Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

1240 lines (1140 sloc) 46.486 kb
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2011, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
package scala.collection
import mutable.ArrayBuffer
import annotation.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 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`.
*/
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 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)`.
*/
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&lt;n&gt;`.
*/
@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</sub> = step(e<sub>n</sub>)`
* where `e<sub>0</sub> = 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</sub> = step(e<sub>n</sub>)`
* where `e<sub>0</sub> = 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.
*
* 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
* }
* }}}
*
* @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.
* @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 consumesTwoIterators
* After calling this method, one should discard the iterator it was called
* on, as well as the one passed as parameter. Using the old iterators is
* undefined and subject to change.
*/
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.
* @note Reuse: $preservesIterator
*/
def hasNext: Boolean
/** Produces the next element of this iterator.
*
* @return the next element of this iterator, if `hasNext` is `true`,
* undefined behavior otherwise.
* @note Reuse: $preservesIterator
*/
def next(): A
/** Tests whether this iterator is empty.
*
* @return `true` if hasNext is false, `false` otherwise.
* @note Reuse: $preservesIterator
*/
def isEmpty: Boolean = !hasNext
/** Tests whether this Iterator can be repeatedly traversed.
*
* @return `false`
* @note Reuse: $preservesIterator
*/
def isTraversableAgain = false
/** Tests whether this Iterator has a known size.
*
* @return `true` for empty Iterators, `false` otherwise.
* @note Reuse: $preservesIterator
*/
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.
* @note Reuse: $consumesAndProducesIterator
*/
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.
* @note Reuse: $consumesAndProducesIterator
*/
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`.
* @note Reuse: $consumesAndProducesIterator
*/
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.
* @note Reuse: $consumesAndProducesIterator
*/
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`.
* @note Reuse: $consumesTwoAndProducesOneIterator
* @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.
* @note Reuse: $consumesAndProducesIterator
*/
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`.
* @note Reuse: $consumesAndProducesIterator
*/
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`.
* @note Reuse: $consumesAndProducesIterator
*/
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`.
* @note Reuse: $consumesAndProducesIterator
*/
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)`.
* @note Reuse: $consumesAndProducesIterator
*/
@migration("`collect` has changed. The previous behavior can be reproduced with `toSeq`.", "2.8.0")
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()) }
}
}
/** Produces a collection containing cummulative results of applying the
* operator going left to right.
*
* $willNotTerminateInf
* $orderDependent
*
* @tparam B the type of the elements in the resulting collection
* @param z the initial value
* @param op the binary operator applied to the intermediate result and the element
* @return iterator with intermediate results
* @note Reuse: $consumesAndProducesIterator
*/
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()
}
/** Produces a collection containing cummulative results of applying the operator going right to left.
* The head of the collection is the last cummulative result.
*
* $willNotTerminateInf
* $orderDependent
*
* @tparam B the type of the elements in the resulting collection
* @param z the initial value
* @param op the binary operator applied to the intermediate result and the element
* @return iterator with intermediate results
* @example {{{
* Iterator(1, 2, 3, 4).scanRight(0)(_ + _).toList == List(10, 9, 7, 4, 0)
* }}}
* @note Reuse: $consumesAndProducesIterator
*/
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`.
* @note Reuse: $consumesAndProducesIterator
*/
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.
* @note Reuse: $consumesOneAndProducesTwoIterators
*/
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.
* @note Reuse: $consumesOneAndProducesTwoIterators
*/
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
* @note Reuse: $consumesAndProducesIterator
*/
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`.
* @note Reuse: $consumesTwoAndProducesOneIterator
*/
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`.
* @note Reuse: $consumesAndProducesIterator
* @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.
*
* @return a new iterator containing pairs consisting of
* corresponding elements of this iterator and their indices.
* @note Reuse: $consumesAndProducesIterator
*/
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.
* @note Reuse: $consumesTwoAndProducesOneIterator
* @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.
*
* @note Reuse: $consumesIterator
* @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`.
* @note Reuse: $consumesIterator
*/
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`.
* @note Reuse: $consumesIterator
*/
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.
* @note Reuse: $consumesIterator
*/
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.
* @note Reuse: $consumesIterator
*/
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.
* @note Reuse: $consumesIterator
*/
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.
* @note Reuse: $consumesIterator
*/
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.
* @note Reuse: $consumesAndProducesIterator
*/
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.
*
* Pads the last segment if necessary so that all segments will
* have the same size.
*
* @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(true)`.
*/
def withPadding(x: => B): this.type = {
pad = Some(() => x)
this
}
/** Public functions which can be used to configure the iterator before use.
*
* Select whether the last segment may be returned with less than `size`
* elements. If not, some elements of the original iterator may not be
* returned at all.
*
* @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`.
*/
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:
* {{{
* // 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
* 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:
* {{{
* // 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
* }}}
*
* @note Reuse: $consumesAndProducesIterator
*/
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 Reuse: $consumesIterator
*/
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.
*
* 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 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 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) = 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.
*
* @note Reuse: $consumesIterator
* @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.
*
* @note Reuse: $consumesTwoIterators
*/
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.
* @note Reuse: $preservesIterator
*/
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)
}
}
Jump to Line
Something went wrong with that request. Please try again.