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|
/* __ *\
** ________ ___ / / ___ Scala API **
** / __/ __// _ | / / / _ | (c) 2003-2006, LAMP/EPFL **
** __\ \/ /__/ __ |/ /__/ __ | **
** /____/\___/_/ |_/____/_/ | | **
** |/ **
\* */
// $Id$
package scala
import Predef._
import collection.mutable.{Buffer, ArrayBuffer}
/** The <code>Iterator</code> object provides various functions for
* creating specialized iterators.
*
* @author Martin Odersky
* @author Matthias Zenger
* @version 1.1, 04/02/2004
*/
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
* @return the iterator on <code>xs</code>.
*/
def fromArray[a](xs: Array[a]): Iterator[a] =
fromArray(xs, 0, xs.length)
/**
* @param xs the array of elements
* @param start ...
* @param length ...
* @return ...
*/
def fromArray[a](xs: Array[a], start: Int, length: Int): Iterator[a] =
new BufferedIterator[a] {
private var i = start
val end = if ((start + length) < xs.length) start else xs.length
def hasNext: Boolean = i < end
def next: a = if (hasNext) { val x = xs(i) ; i = i + 1 ; x }
else throw new NoSuchElementException("next on empty iterator")
def head: a = if (hasNext) xs(i);
else throw new NoSuchElementException("head on empty iterator")
}
/**
* @param str the given string
* @return the iterator on <code>str</code>
*/
def fromString(str: String): Iterator[Char] =
new BufferedIterator[Char] {
private var i = 0
private val len = str.length()
def hasNext = i < len
def next = { val c = str charAt i; i = i + 1; c }
def head = str charAt i
}
/**
* @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.arity
def hasNext = c < cmax
def next = { val a = n element c; 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> = lo</code>
* and <code>e<sub>i</sub> < end</code>.
*
* @param lo the start value of the iterator
* @param end the end value of the iterator
* @return the iterator with values in range <code>[lo;end)</code>.
*/
def range(lo: Int, end: Int): Iterator[Int] =
range(lo, 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> = lo</code>
* and <code>e<sub>i</sub> < end</code>.
*
* @param lo 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>[lo;end)</code>.
*/
def range(lo: Int, end: Int, step: Int): Iterator[Int] = {
assert(step != 0)
new BufferedIterator[Int] {
private var i = lo
def hasNext: Boolean = if (step > 0) i < end else i > end
def next: Int =
if (hasNext) { val j = i; i = i + step; j }
else throw new NoSuchElementException("next on empty iterator")
def head: Int =
if (hasNext) i
else throw new NoSuchElementException("head 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> = lo</code>
* and <code>e<sub>i</sub> < end</code>.
*
* @param lo the start value of the iterator
* @param end the end value of the iterator
* @param step the increment function of the iterator
* @return the iterator with values in range <code>[lo;end)</code>.
*/
def range(lo: Int, end: Int, step: Int => Int): Iterator[Int] =
new BufferedIterator[Int] {
private var i = lo
def hasNext: Boolean = i < end
def next: Int =
if (i < end) { val j = i; i = step(i); j }
else throw new NoSuchElementException("next on empty iterator")
def head: Int =
if (i < end) i
else throw new NoSuchElementException("head 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> = lo</code>.
*
* @param lo the start value of the iterator
* @return the iterator starting at value <code>lo</code>.
*/
def from(lo: Int): Iterator[Int] =
from(lo, 1)
/** Create an iterator with elements
* <code>e<sub>n+1</sub> = e<sub>n</sub> + step</code>
* where <code>e<sub>0</sub> = lo</code>.
*
* @param lo the start value of the iterator
* @param step the increment value of the iterator
* @return the iterator starting at value <code>lo</code>.
*/
def from(lo: Int, step: Int): Iterator[Int] =
new BufferedIterator[Int] {
private var i = lo
def hasNext: Boolean = true
def next: Int = { val j = i; i = i + step; j }
def head: Int = i
}
/** Create an iterator with elements
* <code>e<sub>n+1</sub> = step(e<sub>n</sub>)</code>
* where <code>e<sub>0</sub> = lo</code>.
*
* @param lo the start value of the iterator
* @param step the increment function of the iterator
* @return the iterator starting at value <code>lo</code>.
*/
def from(lo: Int, step: Int => Int): Iterator[Int] =
new BufferedIterator[Int] {
private var i = lo
def hasNext: Boolean = true
def next: Int = { val j = i; i = step(i); j }
def head: Int = i
}
}
/** 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
*/
def take(n: Int) = new Iterator[A] {
var remaining = n
def hasNext = remaining > 0 && Iterator.this.hasNext
def next: A =
if (hasNext) { remaining = 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) { next; drop(n - 1) } else this
/** 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>.
*/
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
}
/** 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>.
*/
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")
}
private def predicatedIterator(p: A => boolean, isFilter: boolean) = new BufferedIterator[A] {
private var hd: A = _
private var ahead: Boolean = false
private var hasMore = Iterator.this.hasNext
private def skip: Unit =
while (!ahead && hasMore) {
hd = Iterator.this.next
hasMore = Iterator.this.hasNext
ahead = p(hd)
}
def hasNext: Boolean = { skip; ahead || isFilter && hasMore }
def next: A =
if (hasNext) { ahead = false; hd }
else throw new NoSuchElementException("next on empty iterator")
def head: A = { skip; hd }
}
/** 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] = predicatedIterator(p, true)
/** 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.
*
* @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] = predicatedIterator(p, false)
/** Skips longest sequence of elements of this iterator which satisfy given
* predicate <code>p</code>, 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] =
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[Pair[A, B]] {
def hasNext = Iterator.this.hasNext && that.hasNext
def next = Pair(Iterator.this.next, that.next)
}
/** Return an iterator that pairs each element of this iterator
* with its index, counting from 0.
*
* @param start the index of the first element.
* @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[Pair[A, int]] {
var idx = 0
def hasNext = Iterator.this.hasNext
def next = {
val ret = Pair(Iterator.this.next, idx)
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): 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 { x => x == 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
}
/** 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.
*/
def reduceLeft[B >: A](op: (B, B) => 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.
*/
def reduceRight[B >: A](op: (B, 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[A] {
private var hd: A = _
private var ahead: Boolean = false
def head: A = {
if (!ahead) {
hd = Iterator.this.next
ahead = true
}
hd
}
def next: A =
if (ahead) { ahead = false; hd } else head;
def hasNext: Boolean = ahead || Iterator.this.hasNext
}
/** 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 = 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: Pair[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
Pair(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): Unit = {
var i = start
while (hasNext) {
xs(i) = next
i = i + 1
}
}
/** 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]): Unit =
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 collection.mutable.ListBuffer[A]
while (hasNext) {
res += next
}
res.toList
}
}
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