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Range iteration specialization: remove trivial bounds #124380

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merged 1 commit into from
Apr 25, 2024
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Range iteration specialization: remove trivial bounds #124380

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20 changes: 7 additions & 13 deletions library/core/src/iter/adapters/step_by.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -515,9 +515,7 @@ macro_rules! spec_int_ranges_r {
unsafe impl StepByBackImpl<Range<$t>> for StepBy<Range<$t>> {

#[inline]
fn spec_next_back(&mut self) -> Option<Self::Item>
where Range<$t>: DoubleEndedIterator + ExactSizeIterator,
{
fn spec_next_back(&mut self) -> Option<Self::Item> {
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@compiler-errors compiler-errors Apr 25, 2024 •
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Forgetting a bound here is sound because we already validate for method compatibility in compare_method_predicate_entailment.

But in this case the bound is not forgotten -- it's just trivial.

let step = self.original_step().get() as $t;
let remaining = self.iter.end;
if remaining > 0 {
Expand All @@ -533,9 +531,7 @@ macro_rules! spec_int_ranges_r {
// We have to repeat them here so that the specialization overrides the StepByImplBack defaults

#[inline]
fn spec_nth_back(&mut self, n: usize) -> Option<Self::Item>
where Self: DoubleEndedIterator,
{
fn spec_nth_back(&mut self, n: usize) -> Option<Self::Item> {
if self.advance_back_by(n).is_err() {
return None;
}
Expand All @@ -544,10 +540,9 @@ macro_rules! spec_int_ranges_r {

#[inline]
fn spec_try_rfold<Acc, F, R>(&mut self, init: Acc, mut f: F) -> R
where
Self: DoubleEndedIterator,
F: FnMut(Acc, Self::Item) -> R,
R: Try<Output = Acc>
where
F: FnMut(Acc, Self::Item) -> R,
R: Try<Output = Acc>
{
let mut accum = init;
while let Some(x) = self.next_back() {
Expand All @@ -558,9 +553,8 @@ macro_rules! spec_int_ranges_r {

#[inline]
fn spec_rfold<Acc, F>(mut self, init: Acc, mut f: F) -> Acc
where
Self: DoubleEndedIterator,
F: FnMut(Acc, Self::Item) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc
{
let mut accum = init;
while let Some(x) = self.next_back() {
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