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implement missing iterator traits for slice::Windows #22166

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Feb 12, 2015
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implement missing iterator traits for slice::Windows #22166

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12 changes: 12 additions & 0 deletions src/libcollections/slice.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2508,6 +2508,18 @@ mod tests {
let wins: &[&[_]] = &[&[1,2,3], &[2,3,4]];
assert_eq!(v.windows(3).collect::<Vec<_>>(), wins);
assert!(v.windows(6).next().is_none());

let wins: &[&[_]] = &[&[3,4], &[2,3], &[1,2]];
assert_eq!(v.windows(2).rev().collect::<Vec<&[_]>>(), wins);
let mut it = v.windows(2);
assert_eq!(it.indexable(), 3);
let win: &[_] = &[1,2];
assert_eq!(it.idx(0).unwrap(), win);
let win: &[_] = &[2,3];
assert_eq!(it.idx(1).unwrap(), win);
let win: &[_] = &[3,4];
assert_eq!(it.idx(2).unwrap(), win);
assert_eq!(it.idx(3), None);
}

#[test]
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38 changes: 36 additions & 2 deletions src/libcore/slice.rs
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Expand Up @@ -1179,8 +1179,42 @@ impl<'a, T> Iterator for Windows<'a, T> {
if self.size > self.v.len() {
(0, Some(0))
} else {
let x = self.v.len() - self.size;
(x.saturating_add(1), x.checked_add(1))
let size = self.v.len() - self.size + 1;
(size, Some(size))
}
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T> DoubleEndedIterator for Windows<'a, T> {
#[inline]
fn next_back(&mut self) -> Option<&'a [T]> {
if self.size > self.v.len() {
None
} else {
let ret = Some(&self.v[self.v.len()-self.size..]);
self.v = &self.v[..self.v.len()-1];
ret
}
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, T> ExactSizeIterator for Windows<'a, T> {}
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This looks like it may not actually be able to be implemented due to this line in size_hint:

(x.saturating_add(1), x.checked_add(1))

If x were uint::MAX then this would return (uint::MAX, None), breaking the contract of ExactSizeIterator. The value of x, however is self.v.len() - self.size and we know that size != 0 so we're guaranteed that the checked_add will always return Some.

Could you update the above size_hint to return (x + 1, Some(x + 1)) to be clear that it is a precise size?


#[unstable(feature = "core", reason = "trait is experimental")]
impl<'a, T> RandomAccessIterator for Windows<'a, T> {
#[inline]
fn indexable(&self) -> uint {
self.size_hint().0
}

#[inline]
fn idx(&mut self, index: uint) -> Option<&'a [T]> {
if index + self.size > self.v.len() {
None
} else {
Some(&self.v[index .. index+self.size])
}
}
}
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