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use std::iter::{Enumerate, ExactSizeIterator};
pub(crate) struct EnumerateAndAdjust<I> {
enumerate: Enumerate<I>,
gap_pos: usize,
gap_len: usize,
}
impl<I> Iterator for EnumerateAndAdjust<I>
where
I: Iterator,
{
type Item = (usize, <I as Iterator>::Item);
fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
self.enumerate
.next()
.map(|(i, elem)| (if i < self.gap_pos { i } else { i + self.gap_len }, elem))
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.enumerate.size_hint()
}
}
pub(crate) trait EnumerateAndAdjustIterator {
fn enumerate_and_adjust(
self,
expected_len: usize,
gap_pos: Option<usize>,
) -> EnumerateAndAdjust<Self>
where
Self: Sized;
}
impl<T: ExactSizeIterator> EnumerateAndAdjustIterator for T {
fn enumerate_and_adjust(
self,
expected_len: usize,
gap_pos: Option<usize>,
) -> EnumerateAndAdjust<Self>
where
Self: Sized,
{
let actual_len = self.len();
EnumerateAndAdjust {
enumerate: self.enumerate(),
gap_pos: gap_pos.unwrap_or(expected_len),
gap_len: expected_len - actual_len,
}
}
}
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