Boost intersperse(_with) performance
I did some benchmark digging into the `intersperse` and `intersperse_with` code as part of the https://internals.rust-lang.org/t/add-iterate-with-separators-iterator-function/18781/13 discussion, and as a result I optimized them a bit, without relying on the peekable iterator.
This commit is contained in:
Yuri Astrakhan
parent
5bd5d214ef
commit
f9259d1b73
@ -1,4 +1,5 @@
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use super::Peekable;
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use core::fmt;
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use core::iter::{Fuse, FusedIterator};
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/// An iterator adapter that places a separator between all elements.
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///
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@ -11,8 +12,16 @@ where
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I::Item: Clone,
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{
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separator: I::Item,
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iter: Peekable<I>,
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needs_sep: bool,
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next_item: Option<I::Item>,
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iter: Fuse<I>,
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}
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#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
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impl<I> FusedIterator for Intersperse<I>
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where
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I: FusedIterator,
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I::Item: Clone,
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{
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}
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impl<I: Iterator> Intersperse<I>
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@ -20,7 +29,8 @@ where
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I::Item: Clone,
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{
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pub(in crate::iter) fn new(iter: I, separator: I::Item) -> Self {
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Self { iter: iter.peekable(), separator, needs_sep: false }
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let mut iter = iter.fuse();
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Self { separator, next_item: iter.next(), iter }
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}
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}
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@ -33,27 +43,31 @@ where
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type Item = I::Item;
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#[inline]
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fn next(&mut self) -> Option<I::Item> {
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if self.needs_sep && self.iter.peek().is_some() {
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self.needs_sep = false;
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Some(self.separator.clone())
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fn next(&mut self) -> Option<Self::Item> {
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if let Some(v) = self.next_item.take() {
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Some(v)
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} else {
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self.needs_sep = true;
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self.iter.next()
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let next_item = self.iter.next();
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if next_item.is_some() {
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self.next_item = next_item;
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Some(self.separator.clone())
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} else {
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None
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}
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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intersperse_size_hint(&self.iter, self.next_item.is_some())
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}
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fn fold<B, F>(self, init: B, f: F) -> B
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where
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Self: Sized,
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F: FnMut(B, Self::Item) -> B,
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{
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let separator = self.separator;
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intersperse_fold(self.iter, init, f, move || separator.clone(), self.needs_sep)
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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intersperse_size_hint(&self.iter, self.needs_sep)
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intersperse_fold(self.iter, init, f, move || separator.clone(), self.next_item)
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}
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}
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@ -67,38 +81,46 @@ where
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I: Iterator,
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{
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separator: G,
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iter: Peekable<I>,
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needs_sep: bool,
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next_item: Option<I::Item>,
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iter: Fuse<I>,
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}
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#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
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impl<I, G> crate::fmt::Debug for IntersperseWith<I, G>
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impl<I, G> FusedIterator for IntersperseWith<I, G>
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where
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I: Iterator + crate::fmt::Debug,
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I::Item: crate::fmt::Debug,
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G: crate::fmt::Debug,
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I: FusedIterator,
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G: FnMut() -> I::Item,
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{
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fn fmt(&self, f: &mut crate::fmt::Formatter<'_>) -> crate::fmt::Result {
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}
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#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
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impl<I, G> fmt::Debug for IntersperseWith<I, G>
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where
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I: Iterator + fmt::Debug,
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I::Item: fmt::Debug,
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G: fmt::Debug,
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{
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_struct("IntersperseWith")
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.field("separator", &self.separator)
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.field("iter", &self.iter)
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.field("needs_sep", &self.needs_sep)
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.field("next_item", &self.next_item)
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.finish()
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}
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}
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#[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
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impl<I, G> crate::clone::Clone for IntersperseWith<I, G>
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impl<I, G> Clone for IntersperseWith<I, G>
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where
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I: Iterator + crate::clone::Clone,
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I::Item: crate::clone::Clone,
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I: Iterator + Clone,
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I::Item: Clone,
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G: Clone,
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{
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fn clone(&self) -> Self {
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IntersperseWith {
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Self {
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separator: self.separator.clone(),
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iter: self.iter.clone(),
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needs_sep: self.needs_sep.clone(),
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next_item: self.next_item.clone(),
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}
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}
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}
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@ -109,7 +131,8 @@ where
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G: FnMut() -> I::Item,
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{
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pub(in crate::iter) fn new(iter: I, separator: G) -> Self {
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Self { iter: iter.peekable(), separator, needs_sep: false }
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let mut iter = iter.fuse();
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Self { separator, next_item: iter.next(), iter }
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}
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}
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@ -122,47 +145,50 @@ where
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type Item = I::Item;
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#[inline]
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fn next(&mut self) -> Option<I::Item> {
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if self.needs_sep && self.iter.peek().is_some() {
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self.needs_sep = false;
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Some((self.separator)())
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fn next(&mut self) -> Option<Self::Item> {
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if let Some(v) = self.next_item.take() {
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Some(v)
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} else {
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self.needs_sep = true;
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self.iter.next()
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let next_item = self.iter.next();
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if next_item.is_some() {
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self.next_item = next_item;
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Some((self.separator)())
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} else {
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None
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}
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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intersperse_size_hint(&self.iter, self.next_item.is_some())
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}
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fn fold<B, F>(self, init: B, f: F) -> B
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where
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Self: Sized,
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F: FnMut(B, Self::Item) -> B,
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{
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intersperse_fold(self.iter, init, f, self.separator, self.needs_sep)
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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intersperse_size_hint(&self.iter, self.needs_sep)
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intersperse_fold(self.iter, init, f, self.separator, self.next_item)
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}
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}
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fn intersperse_size_hint<I>(iter: &I, needs_sep: bool) -> (usize, Option<usize>)
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fn intersperse_size_hint<I>(iter: &I, next_is_elem: bool) -> (usize, Option<usize>)
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where
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I: Iterator,
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{
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let (lo, hi) = iter.size_hint();
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let next_is_elem = !needs_sep;
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(
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lo.saturating_sub(next_is_elem as usize).saturating_add(lo),
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hi.and_then(|hi| hi.saturating_sub(next_is_elem as usize).checked_add(hi)),
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lo.saturating_add(next_is_elem as usize).saturating_add(lo),
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hi.map(|hi| hi.saturating_add(next_is_elem as usize).saturating_add(hi)),
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)
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}
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fn intersperse_fold<I, B, F, G>(
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mut iter: I,
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iter: I,
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init: B,
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mut f: F,
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mut separator: G,
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needs_sep: bool,
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mut next_item: Option<I::Item>,
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) -> B
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where
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I: Iterator,
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@ -171,12 +197,8 @@ where
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{
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let mut accum = init;
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if !needs_sep {
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if let Some(x) = iter.next() {
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accum = f(accum, x);
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} else {
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return accum;
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}
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if let Some(x) = next_item.take() {
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accum = f(accum, x);
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}
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iter.fold(accum, |mut accum, x| {
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