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Merged
merged 3 commits into from
Jan 23, 2015
Merged

Implement ExactSizeIterator for remaining core Iterators where applicable #21453

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8ea6f78
Implement ExactSizeIterator for remaining core Iterators where applic…
Stebalien Jan 20, 2015
a13e721
Use the default `len` implementation in ExactSizeIterator impls
Stebalien Jan 21, 2015
1479de8
Add test cases for ExactSizeIterator impls
Stebalien Jan 21, 2015
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15 changes: 15 additions & 0 deletions src/libcore/iter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1087,6 +1087,9 @@ impl<'a, I> DoubleEndedIterator for ByRef<'a, I> where I: 'a + DoubleEndedIterat
fn next_back(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next_back() }
}

#[stable]
impl<'a, I> ExactSizeIterator for ByRef<'a, I> where I: 'a + ExactSizeIterator {}

/// A trait for iterators over elements which can be added together
#[unstable = "needs to be re-evaluated as part of numerics reform"]
pub trait AdditiveIterator<A> {
Expand Down Expand Up @@ -1790,6 +1793,9 @@ impl<T, I> Iterator for Peekable<T, I> where I: Iterator<Item=T> {
}
}

#[stable]
impl<T, I> ExactSizeIterator for Peekable<T, I> where I: ExactSizeIterator<Item = T> {}
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(copying over from previous comment to continue discussion)

Sorry, that was supposed to be (uint::MAX, Some(uint::MAX)) (copy and paste error).

My basic point is that that if the number of items in an ExactSizeIterator once fit in a uint (required by the spec), it must always fit in a uint regardless of where those items are (moving one from self.iter to self.peeked doesn't change the total number of items).

Ah right, good point! So if the underlying iterator returns (MAX, Some(MAX)) then the only time we'll add 1 is if we've already peeked in which case the underlying iterator will return (MAX-1, Some(MAX-1)).

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Exactly.


#[stable]
impl<T, I> Peekable<T, I> where I: Iterator<Item=T> {
/// Return a reference to the next element of the iterator with out advancing it,
Expand Down Expand Up @@ -1982,6 +1988,9 @@ impl<I> RandomAccessIterator for Skip<I> where I: RandomAccessIterator{
}
}

#[stable]
impl<I> ExactSizeIterator for Skip<I> where I: ExactSizeIterator {}

/// An iterator that only iterates over the first `n` iterations of `iter`.
#[derive(Clone)]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
Expand Down Expand Up @@ -2037,6 +2046,9 @@ impl<I> RandomAccessIterator for Take<I> where I: RandomAccessIterator{
}
}

#[stable]
impl<I> ExactSizeIterator for Take<I> where I: ExactSizeIterator {}


/// An iterator to maintain state while iterating another iterator
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
Expand Down Expand Up @@ -2246,6 +2258,9 @@ impl<I> RandomAccessIterator for Fuse<I> where I: RandomAccessIterator {
}
}

#[stable]
impl<I> ExactSizeIterator for Fuse<I> where I: ExactSizeIterator {}

impl<I> Fuse<I> {
/// Resets the fuse such that the next call to .next() or .next_back() will
/// call the underlying iterator again even if it previously returned None.
Expand Down
61 changes: 57 additions & 4 deletions src/libcoretest/iter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -120,18 +120,32 @@ fn test_iterator_enumerate() {
fn test_iterator_peekable() {
let xs = vec![0u, 1, 2, 3, 4, 5];
let mut it = xs.iter().map(|&x|x).peekable();

assert_eq!(it.len(), 6);
assert_eq!(it.peek().unwrap(), &0);
assert_eq!(it.len(), 6);
assert_eq!(it.next().unwrap(), 0);
assert_eq!(it.len(), 5);
assert_eq!(it.next().unwrap(), 1);
assert_eq!(it.len(), 4);
assert_eq!(it.next().unwrap(), 2);
assert_eq!(it.len(), 3);
assert_eq!(it.peek().unwrap(), &3);
assert_eq!(it.len(), 3);
assert_eq!(it.peek().unwrap(), &3);
assert_eq!(it.len(), 3);
assert_eq!(it.next().unwrap(), 3);
assert_eq!(it.len(), 2);
assert_eq!(it.next().unwrap(), 4);
assert_eq!(it.len(), 1);
assert_eq!(it.peek().unwrap(), &5);
assert_eq!(it.len(), 1);
assert_eq!(it.next().unwrap(), 5);
assert_eq!(it.len(), 0);
assert!(it.peek().is_none());
assert_eq!(it.len(), 0);
assert!(it.next().is_none());
assert_eq!(it.len(), 0);
}

#[test]
Expand Down Expand Up @@ -166,24 +180,45 @@ fn test_iterator_skip() {
let ys = [13, 15, 16, 17, 19, 20, 30];
let mut it = xs.iter().skip(5);
let mut i = 0;
for &x in it {
while let Some(&x) = it.next() {
assert_eq!(x, ys[i]);
i += 1;
assert_eq!(it.len(), xs.len()-5-i);
}
assert_eq!(i, ys.len());
assert_eq!(it.len(), 0);
}

#[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 xs = [0us, 1, 2, 3, 5, 13, 15, 16, 17, 19];
let ys = [0us, 1, 2, 3, 5];
let mut it = xs.iter().take(5);
let mut i = 0;
for &x in it {
assert_eq!(it.len(), 5);
while let Some(&x) = it.next() {
assert_eq!(x, ys[i]);
i += 1;
assert_eq!(it.len(), 5-i);
}
assert_eq!(i, ys.len());
assert_eq!(it.len(), 0);
}

#[test]
fn test_iterator_take_short() {
let xs = [0us, 1, 2, 3];
let ys = [0us, 1, 2, 3];
let mut it = xs.iter().take(5);
let mut i = 0;
assert_eq!(it.len(), 4);
while let Some(&x) = it.next() {
assert_eq!(x, ys[i]);
i += 1;
assert_eq!(it.len(), 4-i);
}
assert_eq!(i, ys.len());
assert_eq!(it.len(), 0);
}

#[test]
Expand Down Expand Up @@ -828,6 +863,24 @@ fn test_repeat() {
assert_eq!(it.next(), Some(42u));
}

#[test]
fn test_fuse() {
let mut it = 0us..3;
assert_eq!(it.len(), 3);
assert_eq!(it.next(), Some(0us));
assert_eq!(it.len(), 2);
assert_eq!(it.next(), Some(1us));
assert_eq!(it.len(), 1);
assert_eq!(it.next(), Some(2us));
assert_eq!(it.len(), 0);
assert_eq!(it.next(), None);
assert_eq!(it.len(), 0);
assert_eq!(it.next(), None);
assert_eq!(it.len(), 0);
assert_eq!(it.next(), None);
assert_eq!(it.len(), 0);
}

#[bench]
fn bench_rposition(b: &mut Bencher) {
let it: Vec<uint> = range(0u, 300).collect();
Expand Down