Improve performance characteristics of Vector iterators to better match Vec iterators #104
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timotree3
suggested changes
Oct 23, 2019
| if n >= self.len() { | ||
| None | ||
| } else { | ||
| self.front_index += n; |
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| fn nth(&mut self, n: usize) -> Option<Self::Item> { | ||
| if n >= self.len() { | ||
| None |
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I don't believe this shortcut is correct. It introduces a bug.
Before this change, this works:
let vec = vector![1, 2, 3];
let mut iter = vec.iter();
assert_eq!(iter.nth(3), None);
assert_eq!(iter.next(), None);Afterwards, it panics because the call to next() returns Some(1).
Since the implementation of next() already has a check for exhaustion, I would remove this if altogether and replace it with its else case.
| impl<'a, A: Clone> ExactSizeIterator for Iter<'a, A> {} | ||
| impl<'a, A: Clone> ExactSizeIterator for Iter<'a, A> { | ||
| fn len(&self) -> usize { | ||
| self.back_index - self.front_index |
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What if this underflows?
Suggested change
| self.back_index - self.front_index | |
| self.back_index.saturating_sub(self.front_index) |
| impl<'a, A: Clone> ExactSizeIterator for IterMut<'a, A> {} | ||
| impl<'a, A: Clone> ExactSizeIterator for IterMut<'a, A> { | ||
| fn len(&self) -> usize { | ||
| self.back_index - self.front_index |
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Suggested change
| self.back_index - self.front_index | |
| self.back_index.saturing_sub(self.front_index) |
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| impl<'a, A: Clone> ExactSizeIterator for Chunks<'a, A> { | ||
| fn len(&self) -> usize { | ||
| self.back_index - self.front_index |
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Suggested change
| self.back_index - self.front_index | |
| self.back_index.saturing_sub(self.front_index) |
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| impl<'a, A: Clone> ExactSizeIterator for ChunksMut<'a, A> { | ||
| fn len(&self) -> usize { | ||
| self.back_index - self.front_index |
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Suggested change
| self.back_index - self.front_index | |
| self.back_index.saturing_sub(self.front_index) |
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In particular provided implementations of
len,count,nth, andnth_backforIter,IterMut,Chunks,ChunksMutthat make use offront_indexandback_indexto improve performance.Similar work might also be useful for
ConsumingIter, but I couldn't easily trace that code to see where/if such improvements would make sense.