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Rollup merge of rust-lang#79173 - DeveloperC286:zip_nth_cleanup, r=ke…
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…nnytm

refactor: removing custom nth Zip fn

Noticed `super_nth()` that seems very similar to `nth()` in `iterator.rs`.

If you look at `nth()` in `iterator.rs` before the commit `ecacc7534b6bf50205c37c89402565b82d95a257`  `super_nth()` looks exactly the same as `fn nth()` in `iterator.rs`.

I may be misunderstanding something, but I think `super_nth()` can just be removed.
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@henryboisdequin
henryboisdequin committed Jan 29, 2021
2 parents 24d2e9a + 152f500 commit 98d7686
Showing 1 changed file with 95 additions and 134 deletions.
229 changes: 95 additions & 134 deletions library/core/src/iter/adapters/zip.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,93 +17,33 @@ pub struct Zip<A, B> {
index: usize,
len: usize,
}
impl<A: Iterator, B: Iterator> Zip<A, B> {
pub(in crate::iter) fn new(a: A, b: B) -> Zip<A, B> {
ZipImpl::new(a, b)
}
fn super_nth(&mut self, mut n: usize) -> Option<(A::Item, B::Item)> {
while let Some(x) = Iterator::next(self) {
if n == 0 {
return Some(x);
}
n -= 1;
}
None
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> Iterator for Zip<A, B>
impl<A, B> Zip<A, B>
where
A: Iterator,
B: Iterator,
{
type Item = (A::Item, B::Item);

#[inline]
fn next(&mut self) -> Option<Self::Item> {
ZipImpl::next(self)
}

#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
ZipImpl::size_hint(self)
}

#[inline]
fn nth(&mut self, n: usize) -> Option<Self::Item> {
ZipImpl::nth(self, n)
}

#[inline]
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
where
Self: TrustedRandomAccess,
{
// SAFETY: `ZipImpl::__iterator_get_unchecked` has same safety
// requirements as `Iterator::__iterator_get_unchecked`.
unsafe { ZipImpl::get_unchecked(self, idx) }
pub(in crate::iter) fn new(a: A, b: B) -> Zip<A, B> {
ZipNew::new(a, b)
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> DoubleEndedIterator for Zip<A, B>
where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,
{
#[inline]
fn next_back(&mut self) -> Option<(A::Item, B::Item)> {
ZipImpl::next_back(self)
fn super_nth(&mut self, n: usize) -> Option<(A::Item, B::Item)> {
self.advance_by(n).ok()?;
self.next()
}
}

// Zip specialization trait
#[doc(hidden)]
trait ZipImpl<A, B> {
type Item;
trait ZipNew<A, B> {
fn new(a: A, b: B) -> Self;
fn next(&mut self) -> Option<Self::Item>;
fn size_hint(&self) -> (usize, Option<usize>);
fn nth(&mut self, n: usize) -> Option<Self::Item>;
fn next_back(&mut self) -> Option<Self::Item>
where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator;
// This has the same safety requirements as `Iterator::__iterator_get_unchecked`
unsafe fn get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item
where
Self: Iterator + TrustedRandomAccess;
}

// General Zip impl
#[doc(hidden)]
impl<A, B> ZipImpl<A, B> for Zip<A, B>
impl<A, B> ZipNew<A, B> for Zip<A, B>
where
A: Iterator,
B: Iterator,
{
type Item = (A::Item, B::Item);
default fn new(a: A, b: B) -> Self {
Zip {
a,
Expand All @@ -112,25 +52,28 @@ where
len: 0, // unused
}
}
}

#[inline]
default fn next(&mut self) -> Option<(A::Item, B::Item)> {
let x = self.a.next()?;
let y = self.b.next()?;
Some((x, y))
}

#[inline]
default fn nth(&mut self, n: usize) -> Option<Self::Item> {
self.super_nth(n)
#[doc(hidden)]
impl<A, B> ZipNew<A, B> for Zip<A, B>
where
A: TrustedRandomAccess + Iterator,
B: TrustedRandomAccess + Iterator,
{
fn new(a: A, b: B) -> Self {
let len = cmp::min(a.size(), b.size());
Zip { a, b, index: 0, len }
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> DoubleEndedIterator for Zip<A, B>
where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,
{
#[inline]
default fn next_back(&mut self) -> Option<(A::Item, B::Item)>
where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,
{
default fn next_back(&mut self) -> Option<(A::Item, B::Item)> {
let a_sz = self.a.len();
let b_sz = self.b.len();
if a_sz != b_sz {
Expand All @@ -151,6 +94,71 @@ where
_ => unreachable!(),
}
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> DoubleEndedIterator for Zip<A, B>
where
A: TrustedRandomAccess + DoubleEndedIterator + ExactSizeIterator,
B: TrustedRandomAccess + DoubleEndedIterator + ExactSizeIterator,
{
#[inline]
fn next_back(&mut self) -> Option<(A::Item, B::Item)> {
let a_side_effect = A::may_have_side_effect();
let b_side_effect = B::may_have_side_effect();
if a_side_effect || b_side_effect {
let sz_a = self.a.size();
let sz_b = self.b.size();
// Adjust a, b to equal length, make sure that only the first call
// of `next_back` does this, otherwise we will break the restriction
// on calls to `self.next_back()` after calling `get_unchecked()`.
if sz_a != sz_b {
if a_side_effect && sz_a > self.len {
for _ in 0..sz_a - cmp::max(self.len, self.index) {
self.a.next_back();
}
}

if b_side_effect && sz_b > self.len {
for _ in 0..sz_b - self.len {
self.b.next_back();
}
}
}
}
if self.index < self.len {
self.len -= 1;
let i = self.len;
// SAFETY: `i` is smaller than the previous value of `self.len`,
// which is also smaller than or equal to `self.a.len()` and `self.b.len()`
unsafe {
Some((self.a.__iterator_get_unchecked(i), self.b.__iterator_get_unchecked(i)))
}
} else {
None
}
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> Iterator for Zip<A, B>
where
A: Iterator,
B: Iterator,
{
type Item = (A::Item, B::Item);

#[inline]
default fn next(&mut self) -> Option<(A::Item, B::Item)> {
let x = self.a.next()?;
let y = self.b.next()?;
Some((x, y))
}

#[inline]
default fn nth(&mut self, n: usize) -> Option<Self::Item> {
self.super_nth(n)
}

#[inline]
default fn size_hint(&self) -> (usize, Option<usize>) {
Expand All @@ -169,25 +177,20 @@ where
(lower, upper)
}

default unsafe fn get_unchecked(&mut self, _idx: usize) -> <Self as Iterator>::Item
default unsafe fn __iterator_get_unchecked(&mut self, _idx: usize) -> <Self as Iterator>::Item
where
Self: TrustedRandomAccess,
{
unreachable!("Always specialized");
}
}

#[doc(hidden)]
impl<A, B> ZipImpl<A, B> for Zip<A, B>
#[stable(feature = "rust1", since = "1.0.0")]
impl<A, B> Iterator for Zip<A, B>
where
A: TrustedRandomAccess + Iterator,
B: TrustedRandomAccess + Iterator,
{
fn new(a: A, b: B) -> Self {
let len = cmp::min(a.size(), b.size());
Zip { a, b, index: 0, len }
}

#[inline]
fn next(&mut self) -> Option<(A::Item, B::Item)> {
if self.index < self.len {
Expand Down Expand Up @@ -243,49 +246,7 @@ where
}

#[inline]
fn next_back(&mut self) -> Option<(A::Item, B::Item)>
where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,
{
let a_side_effect = A::may_have_side_effect();
let b_side_effect = B::may_have_side_effect();
if a_side_effect || b_side_effect {
let sz_a = self.a.size();
let sz_b = self.b.size();
// Adjust a, b to equal length, make sure that only the first call
// of `next_back` does this, otherwise we will break the restriction
// on calls to `self.next_back()` after calling `get_unchecked()`.
if sz_a != sz_b {
let sz_a = self.a.size();
if a_side_effect && sz_a > self.len {
for _ in 0..sz_a - cmp::max(self.len, self.index) {
self.a.next_back();
}
}
let sz_b = self.b.size();
if b_side_effect && sz_b > self.len {
for _ in 0..sz_b - self.len {
self.b.next_back();
}
}
}
}
if self.index < self.len {
self.len -= 1;
let i = self.len;
// SAFETY: `i` is smaller than the previous value of `self.len`,
// which is also smaller than or equal to `self.a.len()` and `self.b.len()`
unsafe {
Some((self.a.__iterator_get_unchecked(i), self.b.__iterator_get_unchecked(i)))
}
} else {
None
}
}

#[inline]
unsafe fn get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item {
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item {
let idx = self.index + idx;
// SAFETY: the caller must uphold the contract for
// `Iterator::__iterator_get_unchecked`.
Expand Down

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