Scala example source code file (Iterator.scala)
The Scala Iterator.scala source code/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.collection
import mutable.ArrayBuffer
import annotation.{ tailrec, migration }
import immutable.Stream
/** The `Iterator` object provides various functions for
* creating specialized iterators.
*
* @author Martin Odersky
* @author Matthias Zenger
* @version 2.8
* @since 2.8
*/
object Iterator {
/** The iterator which produces no values */
val empty = new Iterator[Nothing] {
def hasNext: Boolean = false
def next(): Nothing = throw new NoSuchElementException("next on empty iterator")
}
/** Creates an iterator which produces a single element.
* '''Note:''' Equivalent, but more efficient than Iterator(elem)
* @param elem the element
* @return An iterator which produces `elem` on the first call to `next`,
* and which has no further elements.
*/
def single[A](elem: A) = new Iterator[A] {
private var hasnext = true
def hasNext: Boolean = hasnext
def next(): A =
if (hasnext) { hasnext = false; elem }
else empty.next()
}
/** Creates an iterator with given elements
* @param elems The elements returned one-by-one from the iterator
* @return An iterator which produces the given elements on the
* first calls to `next`, and which has no further elements.
*/
def apply[A](elems: A*): Iterator[A] = elems.iterator
/** Creates iterator that produces the results of some element computation
* a number of times.
* @param n 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`.
*/
def fill[A](len: Int)(elem: => A) = new Iterator[A] {
private var i = 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 n 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)`.
*/
def tabulate[A](end: Int)(f: Int => A) = new Iterator[A] {
private var i = 0
def hasNext: Boolean = i < end
def next(): A =
if (hasNext) { val result = f(i); i += 1; result }
else empty.next()
}
/** 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) = new Iterator[Int] {
if (step == 0) throw new IllegalArgumentException("zero step")
private var i = start
def hasNext: Boolean = (step <= 0 || i < end) && (step >= 0 || i > end)
def next(): Int =
if (hasNext) { val result = i; i += step; 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 Iterator[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 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 Iterator[Int] {
private var i = start
def hasNext: Boolean = true
def next(): Int = { val result = i; i += step; result }
}
/** 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 Iterator[A] {
def hasNext = true
def next = elem
}
@deprecated("use `xs.iterator' or `Iterator(xs)' instead", "2.8.0")
def fromValues[a](xs: a*) = xs.iterator
/** @param xs the array of elements
* @see also: IndexedSeq.iterator and slice
*/
@deprecated("use `xs.iterator' instead", "2.8.0")
def fromArray[a](xs: Array[a]): Iterator[a] =
fromArray(xs, 0, xs.length)
/**
* @param xs the array of elements
* @param start the start index
* @param length the length
* @see also: IndexedSeq.iterator and slice
*/
@deprecated("use `xs.slice(start, start + length).iterator' instead", "2.8.0")
def fromArray[a](xs: Array[a], start: Int, length: Int): Iterator[a] =
xs.slice(start, start + length).iterator
/**
* @param n the product arity
* @return the iterator on `Product<n>`.
*/
@deprecated("use product.productIterator instead", "2.8.0")
def fromProduct(n: Product): Iterator[Any] = new Iterator[Any] {
private var c: Int = 0
private val cmax = n.productArity
def hasNext = c < cmax
def next() = { val a = n productElement c; c += 1; a }
}
/** Create an iterator with elements
* `e<sub>n+1 = step(en)`
* where `e<sub>0 = start`
* and elements are in the range between `start` (inclusive)
* and `end` (exclusive)
*
* @param start the start value of the iterator
* @param end the end value of the iterator
* @param step the increment function of the iterator, must be monotonically increasing or decreasing
* @return the iterator with values in range `[start;end)`.
*/
@deprecated("use Iterator.iterate(start, end - start)(step) instead", "2.8.0")
def range(start: Int, end: Int, step: Int => Int) = new Iterator[Int] {
private val up = step(start) > start
private val down = step(start) < start
private var i = start
def hasNext: Boolean = (!up || i < end) && (!down || i > end)
def next(): Int =
if (hasNext) { val j = i; i = step(i); j }
else empty.next()
}
/** Create an iterator with elements
* `e<sub>n+1 = step(en)`
* where `e<sub>0 = start`.
*
* @param start the start value of the iterator
* @param step the increment function of the iterator
* @return the iterator starting at value `start`.
*/
@deprecated("use iterate(start)(step) instead", "2.8.0")
def from(start: Int, step: Int => Int): Iterator[Int] = new Iterator[Int] {
private var i = start
override def hasNext: Boolean = true
def next(): Int = { val j = i; i = step(i); j }
}
/** Create an iterator that is the concatenation of all iterators
* returned by a given iterator of iterators.
* @param its The iterator which returns on each call to next
* a new iterator whose elements are to be concatenated to the result.
*/
@deprecated("use its.flatten instead", "2.8.0")
def flatten[T](its: Iterator[Iterator[T]]): Iterator[T] = new Iterator[T] {
private var cur = its.next
def hasNext: Boolean = {
while (!cur.hasNext && its.hasNext) cur = its.next
cur.hasNext
}
def next(): T =
(if (hasNext) cur else empty).next()
}
}
import Iterator.empty
/** 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 discards it from the iterator.
*
* @author Martin Odersky, Matthias Zenger
* @version 2.8
* @since 1
* @define willNotTerminateInf
* Note: will not terminate for infinite iterators.
* @define mayNotTerminateInf
* Note: may not terminate for infinite iterators.
*/
trait Iterator[+A] extends TraversableOnce[A] {
self =>
def seq: Iterator[A] = this
/** Tests whether this iterator can provide another element.
* @return `true` if a subsequent call to `next` will yield an element,
* `false` otherwise.
*/
def hasNext: Boolean
/** Produces the next element of this iterator.
* @return the next element of this iterator, if `hasNext` is `true`,
* undefined behavior otherwise.
*/
def next(): A
/** Tests whether this iterator is empty.
* @return `true` if hasNext is false, `false` otherwise.
*/
def isEmpty: Boolean = !hasNext
/** Tests whether this Iterator can be repeatedly traversed.
* @return `false`
*/
def isTraversableAgain = false
/** Tests whether this Iterator has a known size.
*
* @return `true` for empty Iterators, `false` otherwise.
*/
def hasDefiniteSize = isEmpty
/** Selects first ''n'' values of this iterator.
* @param n the number of values to take
* @return an iterator producing only of the first `n` values of this iterator, or else the
* whole iterator, if it produces fewer than `n` values.
*/
def take(n: Int): Iterator[A] = slice(0, n)
/** Advances this iterator past the first ''n'' elements,
* or the length of the iterator, whichever is smaller.
*
* @param n the number of elements to drop
* @return an iterator which produces all values of the current iterator, except
* it omits the first `n` values.
*/
def drop(n: Int): Iterator[A] = slice(n, Int.MaxValue)
/** Creates an iterator returning an interval of the values produced by this iterator.
* @param from the index of the first element in this iterator which forms part of the slice.
* @param until the index of the first element following the slice.
* @return an iterator which advances this iterator past the first `from` elements using `drop`,
* and then takes `until - from` elements, using `take`.
*/
def slice(from: Int, until: Int): Iterator[A] = {
val lo = from max 0
var toDrop = lo
while (toDrop > 0 && self.hasNext) {
self.next()
toDrop -= 1
}
new Iterator[A] {
private var remaining = until - lo
def hasNext = remaining > 0 && self.hasNext
def next(): A =
if (remaining > 0) {
remaining -= 1
self.next()
}
else empty.next()
}
}
/** Creates a new iterator that maps all produced values of this iterator
* to new values using a transformation function.
* @param f the transformation function
* @return a new iterator which transforms every value produced by this
* iterator by applying the function `f` to it.
*/
def map[B](f: A => B): Iterator[B] = new Iterator[B] {
def hasNext = self.hasNext
def next() = f(self.next())
}
/** Concatenates this iterator with another.
* @param that the other iterator
* @return a new iterator that first yields the values produced by this
* iterator followed by the values produced by iterator `that`.
* @usecase def ++(that: => Iterator[A]): Iterator[A]
*/
def ++[B >: A](that: => GenTraversableOnce[B]): Iterator[B] = new Iterator[B] {
// optimize a little bit to prevent n log n behavior.
private var cur : Iterator[B] = self
// since that is by-name, make sure it's only referenced once -
// if "val it = that" is inside the block, then hasNext on an empty
// iterator will continually reevaluate it. (ticket #3269)
lazy val it = that.toIterator
// the eq check is to avoid an infinite loop on "x ++ x"
def hasNext = cur.hasNext || ((cur eq self) && {
it.hasNext && {
cur = it
true
}
})
def next() = { hasNext; cur.next() }
}
/** Creates a new iterator by applying a function to all values produced by this iterator
* and concatenating the results.
*
* @param f the function to apply on each element.
* @return the iterator resulting from applying the given iterator-valued function
* `f` to each value produced by this iterator and concatenating the results.
*/
def flatMap[B](f: A => GenTraversableOnce[B]): Iterator[B] = new Iterator[B] {
private var cur: Iterator[B] = empty
def hasNext: Boolean =
cur.hasNext || self.hasNext && { cur = f(self.next).toIterator; hasNext }
def next(): B = (if (hasNext) cur else empty).next()
}
/** Returns an iterator over all the elements of this iterator that
* satisfy the predicate `p`. The order of the elements
* is preserved.
*
* @param p the predicate used to test values.
* @return an iterator which produces those values of this iterator which satisfy the predicate `p`.
*/
def filter(p: A => Boolean): Iterator[A] = new Iterator[A] {
private var hd: A = _
private var hdDefined: Boolean = false
def hasNext: Boolean = hdDefined || {
do {
if (!self.hasNext) return false
hd = self.next()
} while (!p(hd))
hdDefined = true
true
}
def next() = if (hasNext) { hdDefined = false; hd } else 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`.
*/
def withFilter(p: A => Boolean): Iterator[A] = filter(p)
/** Creates an iterator over all the elements of this iterator which
* do not satisfy a predicate p.
*
* @param p the predicate used to test values.
* @return an iterator which produces those values of this iterator which do not satisfy the predicate `p`.
*/
def filterNot(p: A => Boolean): Iterator[A] = filter(!p(_))
/** Creates an iterator by transforming values
* produced by this iterator with a partial function, dropping those
* values for which the partial function is not defined.
* @param pf the partial function which filters and maps the iterator.
* @return a new iterator which yields each value `x` produced by this iterator for
* which `pf` is defined the image `pf(x)`.
*/
@migration(2, 8,
"This collect implementation bears no relationship to the one before 2.8.\n"+
"The previous behavior can be reproduced with toSeq."
)
def collect[B](pf: PartialFunction[A, B]): Iterator[B] = {
val self = buffered
new Iterator[B] {
private def skip() = while (self.hasNext && !pf.isDefinedAt(self.head)) self.next()
def hasNext = { skip(); self.hasNext }
def next() = { skip(); pf(self.next()) }
}
}
def scanLeft[B](z: B)(op: (B, A) => B): Iterator[B] = new Iterator[B] {
var hasNext = true
var elem = z
def next() = if (hasNext) {
val res = elem
if (self.hasNext) elem = op(elem, self.next())
else hasNext = false
res
} else Iterator.empty.next()
}
def scanRight[B](z: B)(op: (A, B) => B): Iterator[B] = toBuffer.scanRight(z)(op).iterator
/** Takes longest prefix of values produced by this iterator that satisfy a predicate.
* @param p The predicate used to test elements.
* @return An iterator returning the values produced by this iterator, until
* this iterator produces a value that does not satisfy
* the predicate `p`.
*/
def takeWhile(p: A => Boolean): Iterator[A] = new Iterator[A] {
private var hd: A = _
private var hdDefined: Boolean = false
private 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 empty.next()
}
/** 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.
*/
def partition(p: A => Boolean): (Iterator[A], Iterator[A]) = {
val self = buffered
class PartitionIterator(p: A => Boolean) extends Iterator[A] {
var other: PartitionIterator = _
val lookahead = new mutable.Queue[A]
def skip() =
while (self.hasNext && !p(self.head)) {
other.lookahead += self.next
}
def hasNext = !lookahead.isEmpty || { skip(); self.hasNext }
def next() = if (!lookahead.isEmpty) lookahead.dequeue()
else { skip(); self.next() }
}
val l = new PartitionIterator(p)
val r = new PartitionIterator(!p(_))
l.other = r
r.other = l
(l, r)
}
/** Splits this Iterator into a prefix/suffix pair according to a predicate.
*
* @param p the test predicate
* @return a pair of Iterators consisting of the longest prefix of this
* whose elements all satisfy `p`, and the rest of the Iterator.
*/
def span(p: A => Boolean): (Iterator[A], Iterator[A]) = {
val self = buffered
/**
* 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.
*/
class Leading extends Iterator[A] {
private var isDone = false
val lookahead = new mutable.Queue[A]
def advance() = {
self.hasNext && p(self.head) && {
lookahead += self.next
true
}
}
def finish() = {
while (advance()) ()
isDone = true
}
def hasNext = lookahead.nonEmpty || advance()
def next() = {
if (lookahead.isEmpty)
advance()
lookahead.dequeue()
}
}
val leading = new Leading
val trailing = new Iterator[A] {
private lazy val it = {
leading.finish()
self
}
def hasNext = it.hasNext
def next() = it.next()
override def toString = "unknown-if-empty iterator"
}
(leading, trailing)
}
/** Skips longest sequence of elements of this iterator which satisfy given
* predicate `p`, and returns an iterator of the remaining elements.
*
* @param p the predicate used to skip elements.
* @return an iterator consisting of the remaining elements
*/
def dropWhile(p: A => Boolean): Iterator[A] = {
val self = buffered
new Iterator[A] {
var dropped = false
private def skip() =
if (!dropped) {
while (self.hasNext && p(self.head)) self.next()
dropped = true
}
def hasNext = { skip(); self.hasNext }
def next() = { skip(); self.next() }
}
}
/** Creates an iterator formed from this iterator and another iterator
* by combining corresponding values in pairs.
* If one of the two iterators is longer than the other, its remaining
* elements are ignored.
* @param that The iterator providing the second half of each result pair
* @return a new iterator containing pairs consisting of
* corresponding elements of this iterator and `that`. The number
* of elements returned by the new iterator is the
* minimum of the number of elements returned by this
* iterator and `that`.
*/
def zip[B](that: Iterator[B]) = new Iterator[(A, B)] {
def hasNext = self.hasNext && that.hasNext
def next = (self.next, that.next)
}
/** Appends an element value to this iterator until a given target length is reached.
* @param len the target length
* @param elem the padding value
* @return a new iterator consisting of producing all values of this iterator,
* followed by the minimal number of occurrences of `elem` so
* that the number of produced values is at least `len`.
* @usecase def padTo(len: Int, elem: A): Iterator[A]
*/
def padTo[A1 >: A](len: Int, elem: A1) = new Iterator[A1] {
private var count = 0
def hasNext = self.hasNext || count < len
def next = {
count += 1
if (self.hasNext) self.next
else if (count <= len) elem
else empty.next
}
}
/** Creates an iterator that pairs each element produced by this iterator
* with its index, counting from 0.
*/
def zipWithIndex = new Iterator[(A, Int)] {
var idx = 0
def hasNext = self.hasNext
def next = {
val ret = (self.next, idx)
idx += 1
ret
}
}
/** Creates an iterator formed from this iterator and another iterator
* by combining corresponding elements in pairs.
* If one of the two iterators is shorter than the other,
* placeholder elements are used to extend the shorter iterator to the length of the longer.
*
* @param that iterator `that` may have a different length
* as the self iterator.
* @param thisElem element `thisElem` is used to fill up the
* resulting iterator if the self iterator is shorter than
* `that`
* @param thatElem element `thatElem` is used to fill up the
* resulting iterator if `that` is shorter than
* the self iterator
* @return a new iterator containing pairs consisting of
* corresponding values of this iterator and `that`. The length
* of the returned iterator is the maximum of the lengths of this iterator and `that`.
* If this iterator is shorter than `that`, `thisElem` values are used to pad the result.
* If `that` is shorter than this iterator, `thatElem` values are used to pad the result.
* @usecase def zipAll[B](that: Iterator[B], thisElem: A, thatElem: B): Iterator[(A, B)]
*/
def zipAll[B, A1 >: A, B1 >: B](that: Iterator[B], thisElem: A1, thatElem: B1) = new Iterator[(A1, B1)] {
def hasNext = self.hasNext || that.hasNext
def next(): (A1, B1) =
if (self.hasNext) {
if (that.hasNext) (self.next(), that.next())
else (self.next(), thatElem)
} else {
if (that.hasNext) (thisElem, that.next())
else empty.next()
}
}
/** Applies a function `f` to all values produced by this iterator.
*
* @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
*/
def foreach[U](f: A => U) { while (hasNext) f(next()) }
/** Tests whether a predicate holds for all values produced by this iterator.
* $mayNotTerminateInf
*
* @param p the predicate used to test elements.
* @return `true` if the given predicate `p` holds for all values
* produced by this iterator, otherwise `false`.
*/
def forall(p: A => Boolean): Boolean = {
var res = true
while (res && hasNext) res = p(next())
res
}
/** Tests whether a predicate holds for some of the values produced by this iterator.
* $mayNotTerminateInf
*
* @param p the predicate used to test elements.
* @return `true` if the given predicate `p` holds for some of the values
* produced by this iterator, otherwise `false`.
*/
def exists(p: A => Boolean): Boolean = {
var res = false
while (!res && hasNext) res = p(next())
res
}
/** 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 (wrt `==`) to `elem`, `false` otherwise.
*/
def contains(elem: Any): Boolean = exists(_ == elem)
/** Finds the first value produced by the iterator satisfying a
* predicate, if any.
* $mayNotTerminateInf
*
* @param p the predicate used to test values.
* @return an option value containing the first value produced by the iterator that satisfies
* predicate `p`, or `None` if none exists.
*/
def find(p: A => Boolean): Option[A] = {
var res: Option[A] = None
while (res.isEmpty && hasNext) {
val e = next()
if (p(e)) res = Some(e)
}
res
}
/** Returns the index of the first produced value satisfying a predicate, or -1.
* $mayNotTerminateInf
* @param p the predicate to test values
* @return the index of the first produced value satisfying `p`,
* or -1 if such an element does not exist until the end of the iterator is reached.
*/
def indexWhere(p: A => Boolean): Int = {
var i = 0
var found = false
while (!found && hasNext) {
if (p(next())) {
found = true
} else {
i += 1
}
}
if (found) i else -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.
*/
def indexOf[B >: A](elem: B): Int = {
var i = 0
var found = false
while (!found && hasNext) {
if (next() == elem) {
found = true
} else {
i += 1
}
}
if (found) i else -1
}
/** Creates a buffered iterator from this iterator.
* @see BufferedIterator
* @return a buffered iterator producing the same values as this iterator.
*/
def buffered = new BufferedIterator[A] {
private var hd: A = _
private var hdDefined: Boolean = false
def head: A = {
if (!hdDefined) {
hd = next()
hdDefined = true
}
hd
}
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 elements which don't fit evenly.
*
* Typical uses can be achieved via methods `grouped' and `sliding'.
*/
class GroupedIterator[B >: A](self: Iterator[A], size: Int, step: Int) extends Iterator[Seq[B]] {
require(size >= 1 && step >= 1, "size=%d and step=%d, but both must be positive".format(size, step))
private[this] var buffer: ArrayBuffer[B] = ArrayBuffer() // the buffer
private[this] var filled = false // whether the buffer is "hot"
private[this] var _partial = true // whether we deliver short sequences
private[this] var pad: Option[() => B] = None // what to pad short sequences with
/** Public functions which can be used to configure the iterator before use. */
def withPadding(x: => B): this.type = {
pad = Some(() => x)
this
}
def withPartial(x: Boolean): this.type = {
_partial = x
if (_partial == true) // reset pad since otherwise it will take precedence
pad = None
this
}
/** For reasons which remain to be determined, calling
* self.take(n).toSeq cause an infinite loop, so we have
* a slight variation on take for local usage.
*/
private def takeDestructively(size: Int): Seq[A] = {
val buf = new ArrayBuffer[A]
var i = 0
while (self.hasNext && i < size) {
buf += self.next
i += 1
}
buf
}
private def padding(x: Int) = List.fill(x)(pad.get())
private def gap = (step - size) max 0
private def go(count: Int) = {
val prevSize = buffer.size
def isFirst = prevSize == 0
// If there is padding defined we insert it immediately
// so the rest of the code can be oblivious
val xs: Seq[B] = {
val res = takeDestructively(count)
// extra checks so we don't calculate length unless there's reason
if (pad.isDefined && !self.hasNext) {
val shortBy = count - res.length
if (shortBy > 0) res ++ padding(shortBy) else res
}
else res
}
lazy val len = xs.length
lazy val incomplete = len < count
// if 0 elements are requested, or if the number of newly obtained
// elements is less than the gap between sequences, we are done.
def deliver(howMany: Int) = {
(howMany > 0 && (isFirst || len > gap)) && {
if (!isFirst)
buffer trimStart (step min prevSize)
val available =
if (isFirst) len
else howMany min (len - gap)
buffer ++= (xs takeRight available)
filled = true
true
}
}
if (xs.isEmpty) false // self ran out of elements
else if (_partial) deliver(len min size) // if _partial is true, we deliver regardless
else if (incomplete) false // !_partial && incomplete means no more seqs
else if (isFirst) deliver(len) // first element
else deliver(step min size) // the typical case
}
// fill() returns false if no more sequences can be produced
private def fill(): Boolean = {
if (!self.hasNext) false
// the first time we grab size, but after that we grab step
else if (buffer.isEmpty) go(size)
else go(step)
}
def hasNext = filled || fill()
def next = {
if (!filled)
fill()
if (!filled)
throw new NoSuchElementException("next on empty iterator")
filled = false
buffer.toList
}
}
/** Returns an iterator which groups this iterator into fixed size
* blocks. Example usages:
*
* <pre>
* // 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
* </pre>
*/
def grouped[B >: A](size: Int): GroupedIterator[B] =
new GroupedIterator[B](self, size, size)
/** Returns an iterator which presents a "sliding window" view of
* another iterator. The first argument is the window size, and
* the second is how far to advance the window on each iteration;
* defaults to 1. Example usages:
*
* <pre>
* // Returns List(List(1, 2, 3), List(2, 3, 4), List(3, 4, 5))
* (1 to 5).iterator.sliding(3).toList
* // Returns List(List(1, 2, 3, 4), List(4, 5))
* (1 to 5).iterator.sliding(4, 3).toList
* // Returns List(List(1, 2, 3, 4))
* (1 to 5).iterator.sliding(4, 3).withPartial(false).toList
* // Returns List(List(1, 2, 3, 4), List(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
* </pre>
*/
def sliding[B >: A](size: Int, step: Int = 1): GroupedIterator[B] =
new GroupedIterator[B](self, size, step)
/** Returns the number of elements in this iterator.
* $willNotTerminateInf
*
* Note: The iterator is at its end after this method returns.
*/
def length: Int = this.size
/** 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.
*
* @return a pair of iterators
*/
def duplicate: (Iterator[A], Iterator[A]) = {
val gap = new scala.collection.mutable.Queue[A]
var ahead: Iterator[A] = null
class Partner extends Iterator[A] {
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.
* @param from The start index from which to patch
* @param ps The iterator of patch values
* @param replaced The number of values in the original iterator that are replaced by the patch.
*/
def patch[B >: A](from: Int, patchElems: Iterator[B], replaced: Int) = new Iterator[B] {
private var origElems = self
private var i = 0
def hasNext: Boolean =
if (i < from) origElems.hasNext
else patchElems.hasNext || origElems.hasNext
def next(): B = {
val result: B =
if (i < from || !patchElems.hasNext) origElems.next()
else patchElems.next()
i += 1
if (i == from) origElems = origElems drop replaced
result
}
}
/** Copies selected values produced by this iterator to an array.
* Fills the given array `xs` starting at index `start` with at most
* `len` values produced by this iterator.
* Copying will stop once either the end of the current iterator is reached,
* or the end of the array is reached, or `len` elements have been copied.
*
* $willNotTerminateInf
*
* @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
*/
def copyToArray[B >: A](xs: Array[B], start: Int, len: Int): Unit = {
var i = start
val end = start + math.min(len, xs.length)
while (hasNext && i < end) {
xs(i) = next()
i += 1
}
}
/** Tests if another iterator produces the same values as this one.
* $willNotTerminateInf
* @param that the other iterator
* @return `true`, if both iterators produce the same elements in the same order, `false` otherwise.
*/
def sameElements(that: Iterator[_]): Boolean = {
while (hasNext && that.hasNext)
if (next != that.next)
return false
!hasNext && !that.hasNext
}
def toTraversable: Traversable[A] = toStream
def toIterator: Iterator[A] = self
def toStream: Stream[A] =
if (self.hasNext) Stream.cons(self.next, self.toStream)
else Stream.empty[A]
/** Converts this iterator to a string.
* @return `"empty iterator"` or `"non-empty iterator"`, depending on whether or not the iterator is empty.
*/
override def toString = (if (hasNext) "non-empty" else "empty")+" iterator"
/** Returns a new iterator that first yields the elements of this
* iterator followed by the elements provided by iterator `that`.
*/
@deprecated("use `++`", "2.3.2")
def append[B >: A](that: Iterator[B]) = self ++ that
/** Returns index of the first element satisfying a predicate, or -1. */
@deprecated("use `indexWhere` instead", "2.8.0")
def findIndexOf(p: A => Boolean): Int = indexWhere(p)
/** Returns a counted iterator from this iterator.
*/
@deprecated("use zipWithIndex in Iterator", "2.8.0")
def counted = new CountedIterator[A] {
private var cnt = 0
def count = cnt
def hasNext: Boolean = self.hasNext
def next(): A = { cnt += 1; self.next }
}
/** Fills the given array `xs` with the elements of
* this sequence starting at position `start`. Like `copyToArray`,
* but designed to accomodate IO stream operations.
*
* '''Note:''' the array must be large enough to hold `sz` elements.
* @param xs the array to fill.
* @param start the starting index.
* @param sz the maximum number of elements to be read.
*/
@deprecated("use copyToArray instead", "2.8.0")
def readInto[B >: A](xs: Array[B], start: Int, sz: Int) {
var i = start
while (hasNext && i - start < sz) {
xs(i) = next
i += 1
}
}
@deprecated("use copyToArray instead", "2.8.0")
def readInto[B >: A](xs: Array[B], start: Int) {
readInto(xs, start, xs.length - start)
}
@deprecated("use copyToArray instead", "2.8.0")
def readInto[B >: A](xs: Array[B]) {
readInto(xs, 0, xs.length)
}
}
Other Scala examples (source code examples)Here is a short list of links related to this Scala Iterator.scala source code file: |
The search page
Other Scala source code examples at this package level
Click here to learn more about this project
