rust/src/libstd/iterator.rs

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// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
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/*! Composable external iterators
The `Iterator` trait defines an interface for objects which implement iteration as a state machine.
Algorithms like `zip` are provided as `Iterator` implementations which wrap other objects
implementing the `Iterator` trait.
*/
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#[allow(default_methods)]; // solid enough for the use case here
use cmp;
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use iter::{FromIter, Times};
use num::{Zero, One};
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use option::{Option, Some, None};
use ops::{Add, Mul};
use cmp::Ord;
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use clone::Clone;
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/// An interface for dealing with "external iterators". These types of iterators
/// can be resumed at any time as all state is stored internally as opposed to
/// being located on the call stack.
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pub trait Iterator<A> {
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/// Advance the iterator and return the next value. Return `None` when the end is reached.
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fn next(&mut self) -> Option<A>;
/// Return a lower bound and upper bound on the remaining length of the iterator.
///
/// The common use case for the estimate is pre-allocating space to store the results.
#[cfg(not(stage0))]
fn size_hint(&self) -> (Option<uint>, Option<uint>) { (None, None) }
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}
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/// Iterator adaptors provided for every `Iterator` implementation. The adaptor objects are also
/// implementations of the `Iterator` trait.
///
/// In the future these will be default methods instead of a utility trait.
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pub trait IteratorUtil<A> {
/// Chain this iterator with another, returning a new iterator which will
/// finish iterating over the current iterator, and then it will iterate
/// over the other specified iterator.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [0];
/// let b = [1];
/// let mut it = a.iter().chain_(b.iter());
/// assert_eq!(it.next().get(), &0);
/// assert_eq!(it.next().get(), &1);
/// assert!(it.next().is_none());
/// ~~~
fn chain_<U: Iterator<A>>(self, other: U) -> ChainIterator<A, Self, U>;
/// Creates an iterator which iterates over both this and the specified
/// iterators simultaneously, yielding the two elements as pairs. When
/// either iterator returns None, all further invocations of next() will
/// return None.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [0];
/// let b = [1];
/// let mut it = a.iter().zip(b.iter());
/// assert_eq!(it.next().get(), (&0, &1));
/// assert!(it.next().is_none());
/// ~~~
fn zip<B, U: Iterator<B>>(self, other: U) -> ZipIterator<A, Self, B, U>;
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// FIXME: #5898: should be called map
/// Creates a new iterator which will apply the specified function to each
/// element returned by the first, yielding the mapped element instead. This
/// similar to the `vec::map` function.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2];
/// let mut it = a.iter().transform(|&x| 2 * x);
/// assert_eq!(it.next().get(), 2);
/// assert_eq!(it.next().get(), 4);
/// assert!(it.next().is_none());
/// ~~~
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fn transform<'r, B>(self, f: &'r fn(A) -> B) -> MapIterator<'r, A, B, Self>;
/// Creates an iterator which applies the predicate to each element returned
/// by this iterator. Only elements which have the predicate evaluate to
/// `true` will be yielded.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2];
/// let mut it = a.iter().filter(|&x| *x > 1);
/// assert_eq!(it.next().get(), &2);
/// assert!(it.next().is_none());
/// ~~~
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fn filter<'r>(self, predicate: &'r fn(&A) -> bool) -> FilterIterator<'r, A, Self>;
/// Creates an iterator which both filters and maps elements.
/// If the specified function returns None, the element is skipped.
/// Otherwise the option is unwrapped and the new value is yielded.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2];
/// let mut it = a.iter().filter_map(|&x| if x > 1 {Some(2 * x)} else {None});
/// assert_eq!(it.next().get(), 4);
/// assert!(it.next().is_none());
/// ~~~
fn filter_map<'r, B>(self, f: &'r fn(A) -> Option<B>) -> FilterMapIterator<'r, A, B, Self>;
/// Creates an iterator which yields a pair of the value returned by this
/// iterator plus the current index of iteration.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [100, 200];
/// let mut it = a.iter().enumerate();
/// assert_eq!(it.next().get(), (0, &100));
/// assert_eq!(it.next().get(), (1, &200));
/// assert!(it.next().is_none());
/// ~~~
fn enumerate(self) -> EnumerateIterator<A, Self>;
/// Creates an iterator which invokes the predicate on elements until it
/// returns false. Once the predicate returns false, all further elements are
/// yielded.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 2, 1];
/// let mut it = a.iter().skip_while(|&a| *a < 3);
/// assert_eq!(it.next().get(), &3);
/// assert_eq!(it.next().get(), &2);
/// assert_eq!(it.next().get(), &1);
/// assert!(it.next().is_none());
/// ~~~
fn skip_while<'r>(self, predicate: &'r fn(&A) -> bool) -> SkipWhileIterator<'r, A, Self>;
/// Creates an iterator which yields elements so long as the predicate
/// returns true. After the predicate returns false for the first time, no
/// further elements will be yielded.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 2, 1];
/// let mut it = a.iter().take_while(|&a| *a < 3);
/// assert_eq!(it.next().get(), &1);
/// assert_eq!(it.next().get(), &2);
/// assert!(it.next().is_none());
/// ~~~
fn take_while<'r>(self, predicate: &'r fn(&A) -> bool) -> TakeWhileIterator<'r, A, Self>;
/// Creates an iterator which skips the first `n` elements of this iterator,
/// and then it yields all further items.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// let mut it = a.iter().skip(3);
/// assert_eq!(it.next().get(), &4);
/// assert_eq!(it.next().get(), &5);
/// assert!(it.next().is_none());
/// ~~~
fn skip(self, n: uint) -> SkipIterator<A, Self>;
// FIXME: #5898: should be called take
/// Creates an iterator which yields the first `n` elements of this
/// iterator, and then it will always return None.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// let mut it = a.iter().take_(3);
/// assert_eq!(it.next().get(), &1);
/// assert_eq!(it.next().get(), &2);
/// assert_eq!(it.next().get(), &3);
/// assert!(it.next().is_none());
/// ~~~
fn take_(self, n: uint) -> TakeIterator<A, Self>;
/// Creates a new iterator which behaves in a similar fashion to foldl.
/// There is a state which is passed between each iteration and can be
/// mutated as necessary. The yielded values from the closure are yielded
/// from the ScanIterator instance when not None.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// let mut it = a.iter().scan(1, |fac, &x| {
/// *fac = *fac * x;
/// Some(*fac)
/// });
/// assert_eq!(it.next().get(), 1);
/// assert_eq!(it.next().get(), 2);
/// assert_eq!(it.next().get(), 6);
/// assert_eq!(it.next().get(), 24);
/// assert_eq!(it.next().get(), 120);
/// assert!(it.next().is_none());
/// ~~~
fn scan<'r, St, B>(self, initial_state: St, f: &'r fn(&mut St, A) -> Option<B>)
-> ScanIterator<'r, A, B, Self, St>;
/// An adaptation of an external iterator to the for-loop protocol of rust.
///
/// # Example
///
/// ~~~ {.rust}
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/// use std::iterator::Counter;
///
/// for Counter::new(0, 10).advance |i| {
/// io::println(fmt!("%d", i));
/// }
/// ~~~
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fn advance(&mut self, f: &fn(A) -> bool) -> bool;
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/// Loops through the entire iterator, collecting all of the elements into
/// a container implementing `FromIter`.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// let b: ~[int] = a.iter().transform(|&x| x).collect();
/// assert!(a == b);
/// ~~~
fn collect<B: FromIter<A>>(&mut self) -> B;
/// Loops through `n` iterations, returning the `n`th element of the
/// iterator.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// let mut it = a.iter();
/// assert!(it.nth(2).get() == &3);
/// assert!(it.nth(2) == None);
/// ~~~
fn nth(&mut self, n: uint) -> Option<A>;
/// Loops through the entire iterator, returning the last element of the
/// iterator.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// assert!(a.iter().last().get() == &5);
/// ~~~
// FIXME: #5898: should be called `last`
fn last_(&mut self) -> Option<A>;
/// Performs a fold operation over the entire iterator, returning the
/// eventual state at the end of the iteration.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// assert!(a.iter().fold(0, |a, &b| a + b) == 15);
/// ~~~
fn fold<B>(&mut self, start: B, f: &fn(B, A) -> B) -> B;
// FIXME: #5898: should be called len
/// Counts the number of elements in this iterator.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// let mut it = a.iter();
/// assert!(it.len_() == 5);
/// assert!(it.len_() == 0);
/// ~~~
fn len_(&mut self) -> uint;
/// Tests whether the predicate holds true for all elements in the iterator.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// assert!(a.iter().all(|&x| *x > 0));
/// assert!(!a.iter().all(|&x| *x > 2));
/// ~~~
fn all(&mut self, f: &fn(A) -> bool) -> bool;
/// Tests whether any element of an iterator satisfies the specified
/// predicate.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// let mut it = a.iter();
/// assert!(it.any_(|&x| *x == 3));
/// assert!(!it.any_(|&x| *x == 3));
/// ~~~
fn any_(&mut self, f: &fn(A) -> bool) -> bool;
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/// Return the first element satisfying the specified predicate
fn find_(&mut self, predicate: &fn(&A) -> bool) -> Option<A>;
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/// Return the index of the first element satisfying the specified predicate
fn position_(&mut self, predicate: &fn(A) -> bool) -> Option<uint>;
/// Count the number of elements satisfying the specified predicate
fn count(&mut self, predicate: &fn(A) -> bool) -> uint;
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}
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/// Iterator adaptors provided for every `Iterator` implementation. The adaptor objects are also
/// implementations of the `Iterator` trait.
///
/// In the future these will be default methods instead of a utility trait.
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impl<A, T: Iterator<A>> IteratorUtil<A> for T {
#[inline]
fn chain_<U: Iterator<A>>(self, other: U) -> ChainIterator<A, T, U> {
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ChainIterator{a: self, b: other, flag: false}
}
#[inline]
fn zip<B, U: Iterator<B>>(self, other: U) -> ZipIterator<A, T, B, U> {
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ZipIterator{a: self, b: other}
}
// FIXME: #5898: should be called map
#[inline]
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fn transform<'r, B>(self, f: &'r fn(A) -> B) -> MapIterator<'r, A, B, T> {
MapIterator{iter: self, f: f}
}
#[inline]
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fn filter<'r>(self, predicate: &'r fn(&A) -> bool) -> FilterIterator<'r, A, T> {
FilterIterator{iter: self, predicate: predicate}
}
#[inline]
fn filter_map<'r, B>(self, f: &'r fn(A) -> Option<B>) -> FilterMapIterator<'r, A, B, T> {
FilterMapIterator { iter: self, f: f }
}
#[inline]
fn enumerate(self) -> EnumerateIterator<A, T> {
EnumerateIterator{iter: self, count: 0}
}
#[inline]
fn skip_while<'r>(self, predicate: &'r fn(&A) -> bool) -> SkipWhileIterator<'r, A, T> {
SkipWhileIterator{iter: self, flag: false, predicate: predicate}
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}
#[inline]
fn take_while<'r>(self, predicate: &'r fn(&A) -> bool) -> TakeWhileIterator<'r, A, T> {
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TakeWhileIterator{iter: self, flag: false, predicate: predicate}
}
#[inline]
fn skip(self, n: uint) -> SkipIterator<A, T> {
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SkipIterator{iter: self, n: n}
}
// FIXME: #5898: should be called take
#[inline]
fn take_(self, n: uint) -> TakeIterator<A, T> {
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TakeIterator{iter: self, n: n}
}
#[inline]
fn scan<'r, St, B>(self, initial_state: St, f: &'r fn(&mut St, A) -> Option<B>)
-> ScanIterator<'r, A, B, T, St> {
ScanIterator{iter: self, f: f, state: initial_state}
}
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/// A shim implementing the `for` loop iteration protocol for iterator objects
#[inline]
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fn advance(&mut self, f: &fn(A) -> bool) -> bool {
loop {
match self.next() {
Some(x) => {
if !f(x) { return false; }
}
None => { return true; }
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}
}
}
#[inline]
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fn collect<B: FromIter<A>>(&mut self) -> B {
FromIter::from_iter::<A, B>(|f| self.advance(f))
}
/// Return the `n`th item yielded by an iterator.
#[inline]
fn nth(&mut self, mut n: uint) -> Option<A> {
loop {
match self.next() {
Some(x) => if n == 0 { return Some(x) },
None => return None
}
n -= 1;
}
}
/// Return the last item yielded by an iterator.
#[inline]
fn last_(&mut self) -> Option<A> {
let mut last = None;
for self.advance |x| { last = Some(x); }
last
}
/// Reduce an iterator to an accumulated value
#[inline]
fn fold<B>(&mut self, init: B, f: &fn(B, A) -> B) -> B {
let mut accum = init;
loop {
match self.next() {
Some(x) => { accum = f(accum, x); }
None => { break; }
}
}
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accum
}
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/// Count the number of items yielded by an iterator
#[inline]
fn len_(&mut self) -> uint { self.fold(0, |cnt, _x| cnt + 1) }
#[inline]
fn all(&mut self, f: &fn(A) -> bool) -> bool {
for self.advance |x| { if !f(x) { return false; } }
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true
}
#[inline]
fn any_(&mut self, f: &fn(A) -> bool) -> bool {
for self.advance |x| { if f(x) { return true; } }
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false
}
/// Return the first element satisfying the specified predicate
#[inline]
fn find_(&mut self, predicate: &fn(&A) -> bool) -> Option<A> {
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for self.advance |x| {
if predicate(&x) { return Some(x) }
}
None
}
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/// Return the index of the first element satisfying the specified predicate
#[inline]
fn position_(&mut self, predicate: &fn(A) -> bool) -> Option<uint> {
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let mut i = 0;
for self.advance |x| {
if predicate(x) {
return Some(i);
}
i += 1;
}
None
}
#[inline]
fn count(&mut self, predicate: &fn(A) -> bool) -> uint {
let mut i = 0;
for self.advance |x| {
if predicate(x) { i += 1 }
}
i
}
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}
/// A trait for iterators over elements which can be added together
pub trait AdditiveIterator<A> {
/// Iterates over the entire iterator, summing up all the elements
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// let mut it = a.iter().transform(|&x| x);
/// assert!(it.sum() == 15);
/// ~~~
fn sum(&mut self) -> A;
}
impl<A: Add<A, A> + Zero, T: Iterator<A>> AdditiveIterator<A> for T {
#[inline]
fn sum(&mut self) -> A { self.fold(Zero::zero::<A>(), |s, x| s + x) }
}
/// A trait for iterators over elements whose elements can be multiplied
/// together.
pub trait MultiplicativeIterator<A> {
/// Iterates over the entire iterator, multiplying all the elements
///
/// # Example
///
/// ~~~ {.rust}
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/// use std::iterator::Counter;
///
/// fn factorial(n: uint) -> uint {
/// Counter::new(1u, 1).take_while(|&i| i <= n).product()
/// }
/// assert!(factorial(0) == 1);
/// assert!(factorial(1) == 1);
/// assert!(factorial(5) == 120);
/// ~~~
fn product(&mut self) -> A;
}
impl<A: Mul<A, A> + One, T: Iterator<A>> MultiplicativeIterator<A> for T {
#[inline]
fn product(&mut self) -> A { self.fold(One::one::<A>(), |p, x| p * x) }
}
/// A trait for iterators over elements which can be compared to one another.
/// The type of each element must ascribe to the `Ord` trait.
pub trait OrdIterator<A> {
/// Consumes the entire iterator to return the maximum element.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// assert!(a.iter().max().get() == &5);
/// ~~~
fn max(&mut self) -> Option<A>;
/// Consumes the entire iterator to return the minimum element.
///
/// # Example
///
/// ~~~ {.rust}
/// let a = [1, 2, 3, 4, 5];
/// assert!(a.iter().min().get() == &1);
/// ~~~
fn min(&mut self) -> Option<A>;
}
impl<A: Ord, T: Iterator<A>> OrdIterator<A> for T {
#[inline]
fn max(&mut self) -> Option<A> {
self.fold(None, |max, x| {
match max {
None => Some(x),
Some(y) => Some(cmp::max(x, y))
}
})
}
#[inline]
fn min(&mut self) -> Option<A> {
self.fold(None, |min, x| {
match min {
None => Some(x),
Some(y) => Some(cmp::min(x, y))
}
})
}
}
/// An iterator which strings two iterators together
// FIXME #6967: Dummy A parameter to get around type inference bug
pub struct ChainIterator<A, T, U> {
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priv a: T,
priv b: U,
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priv flag: bool
}
impl<A, T: Iterator<A>, U: Iterator<A>> Iterator<A> for ChainIterator<A, T, U> {
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#[inline]
fn next(&mut self) -> Option<A> {
if self.flag {
self.b.next()
} else {
match self.a.next() {
Some(x) => return Some(x),
_ => ()
}
self.flag = true;
self.b.next()
}
}
#[inline]
#[cfg(not(stage0))]
fn size_hint(&self) -> (Option<uint>, Option<uint>) {
let (a_lower, a_upper) = self.a.size_hint();
let (b_lower, b_upper) = self.b.size_hint();
let lower = match (a_lower, b_lower) {
(Some(x), Some(y)) => Some(x + y),
(Some(x), None) => Some(x),
(None, Some(y)) => Some(y),
(None, None) => None
};
let upper = match (a_upper, b_upper) {
(Some(x), Some(y)) => Some(x + y),
_ => None
};
(lower, upper)
}
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}
/// An iterator which iterates two other iterators simultaneously
// FIXME #6967: Dummy A & B parameters to get around type inference bug
pub struct ZipIterator<A, T, B, U> {
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priv a: T,
priv b: U
}
impl<A, B, T: Iterator<A>, U: Iterator<B>> Iterator<(A, B)> for ZipIterator<A, T, B, U> {
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#[inline]
fn next(&mut self) -> Option<(A, B)> {
match (self.a.next(), self.b.next()) {
(Some(x), Some(y)) => Some((x, y)),
_ => None
}
}
}
/// An iterator which maps the values of `iter` with `f`
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pub struct MapIterator<'self, A, B, T> {
priv iter: T,
priv f: &'self fn(A) -> B
}
impl<'self, A, B, T: Iterator<A>> Iterator<B> for MapIterator<'self, A, B, T> {
#[inline]
fn next(&mut self) -> Option<B> {
match self.iter.next() {
Some(a) => Some((self.f)(a)),
_ => None
}
}
#[inline]
#[cfg(not(stage0))]
fn size_hint(&self) -> (Option<uint>, Option<uint>) {
self.iter.size_hint()
}
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}
/// An iterator which filters the elements of `iter` with `predicate`
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pub struct FilterIterator<'self, A, T> {
priv iter: T,
priv predicate: &'self fn(&A) -> bool
}
impl<'self, A, T: Iterator<A>> Iterator<A> for FilterIterator<'self, A, T> {
#[inline]
fn next(&mut self) -> Option<A> {
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for self.iter.advance |x| {
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if (self.predicate)(&x) {
return Some(x);
} else {
loop
}
}
None
}
#[inline]
#[cfg(not(stage0))]
fn size_hint(&self) -> (Option<uint>, Option<uint>) {
let (_, upper) = self.iter.size_hint();
(None, upper) // can't know a lower bound, due to the predicate
}
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}
/// An iterator which uses `f` to both filter and map elements from `iter`
pub struct FilterMapIterator<'self, A, B, T> {
priv iter: T,
priv f: &'self fn(A) -> Option<B>
}
impl<'self, A, B, T: Iterator<A>> Iterator<B> for FilterMapIterator<'self, A, B, T> {
#[inline]
fn next(&mut self) -> Option<B> {
for self.iter.advance |x| {
match (self.f)(x) {
Some(y) => return Some(y),
None => ()
}
}
None
}
#[inline]
#[cfg(not(stage0))]
fn size_hint(&self) -> (Option<uint>, Option<uint>) {
let (_, upper) = self.iter.size_hint();
(None, upper) // can't know a lower bound, due to the predicate
}
}
/// An iterator which yields the current count and the element during iteration
// FIXME #6967: Dummy A parameter to get around type inference bug
pub struct EnumerateIterator<A, T> {
priv iter: T,
priv count: uint
}
impl<A, T: Iterator<A>> Iterator<(uint, A)> for EnumerateIterator<A, T> {
#[inline]
fn next(&mut self) -> Option<(uint, A)> {
match self.iter.next() {
Some(a) => {
let ret = Some((self.count, a));
self.count += 1;
ret
}
_ => None
}
}
}
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/// An iterator which rejects elements while `predicate` is true
pub struct SkipWhileIterator<'self, A, T> {
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priv iter: T,
priv flag: bool,
priv predicate: &'self fn(&A) -> bool
}
impl<'self, A, T: Iterator<A>> Iterator<A> for SkipWhileIterator<'self, A, T> {
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#[inline]
fn next(&mut self) -> Option<A> {
let mut next = self.iter.next();
if self.flag {
next
} else {
loop {
match next {
Some(x) => {
if (self.predicate)(&x) {
next = self.iter.next();
loop
} else {
self.flag = true;
return Some(x)
}
}
None => return None
}
}
}
}
}
/// An iterator which only accepts elements while `predicate` is true
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pub struct TakeWhileIterator<'self, A, T> {
priv iter: T,
priv flag: bool,
priv predicate: &'self fn(&A) -> bool
}
impl<'self, A, T: Iterator<A>> Iterator<A> for TakeWhileIterator<'self, A, T> {
#[inline]
fn next(&mut self) -> Option<A> {
if self.flag {
None
} else {
match self.iter.next() {
Some(x) => {
if (self.predicate)(&x) {
Some(x)
} else {
self.flag = true;
None
}
}
None => None
}
}
}
}
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/// An iterator which skips over `n` elements of `iter`.
// FIXME #6967: Dummy A parameter to get around type inference bug
pub struct SkipIterator<A, T> {
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priv iter: T,
priv n: uint
}
impl<A, T: Iterator<A>> Iterator<A> for SkipIterator<A, T> {
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#[inline]
fn next(&mut self) -> Option<A> {
let mut next = self.iter.next();
if self.n == 0 {
next
} else {
let n = self.n;
for n.times {
match next {
Some(_) => {
next = self.iter.next();
loop
}
None => {
self.n = 0;
return None
}
}
}
self.n = 0;
next
}
}
}
/// An iterator which only iterates over the first `n` iterations of `iter`.
// FIXME #6967: Dummy A parameter to get around type inference bug
pub struct TakeIterator<A, T> {
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priv iter: T,
priv n: uint
}
impl<A, T: Iterator<A>> Iterator<A> for TakeIterator<A, T> {
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#[inline]
fn next(&mut self) -> Option<A> {
let next = self.iter.next();
if self.n != 0 {
self.n -= 1;
next
} else {
None
}
}
}
/// An iterator to maintain state while iterating another iterator
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pub struct ScanIterator<'self, A, B, T, St> {
priv iter: T,
priv f: &'self fn(&mut St, A) -> Option<B>,
/// The current internal state to be passed to the closure next.
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state: St
}
impl<'self, A, B, T: Iterator<A>, St> Iterator<B> for ScanIterator<'self, A, B, T, St> {
#[inline]
fn next(&mut self) -> Option<B> {
self.iter.next().chain(|a| (self.f)(&mut self.state, a))
}
}
/// An iterator which just modifies the contained state throughout iteration.
pub struct UnfoldrIterator<'self, A, St> {
priv f: &'self fn(&mut St) -> Option<A>,
/// Internal state that will be yielded on the next iteration
state: St
}
impl<'self, A, St> UnfoldrIterator<'self, A, St> {
/// Creates a new iterator with the specified closure as the "iterator
/// function" and an initial state to eventually pass to the iterator
#[inline]
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pub fn new<'a>(f: &'a fn(&mut St) -> Option<A>, initial_state: St)
-> UnfoldrIterator<'a, A, St> {
UnfoldrIterator {
f: f,
state: initial_state
}
}
}
impl<'self, A, St> Iterator<A> for UnfoldrIterator<'self, A, St> {
#[inline]
fn next(&mut self) -> Option<A> {
(self.f)(&mut self.state)
}
}
/// An infinite iterator starting at `start` and advancing by `step` with each
/// iteration
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pub struct Counter<A> {
/// The current state the counter is at (next value to be yielded)
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state: A,
/// The amount that this iterator is stepping by
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step: A
}
impl<A> Counter<A> {
/// Creates a new counter with the specified start/step
#[inline]
pub fn new(start: A, step: A) -> Counter<A> {
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Counter{state: start, step: step}
}
}
impl<A: Add<A, A> + Clone> Iterator<A> for Counter<A> {
#[inline]
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fn next(&mut self) -> Option<A> {
let result = self.state.clone();
self.state = self.state.add(&self.step); // FIXME: #6050
Some(result)
}
}
#[cfg(test)]
mod tests {
use super::*;
use prelude::*;
use iter;
use uint;
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#[test]
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fn test_counter_from_iter() {
let mut it = Counter::new(0, 5).take_(10);
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let xs: ~[int] = iter::FromIter::from_iter::<int, ~[int]>(|f| it.advance(f));
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assert_eq!(xs, ~[0, 5, 10, 15, 20, 25, 30, 35, 40, 45]);
}
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#[test]
fn test_iterator_chain() {
let xs = [0u, 1, 2, 3, 4, 5];
let ys = [30u, 40, 50, 60];
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let expected = [0, 1, 2, 3, 4, 5, 30, 40, 50, 60];
let mut it = xs.iter().chain_(ys.iter());
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let mut i = 0;
for it.advance |&x| {
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assert_eq!(x, expected[i]);
i += 1;
}
assert_eq!(i, expected.len());
let ys = Counter::new(30u, 10).take_(4);
let mut it = xs.iter().transform(|&x| x).chain_(ys);
let mut i = 0;
for it.advance |x| {
assert_eq!(x, expected[i]);
i += 1;
}
assert_eq!(i, expected.len());
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}
#[test]
fn test_filter_map() {
let mut it = Counter::new(0u, 1u).take_(10)
.filter_map(|x| if x.is_even() { Some(x*x) } else { None });
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assert_eq!(it.collect::<~[uint]>(), ~[0*0, 2*2, 4*4, 6*6, 8*8]);
}
#[test]
fn test_iterator_enumerate() {
let xs = [0u, 1, 2, 3, 4, 5];
let mut it = xs.iter().enumerate();
for it.advance |(i, &x)| {
assert_eq!(i, x);
}
}
#[test]
fn test_iterator_take_while() {
let xs = [0u, 1, 2, 3, 5, 13, 15, 16, 17, 19];
let ys = [0u, 1, 2, 3, 5, 13];
let mut it = xs.iter().take_while(|&x| *x < 15u);
let mut i = 0;
for it.advance |&x| {
assert_eq!(x, ys[i]);
i += 1;
}
assert_eq!(i, ys.len());
}
#[test]
fn test_iterator_skip_while() {
let xs = [0u, 1, 2, 3, 5, 13, 15, 16, 17, 19];
let ys = [15, 16, 17, 19];
let mut it = xs.iter().skip_while(|&x| *x < 15u);
let mut i = 0;
for it.advance |&x| {
assert_eq!(x, ys[i]);
i += 1;
}
assert_eq!(i, ys.len());
}
#[test]
fn test_iterator_skip() {
let xs = [0u, 1, 2, 3, 5, 13, 15, 16, 17, 19, 20, 30];
let ys = [13, 15, 16, 17, 19, 20, 30];
let mut it = xs.iter().skip(5);
let mut i = 0;
for it.advance |&x| {
assert_eq!(x, ys[i]);
i += 1;
}
assert_eq!(i, ys.len());
}
#[test]
fn test_iterator_take() {
let xs = [0u, 1, 2, 3, 5, 13, 15, 16, 17, 19];
let ys = [0u, 1, 2, 3, 5];
let mut it = xs.iter().take_(5);
let mut i = 0;
for it.advance |&x| {
assert_eq!(x, ys[i]);
i += 1;
}
assert_eq!(i, ys.len());
}
#[test]
fn test_iterator_scan() {
// test the type inference
fn add(old: &mut int, new: &uint) -> Option<float> {
*old += *new as int;
Some(*old as float)
}
let xs = [0u, 1, 2, 3, 4];
let ys = [0f, 1f, 3f, 6f, 10f];
let mut it = xs.iter().scan(0, add);
let mut i = 0;
for it.advance |x| {
assert_eq!(x, ys[i]);
i += 1;
}
assert_eq!(i, ys.len());
}
#[test]
fn test_unfoldr() {
fn count(st: &mut uint) -> Option<uint> {
if *st < 10 {
let ret = Some(*st);
*st += 1;
ret
} else {
None
}
}
let mut it = UnfoldrIterator::new(count, 0);
let mut i = 0;
for it.advance |counted| {
assert_eq!(counted, i);
i += 1;
}
assert_eq!(i, 10);
}
#[test]
fn test_iterator_nth() {
let v = &[0, 1, 2, 3, 4];
for uint::range(0, v.len()) |i| {
assert_eq!(v.iter().nth(i).unwrap(), &v[i]);
}
}
#[test]
fn test_iterator_last() {
let v = &[0, 1, 2, 3, 4];
assert_eq!(v.iter().last_().unwrap(), &4);
assert_eq!(v.slice(0, 1).iter().last_().unwrap(), &0);
}
#[test]
fn test_iterator_len() {
let v = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
assert_eq!(v.slice(0, 4).iter().len_(), 4);
assert_eq!(v.slice(0, 10).iter().len_(), 10);
assert_eq!(v.slice(0, 0).iter().len_(), 0);
}
#[test]
fn test_iterator_sum() {
let v = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
assert_eq!(v.slice(0, 4).iter().transform(|&x| x).sum(), 6);
assert_eq!(v.iter().transform(|&x| x).sum(), 55);
assert_eq!(v.slice(0, 0).iter().transform(|&x| x).sum(), 0);
}
#[test]
fn test_iterator_product() {
let v = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
assert_eq!(v.slice(0, 4).iter().transform(|&x| x).product(), 0);
assert_eq!(v.slice(1, 5).iter().transform(|&x| x).product(), 24);
assert_eq!(v.slice(0, 0).iter().transform(|&x| x).product(), 1);
}
#[test]
fn test_iterator_max() {
let v = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
assert_eq!(v.slice(0, 4).iter().transform(|&x| x).max(), Some(3));
assert_eq!(v.iter().transform(|&x| x).max(), Some(10));
assert_eq!(v.slice(0, 0).iter().transform(|&x| x).max(), None);
}
#[test]
fn test_iterator_min() {
let v = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
assert_eq!(v.slice(0, 4).iter().transform(|&x| x).min(), Some(0));
assert_eq!(v.iter().transform(|&x| x).min(), Some(0));
assert_eq!(v.slice(0, 0).iter().transform(|&x| x).min(), None);
}
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#[test]
fn test_collect() {
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let a = ~[1, 2, 3, 4, 5];
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let b: ~[int] = a.iter().transform(|&x| x).collect();
assert_eq!(a, b);
}
#[test]
fn test_all() {
let v = ~&[1, 2, 3, 4, 5];
assert!(v.iter().all(|&x| x < 10));
assert!(!v.iter().all(|&x| x.is_even()));
assert!(!v.iter().all(|&x| x > 100));
assert!(v.slice(0, 0).iter().all(|_| fail!()));
}
#[test]
fn test_any() {
let v = ~&[1, 2, 3, 4, 5];
assert!(v.iter().any_(|&x| x < 10));
assert!(v.iter().any_(|&x| x.is_even()));
assert!(!v.iter().any_(|&x| x > 100));
assert!(!v.slice(0, 0).iter().any_(|_| fail!()));
}
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#[test]
fn test_find() {
let v = &[1, 3, 9, 27, 103, 14, 11];
assert_eq!(*v.iter().find_(|x| *x & 1 == 0).unwrap(), 14);
assert_eq!(*v.iter().find_(|x| *x % 3 == 0).unwrap(), 3);
assert!(v.iter().find_(|x| *x % 12 == 0).is_none());
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}
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#[test]
fn test_position() {
let v = &[1, 3, 9, 27, 103, 14, 11];
assert_eq!(v.iter().position_(|x| *x & 1 == 0).unwrap(), 5);
assert_eq!(v.iter().position_(|x| *x % 3 == 0).unwrap(), 1);
assert!(v.iter().position_(|x| *x % 12 == 0).is_none());
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}
#[test]
fn test_count() {
let xs = &[1, 2, 2, 1, 5, 9, 0, 2];
assert_eq!(xs.iter().count(|x| *x == 2), 3);
assert_eq!(xs.iter().count(|x| *x == 5), 1);
assert_eq!(xs.iter().count(|x| *x == 95), 0);
}
}