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|
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2008, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | http://scala-lang.org/ **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
// $Id$
package scala
import Predef._
import collection.mutable.{Buffer, ListBuffer, ArrayBuffer}
/** The <code>Iterator</code> object provides various functions for
* creating specialized iterators.
*
* @author Martin Odersky
* @author Matthias Zenger
* @version 1.2, 10/02/2007
*/
object Iterator {
val empty = new Iterator[Nothing] {
def hasNext: Boolean = false
def next(): Nothing = throw new NoSuchElementException("next on empty iterator")
}
/**
* @param x the element
* @return the iterator with one single element
*/
def single[a](x: a) = new Iterator[a] {
private var hasnext = true
def hasNext: Boolean = hasnext
def next(): a =
if (hasnext) { hasnext = false; x }
else throw new NoSuchElementException("next on empty iterator")
}
def fromValues[a](xs: a*) = xs.elements
/**
* @param xs the array of elements
* @see also: RandomAccessSeq.elements and slice
*/
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: RandomAccessSeq.elements and slice
*/
@throws(classOf[NoSuchElementException])
def fromArray[a](xs: Array[a], start: Int, length: Int): Iterator[a] =
new BufferedIterator.Advanced[a] {
private var i = start
val end = if (start + length < xs.length) start + length else xs.length
override def hasNext: Boolean = i < end
def next(): a =
if (hasNext) { val x = xs(i) ; i += 1 ; x }
else throw new NoSuchElementException("next on empty iterator")
override protected def defaultPeek : a = throw new NoSuchElementException("no lookahead")
override def peekList(sz: Int): Seq[a] =
xs.slice(i, if (i + sz > xs.length) xs.length else i + sz)
}
/**
* @param str the given string
* @return the iterator on <code>str</code>
* @deprecated replaced by <code>str.elements</code>
*/
@deprecated def fromString(str: String): Iterator[Char] =
new BufferedIterator.Advanced[Char] {
private var i = 0
private val len = str.length()
override def hasNext = i < len
def next = { val c = str charAt i; i += 1; c }
override protected def defaultPeek : Char = throw new NoSuchElementException
override def peekList(sz: Int): Seq[Char] =
str.substring(i, if (i + sz > str.length) str.length else i + sz)
}
/**
* @param n the product arity
* @return the iterator on <code>Product<n></code>.
*/
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 }
}
/**
* @deprecated use <code>fromProduct</code> instead.
*/
@deprecated
def fromCaseClass(n: Product) = fromProduct(n)
/** Create an iterator with elements
* <code>e<sub>n+1</sub> = e<sub>n</sub> + 1</code>
* where <code>e<sub>0</sub> = start</code>
* and <code>e<sub>i</sub> < end</code>. However,
* if <code>start ≥ end</code>, then it will return an empty range.
*
* @param start the start value of the iterator
* @param end the end value of the iterator
* @return the iterator with values in range <code>[start;end)</code>.
*/
def range(start: Int, end: Int): Iterator[Int] = range(start, end, 1)
/** Create an iterator with elements
* <code>e<sub>n+1</sub> = e<sub>n</sub> + step</code>
* where <code>e<sub>0</sub> = start</code>
* and elements are in the range between <code>start</code> (inclusive)
* and <code>end</code> (exclusive)
*
* @param start the start value of the iterator
* @param end the end value of the iterator
* @param step the increment value of the iterator (must be positive or negative)
* @return the iterator with values in range <code>[start;end)</code>.
*/
@throws(classOf[NoSuchElementException])
def range(start: Int, end: Int, step: Int) = new Iterator[Int] {
private var i = start
def hasNext: Boolean = (step <= 0 || i < end) && (step >= 0 || i > end)
def next(): Int =
if (hasNext) { val j = i; i += step; j }
else throw new NoSuchElementException("next on empty iterator")
}
/** Create an iterator with elements
* <code>e<sub>n+1</sub> = step(e<sub>n</sub>)</code>
* where <code>e<sub>0</sub> = start</code>
* and elements are in the range between <code>start</code> (inclusive)
* and <code>end</code> (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 <code>[start;end)</code>.
*/
@throws(classOf[NoSuchElementException])
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 throw new NoSuchElementException("next on empty iterator")
}
/** Create an iterator with elements
* <code>e<sub>n+1</sub> = e<sub>n</sub> + 1</code>
* where <code>e<sub>0</sub> = start</code>.
*
* @param start the start value of the iterator
* @return the iterator starting at value <code>start</code>.
*/
def from(start: Int): Iterator[Int] = from(start, 1)
/** Create an iterator with elements
* <code>e<sub>n+1</sub> = e<sub>n</sub> + step</code>
* where <code>e<sub>0</sub> = start</code>.
*
* @param start the start value of the iterator
* @param step the increment value of the iterator
* @return the iterator starting at value <code>start</code>.
*/
def from(start: Int, step: Int): Iterator[Int] = from(start, {x:Int => x + step})
/** Create an iterator with elements
* <code>e<sub>n+1</sub> = step(e<sub>n</sub>)</code>
* where <code>e<sub>0</sub> = start</code>.
*
* @param start the start value of the iterator
* @param step the increment function of the iterator
* @return the iterator starting at value <code>start</code>.
*/
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 concantenation 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.
*/
def flatten[T](its: Iterator[Iterator[T]]): Iterator[T] = new Iterator[T] {
private var it = its.next
def hasNext: Boolean = {
while (!it.hasNext && its.hasNext) it = its.next
it.hasNext
}
def next(): T =
if (hasNext) it.next
else empty.next()
}
}
/** Iterators are data structures that allow to iterate over a sequence
* of elements. They have a <code>hasNext</code> method for checking
* if there is a next element available, and a <code>next</code> method
* which returns the next element and discards it from the iterator.
*
* @author Martin Odersky, Matthias Zenger
* @version 1.2, 15/03/2004
*/
trait Iterator[+A] {
/** Does this iterator provide another element?
*/
def hasNext: Boolean
/** Returns the next element.
*/
def next(): A
/** Returns a new iterator that iterates only over the first <code>n</code>
* elements.
*
* @param n the number of elements to take
* @return the new iterator
*/
@throws(classOf[NoSuchElementException])
def take(n: Int): Iterator[A] = new Iterator[A] {
var remaining = n
def hasNext = remaining > 0 && Iterator.this.hasNext
def next(): A =
if (hasNext) { remaining -= 1; Iterator.this.next }
else throw new NoSuchElementException("next on empty iterator")
}
/** Removes the first <code>n</code> elements from this iterator.
*
* @param n the number of elements to drop
* @return the new iterator
*/
def drop(n: Int): Iterator[A] =
if (n > 0 && hasNext) { next; drop(n - 1) } else this
/** A sub-iterator of <code>until - from elements
* starting at index <code>from</code>
*
* @param from The index of the first element of the slice
* @param until The index of the element following the slice
*/
def slice(from: Int, until: Int): Iterator[A] = drop(from).take(until - from)
/** Returns a new iterator that maps all elements of this iterator
* to new elements using function <code>f</code>.
*/
def map[B](f: A => B): Iterator[B] = new Iterator[B] {
def hasNext = Iterator.this.hasNext
def next() = f(Iterator.this.next)
}
/** Returns a new iterator that first yields the elements of this
* iterator followed by the elements provided by iterator <code>that</code>.
* @deprecated use <code>++</code>
*/
def append[B >: A](that: Iterator[B]) = new Iterator[B] {
def hasNext = Iterator.this.hasNext || that.hasNext
def next() = if (Iterator.this.hasNext) Iterator.this.next else that.next
}
/** Returns a new iterator that first yields the elements of this
* iterator followed by the elements provided by iterator <code>that</code>.
*/
def ++[B >: A](that: => Iterator[B]) = new Iterator[B] {
// optimize a little bit to prevent n log n behavior.
var what : Iterator[B] = Iterator.this
def hasNext = if (what.hasNext) true
else if (what eq Iterator.this) {
what = that
what.hasNext
} else false
def next = { hasNext; what.next }
}
/** Applies the given function <code>f</code> to each element of
* this iterator, then concatenates the results.
*
* @param f the function to apply on each element.
* @return an iterator over <code>f(a<sub>0</sub>), ... ,
* f(a<sub>n</sub>)</code> if this iterator yields the
* elements <code>a<sub>0</sub>, ..., a<sub>n</sub></code>.
*/
@throws(classOf[NoSuchElementException])
def flatMap[B](f: A => Iterator[B]): Iterator[B] = new Iterator[B] {
private var cur: Iterator[B] = Iterator.empty
def hasNext: Boolean =
if (cur.hasNext) true
else if (Iterator.this.hasNext) {
cur = f(Iterator.this.next)
hasNext
} else false
def next(): B =
if (cur.hasNext) cur.next
else if (Iterator.this.hasNext) {
cur = f(Iterator.this.next)
next
} else throw new NoSuchElementException("next on empty iterator")
}
protected class PredicatedIterator(p : A => Boolean) extends BufferedIterator.Default[A] {
protected def doEnd : Boolean = false
protected override def fill(sz: Int): Seq[A] = {
while (true) {
if (!Iterator.this.hasNext) return Nil
val ret = Iterator.this.next
if (p(ret)) return ret :: Nil
if (doEnd) return Nil
}
throw new Error
}
}
protected class TakeWhileIterator(p : A => Boolean) extends PredicatedIterator(p) {
private var ended = false
override protected def doEnd = {
ended = true; true
}
override protected def fill(sz : Int) : Seq[A] =
if (ended) Nil else super.fill(sz)
}
/** Returns an iterator over all the elements of this iterator that
* satisfy the predicate <code>p</code>. The order of the elements
* is preserved.
*
* @param p the predicate used to filter the iterator.
* @return the elements of this iterator satisfying <code>p</code>.
*/
def filter(p: A => Boolean): Iterator[A] = new PredicatedIterator(p)
/** Returns an iterator over the longest prefix of this iterator such that
* all elements of the result satisfy the predicate <code>p</code>.
* The order of the elements is preserved.
*
* The behavior of <code>this</code> iterator is undefined after this method invocation.
*
* @param p the predicate used to filter the iterator.
* @return the longest prefix of this iterator satisfying <code>p</code>.
*/
def takeWhile(p: A => Boolean): Iterator[A] = new TakeWhileIterator(p)
/** Skips longest sequence of elements of this iterator which satisfy given
* predicate <code>p</code>, and returns an iterator of the remaining elements.
*
* The behavior of <code>this</code> iterator is undefined after this method invocation.
*
* @param p the predicate used to skip elements.
* @return an iterator consisting of the remaining elements
*/
def dropWhile(p: A => Boolean): Iterator[A] =
if (hasNext) {
val x = next
if (p(x)) dropWhile(p)
else Iterator.single(x) append this
} else this
/** Return an iterator formed from this iterator and the specified iterator
* <code>that</code> by associating each element of the former with
* the element at the same position in the latter.
* If one of the two iterators is longer than the other, its remaining elements are ignored.
*
* @return an iterator yielding <code>{a<sub>0</sub>,b<sub>0</sub>},
* {a<sub>1</sub>,b<sub>1</sub>}, ...</code> where
* <code>a<sub>i</sub></code> are the elements from this iterator
* and <code>b<sub>i</sub></code> are the elements from iterator
* <code>that</code>.
*/
def zip[B](that: Iterator[B]) = new Iterator[(A, B)] {
def hasNext = Iterator.this.hasNext && that.hasNext
def next = (Iterator.this.next, that.next)
}
/** Return an iterator that pairs each element of this iterator
* with its index, counting from 0.
*
* @return an iterator yielding <code>{a<sub>0</sub>,0},
* {a<sub>1</sub>,1}...</code> where <code>a<sub>i</sub></code>
* are the elements from this iterator.
*/
def zipWithIndex = new Iterator[(A, Int)] {
var idx = 0
def hasNext = Iterator.this.hasNext
def next = {
val ret = (Iterator.this.next, idx)
idx += 1
ret
}
}
/** Apply a function <code>f</code> to all elements of this
* iterable object.
*
* @param f a function that is applied to every element.
*/
def foreach(f: A => Unit) { while (hasNext) f(next) }
/** Apply a predicate <code>p</code> to all elements of this
* iterable object and return <code>true</code> iff the predicate yields
* <code>true</code> for all elements.
*
* @param p the predicate
* @return <code>true</code> iff the predicate yields <code>true</code>
* for all elements.
*/
def forall(p: A => Boolean): Boolean = {
var res = true
while (res && hasNext) res = p(next)
res
}
/** Apply a predicate <code>p</code> to all elements of this
* iterable object and return true, iff there is at least one
* element for which <code>p</code> yields <code>true</code>.
*
* @param p the predicate
* @return <code>true</code> iff the predicate yields <code>true</code>
* for at least one element.
*/
def exists(p: A => Boolean): Boolean = {
var res = false
while (!res && hasNext) res = p(next)
res
}
/** Tests if the given value <code>elem</code> is a member of this iterator.
*
* @param elem element whose membership has to be tested.
* @return <code>true</code> iff there is an element of this iterator which
* is equal (w.r.t. <code>==</code>) to <code>elem</code>.
*/
def contains(elem: Any): Boolean = exists { _ == elem }
/** Find and return the first element of the iterable object satisfying a
* predicate, if any.
*
* @param p the predicate
* @return the first element in the iterable object satisfying
* <code>p</code>, or <code>None</code> 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 index of the first element satisying a predicate, or -1.
*
* @note may not terminate for infinite-sized collections.
* @param p the predicate
* @return the index of the first element satisfying <code>p</code>,
* or -1 if such an element does not exist
*/
def findIndexOf(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 occurence of the specified
* object in this iterable object.
*
* @note may not terminate for infinite-sized collections.
* @param elem element to search for.
* @return the index in this sequence of the first occurence of the
* specified element, or -1 if the sequence does not contain
* this element.
*/
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
}
/** Combines the elements of this iterator together using the binary
* operator <code>op</code>, from left to right, and starting with
* the value <code>z</code>.
*
* @return <code>op(... (op(op(z,a<sub>0</sub>),a<sub>1</sub>) ...),
* a<sub>n</sub>)</code> if the iterator yields elements
* <code>a<sub>0</sub>, a<sub>1</sub>, ..., a<sub>n</sub></code>.
*/
def foldLeft[B](z: B)(op: (B, A) => B): B = {
var acc = z
while (hasNext) acc = op(acc, next)
acc
}
/** Combines the elements of this iterator together using the binary
* operator <code>op</code>, from right to left, and starting with
* the value <code>z</code>.
*
* @return <code>a<sub>0</sub> op (... op (a<sub>n</sub> op z)...)</code>
* if the iterator yields elements <code>a<sub>0</sub>, a<sub>1</sub>, ...,
* a<sub>n</sub></code>.
*/
def foldRight[B](z: B)(op: (A, B) => B): B = {
def fold(z: B): B = if (hasNext) op(next, fold(z)) else z
fold(z)
}
/** Similar to <code>foldLeft</code> but can be used as
* an operator with the order of iterator and zero arguments reversed.
* That is, <code>z /: xs</code> is the same as <code>xs foldLeft z</code>.
*
* @param z the left argument of the first application of <code>op</code>
* (evaluation occurs from left to right).
* @param op the applied operator.
* @return the result value
* @see <code><a href="#foldLeft">foldLeft</a></code>.
*/
def /:[B](z: B)(op: (B, A) => B): B = foldLeft(z)(op)
/** An alias for <code>foldRight</code>.
* That is, <code>xs :\ z</code> is the same as <code>xs foldRight z</code>.
*
* @param z the right argument of the first application of <code>op</code>
* (evaluation occurs from right to left).
* @param op the applied operator.
* @return the result value.
* @see <code><a href="#foldRight">foldRight</a></code>.
*/
def :\[B](z: B)(op: (A, B) => B): B = foldRight(z)(op)
/** Combines the elements of this iterator together using the binary
* operator <code>op</code>, from left to right
* @param op The operator to apply
* @return <code>op(... op(a<sub>0</sub>,a<sub>1</sub>), ..., a<sub>n</sub>)</code>
if the iterator yields elements
* <code>a<sub>0</sub>, a<sub>1</sub>, ..., a<sub>n</sub></code>.
* @throws Predef.UnsupportedOperationException if the iterator is empty.
*/
@throws(classOf[UnsupportedOperationException])
def reduceLeft[B >: A](op: (B, A) => B): B = {
if (hasNext) foldLeft[B](next)(op)
else throw new UnsupportedOperationException("empty.reduceLeft")
}
/** Combines the elements of this iterator together using the binary
* operator <code>op</code>, from right to left
* @param op The operator to apply
*
* @return <code>a<sub>0</sub> op (... op (a<sub>n-1</sub> op a<sub>n</sub>)...)</code>
* if the iterator yields elements <code>a<sub>0</sub>, a<sub>1</sub>, ...,
* a<sub>n</sub></code>.
* @throws Predef.UnsupportedOperationException if the iterator is empty.
*/
@throws(classOf[UnsupportedOperationException])
def reduceRight[B >: A](op: (A, B) => B): B = {
if (!hasNext) throw new UnsupportedOperationException("empty.reduceRight")
val x = next
if (hasNext) op(x, reduceRight(op))
else x
}
/** Returns a buffered iterator from this iterator.
*/
def buffered: BufferedIterator[A] = new BufferedIterator.Default[A] {
protected def fill(sz : Int) = if (Iterator.this.hasNext) (Iterator.this.next) :: Nil else Nil
}
/** Returns a counted iterator from this iterator.
*/
def counted = new CountedIterator[A] {
private var cnt = -1
def count = cnt
def hasNext: Boolean = Iterator.this.hasNext
def next(): A = { cnt += 1; Iterator.this.next }
}
/** Creates two new iterators that both iterate over the same elements
* than this iterator (in the same order).
*
* @return a pair of iterators
*/
def duplicate: (Iterator[A], Iterator[A]) = {
var xs: List[A] = Nil
var ahead: Iterator[A] = null
class Partner extends Iterator[A] {
var ys: List[A] = Nil
def hasNext: Boolean = Iterator.this.synchronized (
((this == ahead) && Iterator.this.hasNext) ||
((this != ahead) && (!xs.isEmpty || !ys.isEmpty || Iterator.this.hasNext))
)
def next(): A = Iterator.this.synchronized {
if (this == ahead) {
val e = Iterator.this.next
xs = e :: xs; e
} else {
if (ys.isEmpty) {
ys = xs.reverse
xs = Nil
}
ys match {
case Nil =>
val e = Iterator.this.next
ahead = this
xs = e :: xs; e
case z :: zs =>
ys = zs; z
}
}
}
}
ahead = new Partner
(ahead, new Partner)
}
/** Fills the given array <code>xs</code> with the elements of
* this sequence starting at position <code>start</code>.
*
* @param xs the array to fill.
* @param start the starting index.
* @pre the array must be large enough to hold all elements.
*/
def copyToArray[B >: A](xs: Array[B], start: Int) {
var i = start
while (hasNext) {
xs(i) = next
i += 1
}
}
/** Fills the given array <code>xs</code> with the elements of
* this sequence starting at position <code>start</code>. Like <code>copyToArray</code>,
* but designed to accomodate IO stream operations.
*
* @param xs the array to fill.
* @param start the starting index.
* @param sz the maximum number of elements to be read.
* @pre the array must be large enough to hold <code>sz</code> elements.
*/
def readInto[B >: A](xs: Array[B], start: Int, sz: Int) {
var i = start
while (hasNext && i - start < sz) {
xs(i) = next
i += 1
}
}
def readInto[B >: A](xs: Array[B], start: Int) {
readInto(xs, start, xs.length - start)
}
def readInto[B >: A](xs: Array[B]) {
readInto(xs, 0, xs.length)
}
/** Copy all elements to a buffer
* @param The buffer to which elements are copied
* @return The buffer to which elements are copied
*/
def copyToBuffer[B >: A](dest: Buffer[B]) {
while (hasNext) dest += next
}
/** Transform this iterator into a list of all elements.
*
* @return a list which enumerates all elements of this iterator.
*/
def toList: List[A] = {
val res = new ListBuffer[A]
while (hasNext) res += next
res.toList
}
/** Collect elements into a seq.
*
* @return a seq which enumerates all elements of this iterator.
*/
def collect: Seq[A] = {
val buffer = new ArrayBuffer[A]
this copyToBuffer buffer
buffer.readOnly
}
/** Returns a string representation of the elements in this iterator. The resulting string
* begins with the string <code>start</code> and is finished by the string
* <code>end</code>. Inside, the string representations of elements (w.r.t.
* the method <code>toString()</code>) are separated by the string
* <code>sep</code>.
* <p/>
* Ex: <br/>
* <code>List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"</code>
*
* @param start starting string.
* @param sep separator string.
* @param end ending string.
* @return a string representation of this iterable object.
*/
def mkString(start: String, sep: String, end: String): String = {
val buf = new StringBuilder
addString(buf, start, sep, end).toString
}
/** Returns a string representation of this iterable object. The string
* representations of elements (w.r.t. the method <code>toString()</code>)
* are separated by the string <code>sep</code>.
*
* @param sep separator string.
* @return a string representation of this iterable object.
*/
def mkString(sep: String): String = this.mkString("", sep, "")
/** Returns a string representation of this iterable object. The string
* representations of elements (w.r.t. the method <code>toString()</code>)
* are separated by a comma.
*
* @return a string representation of this iterable object.
*/
def mkString: String =
mkString("")
/** Write all elements of this string into given string builder.
*
* @param buf ...
* @param start the starting string
* @param sep the separator string
* @param end the ending string
* @return ...
*/
def addString(buf: StringBuilder, start: String, sep: String, end: String): StringBuilder = {
buf.append(start)
val elems = this
if (elems.hasNext) buf.append(elems.next)
while (elems.hasNext) {
buf.append(sep); buf.append(elems.next)
}
buf.append(end)
}
override def toString = (if (hasNext) "non-empty" else "empty")+" iterator"
}
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