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Auto merge of #44856 - cuviper:more-fold, r=dtolnay 

Add more custom folding to `core::iter` adaptors

Many of the iterator adaptors will perform faster folds if they forward
to their inner iterator's folds, especially for inner types like `Chain`
which are optimized too.  The following types are newly specialized:

| Type        | `fold` | `rfold` |
| ----------- | ------ | ------- |
| `Enumerate` | ✓      | ✓       |
| `Filter`    | ✓      | ✓       |
| `FilterMap` | ✓      | ✓       |
| `FlatMap`   | exists | ✓       |
| `Fuse`      | ✓      | ✓       |
| `Inspect`   | ✓      | ✓       |
| `Peekable`  | ✓      | N/A¹    |
| `Skip`      | ✓      | N/A²    |
| `SkipWhile` | ✓      | N/A¹    |

¹ not a `DoubleEndedIterator`

² `Skip::next_back` doesn't pull skipped items at all, but this couldn't
be avoided if `Skip::rfold` were to call its inner iterator's `rfold`.

Benchmarks
----------

In the following results, plain `_sum` computes the sum of a million
integers -- note that `sum()` is implemented with `fold()`.  The
`_ref_sum` variants do the same on a `by_ref()` iterator, which is
limited to calling `next()` one by one, without specialized `fold`.

The `chain` variants perform the same tests on two iterators chained
together, to show a greater benefit of forwarding `fold` internally.

    test iter::bench_enumerate_chain_ref_sum  ... bench:   2,216,264 ns/iter (+/- 29,228)
    test iter::bench_enumerate_chain_sum      ... bench:     922,380 ns/iter (+/- 2,676)
    test iter::bench_enumerate_ref_sum        ... bench:     476,094 ns/iter (+/- 7,110)
    test iter::bench_enumerate_sum            ... bench:     476,438 ns/iter (+/- 3,334)

    test iter::bench_filter_chain_ref_sum     ... bench:   2,266,095 ns/iter (+/- 6,051)
    test iter::bench_filter_chain_sum         ... bench:     745,594 ns/iter (+/- 2,013)
    test iter::bench_filter_ref_sum           ... bench:     889,696 ns/iter (+/- 1,188)
    test iter::bench_filter_sum               ... bench:     667,325 ns/iter (+/- 1,894)

    test iter::bench_filter_map_chain_ref_sum ... bench:   2,259,195 ns/iter (+/- 353,440)
    test iter::bench_filter_map_chain_sum     ... bench:   1,223,280 ns/iter (+/- 1,972)
    test iter::bench_filter_map_ref_sum       ... bench:     611,607 ns/iter (+/- 2,507)
    test iter::bench_filter_map_sum           ... bench:     611,610 ns/iter (+/- 472)

    test iter::bench_fuse_chain_ref_sum       ... bench:   2,246,106 ns/iter (+/- 22,395)
    test iter::bench_fuse_chain_sum           ... bench:     634,887 ns/iter (+/- 1,341)
    test iter::bench_fuse_ref_sum             ... bench:     444,816 ns/iter (+/- 1,748)
    test iter::bench_fuse_sum                 ... bench:     316,954 ns/iter (+/- 2,616)

    test iter::bench_inspect_chain_ref_sum    ... bench:   2,245,431 ns/iter (+/- 21,371)
    test iter::bench_inspect_chain_sum        ... bench:     631,645 ns/iter (+/- 4,928)
    test iter::bench_inspect_ref_sum          ... bench:     317,437 ns/iter (+/- 702)
    test iter::bench_inspect_sum              ... bench:     315,942 ns/iter (+/- 4,320)

    test iter::bench_peekable_chain_ref_sum   ... bench:   2,243,585 ns/iter (+/- 12,186)
    test iter::bench_peekable_chain_sum       ... bench:     634,848 ns/iter (+/- 1,712)
    test iter::bench_peekable_ref_sum         ... bench:     444,808 ns/iter (+/- 480)
    test iter::bench_peekable_sum             ... bench:     317,133 ns/iter (+/- 3,309)

    test iter::bench_skip_chain_ref_sum       ... bench:   1,778,734 ns/iter (+/- 2,198)
    test iter::bench_skip_chain_sum           ... bench:     761,850 ns/iter (+/- 1,645)
    test iter::bench_skip_ref_sum             ... bench:     478,207 ns/iter (+/- 119,252)
    test iter::bench_skip_sum                 ... bench:     315,614 ns/iter (+/- 3,054)

    test iter::bench_skip_while_chain_ref_sum ... bench:   2,486,370 ns/iter (+/- 4,845)
    test iter::bench_skip_while_chain_sum     ... bench:     633,915 ns/iter (+/- 5,892)
    test iter::bench_skip_while_ref_sum       ... bench:     666,926 ns/iter (+/- 804)
    test iter::bench_skip_while_sum           ... bench:     444,405 ns/iter (+/- 571)
This commit is contained in:
bors 2017-09-29 12:56:24 +00:00
parent d514263ce3 13724fafdc
commit 09ee9b723a
4 changed files with 471 additions and 33 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

151
src/libcore/benches/iter.rs
View File

@ -147,40 +147,131 @@ fn bench_for_each_chain_ref_fold(b: &mut Bencher) {
});
}
#[bench]
fn bench_flat_map_sum(b: &mut Bencher) {
b.iter(|| -> i64 {
(0i64..1000).flat_map(|x| x..x+1000)
.map(black_box)
.sum()
});
/// Helper to benchmark `sum` for iterators taken by value which
/// can optimize `fold`, and by reference which cannot.
macro_rules! bench_sums {
($bench_sum:ident, $bench_ref_sum:ident, $iter:expr) => {
#[bench]
fn $bench_sum(b: &mut Bencher) {
b.iter(|| -> i64 {
$iter.map(black_box).sum()
});
}
#[bench]
fn $bench_ref_sum(b: &mut Bencher) {
b.iter(|| -> i64 {
$iter.map(black_box).by_ref().sum()
});
}
}
}
#[bench]
fn bench_flat_map_ref_sum(b: &mut Bencher) {
b.iter(|| -> i64 {
(0i64..1000).flat_map(|x| x..x+1000)
.map(black_box)
.by_ref()
.sum()
});
bench_sums! {
bench_flat_map_sum,
bench_flat_map_ref_sum,
(0i64..1000).flat_map(|x| x..x+1000)
}
#[bench]
fn bench_flat_map_chain_sum(b: &mut Bencher) {
b.iter(|| -> i64 {
(0i64..1000000).flat_map(|x| once(x).chain(once(x)))
.map(black_box)
.sum()
});
bench_sums! {
bench_flat_map_chain_sum,
bench_flat_map_chain_ref_sum,
(0i64..1000000).flat_map(|x| once(x).chain(once(x)))
}
#[bench]
fn bench_flat_map_chain_ref_sum(b: &mut Bencher) {
b.iter(|| -> i64 {
(0i64..1000000).flat_map(|x| once(x).chain(once(x)))
.map(black_box)
.by_ref()
.sum()
});
bench_sums! {
bench_enumerate_sum,
bench_enumerate_ref_sum,
(0i64..1000000).enumerate().map(|(i, x)| x * i as i64)
}
bench_sums! {
bench_enumerate_chain_sum,
bench_enumerate_chain_ref_sum,
(0i64..1000000).chain(0..1000000).enumerate().map(|(i, x)| x * i as i64)
}
bench_sums! {
bench_filter_sum,
bench_filter_ref_sum,
(0i64..1000000).filter(|x| x % 2 == 0)
}
bench_sums! {
bench_filter_chain_sum,
bench_filter_chain_ref_sum,
(0i64..1000000).chain(0..1000000).filter(|x| x % 2 == 0)
}
bench_sums! {
bench_filter_map_sum,
bench_filter_map_ref_sum,
(0i64..1000000).filter_map(|x| x.checked_mul(x))
}
bench_sums! {
bench_filter_map_chain_sum,
bench_filter_map_chain_ref_sum,
(0i64..1000000).chain(0..1000000).filter_map(|x| x.checked_mul(x))
}
bench_sums! {
bench_fuse_sum,
bench_fuse_ref_sum,
(0i64..1000000).fuse()
}
bench_sums! {
bench_fuse_chain_sum,
bench_fuse_chain_ref_sum,
(0i64..1000000).chain(0..1000000).fuse()
}
bench_sums! {
bench_inspect_sum,
bench_inspect_ref_sum,
(0i64..1000000).inspect(|_| {})
}
bench_sums! {
bench_inspect_chain_sum,
bench_inspect_chain_ref_sum,
(0i64..1000000).chain(0..1000000).inspect(|_| {})
}
bench_sums! {
bench_peekable_sum,
bench_peekable_ref_sum,
(0i64..1000000).peekable()
}
bench_sums! {
bench_peekable_chain_sum,
bench_peekable_chain_ref_sum,
(0i64..1000000).chain(0..1000000).peekable()
}
bench_sums! {
bench_skip_sum,
bench_skip_ref_sum,
(0i64..1000000).skip(1000)
}
bench_sums! {
bench_skip_chain_sum,
bench_skip_chain_ref_sum,
(0i64..1000000).chain(0..1000000).skip(1000)
}
bench_sums! {
bench_skip_while_sum,
bench_skip_while_ref_sum,
(0i64..1000000).skip_while(|&x| x < 1000)
}
bench_sums! {
bench_skip_while_chain_sum,
bench_skip_while_chain_ref_sum,
(0i64..1000000).chain(0..1000000).skip_while(|&x| x < 1000)
}

172
src/libcore/iter/mod.rs
View File

@ -1250,6 +1250,18 @@ impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool
}
count
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
let mut predicate = self.predicate;
self.iter.fold(init, move |acc, item| if predicate(&item) {
fold(acc, item)
} else {
acc
})
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@ -1265,6 +1277,18 @@ impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
}
None
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
let mut predicate = self.predicate;
self.iter.rfold(init, move |acc, item| if predicate(&item) {
fold(acc, item)
} else {
acc
})
}
}
#[unstable(feature = "fused", issue = "35602")]
@ -1316,6 +1340,17 @@ impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
let mut f = self.f;
self.iter.fold(init, move |acc, item| match f(item) {
Some(x) => fold(acc, x),
None => acc,
})
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@ -1331,6 +1366,17 @@ impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
}
None
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
let mut f = self.f;
self.iter.rfold(init, move |acc, item| match f(item) {
Some(x) => fold(acc, x),
None => acc,
})
}
}
#[unstable(feature = "fused", issue = "35602")]
@ -1395,6 +1441,19 @@ impl<I> Iterator for Enumerate<I> where I: Iterator {
fn count(self) -> usize {
self.iter.count()
}
#[inline]
#[rustc_inherit_overflow_checks]
fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
let mut count = self.count;
self.iter.fold(init, move |acc, item| {
let acc = fold(acc, (count, item));
count += 1;
acc
})
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@ -1410,6 +1469,19 @@ impl<I> DoubleEndedIterator for Enumerate<I> where
(self.count + len, a)
})
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
// Can safely add and subtract the count, as `ExactSizeIterator` promises
// that the number of elements fits into a `usize`.
let mut count = self.count + self.iter.len();
self.iter.rfold(init, move |acc, item| {
count -= 1;
fold(acc, (count, item))
})
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@ -1521,6 +1593,18 @@ impl<I: Iterator> Iterator for Peekable<I> {
let hi = hi.and_then(|x| x.checked_add(peek_len));
(lo, hi)
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
let acc = match self.peeked {
Some(None) => return init,
Some(Some(v)) => fold(init, v),
None => init,
};
self.iter.fold(acc, fold)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@ -1629,6 +1713,19 @@ impl<I: Iterator, P> Iterator for SkipWhile<I, P>
let (_, upper) = self.iter.size_hint();
(0, upper) // can't know a lower bound, due to the predicate
}
#[inline]
fn fold<Acc, Fold>(mut self, mut init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
if !self.flag {
match self.next() {
Some(v) => init = fold(init, v),
None => return init,
}
}
self.iter.fold(init, fold)
}
}
#[unstable(feature = "fused", issue = "35602")]
@ -1769,6 +1866,19 @@ impl<I> Iterator for Skip<I> where I: Iterator {
(lower, upper)
}
#[inline]
fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
if self.n > 0 {
// nth(n) skips n+1
if self.iter.nth(self.n - 1).is_none() {
return init;
}
}
self.iter.fold(init, fold)
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@ -1991,6 +2101,16 @@ impl<I: DoubleEndedIterator, U, F> DoubleEndedIterator for FlatMap<I, U, F> wher
}
}
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.frontiter.into_iter()
.chain(self.iter.map(self.f).map(U::into_iter))
.chain(self.backiter)
.rfold(init, |acc, iter| iter.rfold(acc, &mut fold))
}
}
#[unstable(feature = "fused", issue = "35602")]
@ -2068,6 +2188,17 @@ impl<I> Iterator for Fuse<I> where I: Iterator {
self.iter.size_hint()
}
}
#[inline]
default fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
if self.done {
init
} else {
self.iter.fold(init, fold)
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@ -2082,6 +2213,17 @@ impl<I> DoubleEndedIterator for Fuse<I> where I: DoubleEndedIterator {
next
}
}
#[inline]
default fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
if self.done {
init
} else {
self.iter.rfold(init, fold)
}
}
}
unsafe impl<I> TrustedRandomAccess for Fuse<I>
@ -2122,6 +2264,13 @@ impl<I> Iterator for Fuse<I> where I: FusedIterator {
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.fold(init, fold)
}
}
#[unstable(feature = "fused", reason = "recently added", issue = "35602")]
@ -2132,6 +2281,13 @@ impl<I> DoubleEndedIterator for Fuse<I>
fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
self.iter.next_back()
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.iter.rfold(init, fold)
}
}
@ -2196,6 +2352,14 @@ impl<I: Iterator, F> Iterator for Inspect<I, F> where F: FnMut(&I::Item) {
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
#[inline]
fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
let mut f = self.f;
self.iter.fold(init, move |acc, item| { f(&item); fold(acc, item) })
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@ -2207,6 +2371,14 @@ impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
let next = self.iter.next_back();
self.do_inspect(next)
}
#[inline]
fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
let mut f = self.f;
self.iter.rfold(init, move |acc, item| { f(&item); fold(acc, item) })
}
}
#[stable(feature = "rust1", since = "1.0.0")]

180
src/libcore/tests/iter.rs
View File

@ -248,6 +248,25 @@ fn test_filter_map() {
assert_eq!(it.collect::<Vec<usize>>(), [0*0, 2*2, 4*4, 6*6, 8*8]);
}
#[test]
fn test_filter_map_fold() {
let xs = [0, 1, 2, 3, 4, 5, 6, 7, 8];
let ys = [0*0, 2*2, 4*4, 6*6, 8*8];
let it = xs.iter().filter_map(|&x| if x % 2 == 0 { Some(x*x) } else { None });
let i = it.fold(0, |i, x| {
assert_eq!(x, ys[i]);
i + 1
});
assert_eq!(i, ys.len());
let it = xs.iter().filter_map(|&x| if x % 2 == 0 { Some(x*x) } else { None });
let i = it.rfold(ys.len(), |i, x| {
assert_eq!(x, ys[i - 1]);
i - 1
});
assert_eq!(i, 0);
}
#[test]
fn test_iterator_enumerate() {
let xs = [0, 1, 2, 3, 4, 5];
@ -282,7 +301,31 @@ fn test_iterator_enumerate_nth() {
#[test]
fn test_iterator_enumerate_count() {
let xs = [0, 1, 2, 3, 4, 5];
assert_eq!(xs.iter().count(), 6);
assert_eq!(xs.iter().enumerate().count(), 6);
}
#[test]
fn test_iterator_enumerate_fold() {
let xs = [0, 1, 2, 3, 4, 5];
let mut it = xs.iter().enumerate();
// steal a couple to get an interesting offset
assert_eq!(it.next(), Some((0, &0)));
assert_eq!(it.next(), Some((1, &1)));
let i = it.fold(2, |i, (j, &x)| {
assert_eq!(i, j);
assert_eq!(x, xs[j]);
i + 1
});
assert_eq!(i, xs.len());
let mut it = xs.iter().enumerate();
assert_eq!(it.next(), Some((0, &0)));
let i = it.rfold(xs.len() - 1, |i, (j, &x)| {
assert_eq!(i, j);
assert_eq!(x, xs[j]);
i - 1
});
assert_eq!(i, 0);
}
#[test]
@ -291,6 +334,25 @@ fn test_iterator_filter_count() {
assert_eq!(xs.iter().filter(|&&x| x % 2 == 0).count(), 5);
}
#[test]
fn test_iterator_filter_fold() {
let xs = [0, 1, 2, 3, 4, 5, 6, 7, 8];
let ys = [0, 2, 4, 6, 8];
let it = xs.iter().filter(|&&x| x % 2 == 0);
let i = it.fold(0, |i, &x| {
assert_eq!(x, ys[i]);
i + 1
});
assert_eq!(i, ys.len());
let it = xs.iter().filter(|&&x| x % 2 == 0);
let i = it.rfold(ys.len(), |i, &x| {
assert_eq!(x, ys[i - 1]);
i - 1
});
assert_eq!(i, 0);
}
#[test]
fn test_iterator_peekable() {
let xs = vec![0, 1, 2, 3, 4, 5];
@ -381,6 +443,18 @@ fn test_iterator_peekable_last() {
assert_eq!(it.last(), None);
}
#[test]
fn test_iterator_peekable_fold() {
let xs = [0, 1, 2, 3, 4, 5];
let mut it = xs.iter().peekable();
assert_eq!(it.peek(), Some(&&0));
let i = it.fold(0, |i, &x| {
assert_eq!(x, xs[i]);
i + 1
});
assert_eq!(i, xs.len());
}
/// This is an iterator that follows the Iterator contract,
/// but it is not fused. After having returned None once, it will start
/// producing elements if .next() is called again.
@ -470,6 +544,26 @@ fn test_iterator_skip_while() {
assert_eq!(i, ys.len());
}
#[test]
fn test_iterator_skip_while_fold() {
let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19];
let ys = [15, 16, 17, 19];
let it = xs.iter().skip_while(|&x| *x < 15);
let i = it.fold(0, |i, &x| {
assert_eq!(x, ys[i]);
i + 1
});
assert_eq!(i, ys.len());
let mut it = xs.iter().skip_while(|&x| *x < 15);
assert_eq!(it.next(), Some(&ys[0])); // process skips before folding
let i = it.fold(1, |i, &x| {
assert_eq!(x, ys[i]);
i + 1
});
assert_eq!(i, ys.len());
}
#[test]
fn test_iterator_skip() {
let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19, 20, 30];
@ -566,6 +660,26 @@ fn test_iterator_skip_last() {
assert_eq!(it.last(), Some(&30));
}
#[test]
fn test_iterator_skip_fold() {
let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19, 20, 30];
let ys = [13, 15, 16, 17, 19, 20, 30];
let it = xs.iter().skip(5);
let i = it.fold(0, |i, &x| {
assert_eq!(x, ys[i]);
i + 1
});
assert_eq!(i, ys.len());
let mut it = xs.iter().skip(5);
assert_eq!(it.next(), Some(&ys[0])); // process skips before folding
let i = it.fold(1, |i, &x| {
assert_eq!(x, ys[i]);
i + 1
});
assert_eq!(i, ys.len());
}
#[test]
fn test_iterator_take() {
let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19];
@ -661,13 +775,22 @@ fn test_iterator_flat_map_fold() {
let xs = [0, 3, 6];
let ys = [1, 2, 3, 4, 5, 6, 7];
let mut it = xs.iter().flat_map(|&x| x..x+3);
it.next();
it.next_back();
assert_eq!(it.next(), Some(0));
assert_eq!(it.next_back(), Some(8));
let i = it.fold(0, |i, x| {
assert_eq!(x, ys[i]);
i + 1
});
assert_eq!(i, ys.len());
let mut it = xs.iter().flat_map(|&x| x..x+3);
assert_eq!(it.next(), Some(0));
assert_eq!(it.next_back(), Some(8));
let i = it.rfold(ys.len(), |i, x| {
assert_eq!(x, ys[i - 1]);
i - 1
});
assert_eq!(i, 0);
}
#[test]
@ -684,6 +807,32 @@ fn test_inspect() {
assert_eq!(&xs[..], &ys[..]);
}
#[test]
fn test_inspect_fold() {
let xs = [1, 2, 3, 4];
let mut n = 0;
{
let it = xs.iter().inspect(|_| n += 1);
let i = it.fold(0, |i, &x| {
assert_eq!(x, xs[i]);
i + 1
});
assert_eq!(i, xs.len());
}
assert_eq!(n, xs.len());
let mut n = 0;
{
let it = xs.iter().inspect(|_| n += 1);
let i = it.rfold(xs.len(), |i, &x| {
assert_eq!(x, xs[i - 1]);
i - 1
});
assert_eq!(i, 0);
}
assert_eq!(n, xs.len());
}
#[test]
fn test_cycle() {
let cycle_len = 3;
@ -1241,6 +1390,31 @@ fn test_fuse_count() {
// Can't check len now because count consumes.
}
#[test]
fn test_fuse_fold() {
let xs = [0, 1, 2];
let it = xs.iter(); // `FusedIterator`
let i = it.fuse().fold(0, |i, &x| {
assert_eq!(x, xs[i]);
i + 1
});
assert_eq!(i, xs.len());
let it = xs.iter(); // `FusedIterator`
let i = it.fuse().rfold(xs.len(), |i, &x| {
assert_eq!(x, xs[i - 1]);
i - 1
});
assert_eq!(i, 0);
let it = xs.iter().scan((), |_, &x| Some(x)); // `!FusedIterator`
let i = it.fuse().fold(0, |i, x| {
assert_eq!(x, xs[i]);
i + 1
});
assert_eq!(i, xs.len());
}
#[test]
fn test_once() {
let mut it = once(42);

1
src/libcore/tests/lib.rs
View File

@ -25,6 +25,7 @@
#![feature(inclusive_range)]
#![feature(inclusive_range_syntax)]
#![feature(iter_rfind)]
#![feature(iter_rfold)]
#![feature(nonzero)]
#![feature(rand)]
#![feature(raw)]