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Use internal iteration in Iterator::is_sorted_by #82198

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Feb 17, 2021
Merged

Use internal iteration in Iterator::is_sorted_by #82198

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25 changes: 16 additions & 9 deletions library/core/src/iter/traits/iterator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3317,24 +3317,31 @@ pub trait Iterator {
///
/// [`is_sorted`]: Iterator::is_sorted
#[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
fn is_sorted_by<F>(mut self, mut compare: F) -> bool
fn is_sorted_by<F>(mut self, compare: F) -> bool
where
Self: Sized,
F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering>,
{
#[inline]
fn check<'a, T>(
last: &'a mut T,
mut compare: impl FnMut(&T, &T) -> Option<Ordering> + 'a,
) -> impl FnMut(T) -> bool + 'a {
move |curr| {
if let Some(Ordering::Greater) | None = compare(&last, &curr) {
return false;
}
*last = curr;
true
}
}

let mut last = match self.next() {
Some(e) => e,
None => return true,
};

while let Some(curr) = self.next() {
if let Some(Ordering::Greater) | None = compare(&last, &curr) {
return false;
}
last = curr;
}

true
self.all(check(&mut last, compare))
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Seems like it'd be cleaner to just use a closure.

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All the other Iterator's methods use separate functions like that, I guess to reduce generics bloat.

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@sfackler sfackler Feb 16, 2021 •
edited
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Oh right, it avoids an extra implicit parameter of the actual iterator type I guess?

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This is a really good use case for #77960.

}

/// Checks if the elements of this iterator are sorted using the given key extraction
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