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Undo the Sized specialization from Iterator::nth #46074

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Merged
merged 1 commit into from
Nov 19, 2017
Merged

Undo the Sized specialization from Iterator::nth #46074

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32 changes: 6 additions & 26 deletions src/libcore/iter/iterator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -253,8 +253,12 @@ pub trait Iterator {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn nth(&mut self, n: usize) -> Option<Self::Item> {
self.spec_nth(n)
fn nth(&mut self, mut n: usize) -> Option<Self::Item> {
for x in self {
if n == 0 { return Some(x) }
n -= 1;
}
None
}

/// Creates an iterator starting at the same point, but stepping by
Expand Down Expand Up @@ -2381,27 +2385,3 @@ impl<'a, I: Iterator + ?Sized> Iterator for &'a mut I {
(**self).nth(n)
}
}


trait SpecIterator : Iterator {
fn spec_nth(&mut self, n: usize) -> Option<Self::Item>;
}

impl<I: Iterator + ?Sized> SpecIterator for I {
default fn spec_nth(&mut self, mut n: usize) -> Option<Self::Item> {
for x in self {
if n == 0 { return Some(x) }
n -= 1;
}
None
}
}

impl<I: Iterator + Sized> SpecIterator for I {
fn spec_nth(&mut self, n: usize) -> Option<Self::Item> {
self.try_fold(n, move |i, x| {
if i == 0 { LoopState::Break(x) }
else { LoopState::Continue(i - 1) }
}).break_value()
}
}