2 use crate::fmt::{self, Debug};
3 use crate::iter::{DoubleEndedIterator, ExactSizeIterator, FusedIterator, Iterator};
4 use crate::iter::{InPlaceIterable, SourceIter, TrustedLen};
6 /// An iterator that iterates two other iterators simultaneously.
8 /// This `struct` is created by [`zip`] or [`Iterator::zip`].
9 /// See their documentation for more.
11 #[must_use = "iterators are lazy and do nothing unless consumed"]
12 #[stable(feature = "rust1", since = "1.0.0")]
13 pub struct Zip<A, B> {
16 // index, len and a_len are only used by the specialized version of zip
21 impl<A: Iterator, B: Iterator> Zip<A, B> {
22 pub(in crate::iter) fn new(a: A, b: B) -> Zip<A, B> {
25 fn super_nth(&mut self, mut n: usize) -> Option<(A::Item, B::Item)> {
26 while let Some(x) = Iterator::next(self) {
36 /// Converts the arguments to iterators and zips them.
38 /// See the documentation of [`Iterator::zip`] for more.
43 /// use std::iter::zip;
45 /// let xs = [1, 2, 3];
46 /// let ys = [4, 5, 6];
48 /// let mut iter = zip(xs, ys);
50 /// assert_eq!(iter.next().unwrap(), (1, 4));
51 /// assert_eq!(iter.next().unwrap(), (2, 5));
52 /// assert_eq!(iter.next().unwrap(), (3, 6));
53 /// assert!(iter.next().is_none());
55 /// // Nested zips are also possible:
56 /// let zs = [7, 8, 9];
58 /// let mut iter = zip(zip(xs, ys), zs);
60 /// assert_eq!(iter.next().unwrap(), ((1, 4), 7));
61 /// assert_eq!(iter.next().unwrap(), ((2, 5), 8));
62 /// assert_eq!(iter.next().unwrap(), ((3, 6), 9));
63 /// assert!(iter.next().is_none());
65 #[stable(feature = "iter_zip", since = "1.59.0")]
66 pub fn zip<A, B>(a: A, b: B) -> Zip<A::IntoIter, B::IntoIter>
71 ZipImpl::new(a.into_iter(), b.into_iter())
74 #[stable(feature = "rust1", since = "1.0.0")]
75 impl<A, B> Iterator for Zip<A, B>
80 type Item = (A::Item, B::Item);
83 fn next(&mut self) -> Option<Self::Item> {
88 fn size_hint(&self) -> (usize, Option<usize>) {
89 ZipImpl::size_hint(self)
93 fn nth(&mut self, n: usize) -> Option<Self::Item> {
98 unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
100 Self: TrustedRandomAccessNoCoerce,
102 // SAFETY: `ZipImpl::__iterator_get_unchecked` has same safety
103 // requirements as `Iterator::__iterator_get_unchecked`.
104 unsafe { ZipImpl::get_unchecked(self, idx) }
108 #[stable(feature = "rust1", since = "1.0.0")]
109 impl<A, B> DoubleEndedIterator for Zip<A, B>
111 A: DoubleEndedIterator + ExactSizeIterator,
112 B: DoubleEndedIterator + ExactSizeIterator,
115 fn next_back(&mut self) -> Option<(A::Item, B::Item)> {
116 ZipImpl::next_back(self)
120 // Zip specialization trait
122 trait ZipImpl<A, B> {
124 fn new(a: A, b: B) -> Self;
125 fn next(&mut self) -> Option<Self::Item>;
126 fn size_hint(&self) -> (usize, Option<usize>);
127 fn nth(&mut self, n: usize) -> Option<Self::Item>;
128 fn next_back(&mut self) -> Option<Self::Item>
130 A: DoubleEndedIterator + ExactSizeIterator,
131 B: DoubleEndedIterator + ExactSizeIterator;
132 // This has the same safety requirements as `Iterator::__iterator_get_unchecked`
133 unsafe fn get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item
135 Self: Iterator + TrustedRandomAccessNoCoerce;
138 // Work around limitations of specialization, requiring `default` impls to be repeated
139 // in intermediary impls.
140 macro_rules! zip_impl_general_defaults {
142 default fn new(a: A, b: B) -> Self {
153 default fn next(&mut self) -> Option<(A::Item, B::Item)> {
154 let x = self.a.next()?;
155 let y = self.b.next()?;
160 default fn nth(&mut self, n: usize) -> Option<Self::Item> {
165 default fn next_back(&mut self) -> Option<(A::Item, B::Item)>
167 A: DoubleEndedIterator + ExactSizeIterator,
168 B: DoubleEndedIterator + ExactSizeIterator,
170 // The function body below only uses `self.a/b.len()` and `self.a/b.next_back()`
171 // and doesn’t call `next_back` too often, so this implementation is safe in
172 // the `TrustedRandomAccessNoCoerce` specialization
174 let a_sz = self.a.len();
175 let b_sz = self.b.len();
177 // Adjust a, b to equal length
179 for _ in 0..a_sz - b_sz {
183 for _ in 0..b_sz - a_sz {
188 match (self.a.next_back(), self.b.next_back()) {
189 (Some(x), Some(y)) => Some((x, y)),
190 (None, None) => None,
199 impl<A, B> ZipImpl<A, B> for Zip<A, B>
204 type Item = (A::Item, B::Item);
206 zip_impl_general_defaults! {}
209 default fn size_hint(&self) -> (usize, Option<usize>) {
210 let (a_lower, a_upper) = self.a.size_hint();
211 let (b_lower, b_upper) = self.b.size_hint();
213 let lower = cmp::min(a_lower, b_lower);
215 let upper = match (a_upper, b_upper) {
216 (Some(x), Some(y)) => Some(cmp::min(x, y)),
217 (Some(x), None) => Some(x),
218 (None, Some(y)) => Some(y),
219 (None, None) => None,
225 default unsafe fn get_unchecked(&mut self, _idx: usize) -> <Self as Iterator>::Item
227 Self: TrustedRandomAccessNoCoerce,
229 unreachable!("Always specialized");
234 impl<A, B> ZipImpl<A, B> for Zip<A, B>
236 A: TrustedRandomAccessNoCoerce + Iterator,
237 B: TrustedRandomAccessNoCoerce + Iterator,
239 zip_impl_general_defaults! {}
242 default fn size_hint(&self) -> (usize, Option<usize>) {
243 let size = cmp::min(self.a.size(), self.b.size());
248 unsafe fn get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item {
249 let idx = self.index + idx;
250 // SAFETY: the caller must uphold the contract for
251 // `Iterator::__iterator_get_unchecked`.
252 unsafe { (self.a.__iterator_get_unchecked(idx), self.b.__iterator_get_unchecked(idx)) }
257 impl<A, B> ZipImpl<A, B> for Zip<A, B>
259 A: TrustedRandomAccess + Iterator,
260 B: TrustedRandomAccess + Iterator,
262 fn new(a: A, b: B) -> Self {
263 let a_len = a.size();
264 let len = cmp::min(a_len, b.size());
265 Zip { a, b, index: 0, len, a_len }
269 fn next(&mut self) -> Option<(A::Item, B::Item)> {
270 if self.index < self.len {
272 // since get_unchecked executes code which can panic we increment the counters beforehand
273 // so that the same index won't be accessed twice, as required by TrustedRandomAccess
275 // SAFETY: `i` is smaller than `self.len`, thus smaller than `self.a.len()` and `self.b.len()`
277 Some((self.a.__iterator_get_unchecked(i), self.b.__iterator_get_unchecked(i)))
279 } else if A::MAY_HAVE_SIDE_EFFECT && self.index < self.a_len {
281 // as above, increment before executing code that may panic
284 // match the base implementation's potential side effects
285 // SAFETY: we just checked that `i` < `self.a.len()`
287 self.a.__iterator_get_unchecked(i);
296 fn size_hint(&self) -> (usize, Option<usize>) {
297 let len = self.len - self.index;
302 fn nth(&mut self, n: usize) -> Option<Self::Item> {
303 let delta = cmp::min(n, self.len - self.index);
304 let end = self.index + delta;
305 while self.index < end {
307 // since get_unchecked executes code which can panic we increment the counters beforehand
308 // so that the same index won't be accessed twice, as required by TrustedRandomAccess
310 if A::MAY_HAVE_SIDE_EFFECT {
311 // SAFETY: the usage of `cmp::min` to calculate `delta`
312 // ensures that `end` is smaller than or equal to `self.len`,
313 // so `i` is also smaller than `self.len`.
315 self.a.__iterator_get_unchecked(i);
318 if B::MAY_HAVE_SIDE_EFFECT {
319 // SAFETY: same as above.
321 self.b.__iterator_get_unchecked(i);
326 self.super_nth(n - delta)
330 fn next_back(&mut self) -> Option<(A::Item, B::Item)>
332 A: DoubleEndedIterator + ExactSizeIterator,
333 B: DoubleEndedIterator + ExactSizeIterator,
335 if A::MAY_HAVE_SIDE_EFFECT || B::MAY_HAVE_SIDE_EFFECT {
336 let sz_a = self.a.size();
337 let sz_b = self.b.size();
338 // Adjust a, b to equal length, make sure that only the first call
339 // of `next_back` does this, otherwise we will break the restriction
340 // on calls to `self.next_back()` after calling `get_unchecked()`.
342 let sz_a = self.a.size();
343 if A::MAY_HAVE_SIDE_EFFECT && sz_a > self.len {
344 for _ in 0..sz_a - self.len {
345 // since next_back() may panic we increment the counters beforehand
346 // to keep Zip's state in sync with the underlying iterator source
350 debug_assert_eq!(self.a_len, self.len);
352 let sz_b = self.b.size();
353 if B::MAY_HAVE_SIDE_EFFECT && sz_b > self.len {
354 for _ in 0..sz_b - self.len {
360 if self.index < self.len {
361 // since get_unchecked executes code which can panic we increment the counters beforehand
362 // so that the same index won't be accessed twice, as required by TrustedRandomAccess
366 // SAFETY: `i` is smaller than the previous value of `self.len`,
367 // which is also smaller than or equal to `self.a.len()` and `self.b.len()`
369 Some((self.a.__iterator_get_unchecked(i), self.b.__iterator_get_unchecked(i)))
377 #[stable(feature = "rust1", since = "1.0.0")]
378 impl<A, B> ExactSizeIterator for Zip<A, B>
380 A: ExactSizeIterator,
381 B: ExactSizeIterator,
386 #[unstable(feature = "trusted_random_access", issue = "none")]
387 unsafe impl<A, B> TrustedRandomAccess for Zip<A, B>
389 A: TrustedRandomAccess,
390 B: TrustedRandomAccess,
395 #[unstable(feature = "trusted_random_access", issue = "none")]
396 unsafe impl<A, B> TrustedRandomAccessNoCoerce for Zip<A, B>
398 A: TrustedRandomAccessNoCoerce,
399 B: TrustedRandomAccessNoCoerce,
401 const MAY_HAVE_SIDE_EFFECT: bool = A::MAY_HAVE_SIDE_EFFECT || B::MAY_HAVE_SIDE_EFFECT;
404 #[stable(feature = "fused", since = "1.26.0")]
405 impl<A, B> FusedIterator for Zip<A, B>
412 #[unstable(feature = "trusted_len", issue = "37572")]
413 unsafe impl<A, B> TrustedLen for Zip<A, B>
420 // Arbitrarily selects the left side of the zip iteration as extractable "source"
421 // it would require negative trait bounds to be able to try both
422 #[unstable(issue = "none", feature = "inplace_iteration")]
423 unsafe impl<A, B> SourceIter for Zip<A, B>
427 type Source = A::Source;
430 unsafe fn as_inner(&mut self) -> &mut A::Source {
431 // SAFETY: unsafe function forwarding to unsafe function with the same requirements
432 unsafe { SourceIter::as_inner(&mut self.a) }
436 // Since SourceIter forwards the left hand side we do the same here
437 #[unstable(issue = "none", feature = "inplace_iteration")]
438 unsafe impl<A: InPlaceIterable, B: Iterator> InPlaceIterable for Zip<A, B> {}
440 #[stable(feature = "rust1", since = "1.0.0")]
441 impl<A: Debug, B: Debug> Debug for Zip<A, B> {
442 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
448 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result;
451 impl<A: Debug, B: Debug> ZipFmt<A, B> for Zip<A, B> {
452 default fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
453 f.debug_struct("Zip").field("a", &self.a).field("b", &self.b).finish()
457 impl<A: Debug + TrustedRandomAccessNoCoerce, B: Debug + TrustedRandomAccessNoCoerce> ZipFmt<A, B>
460 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
461 // It's *not safe* to call fmt on the contained iterators, since once
462 // we start iterating they're in strange, potentially unsafe, states.
463 f.debug_struct("Zip").finish()
467 /// An iterator whose items are random-accessible efficiently
471 /// The iterator's `size_hint` must be exact and cheap to call.
473 /// `TrustedRandomAccessNoCoerce::size` may not be overridden.
475 /// All subtypes and all supertypes of `Self` must also implement `TrustedRandomAccess`.
476 /// In particular, this means that types with non-invariant parameters usually can not have
477 /// an impl for `TrustedRandomAccess` that depends on any trait bounds on such parameters, except
478 /// for bounds that come from the respective struct/enum definition itself, or bounds involving
479 /// traits that themselves come with a guarantee similar to this one.
481 /// If `Self: ExactSizeIterator` then `self.len()` must always produce results consistent
482 /// with `self.size()`.
484 /// If `Self: Iterator`, then `<Self as Iterator>::__iterator_get_unchecked(&mut self, idx)`
485 /// must be safe to call provided the following conditions are met.
487 /// 1. `0 <= idx` and `idx < self.size()`.
488 /// 2. If `Self: !Clone`, then `self.__iterator_get_unchecked(idx)` is never called with the same
489 /// index on `self` more than once.
490 /// 3. After `self.__iterator_get_unchecked(idx)` has been called, then `self.next_back()` will
491 /// only be called at most `self.size() - idx - 1` times. If `Self: Clone` and `self` is cloned,
492 /// then this number is calculated for `self` and its clone individually,
493 /// but `self.next_back()` calls that happened before the cloning count for both `self` and the clone.
494 /// 4. After `self.__iterator_get_unchecked(idx)` has been called, then only the following methods
495 /// will be called on `self` or on any new clones of `self`:
496 /// * `std::clone::Clone::clone`
497 /// * `std::iter::Iterator::size_hint`
498 /// * `std::iter::DoubleEndedIterator::next_back`
499 /// * `std::iter::ExactSizeIterator::len`
500 /// * `std::iter::Iterator::__iterator_get_unchecked`
501 /// * `std::iter::TrustedRandomAccessNoCoerce::size`
502 /// 5. If `T` is a subtype of `Self`, then `self` is allowed to be coerced
503 /// to `T`. If `self` is coerced to `T` after `self.__iterator_get_unchecked(idx)` has already
504 /// been called, then no methods except for the ones listed under 4. are allowed to be called
505 /// on the resulting value of type `T`, either. Multiple such coercion steps are allowed.
506 /// Regarding 2. and 3., the number of times `__iterator_get_unchecked(idx)` or `next_back()` is
507 /// called on `self` and the resulting value of type `T` (and on further coercion results with
508 /// sub-subtypes) are added together and their sums must not exceed the specified bounds.
510 /// Further, given that these conditions are met, it must guarantee that:
512 /// * It does not change the value returned from `size_hint`
513 /// * It must be safe to call the methods listed above on `self` after calling
514 /// `self.__iterator_get_unchecked(idx)`, assuming that the required traits are implemented.
515 /// * It must also be safe to drop `self` after calling `self.__iterator_get_unchecked(idx)`.
516 /// * If `T` is a subtype of `Self`, then it must be safe to coerce `self` to `T`.
518 // FIXME: Clarify interaction with SourceIter/InPlaceIterable. Calling `SourceIter::as_inner`
519 // after `__iterator_get_unchecked` is supposed to be allowed.
521 #[unstable(feature = "trusted_random_access", issue = "none")]
522 #[rustc_specialization_trait]
523 pub unsafe trait TrustedRandomAccess: TrustedRandomAccessNoCoerce {}
525 /// Like [`TrustedRandomAccess`] but without any of the requirements / guarantees around
526 /// coercions to subtypes after `__iterator_get_unchecked` (they aren’t allowed here!), and
527 /// without the requirement that subtypes / supertypes implement `TrustedRandomAccessNoCoerce`.
529 /// This trait was created in PR #85874 to fix soundness issue #85873 without performance regressions.
530 /// It is subject to change as we might want to build a more generally useful (for performance
531 /// optimizations) and more sophisticated trait or trait hierarchy that replaces or extends
532 /// [`TrustedRandomAccess`] and `TrustedRandomAccessNoCoerce`.
534 #[unstable(feature = "trusted_random_access", issue = "none")]
535 #[rustc_specialization_trait]
536 pub unsafe trait TrustedRandomAccessNoCoerce: Sized {
537 // Convenience method.
538 fn size(&self) -> usize
544 /// `true` if getting an iterator element may have side effects.
545 /// Remember to take inner iterators into account.
546 const MAY_HAVE_SIDE_EFFECT: bool;
549 /// Like `Iterator::__iterator_get_unchecked`, but doesn't require the compiler to
550 /// know that `U: TrustedRandomAccess`.
554 /// Same requirements calling `get_unchecked` directly.
557 pub(in crate::iter::adapters) unsafe fn try_get_unchecked<I>(it: &mut I, idx: usize) -> I::Item
561 // SAFETY: the caller must uphold the contract for
562 // `Iterator::__iterator_get_unchecked`.
563 unsafe { it.try_get_unchecked(idx) }
566 unsafe trait SpecTrustedRandomAccess: Iterator {
567 /// If `Self: TrustedRandomAccess`, it must be safe to call
568 /// `Iterator::__iterator_get_unchecked(self, index)`.
569 unsafe fn try_get_unchecked(&mut self, index: usize) -> Self::Item;
572 unsafe impl<I: Iterator> SpecTrustedRandomAccess for I {
573 default unsafe fn try_get_unchecked(&mut self, _: usize) -> Self::Item {
574 panic!("Should only be called on TrustedRandomAccess iterators");
578 unsafe impl<I: Iterator + TrustedRandomAccessNoCoerce> SpecTrustedRandomAccess for I {
580 unsafe fn try_get_unchecked(&mut self, index: usize) -> Self::Item {
581 // SAFETY: the caller must uphold the contract for
582 // `Iterator::__iterator_get_unchecked`.
583 unsafe { self.__iterator_get_unchecked(index) }