElement = a
nextElementDefined = true
true
}
else hasNext
})
def next(): A =
if (hasNext) {
nextElementDefined = false
nextElement
} else {
Iterator.empty.next()
}
}
def map[B](f: A => B): Iterator[B] = new AbstractIterator[B] {
override def knownSize = self.knownSize
def hasNext = self.hasNext
def next() = f(self.next())
}
def flatMap[B](f: A => IterableOnce[B]): Iterator[B] = new AbstractIterator[B] {
private[this] var cur: Iterator[B] = Iterator.empty
/** Trillium logic boolean: -1 = unknown, 0 = false, 1 = true */
private[this] var _hasNext: Int = -1
def nextCur(): Unit = {
cur = Iterator.empty
cur = f(self.next()).iterator
_hasNext = -1
}
def hasNext: Boolean = {
if (_hasNext == -1) {
while (!cur.hasNext) {
if (!self.hasNext) {
_hasNext = 0
// since we know we are exhausted, we can release cur for gc, and as well replace with
// static Iterator.empty which will support efficient subsequent `hasNext`/`next` calls
cur = Iterator.empty
return false
}
nextCur()
}
_hasNext = 1
true
} else _hasNext == 1
}
def next(): B = {
if (hasNext) {
_hasNext = -1
}
cur.next()
}
}
def flatten[B](implicit ev: A => IterableOnce[B]): Iterator[B] =
flatMap[B](ev)
def concat[B >: A](xs: => IterableOnce[B]): Iterator[B] = new Iterator.ConcatIterator[B](self).concat(xs)
@`inline` final def ++ [B >: A](xs: => IterableOnce[B]): Iterator[B] = concat(xs)
def take(n: Int): Iterator[A] = sliceIterator(0, n max 0)
def takeWhile(p: A => Boolean): Iterator[A] = new AbstractIterator[A] {
private[this] var hd: A = _
private[this] var hdDefined: Boolean = false
private[this] var tail: Iterator[A] = self
def hasNext = hdDefined || tail.hasNext && {
hd = tail.next()
if (p(hd)) hdDefined = true
else tail = Iterator.empty
hdDefined
}
def next() = if (hasNext) { hdDefined = false; hd } else Iterator.empty.next()
}
def drop(n: Int): Iterator[A] = sliceIterator(n, -1)
def dropWhile(p: A => Boolean): Iterator[A] = new AbstractIterator[A] {
// Magic value: -1 = hasn't dropped, 0 = found first, 1 = defer to parent iterator
private[this] var status = -1
// Local buffering to avoid double-wrap with .buffered
private[this] var fst: A = _
def hasNext: Boolean =
if (status == 1) self.hasNext
else if (status == 0) true
else {
while (self.hasNext) {
val a = self.next()
if (!p(a)) {
fst = a
status = 0
return true
}
}
status = 1
false
}
def next() =
if (hasNext) {
if (status == 1) self.next()
else {
status = 1
fst
}
}
else Iterator.empty.next()
}
/**
* @inheritdoc
*
* @note Reuse: $consumesOneAndProducesTwoIterators
*/
def span(p: A => Boolean): (Iterator[A], Iterator[A]) = {
/*
* Giving a name to following iterator (as opposed to trailing) because
* anonymous class is represented as a structural type that trailing
* iterator is referring (the finish() method) and thus triggering
* handling of structural calls. It's not what's intended here.
*/
final class Leading extends AbstractIterator[A] {
private[this] var lookahead: mutable.Queue[A] = null
private[this] var hd: A = _
/* Status is kept with magic numbers
* 1 means next element is in hd and we're still reading into this iterator
* 0 means we're still reading but haven't found a next element
* -1 means we are done reading into the iterator, so we must rely on lookahead
* -2 means we are done but have saved hd for the other iterator to use as its first element
*/
private[this] var status = 0
private def store(a: A): Unit = {
if (lookahead == null) lookahead = new mutable.Queue[A]
lookahead += a
}
def hasNext = {
if (status < 0) (lookahead ne null) && lookahead.nonEmpty
else if (status > 0) true
else {
if (self.hasNext) {
hd = self.next()
status = if (p(hd)) 1 else -2
}
else status = -1
status > 0
}
}
def next() = {
if (hasNext) {
if (status == 1) { status = 0; hd }
else lookahead.dequeue()
}
else Iterator.empty.next()
}
@tailrec
def finish(): Boolean = status match {
case -2 => status = -1 ; true
case -1 => false
case 1 => store(hd) ; status = 0 ; finish()
case 0 =>
status = -1
while (self.hasNext) {
val a = self.next()
if (p(a)) store(a)
else {
hd = a
return true
}
}
false
}
def trailer: A = hd
}
val leading = new Leading
val trailing = new AbstractIterator[A] {
private[this] var myLeading = leading
/* Status flag meanings:
* -1 not yet accessed
* 0 single element waiting in leading
* 1 defer to self
* 2 self.hasNext already
* 3 exhausted
*/
private[this] var status = -1
def hasNext = status match {
case 3 => false
case 2 => true
case 1 => if (self.hasNext) { status = 2 ; true } else { status = 3 ; false }
case 0 => true
case _ =>
if (myLeading.finish()) { status = 0 ; true } else { status = 1 ; myLeading = null ; hasNext }
}
def next() = {
if (hasNext) {
if (status == 0) {
status = 1
val res = myLeading.trailer
myLeading = null
res
} else {
status = 1
self.next()
}
}
else Iterator.empty.next()
}
}
(leading, trailing)
}
def slice(from: Int, until: Int): Iterator[A] = sliceIterator(from, until max 0)
/** Creates an optionally bounded slice, unbounded if `until` is negative. */
protected def sliceIterator(from: Int, until: Int): Iterator[A] = {
val lo = from max 0
val rest =
if (until < 0) -1 // unbounded
else if (until <= lo) 0 // empty
else until - lo // finite
if (rest == 0) Iterator.empty
else new Iterator.SliceIterator(this, lo, rest)
}
def zip[B](that: IterableOnce[B]): Iterator[(A, B)] = new AbstractIterator[(A, B)] {
val thatIterator = that.iterator
override def knownSize = self.knownSize min thatIterator.knownSize
def hasNext = self.hasNext && thatIterator.hasNext
def next() = (self.next(), thatIterator.next())
}
def zipAll[A1 >: A, B](that: IterableOnce[B], thisElem: A1, thatElem: B): Iterator[(A1, B)] = new AbstractIterator[(A1, B)] {
val thatIterator = that.iterator
override def knownSize = {
val thisSize = self.knownSize
val thatSize = thatIterator.knownSize
if (thisSize < 0 || thatSize < 0) -1
else thisSize max thatSize
}
def hasNext = self.hasNext || thatIterator.hasNext
def next(): (A1, B) = {
val next1 = self.hasNext
val next2 = thatIterator.hasNext
if(!(next1 || next2)) throw new NoSuchElementException
(if(next1) self.next() else thisElem, if(next2) thatIterator.next() else thatElem)
}
}
def zipWithIndex: Iterator[(A, Int)] = new AbstractIterator[(A, Int)] {
var idx = 0
override def knownSize = self.knownSize
def hasNext = self.hasNext
def next() = {
val ret = (self.next(), idx)
idx += 1
ret
}
}
/** Checks whether corresponding elements of the given iterable collection
* compare equal (with respect to `==`) to elements of this $coll.
*
* @param that the collection to compare
* @tparam B the type of the elements of collection `that`.
* @return `true` if both collections contain equal elements in the same order, `false` otherwise.
*
* @inheritdoc
*/
def sameElements[B >: A](that: IterableOnce[B]): Boolean = {
val those = that.iterator
while (hasNext && those.hasNext)
if (next() != those.next())
return false
// At that point we know that *at least one* iterator has no next element
// If *both* of them have no elements then the collections are the same
hasNext == those.hasNext
}
/** Creates two new iterators that both iterate over the same elements
* as this iterator (in the same order). The duplicate iterators are
* considered equal if they are positioned at the same element.
*
* Given that most methods on iterators will make the original iterator
* unfit for further use, this methods provides a reliable way of calling
* multiple such methods on an iterator.
*
* @return a pair of iterators
* @note The implementation may allocate temporary storage for elements
* iterated by one iterator but not yet by the other.
* @note Reuse: $consumesOneAndProducesTwoIterators
*/
def duplicate: (Iterator[A], Iterator[A]) = {
val gap = new scala.collection.mutable.Queue[A]
var ahead: Iterator[A] = null
class Partner extends AbstractIterator[A] {
override def knownSize: Int = self.synchronized {
val thisSize = self.knownSize
if (this eq ahead) thisSize
else if (thisSize < 0 || gap.knownSize < 0) -1
else thisSize + gap.knownSize
}
def hasNext: Boolean = self.synchronized {
(this ne ahead) && !gap.isEmpty || self.hasNext
}
def next(): A = self.synchronized {
if (gap.isEmpty) ahead = this
if (this eq ahead) {
val e = self.next()
gap enqueue e
e
} else gap.dequeue()
}
// to verify partnerhood we use reference equality on gap because
// type testing does not discriminate based on origin.
private def compareGap(queue: scala.collection.mutable.Queue[A]) = gap eq queue
override def hashCode = gap.hashCode()
override def equals(other: Any) = other match {
case x: Partner => x.compareGap(gap) && gap.isEmpty
case _ => super.equals(other)
}
}
(new Partner, new Partner)
}
/** Returns this iterator with patched values.
* Patching at negative indices is the same as patching starting at 0.
* Patching at indices at or larger than the length of the original iterator appends the patch to the end.
* If more values are replaced than actually exist, the excess is ignored.
*
* @param from The start index from which to patch
* @param patchElems The iterator of patch values
* @param replaced The number of values in the original iterator that are replaced by the patch.
* @note Reuse: $consumesTwoAndProducesOneIterator
*/
def patch[B >: A](from: Int, patchElems: Iterator[B], replaced: Int): Iterator[B] =
new AbstractIterator[B] {
private[this] var origElems = self
// > 0 => that many more elems from `origElems` before switching to `patchElems`
// 0 => need to drop elems from `origElems` and start using `patchElems`
// -1 => have dropped elems from `origElems`, will be using `patchElems` until it's empty
// and then using what's left of `origElems` after the drop
private[this] var state = if (from > 0) from else 0
// checks state and handles 0 => -1
@inline private[this] def switchToPatchIfNeeded(): Unit =
if (state == 0) {
origElems = origElems drop replaced
state = -1
}
def hasNext: Boolean = {
switchToPatchIfNeeded()
origElems.hasNext || patchElems.hasNext
}
def next(): B = {
switchToPatchIfNeeded()
if (state < 0 /* == -1 */) {
if (patchElems.hasNext) patchElems.next()
else origElems.next()
}
else {
if (origElems.hasNext) {
state -= 1
origElems.next()
}
else {
state = -1
patchElems.next()
}
}
}
}
override def tapEach[U](f: A => U): Iterator[A] = new AbstractIterator[A] {
override def knownSize = self.knownSize
override def hasNext = self.hasNext
override def next() = {
val _next = self.next()
f(_next)
_next
}
}
/** Converts this iterator to a string.
*
* @return `""`
* @note Reuse: $preservesIterator
*/
override def toString = ""
@deprecated("Iterator.seq always returns the iterator itself", "2.13.0")
def seq: this.type = this
}
@SerialVersionUID(3L)
object Iterator extends IterableFactory[Iterator] {
private[this] val _empty: Iterator[Nothing] = new AbstractIterator[Nothing] {
def hasNext = false
def next() = throw new NoSuchElementException("next on empty iterator")
override def knownSize: Int = 0
override protected def sliceIterator(from: Int, until: Int): AbstractIterator[Nothing] = this
}
/** Creates a target $coll from an existing source collection
*
* @param source Source collection
* @tparam A the type of the collection’s elements
* @return a new $coll with the elements of `source`
*/
override def from[A](source: IterableOnce[A]): Iterator[A] = source.iterator
/** The iterator which produces no values. */
@`inline` final def empty[T]: Iterator[T] = _empty
def single[A](a: A): Iterator[A] = new AbstractIterator[A] {
private[this] var consumed: Boolean = false
def hasNext = !consumed
def next() = if (consumed) empty.next() else { consumed = true; a }
override protected def sliceIterator(from: Int, until: Int) =
if (consumed || from > 0 || until == 0) empty
else this
}
override def apply[A](xs: A*): Iterator[A] = xs.iterator
/**
* @return A builder for $Coll objects.
* @tparam A the type of the ${coll}’s elements
*/
def newBuilder[A]: Builder[A, Iterator[A]] =
new ImmutableBuilder[A, Iterator[A]](empty[A]) {
override def addOne(elem: A): this.type = { elems = elems ++ single(elem); this }
}
/** Creates iterator that produces the results of some element computation a number of times.
*
* @param len the number of elements returned by the iterator.
* @param elem the element computation
* @return An iterator that produces the results of `n` evaluations of `elem`.
*/
override def fill[A](len: Int)(elem: => A): Iterator[A] = new AbstractIterator[A] {
private[this] var i = 0
override def knownSize: Int = (len - i) max 0
def hasNext: Boolean = i < len
def next(): A =
if (hasNext) { i += 1; elem }
else empty.next()
}
/** Creates an iterator producing the values of a given function over a range of integer values starting from 0.
*
* @param end The number of elements returned by the iterator
* @param f The function computing element values
* @return An iterator that produces the values `f(0), ..., f(n -1)`.
*/
override def tabulate[A](end: Int)(f: Int => A): Iterator[A] = new AbstractIterator[A] {
private[this] var i = 0
override def knownSize: Int = (end - i) max 0
def hasNext: Boolean = i < end
def next(): A =
if (hasNext) { val result = f(i); i += 1; result }
else empty.next()
}
/** Creates an infinite-length iterator which returns successive values from some start value.
* @param start the start value of the iterator
* @return the iterator producing the infinite sequence of values `start, start + 1, start + 2, ...`
*/
def from(start: Int): Iterator[Int] = from(start, 1)
/** Creates an infinite-length iterator returning values equally spaced apart.
*
* @param start the start value of the iterator
* @param step the increment between successive values
* @return the iterator producing the infinite sequence of values `start, start + 1 * step, start + 2 * step, ...`
*/
def from(start: Int, step: Int): Iterator[Int] = new AbstractIterator[Int] {
private[this] var i = start
def hasNext: Boolean = true
def next(): Int = { val result = i; i += step; result }
}
/** Creates nn iterator returning successive values in some integer interval.
*
* @param start the start value of the iterator
* @param end the end value of the iterator (the first value NOT returned)
* @return the iterator producing values `start, start + 1, ..., end - 1`
*/
def range(start: Int, end: Int): Iterator[Int] = range(start, end, 1)
/** An iterator producing equally spaced values in some integer interval.
*
* @param start the start value of the iterator
* @param end the end value of the iterator (the first value NOT returned)
* @param step the increment value of the iterator (must be positive or negative)
* @return the iterator producing values `start, start + step, ...` up to, but excluding `end`
*/
def range(start: Int, end: Int, step: Int): Iterator[Int] = new AbstractIterator[Int] {
if (step == 0) throw new IllegalArgumentException("zero step")
private[this] var i = start
private[this] var hasOverflowed = false
override def knownSize: Int = {
val size = math.ceil((end.toLong - i.toLong) / step.toDouble)
if (size < 0) 0
else if (size > Int.MaxValue) -1
else size.toInt
}
def hasNext: Boolean = {
(step <= 0 || i < end) && (step >= 0 || i > end) && !hasOverflowed
}
def next(): Int =
if (hasNext) {
val result = i
val nextValue = i + step
hasOverflowed = (step > 0) == nextValue < i
i = nextValue
result
}
else empty.next()
}
/** Creates an infinite iterator that repeatedly applies a given function to the previous result.
*
* @param start the start value of the iterator
* @param f the function that's repeatedly applied
* @return the iterator producing the infinite sequence of values `start, f(start), f(f(start)), ...`
*/
def iterate[T](start: T)(f: T => T): Iterator[T] = new AbstractIterator[T] {
private[this] var first = true
private[this] var acc = start
def hasNext: Boolean = true
def next(): T = {
if (first) first = false
else acc = f(acc)
acc
}
}
/** Creates an Iterator that uses a function `f` to produce elements of type `A`
* and update an internal state of type `S`.
*
* @param init State initial value
* @param f Computes the next element (or returns `None` to signal
* the end of the collection)
* @tparam A Type of the elements
* @tparam S Type of the internal state
* @return an Iterator that produces elements using `f` until `f` returns `None`
*/
override def unfold[A, S](init: S)(f: S => Option[(A, S)]): Iterator[A] = new UnfoldIterator(init)(f)
/** Creates an infinite-length iterator returning the results of evaluating an expression.
* The expression is recomputed for every element.
*
* @param elem the element computation.
* @return the iterator containing an infinite number of results of evaluating `elem`.
*/
def continually[A](elem: => A): Iterator[A] = new AbstractIterator[A] {
def hasNext = true
def next() = elem
}
/** Creates an iterator to which other iterators can be appended efficiently.
* Nested ConcatIterators are merged to avoid blowing the stack.
*/
private final class ConcatIterator[+A](private var current: Iterator[A @uncheckedVariance]) extends AbstractIterator[A] {
private var tail: ConcatIteratorCell[A @uncheckedVariance] = null
private var last: ConcatIteratorCell[A @uncheckedVariance] = null
private var currentHasNextChecked = false
def hasNext =
if (currentHasNextChecked) true
else if (current == null) false
else if (current.hasNext) {
currentHasNextChecked = true
true
}
else {
// If we advanced the current iterator to a ConcatIterator, merge it into this one
@tailrec def merge(): Unit =
if (current.isInstanceOf[ConcatIterator[_]]) {
val c = current.asInstanceOf[ConcatIterator[A]]
current = c.current
currentHasNextChecked = c.currentHasNextChecked
if (c.tail != null) {
if (last == null) last = c.last
c.last.tail = tail
tail = c.tail
}
merge()
}
// Advance current to the next non-empty iterator
// current is set to null when all iterators are exhausted
@tailrec def advance(): Boolean =
if (tail == null) {
current = null
last = null
false
}
else {
current = tail.headIterator
if (last eq tail) last = last.tail
tail = tail.tail
merge()
if (currentHasNextChecked) true
else if (current != null && current.hasNext) {
currentHasNextChecked = true
true
} else advance()
}
advance()
}
def next() =
if (hasNext) {
currentHasNextChecked = false
current.next()
} else Iterator.empty.next()
override def concat[B >: A](that: => IterableOnce[B]): Iterator[B] = {
val c = new ConcatIteratorCell[B](that, null).asInstanceOf[ConcatIteratorCell[A]]
if (tail == null) {
tail = c
last = c
}
else {
last.tail = c
last = c
}
if (current == null) current = Iterator.empty
this
}
}
private[this] final class ConcatIteratorCell[A](head: => IterableOnce[A], var tail: ConcatIteratorCell[A]) {
def headIterator: Iterator[A] = head.iterator
}
/** Creates a delegating iterator capped by a limit count. Negative limit means unbounded.
* Lazily skip to start on first evaluation. Avoids daisy-chained iterators due to slicing.
*/
private[scala] final class SliceIterator[A](val underlying: Iterator[A], start: Int, limit: Int) extends AbstractIterator[A] {
private[this] var remaining = limit
private[this] var dropping = start
@inline private def unbounded = remaining < 0
private def skip(): Unit =
while (dropping > 0) {
if (underlying.hasNext) {
underlying.next()
dropping -= 1
} else
dropping = 0
}
override def knownSize: Int = {
val size = underlying.knownSize
if (size < 0) -1
else {
val dropSize = 0 max (size - dropping)
if (unbounded) dropSize
else remaining min dropSize
}
}
def hasNext = { skip(); remaining != 0 && underlying.hasNext }
def next() = {
skip()
if (remaining > 0) {
remaining -= 1
underlying.next()
}
else if (unbounded) underlying.next()
else empty.next()
}
override protected def sliceIterator(from: Int, until: Int): Iterator[A] = {
val lo = from max 0
def adjustedBound =
if (unbounded) -1
else 0 max (remaining - lo)
val rest =
if (until < 0) adjustedBound // respect current bound, if any
else if (until <= lo) 0 // empty
else if (unbounded) until - lo // now finite
else adjustedBound min (until - lo) // keep lesser bound
if (rest == 0) empty
else {
dropping = {
val sum = dropping + lo
if (sum < 0) Int.MaxValue else sum
}
remaining = rest
this
}
}
}
/** Creates an iterator that uses a function `f` to produce elements of
* type `A` and update an internal state of type `S`.
*/
private final class UnfoldIterator[A, S](init: S)(f: S => Option[(A, S)]) extends AbstractIterator[A] {
private[this] var state: S = init
private[this] var nextResult: Option[(A, S)] = null
override def hasNext: Boolean = {
if (nextResult eq null) {
nextResult = {
val res = f(state)
if (res eq null) throw new NullPointerException("null during unfold")
res
}
state = null.asInstanceOf[S] // allow GC
}
nextResult.isDefined
}
override def next(): A = {
if (hasNext) {
val (value, newState) = nextResult.get
state = newState
nextResult = null
value
} else Iterator.empty.next()
}
}
}
/** Explicit instantiation of the `Iterator` trait to reduce class file size in subclasses. */
abstract class AbstractIterator[+A] extends Iterator[A]
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