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use crate::cmp;
use crate::fmt::{self, Debug};
use crate::iter::{FusedIterator, TrustedFused};
use crate::iter::{InPlaceIterable, SourceIter, TrustedLen, UncheckedIterator};
use crate::num::NonZeroUsize;
/// An iterator that iterates two other iterators simultaneously.
///
/// This `struct` is created by [`zip`] or [`Iterator::zip`].
/// See their documentation for more.
#[derive(Clone)]
#[must_use = "iterators are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Zip<A, B> {
a: A,
b: B,
// index, len and a_len are only used by the specialized version of zip
index: usize,
len: usize,
a_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
}
}
/// Converts the arguments to iterators and zips them.
///
/// See the documentation of [`Iterator::zip`] for more.
///
/// # Examples
///
/// ```
/// use std::iter::zip;
///
/// let xs = [1, 2, 3];
/// let ys = [4, 5, 6];
///
/// let mut iter = zip(xs, ys);
///
/// assert_eq!(iter.next().unwrap(), (1, 4));
/// assert_eq!(iter.next().unwrap(), (2, 5));
/// assert_eq!(iter.next().unwrap(), (3, 6));
/// assert!(iter.next().is_none());
///
/// // Nested zips are also possible:
/// let zs = [7, 8, 9];
///
/// let mut iter = zip(zip(xs, ys), zs);
///
/// assert_eq!(iter.next().unwrap(), ((1, 4), 7));
/// assert_eq!(iter.next().unwrap(), ((2, 5), 8));
/// assert_eq!(iter.next().unwrap(), ((3, 6), 9));
/// assert!(iter.next().is_none());
/// ```
#[stable(feature = "iter_zip", since = "1.59.0")]
pub fn zip<A, B>(a: A, b: B) -> Zip<A::IntoIter, B::IntoIter>
where
A: IntoIterator,
B: IntoIterator,
{
ZipImpl::new(a.into_iter(), b.into_iter())
}
#[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]
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]
fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
ZipImpl::fold(self, init, f)
}
#[inline]
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
where
Self: TrustedRandomAccessNoCoerce,
{
// SAFETY: `ZipImpl::__iterator_get_unchecked` has same safety
// requirements as `Iterator::__iterator_get_unchecked`.
unsafe { ZipImpl::get_unchecked(self, idx) }
}
}
#[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)
}
}
// Zip specialization trait
#[doc(hidden)]
trait ZipImpl<A, B> {
type Item;
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;
fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc;
// 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 + TrustedRandomAccessNoCoerce;
}
// Work around limitations of specialization, requiring `default` impls to be repeated
// in intermediary impls.
macro_rules! zip_impl_general_defaults {
() => {
default fn new(a: A, b: B) -> Self {
Zip {
a,
b,
index: 0, // unused
len: 0, // unused
a_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)
}
#[inline]
default fn next_back(&mut self) -> Option<(A::Item, B::Item)>
where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,
{
// The function body below only uses `self.a/b.len()` and `self.a/b.next_back()`
// and doesn’t call `next_back` too often, so this implementation is safe in
// the `TrustedRandomAccessNoCoerce` specialization
let a_sz = self.a.len();
let b_sz = self.b.len();
if a_sz != b_sz {
// Adjust a, b to equal length
if a_sz > b_sz {
for _ in 0..a_sz - b_sz {
self.a.next_back();
}
} else {
for _ in 0..b_sz - a_sz {
self.b.next_back();
}
}
}
match (self.a.next_back(), self.b.next_back()) {
(Some(x), Some(y)) => Some((x, y)),
(None, None) => None,
_ => unreachable!(),
}
}
};
}
// General Zip impl
#[doc(hidden)]
impl<A, B> ZipImpl<A, B> for Zip<A, B>
where
A: Iterator,
B: Iterator,
{
type Item = (A::Item, B::Item);
zip_impl_general_defaults! {}
#[inline]
default fn size_hint(&self) -> (usize, Option<usize>) {
let (a_lower, a_upper) = self.a.size_hint();
let (b_lower, b_upper) = self.b.size_hint();
let lower = cmp::min(a_lower, b_lower);
let upper = match (a_upper, b_upper) {
(Some(x), Some(y)) => Some(cmp::min(x, y)),
(Some(x), None) => Some(x),
(None, Some(y)) => Some(y),
(None, None) => None,
};
(lower, upper)
}
default unsafe fn get_unchecked(&mut self, _idx: usize) -> <Self as Iterator>::Item
where
Self: TrustedRandomAccessNoCoerce,
{
unreachable!("Always specialized");
}
#[inline]
default fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
SpecFold::spec_fold(self, init, f)
}
}
#[doc(hidden)]
impl<A, B> ZipImpl<A, B> for Zip<A, B>
where
A: TrustedRandomAccessNoCoerce + Iterator,
B: TrustedRandomAccessNoCoerce + Iterator,
{
zip_impl_general_defaults! {}
#[inline]
default fn size_hint(&self) -> (usize, Option<usize>) {
let size = cmp::min(self.a.size(), self.b.size());
(size, Some(size))
}
#[inline]
unsafe fn 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`.
unsafe { (self.a.__iterator_get_unchecked(idx), self.b.__iterator_get_unchecked(idx)) }
}
#[inline]
fn fold<Acc, F>(mut self, init: Acc, mut f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
let mut accum = init;
let len = ZipImpl::size_hint(&self).0;
for i in 0..len {
// SAFETY: since Self: TrustedRandomAccessNoCoerce we can trust the size-hint to
// calculate the length and then use that to do unchecked iteration.
// fold consumes the iterator so we don't need to fixup any state.
unsafe {
accum = f(accum, self.get_unchecked(i));
}
}
accum
}
}
#[doc(hidden)]
impl<A, B> ZipImpl<A, B> for Zip<A, B>
where
A: TrustedRandomAccess + Iterator,
B: TrustedRandomAccess + Iterator,
{
fn new(a: A, b: B) -> Self {
let a_len = a.size();
let len = cmp::min(a_len, b.size());
Zip { a, b, index: 0, len, a_len }
}
#[inline]
fn next(&mut self) -> Option<(A::Item, B::Item)> {
if self.index < self.len {
let i = self.index;
// since get_unchecked executes code which can panic we increment the counters beforehand
// so that the same index won't be accessed twice, as required by TrustedRandomAccess
self.index += 1;
// SAFETY: `i` is smaller than `self.len`, thus smaller than `self.a.len()` and `self.b.len()`
unsafe {
Some((self.a.__iterator_get_unchecked(i), self.b.__iterator_get_unchecked(i)))
}
} else if A::MAY_HAVE_SIDE_EFFECT && self.index < self.a_len {
let i = self.index;
// as above, increment before executing code that may panic
self.index += 1;
self.len += 1;
// match the base implementation's potential side effects
// SAFETY: we just checked that `i` < `self.a.len()`
unsafe {
self.a.__iterator_get_unchecked(i);
}
None
} else {
None
}
}
#[inline]
fn size_hint(&self) -> (usize, Option<usize>) {
let len = self.len - self.index;
(len, Some(len))
}
#[inline]
fn nth(&mut self, n: usize) -> Option<Self::Item> {
let delta = cmp::min(n, self.len - self.index);
let end = self.index + delta;
while self.index < end {
let i = self.index;
// since get_unchecked executes code which can panic we increment the counters beforehand
// so that the same index won't be accessed twice, as required by TrustedRandomAccess
self.index += 1;
if A::MAY_HAVE_SIDE_EFFECT {
// SAFETY: the usage of `cmp::min` to calculate `delta`
// ensures that `end` is smaller than or equal to `self.len`,
// so `i` is also smaller than `self.len`.
unsafe {
self.a.__iterator_get_unchecked(i);
}
}
if B::MAY_HAVE_SIDE_EFFECT {
// SAFETY: same as above.
unsafe {
self.b.__iterator_get_unchecked(i);
}
}
}
self.super_nth(n - delta)
}
#[inline]
fn next_back(&mut self) -> Option<(A::Item, B::Item)>
where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,
{
if A::MAY_HAVE_SIDE_EFFECT || B::MAY_HAVE_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::MAY_HAVE_SIDE_EFFECT && sz_a > self.len {
for _ in 0..sz_a - self.len {
// since next_back() may panic we increment the counters beforehand
// to keep Zip's state in sync with the underlying iterator source
self.a_len -= 1;
self.a.next_back();
}
debug_assert_eq!(self.a_len, self.len);
}
let sz_b = self.b.size();
if B::MAY_HAVE_SIDE_EFFECT && sz_b > self.len {
for _ in 0..sz_b - self.len {
self.b.next_back();
}
}
}
}
if self.index < self.len {
// since get_unchecked executes code which can panic we increment the counters beforehand
// so that the same index won't be accessed twice, as required by TrustedRandomAccess
self.len -= 1;
self.a_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> ExactSizeIterator for Zip<A, B>
where
A: ExactSizeIterator,
B: ExactSizeIterator,
{
}
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<A, B> TrustedRandomAccess for Zip<A, B>
where
A: TrustedRandomAccess,
B: TrustedRandomAccess,
{
}
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<A, B> TrustedRandomAccessNoCoerce for Zip<A, B>
where
A: TrustedRandomAccessNoCoerce,
B: TrustedRandomAccessNoCoerce,
{
const MAY_HAVE_SIDE_EFFECT: bool = A::MAY_HAVE_SIDE_EFFECT || B::MAY_HAVE_SIDE_EFFECT;
}
#[stable(feature = "fused", since = "1.26.0")]
impl<A, B> FusedIterator for Zip<A, B>
where
A: FusedIterator,
B: FusedIterator,
{
}
#[unstable(issue = "none", feature = "trusted_fused")]
unsafe impl<A, B> TrustedFused for Zip<A, B>
where
A: TrustedFused,
B: TrustedFused,
{
}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<A, B> TrustedLen for Zip<A, B>
where
A: TrustedLen,
B: TrustedLen,
{
}
impl<A, B> UncheckedIterator for Zip<A, B>
where
A: UncheckedIterator,
B: UncheckedIterator,
{
}
// Arbitrarily selects the left side of the zip iteration as extractable "source"
// it would require negative trait bounds to be able to try both
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<A, B> SourceIter for Zip<A, B>
where
A: SourceIter,
{
type Source = A::Source;
#[inline]
unsafe fn as_inner(&mut self) -> &mut A::Source {
// SAFETY: unsafe function forwarding to unsafe function with the same requirements
unsafe { SourceIter::as_inner(&mut self.a) }
}
}
// Since SourceIter forwards the left hand side we do the same here
#[unstable(issue = "none", feature = "inplace_iteration")]
unsafe impl<A: InPlaceIterable, B> InPlaceIterable for Zip<A, B> {
const EXPAND_BY: Option<NonZeroUsize> = A::EXPAND_BY;
const MERGE_BY: Option<NonZeroUsize> = A::MERGE_BY;
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<A: Debug, B: Debug> Debug for Zip<A, B> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
ZipFmt::fmt(self, f)
}
}
trait ZipFmt<A, B> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result;
}
impl<A: Debug, B: Debug> ZipFmt<A, B> for Zip<A, B> {
default fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Zip").field("a", &self.a).field("b", &self.b).finish()
}
}
impl<A: Debug + TrustedRandomAccessNoCoerce, B: Debug + TrustedRandomAccessNoCoerce> ZipFmt<A, B>
for Zip<A, B>
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// It's *not safe* to call fmt on the contained iterators, since once
// we start iterating they're in strange, potentially unsafe, states.
f.debug_struct("Zip").finish()
}
}
/// An iterator whose items are random-accessible efficiently
///
/// # Safety
///
/// The iterator's `size_hint` must be exact and cheap to call.
///
/// `TrustedRandomAccessNoCoerce::size` may not be overridden.
///
/// All subtypes and all supertypes of `Self` must also implement `TrustedRandomAccess`.
/// In particular, this means that types with non-invariant parameters usually can not have
/// an impl for `TrustedRandomAccess` that depends on any trait bounds on such parameters, except
/// for bounds that come from the respective struct/enum definition itself, or bounds involving
/// traits that themselves come with a guarantee similar to this one.
///
/// If `Self: ExactSizeIterator` then `self.len()` must always produce results consistent
/// with `self.size()`.
///
/// If `Self: Iterator`, then `<Self as Iterator>::__iterator_get_unchecked(&mut self, idx)`
/// must be safe to call provided the following conditions are met.
///
/// 1. `0 <= idx` and `idx < self.size()`.
/// 2. If `Self: !Clone`, then `self.__iterator_get_unchecked(idx)` is never called with the same
/// index on `self` more than once.
/// 3. After `self.__iterator_get_unchecked(idx)` has been called, then `self.next_back()` will
/// only be called at most `self.size() - idx - 1` times. If `Self: Clone` and `self` is cloned,
/// then this number is calculated for `self` and its clone individually,
/// but `self.next_back()` calls that happened before the cloning count for both `self` and the clone.
/// 4. After `self.__iterator_get_unchecked(idx)` has been called, then only the following methods
/// will be called on `self` or on any new clones of `self`:
/// * `std::clone::Clone::clone`
/// * `std::iter::Iterator::size_hint`
/// * `std::iter::DoubleEndedIterator::next_back`
/// * `std::iter::ExactSizeIterator::len`
/// * `std::iter::Iterator::__iterator_get_unchecked`
/// * `std::iter::TrustedRandomAccessNoCoerce::size`
/// 5. If `T` is a subtype of `Self`, then `self` is allowed to be coerced
/// to `T`. If `self` is coerced to `T` after `self.__iterator_get_unchecked(idx)` has already
/// been called, then no methods except for the ones listed under 4. are allowed to be called
/// on the resulting value of type `T`, either. Multiple such coercion steps are allowed.
/// Regarding 2. and 3., the number of times `__iterator_get_unchecked(idx)` or `next_back()` is
/// called on `self` and the resulting value of type `T` (and on further coercion results with
/// sub-subtypes) are added together and their sums must not exceed the specified bounds.
///
/// Further, given that these conditions are met, it must guarantee that:
///
/// * It does not change the value returned from `size_hint`
/// * It must be safe to call the methods listed above on `self` after calling
/// `self.__iterator_get_unchecked(idx)`, assuming that the required traits are implemented.
/// * It must also be safe to drop `self` after calling `self.__iterator_get_unchecked(idx)`.
/// * If `T` is a subtype of `Self`, then it must be safe to coerce `self` to `T`.
//
// FIXME: Clarify interaction with SourceIter/InPlaceIterable. Calling `SourceIter::as_inner`
// after `__iterator_get_unchecked` is supposed to be allowed.
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
#[rustc_specialization_trait]
pub unsafe trait TrustedRandomAccess: TrustedRandomAccessNoCoerce {}
/// Like [`TrustedRandomAccess`] but without any of the requirements / guarantees around
/// coercions to subtypes after `__iterator_get_unchecked` (they aren’t allowed here!), and
/// without the requirement that subtypes / supertypes implement `TrustedRandomAccessNoCoerce`.
///
/// This trait was created in PR #85874 to fix soundness issue #85873 without performance regressions.
/// It is subject to change as we might want to build a more generally useful (for performance
/// optimizations) and more sophisticated trait or trait hierarchy that replaces or extends
/// [`TrustedRandomAccess`] and `TrustedRandomAccessNoCoerce`.
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
#[rustc_specialization_trait]
pub unsafe trait TrustedRandomAccessNoCoerce: Sized {
// Convenience method.
fn size(&self) -> usize
where
Self: Iterator,
{
self.size_hint().0
}
/// `true` if getting an iterator element may have side effects.
/// Remember to take inner iterators into account.
const MAY_HAVE_SIDE_EFFECT: bool;
}
/// Like `Iterator::__iterator_get_unchecked`, but doesn't require the compiler to
/// know that `U: TrustedRandomAccess`.
///
/// ## Safety
///
/// Same requirements calling `get_unchecked` directly.
#[doc(hidden)]
#[inline]
pub(in crate::iter::adapters) unsafe fn try_get_unchecked<I>(it: &mut I, idx: usize) -> I::Item
where
I: Iterator,
{
// SAFETY: the caller must uphold the contract for
// `Iterator::__iterator_get_unchecked`.
unsafe { it.try_get_unchecked(idx) }
}
unsafe trait SpecTrustedRandomAccess: Iterator {
/// If `Self: TrustedRandomAccess`, it must be safe to call
/// `Iterator::__iterator_get_unchecked(self, index)`.
unsafe fn try_get_unchecked(&mut self, index: usize) -> Self::Item;
}
unsafe impl<I: Iterator> SpecTrustedRandomAccess for I {
default unsafe fn try_get_unchecked(&mut self, _: usize) -> Self::Item {
panic!("Should only be called on TrustedRandomAccess iterators");
}
}
unsafe impl<I: Iterator + TrustedRandomAccessNoCoerce> SpecTrustedRandomAccess for I {
#[inline]
unsafe fn try_get_unchecked(&mut self, index: usize) -> Self::Item {
// SAFETY: the caller must uphold the contract for
// `Iterator::__iterator_get_unchecked`.
unsafe { self.__iterator_get_unchecked(index) }
}
}
trait SpecFold: Iterator {
fn spec_fold<B, F>(self, init: B, f: F) -> B
where
Self: Sized,
F: FnMut(B, Self::Item) -> B;
}
impl<A: Iterator, B: Iterator> SpecFold for Zip<A, B> {
// Adapted from default impl from the Iterator trait
#[inline]
default fn spec_fold<Acc, F>(mut self, init: Acc, mut f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
let mut accum = init;
while let Some(x) = ZipImpl::next(&mut self) {
accum = f(accum, x);
}
accum
}
}
impl<A: TrustedLen, B: TrustedLen> SpecFold for Zip<A, B> {
#[inline]
fn spec_fold<Acc, F>(mut self, init: Acc, mut f: F) -> Acc
where
F: FnMut(Acc, Self::Item) -> Acc,
{
let mut accum = init;
loop {
let (upper, more) = if let Some(upper) = ZipImpl::size_hint(&self).1 {
(upper, false)
} else {
// Per TrustedLen contract a None upper bound means more than usize::MAX items
(usize::MAX, true)
};
for _ in 0..upper {
let pair =
// SAFETY: TrustedLen guarantees that at least `upper` many items are available
// therefore we know they can't be None
unsafe { (self.a.next().unwrap_unchecked(), self.b.next().unwrap_unchecked()) };
accum = f(accum, pair);
}
if !more {
break;
}
}
accum
}
}