1 // Copyright 2013-2016 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Composable external iteration.
13 //! If you've found yourself with a collection of some kind, and needed to
14 //! perform an operation on the elements of said collection, you'll quickly run
15 //! into 'iterators'. Iterators are heavily used in idiomatic Rust code, so
16 //! it's worth becoming familiar with them.
18 //! Before explaining more, let's talk about how this module is structured:
22 //! This module is largely organized by type:
24 //! * [Traits] are the core portion: these traits define what kind of iterators
25 //! exist and what you can do with them. The methods of these traits are worth
26 //! putting some extra study time into.
27 //! * [Functions] provide some helpful ways to create some basic iterators.
28 //! * [Structs] are often the return types of the various methods on this
29 //! module's traits. You'll usually want to look at the method that creates
30 //! the `struct`, rather than the `struct` itself. For more detail about why,
31 //! see '[Implementing Iterator](#implementing-iterator)'.
34 //! [Functions]: #functions
35 //! [Structs]: #structs
37 //! That's it! Let's dig into iterators.
41 //! The heart and soul of this module is the [`Iterator`] trait. The core of
42 //! [`Iterator`] looks like this:
47 //! fn next(&mut self) -> Option<Self::Item>;
51 //! An iterator has a method, [`next`], which when called, returns an
52 //! [`Option`]`<Item>`. [`next`] will return `Some(Item)` as long as there
53 //! are elements, and once they've all been exhausted, will return `None` to
54 //! indicate that iteration is finished. Individual iterators may choose to
55 //! resume iteration, and so calling [`next`] again may or may not eventually
56 //! start returning `Some(Item)` again at some point.
58 //! [`Iterator`]'s full definition includes a number of other methods as well,
59 //! but they are default methods, built on top of [`next`], and so you get
62 //! Iterators are also composable, and it's common to chain them together to do
63 //! more complex forms of processing. See the [Adapters](#adapters) section
64 //! below for more details.
66 //! [`Iterator`]: trait.Iterator.html
67 //! [`next`]: trait.Iterator.html#tymethod.next
68 //! [`Option`]: ../../std/option/enum.Option.html
70 //! # The three forms of iteration
72 //! There are three common methods which can create iterators from a collection:
74 //! * `iter()`, which iterates over `&T`.
75 //! * `iter_mut()`, which iterates over `&mut T`.
76 //! * `into_iter()`, which iterates over `T`.
78 //! Various things in the standard library may implement one or more of the
79 //! three, where appropriate.
81 //! # Implementing Iterator
83 //! Creating an iterator of your own involves two steps: creating a `struct` to
84 //! hold the iterator's state, and then `impl`ementing [`Iterator`] for that
85 //! `struct`. This is why there are so many `struct`s in this module: there is
86 //! one for each iterator and iterator adapter.
88 //! Let's make an iterator named `Counter` which counts from `1` to `5`:
91 //! // First, the struct:
93 //! /// An iterator which counts from one to five
98 //! // we want our count to start at one, so let's add a new() method to help.
99 //! // This isn't strictly necessary, but is convenient. Note that we start
100 //! // `count` at zero, we'll see why in `next()`'s implementation below.
102 //! fn new() -> Counter {
103 //! Counter { count: 0 }
107 //! // Then, we implement `Iterator` for our `Counter`:
109 //! impl Iterator for Counter {
110 //! // we will be counting with usize
111 //! type Item = usize;
113 //! // next() is the only required method
114 //! fn next(&mut self) -> Option<usize> {
115 //! // increment our count. This is why we started at zero.
118 //! // check to see if we've finished counting or not.
119 //! if self.count < 6 {
127 //! // And now we can use it!
129 //! let mut counter = Counter::new();
131 //! let x = counter.next().unwrap();
132 //! println!("{}", x);
134 //! let x = counter.next().unwrap();
135 //! println!("{}", x);
137 //! let x = counter.next().unwrap();
138 //! println!("{}", x);
140 //! let x = counter.next().unwrap();
141 //! println!("{}", x);
143 //! let x = counter.next().unwrap();
144 //! println!("{}", x);
147 //! This will print `1` through `5`, each on their own line.
149 //! Calling `next()` this way gets repetitive. Rust has a construct which can
150 //! call `next()` on your iterator, until it reaches `None`. Let's go over that
153 //! # for Loops and IntoIterator
155 //! Rust's `for` loop syntax is actually sugar for iterators. Here's a basic
156 //! example of `for`:
159 //! let values = vec![1, 2, 3, 4, 5];
161 //! for x in values {
162 //! println!("{}", x);
166 //! This will print the numbers one through five, each on their own line. But
167 //! you'll notice something here: we never called anything on our vector to
168 //! produce an iterator. What gives?
170 //! There's a trait in the standard library for converting something into an
171 //! iterator: [`IntoIterator`]. This trait has one method, [`into_iter`],
172 //! which converts the thing implementing [`IntoIterator`] into an iterator.
173 //! Let's take a look at that `for` loop again, and what the compiler converts
176 //! [`IntoIterator`]: trait.IntoIterator.html
177 //! [`into_iter`]: trait.IntoIterator.html#tymethod.into_iter
180 //! let values = vec![1, 2, 3, 4, 5];
182 //! for x in values {
183 //! println!("{}", x);
187 //! Rust de-sugars this into:
190 //! let values = vec![1, 2, 3, 4, 5];
192 //! let result = match IntoIterator::into_iter(values) {
193 //! mut iter => loop {
195 //! match iter.next() {
196 //! Some(val) => next = val,
200 //! let () = { println!("{}", x); };
207 //! First, we call `into_iter()` on the value. Then, we match on the iterator
208 //! that returns, calling [`next`] over and over until we see a `None`. At
209 //! that point, we `break` out of the loop, and we're done iterating.
211 //! There's one more subtle bit here: the standard library contains an
212 //! interesting implementation of [`IntoIterator`]:
214 //! ```ignore (only-for-syntax-highlight)
215 //! impl<I: Iterator> IntoIterator for I
218 //! In other words, all [`Iterator`]s implement [`IntoIterator`], by just
219 //! returning themselves. This means two things:
221 //! 1. If you're writing an [`Iterator`], you can use it with a `for` loop.
222 //! 2. If you're creating a collection, implementing [`IntoIterator`] for it
223 //! will allow your collection to be used with the `for` loop.
227 //! Functions which take an [`Iterator`] and return another [`Iterator`] are
228 //! often called 'iterator adapters', as they're a form of the 'adapter
231 //! Common iterator adapters include [`map`], [`take`], and [`filter`].
232 //! For more, see their documentation.
234 //! [`map`]: trait.Iterator.html#method.map
235 //! [`take`]: trait.Iterator.html#method.take
236 //! [`filter`]: trait.Iterator.html#method.filter
240 //! Iterators (and iterator [adapters](#adapters)) are *lazy*. This means that
241 //! just creating an iterator doesn't _do_ a whole lot. Nothing really happens
242 //! until you call [`next`]. This is sometimes a source of confusion when
243 //! creating an iterator solely for its side effects. For example, the [`map`]
244 //! method calls a closure on each element it iterates over:
247 //! # #![allow(unused_must_use)]
248 //! let v = vec![1, 2, 3, 4, 5];
249 //! v.iter().map(|x| println!("{}", x));
252 //! This will not print any values, as we only created an iterator, rather than
253 //! using it. The compiler will warn us about this kind of behavior:
256 //! warning: unused result which must be used: iterator adaptors are lazy and
257 //! do nothing unless consumed
260 //! The idiomatic way to write a [`map`] for its side effects is to use a
261 //! `for` loop instead:
264 //! let v = vec![1, 2, 3, 4, 5];
267 //! println!("{}", x);
271 //! [`map`]: trait.Iterator.html#method.map
273 //! The two most common ways to evaluate an iterator are to use a `for` loop
274 //! like this, or using the [`collect`] method to produce a new collection.
276 //! [`collect`]: trait.Iterator.html#method.collect
280 //! Iterators do not have to be finite. As an example, an open-ended range is
281 //! an infinite iterator:
284 //! let numbers = 0..;
287 //! It is common to use the [`take`] iterator adapter to turn an infinite
288 //! iterator into a finite one:
291 //! let numbers = 0..;
292 //! let five_numbers = numbers.take(5);
294 //! for number in five_numbers {
295 //! println!("{}", number);
299 //! This will print the numbers `0` through `4`, each on their own line.
301 //! Bear in mind that methods on infinite iterators, even those for which a
302 //! result can be determined mathematically in finite time, may not terminate.
303 //! Specifically, methods such as [`min`], which in the general case require
304 //! traversing every element in the iterator, are likely not to return
305 //! successfully for any infinite iterators.
308 //! let ones = std::iter::repeat(1);
309 //! let least = ones.min().unwrap(); // Oh no! An infinite loop!
310 //! // `ones.min()` causes an infinite loop, so we won't reach this point!
311 //! println!("The smallest number one is {}.", least);
314 //! [`take`]: trait.Iterator.html#method.take
315 //! [`min`]: trait.Iterator.html#method.min
317 #![stable(feature = "rust1", since = "1.0.0")]
321 use iter_private::TrustedRandomAccess;
326 #[stable(feature = "rust1", since = "1.0.0")]
327 pub use self::iterator::Iterator;
329 #[unstable(feature = "step_trait",
330 reason = "likely to be replaced by finer-grained traits",
332 pub use self::range::Step;
334 #[stable(feature = "rust1", since = "1.0.0")]
335 pub use self::sources::{Repeat, repeat};
336 #[stable(feature = "iterator_repeat_with", since = "1.28.0")]
337 pub use self::sources::{RepeatWith, repeat_with};
338 #[stable(feature = "iter_empty", since = "1.2.0")]
339 pub use self::sources::{Empty, empty};
340 #[stable(feature = "iter_once", since = "1.2.0")]
341 pub use self::sources::{Once, once};
343 #[stable(feature = "rust1", since = "1.0.0")]
344 pub use self::traits::{FromIterator, IntoIterator, DoubleEndedIterator, Extend};
345 #[stable(feature = "rust1", since = "1.0.0")]
346 pub use self::traits::{ExactSizeIterator, Sum, Product};
347 #[stable(feature = "fused", since = "1.26.0")]
348 pub use self::traits::FusedIterator;
349 #[unstable(feature = "trusted_len", issue = "37572")]
350 pub use self::traits::TrustedLen;
357 /// Transparent newtype used to implement foo methods in terms of try_foo.
358 /// Important until #43278 is fixed; might be better as `Result<T, !>` later.
359 struct AlwaysOk<T>(pub T);
361 impl<T> Try for AlwaysOk<T> {
365 fn into_result(self) -> Result<Self::Ok, Self::Error> { Ok(self.0) }
367 fn from_error(v: Self::Error) -> Self { v }
369 fn from_ok(v: Self::Ok) -> Self { AlwaysOk(v) }
372 /// Used to make try_fold closures more like normal loops
374 enum LoopState<C, B> {
379 impl<C, B> Try for LoopState<C, B> {
383 fn into_result(self) -> Result<Self::Ok, Self::Error> {
385 LoopState::Continue(y) => Ok(y),
386 LoopState::Break(x) => Err(x),
390 fn from_error(v: Self::Error) -> Self { LoopState::Break(v) }
392 fn from_ok(v: Self::Ok) -> Self { LoopState::Continue(v) }
395 impl<C, B> LoopState<C, B> {
397 fn break_value(self) -> Option<B> {
399 LoopState::Continue(..) => None,
400 LoopState::Break(x) => Some(x),
405 impl<R: Try> LoopState<R::Ok, R> {
407 fn from_try(r: R) -> Self {
408 match Try::into_result(r) {
409 Ok(v) => LoopState::Continue(v),
410 Err(v) => LoopState::Break(Try::from_error(v)),
414 fn into_try(self) -> R {
416 LoopState::Continue(v) => Try::from_ok(v),
417 LoopState::Break(v) => v,
422 /// A double-ended iterator with the direction inverted.
424 /// This `struct` is created by the [`rev`] method on [`Iterator`]. See its
425 /// documentation for more.
427 /// [`rev`]: trait.Iterator.html#method.rev
428 /// [`Iterator`]: trait.Iterator.html
429 #[derive(Clone, Debug)]
430 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
431 #[stable(feature = "rust1", since = "1.0.0")]
436 #[stable(feature = "rust1", since = "1.0.0")]
437 impl<I> Iterator for Rev<I> where I: DoubleEndedIterator {
438 type Item = <I as Iterator>::Item;
441 fn next(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next_back() }
443 fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
445 fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R where
446 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
448 self.iter.try_rfold(init, f)
451 fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
452 where F: FnMut(Acc, Self::Item) -> Acc,
454 self.iter.rfold(init, f)
458 fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
459 where P: FnMut(&Self::Item) -> bool
461 self.iter.rfind(predicate)
465 fn rposition<P>(&mut self, predicate: P) -> Option<usize> where
466 P: FnMut(Self::Item) -> bool
468 self.iter.position(predicate)
472 #[stable(feature = "rust1", since = "1.0.0")]
473 impl<I> DoubleEndedIterator for Rev<I> where I: DoubleEndedIterator {
475 fn next_back(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next() }
477 fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
478 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
480 self.iter.try_fold(init, f)
483 fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
484 where F: FnMut(Acc, Self::Item) -> Acc,
486 self.iter.fold(init, f)
489 fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
490 where P: FnMut(&Self::Item) -> bool
492 self.iter.find(predicate)
496 #[stable(feature = "rust1", since = "1.0.0")]
497 impl<I> ExactSizeIterator for Rev<I>
498 where I: ExactSizeIterator + DoubleEndedIterator
500 fn len(&self) -> usize {
504 fn is_empty(&self) -> bool {
509 #[stable(feature = "fused", since = "1.26.0")]
510 impl<I> FusedIterator for Rev<I>
511 where I: FusedIterator + DoubleEndedIterator {}
513 #[unstable(feature = "trusted_len", issue = "37572")]
514 unsafe impl<I> TrustedLen for Rev<I>
515 where I: TrustedLen + DoubleEndedIterator {}
517 /// An iterator that clones the elements of an underlying iterator.
519 /// This `struct` is created by the [`cloned`] method on [`Iterator`]. See its
520 /// documentation for more.
522 /// [`cloned`]: trait.Iterator.html#method.cloned
523 /// [`Iterator`]: trait.Iterator.html
524 #[stable(feature = "iter_cloned", since = "1.1.0")]
525 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
526 #[derive(Clone, Debug)]
527 pub struct Cloned<I> {
531 #[stable(feature = "iter_cloned", since = "1.1.0")]
532 impl<'a, I, T: 'a> Iterator for Cloned<I>
533 where I: Iterator<Item=&'a T>, T: Clone
537 fn next(&mut self) -> Option<T> {
538 self.it.next().cloned()
541 fn size_hint(&self) -> (usize, Option<usize>) {
545 fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where
546 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
548 self.it.try_fold(init, move |acc, elt| f(acc, elt.clone()))
551 fn fold<Acc, F>(self, init: Acc, mut f: F) -> Acc
552 where F: FnMut(Acc, Self::Item) -> Acc,
554 self.it.fold(init, move |acc, elt| f(acc, elt.clone()))
558 #[stable(feature = "iter_cloned", since = "1.1.0")]
559 impl<'a, I, T: 'a> DoubleEndedIterator for Cloned<I>
560 where I: DoubleEndedIterator<Item=&'a T>, T: Clone
562 fn next_back(&mut self) -> Option<T> {
563 self.it.next_back().cloned()
566 fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R where
567 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
569 self.it.try_rfold(init, move |acc, elt| f(acc, elt.clone()))
572 fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
573 where F: FnMut(Acc, Self::Item) -> Acc,
575 self.it.rfold(init, move |acc, elt| f(acc, elt.clone()))
579 #[stable(feature = "iter_cloned", since = "1.1.0")]
580 impl<'a, I, T: 'a> ExactSizeIterator for Cloned<I>
581 where I: ExactSizeIterator<Item=&'a T>, T: Clone
583 fn len(&self) -> usize {
587 fn is_empty(&self) -> bool {
592 #[stable(feature = "fused", since = "1.26.0")]
593 impl<'a, I, T: 'a> FusedIterator for Cloned<I>
594 where I: FusedIterator<Item=&'a T>, T: Clone
598 unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
599 where I: TrustedRandomAccess<Item=&'a T>, T: Clone
601 default unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
602 self.it.get_unchecked(i).clone()
606 default fn may_have_side_effect() -> bool { true }
610 unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
611 where I: TrustedRandomAccess<Item=&'a T>, T: Copy
613 unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
614 *self.it.get_unchecked(i)
618 fn may_have_side_effect() -> bool { false }
621 #[unstable(feature = "trusted_len", issue = "37572")]
622 unsafe impl<'a, I, T: 'a> TrustedLen for Cloned<I>
623 where I: TrustedLen<Item=&'a T>,
627 /// An iterator that repeats endlessly.
629 /// This `struct` is created by the [`cycle`] method on [`Iterator`]. See its
630 /// documentation for more.
632 /// [`cycle`]: trait.Iterator.html#method.cycle
633 /// [`Iterator`]: trait.Iterator.html
634 #[derive(Clone, Debug)]
635 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
636 #[stable(feature = "rust1", since = "1.0.0")]
637 pub struct Cycle<I> {
642 #[stable(feature = "rust1", since = "1.0.0")]
643 impl<I> Iterator for Cycle<I> where I: Clone + Iterator {
644 type Item = <I as Iterator>::Item;
647 fn next(&mut self) -> Option<<I as Iterator>::Item> {
648 match self.iter.next() {
649 None => { self.iter = self.orig.clone(); self.iter.next() }
655 fn size_hint(&self) -> (usize, Option<usize>) {
656 // the cycle iterator is either empty or infinite
657 match self.orig.size_hint() {
658 sz @ (0, Some(0)) => sz,
660 _ => (usize::MAX, None)
665 #[stable(feature = "fused", since = "1.26.0")]
666 impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {}
668 /// An iterator for stepping iterators by a custom amount.
670 /// This `struct` is created by the [`step_by`] method on [`Iterator`]. See
671 /// its documentation for more.
673 /// [`step_by`]: trait.Iterator.html#method.step_by
674 /// [`Iterator`]: trait.Iterator.html
675 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
676 #[stable(feature = "iterator_step_by", since = "1.28.0")]
677 #[derive(Clone, Debug)]
678 pub struct StepBy<I> {
684 #[stable(feature = "iterator_step_by", since = "1.28.0")]
685 impl<I> Iterator for StepBy<I> where I: Iterator {
689 fn next(&mut self) -> Option<Self::Item> {
691 self.first_take = false;
694 self.iter.nth(self.step)
699 fn size_hint(&self) -> (usize, Option<usize>) {
700 let inner_hint = self.iter.size_hint();
703 let f = |n| if n == 0 { 0 } else { 1 + (n-1)/(self.step+1) };
704 (f(inner_hint.0), inner_hint.1.map(f))
706 let f = |n| n / (self.step+1);
707 (f(inner_hint.0), inner_hint.1.map(f))
712 fn nth(&mut self, mut n: usize) -> Option<Self::Item> {
714 self.first_take = false;
715 let first = self.iter.next();
721 // n and self.step are indices, we need to add 1 to get the amount of elements
722 // When calling `.nth`, we need to subtract 1 again to convert back to an index
723 // step + 1 can't overflow because `.step_by` sets `self.step` to `step - 1`
724 let mut step = self.step + 1;
725 // n + 1 could overflow
726 // thus, if n is usize::MAX, instead of adding one, we call .nth(step)
728 self.iter.nth(step - 1);
735 let mul = n.checked_mul(step);
736 if unsafe { intrinsics::likely(mul.is_some()) } {
737 return self.iter.nth(mul.unwrap() - 1);
739 let div_n = usize::MAX / n;
740 let div_step = usize::MAX / step;
741 let nth_n = div_n * n;
742 let nth_step = div_step * step;
743 let nth = if nth_n > nth_step {
750 self.iter.nth(nth - 1);
755 // StepBy can only make the iterator shorter, so the len will still fit.
756 #[stable(feature = "iterator_step_by", since = "1.28.0")]
757 impl<I> ExactSizeIterator for StepBy<I> where I: ExactSizeIterator {}
759 /// An iterator that strings two iterators together.
761 /// This `struct` is created by the [`chain`] method on [`Iterator`]. See its
762 /// documentation for more.
764 /// [`chain`]: trait.Iterator.html#method.chain
765 /// [`Iterator`]: trait.Iterator.html
766 #[derive(Clone, Debug)]
767 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
768 #[stable(feature = "rust1", since = "1.0.0")]
769 pub struct Chain<A, B> {
775 // The iterator protocol specifies that iteration ends with the return value
776 // `None` from `.next()` (or `.next_back()`) and it is unspecified what
777 // further calls return. The chain adaptor must account for this since it uses
780 // It uses three states:
782 // - Both: `a` and `b` are remaining
783 // - Front: `a` remaining
784 // - Back: `b` remaining
786 // The fourth state (neither iterator is remaining) only occurs after Chain has
787 // returned None once, so we don't need to store this state.
788 #[derive(Clone, Debug)]
790 // both front and back iterator are remaining
792 // only front is remaining
794 // only back is remaining
798 #[stable(feature = "rust1", since = "1.0.0")]
799 impl<A, B> Iterator for Chain<A, B> where
801 B: Iterator<Item = A::Item>
806 fn next(&mut self) -> Option<A::Item> {
808 ChainState::Both => match self.a.next() {
809 elt @ Some(..) => elt,
811 self.state = ChainState::Back;
815 ChainState::Front => self.a.next(),
816 ChainState::Back => self.b.next(),
821 #[rustc_inherit_overflow_checks]
822 fn count(self) -> usize {
824 ChainState::Both => self.a.count() + self.b.count(),
825 ChainState::Front => self.a.count(),
826 ChainState::Back => self.b.count(),
830 fn try_fold<Acc, F, R>(&mut self, init: Acc, mut f: F) -> R where
831 Self: Sized, F: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
833 let mut accum = init;
835 ChainState::Both | ChainState::Front => {
836 accum = self.a.try_fold(accum, &mut f)?;
837 if let ChainState::Both = self.state {
838 self.state = ChainState::Back;
843 if let ChainState::Back = self.state {
844 accum = self.b.try_fold(accum, &mut f)?;
849 fn fold<Acc, F>(self, init: Acc, mut f: F) -> Acc
850 where F: FnMut(Acc, Self::Item) -> Acc,
852 let mut accum = init;
854 ChainState::Both | ChainState::Front => {
855 accum = self.a.fold(accum, &mut f);
860 ChainState::Both | ChainState::Back => {
861 accum = self.b.fold(accum, &mut f);
869 fn nth(&mut self, mut n: usize) -> Option<A::Item> {
871 ChainState::Both | ChainState::Front => {
872 for x in self.a.by_ref() {
878 if let ChainState::Both = self.state {
879 self.state = ChainState::Back;
882 ChainState::Back => {}
884 if let ChainState::Back = self.state {
892 fn find<P>(&mut self, mut predicate: P) -> Option<Self::Item> where
893 P: FnMut(&Self::Item) -> bool,
896 ChainState::Both => match self.a.find(&mut predicate) {
898 self.state = ChainState::Back;
899 self.b.find(predicate)
903 ChainState::Front => self.a.find(predicate),
904 ChainState::Back => self.b.find(predicate),
909 fn last(self) -> Option<A::Item> {
911 ChainState::Both => {
912 // Must exhaust a before b.
913 let a_last = self.a.last();
914 let b_last = self.b.last();
917 ChainState::Front => self.a.last(),
918 ChainState::Back => self.b.last()
923 fn size_hint(&self) -> (usize, Option<usize>) {
924 let (a_lower, a_upper) = self.a.size_hint();
925 let (b_lower, b_upper) = self.b.size_hint();
927 let lower = a_lower.saturating_add(b_lower);
929 let upper = match (a_upper, b_upper) {
930 (Some(x), Some(y)) => x.checked_add(y),
938 #[stable(feature = "rust1", since = "1.0.0")]
939 impl<A, B> DoubleEndedIterator for Chain<A, B> where
940 A: DoubleEndedIterator,
941 B: DoubleEndedIterator<Item=A::Item>,
944 fn next_back(&mut self) -> Option<A::Item> {
946 ChainState::Both => match self.b.next_back() {
947 elt @ Some(..) => elt,
949 self.state = ChainState::Front;
953 ChainState::Front => self.a.next_back(),
954 ChainState::Back => self.b.next_back(),
958 fn try_rfold<Acc, F, R>(&mut self, init: Acc, mut f: F) -> R where
959 Self: Sized, F: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
961 let mut accum = init;
963 ChainState::Both | ChainState::Back => {
964 accum = self.b.try_rfold(accum, &mut f)?;
965 if let ChainState::Both = self.state {
966 self.state = ChainState::Front;
971 if let ChainState::Front = self.state {
972 accum = self.a.try_rfold(accum, &mut f)?;
977 fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
978 where F: FnMut(Acc, Self::Item) -> Acc,
980 let mut accum = init;
982 ChainState::Both | ChainState::Back => {
983 accum = self.b.rfold(accum, &mut f);
988 ChainState::Both | ChainState::Front => {
989 accum = self.a.rfold(accum, &mut f);
998 // Note: *both* must be fused to handle double-ended iterators.
999 #[stable(feature = "fused", since = "1.26.0")]
1000 impl<A, B> FusedIterator for Chain<A, B>
1001 where A: FusedIterator,
1002 B: FusedIterator<Item=A::Item>,
1005 #[unstable(feature = "trusted_len", issue = "37572")]
1006 unsafe impl<A, B> TrustedLen for Chain<A, B>
1007 where A: TrustedLen, B: TrustedLen<Item=A::Item>,
1010 /// An iterator that iterates two other iterators simultaneously.
1012 /// This `struct` is created by the [`zip`] method on [`Iterator`]. See its
1013 /// documentation for more.
1015 /// [`zip`]: trait.Iterator.html#method.zip
1016 /// [`Iterator`]: trait.Iterator.html
1017 #[derive(Clone, Debug)]
1018 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1019 #[stable(feature = "rust1", since = "1.0.0")]
1020 pub struct Zip<A, B> {
1023 // index and len are only used by the specialized version of zip
1028 #[stable(feature = "rust1", since = "1.0.0")]
1029 impl<A, B> Iterator for Zip<A, B> where A: Iterator, B: Iterator
1031 type Item = (A::Item, B::Item);
1034 fn next(&mut self) -> Option<Self::Item> {
1039 fn size_hint(&self) -> (usize, Option<usize>) {
1040 ZipImpl::size_hint(self)
1044 fn nth(&mut self, n: usize) -> Option<Self::Item> {
1045 ZipImpl::nth(self, n)
1049 #[stable(feature = "rust1", since = "1.0.0")]
1050 impl<A, B> DoubleEndedIterator for Zip<A, B> where
1051 A: DoubleEndedIterator + ExactSizeIterator,
1052 B: DoubleEndedIterator + ExactSizeIterator,
1055 fn next_back(&mut self) -> Option<(A::Item, B::Item)> {
1056 ZipImpl::next_back(self)
1060 // Zip specialization trait
1062 trait ZipImpl<A, B> {
1064 fn new(a: A, b: B) -> Self;
1065 fn next(&mut self) -> Option<Self::Item>;
1066 fn size_hint(&self) -> (usize, Option<usize>);
1067 fn nth(&mut self, n: usize) -> Option<Self::Item>;
1068 fn super_nth(&mut self, mut n: usize) -> Option<Self::Item> {
1069 while let Some(x) = self.next() {
1070 if n == 0 { return Some(x) }
1075 fn next_back(&mut self) -> Option<Self::Item>
1076 where A: DoubleEndedIterator + ExactSizeIterator,
1077 B: DoubleEndedIterator + ExactSizeIterator;
1082 impl<A, B> ZipImpl<A, B> for Zip<A, B>
1083 where A: Iterator, B: Iterator
1085 type Item = (A::Item, B::Item);
1086 default fn new(a: A, b: B) -> Self {
1096 default fn next(&mut self) -> Option<(A::Item, B::Item)> {
1097 self.a.next().and_then(|x| {
1098 self.b.next().and_then(|y| {
1105 default fn nth(&mut self, n: usize) -> Option<Self::Item> {
1110 default fn next_back(&mut self) -> Option<(A::Item, B::Item)>
1111 where A: DoubleEndedIterator + ExactSizeIterator,
1112 B: DoubleEndedIterator + ExactSizeIterator
1114 let a_sz = self.a.len();
1115 let b_sz = self.b.len();
1117 // Adjust a, b to equal length
1119 for _ in 0..a_sz - b_sz { self.a.next_back(); }
1121 for _ in 0..b_sz - a_sz { self.b.next_back(); }
1124 match (self.a.next_back(), self.b.next_back()) {
1125 (Some(x), Some(y)) => Some((x, y)),
1126 (None, None) => None,
1127 _ => unreachable!(),
1132 default fn size_hint(&self) -> (usize, Option<usize>) {
1133 let (a_lower, a_upper) = self.a.size_hint();
1134 let (b_lower, b_upper) = self.b.size_hint();
1136 let lower = cmp::min(a_lower, b_lower);
1138 let upper = match (a_upper, b_upper) {
1139 (Some(x), Some(y)) => Some(cmp::min(x,y)),
1140 (Some(x), None) => Some(x),
1141 (None, Some(y)) => Some(y),
1142 (None, None) => None
1150 impl<A, B> ZipImpl<A, B> for Zip<A, B>
1151 where A: TrustedRandomAccess, B: TrustedRandomAccess
1153 fn new(a: A, b: B) -> Self {
1154 let len = cmp::min(a.len(), b.len());
1164 fn next(&mut self) -> Option<(A::Item, B::Item)> {
1165 if self.index < self.len {
1169 Some((self.a.get_unchecked(i), self.b.get_unchecked(i)))
1171 } else if A::may_have_side_effect() && self.index < self.a.len() {
1172 // match the base implementation's potential side effects
1174 self.a.get_unchecked(self.index);
1184 fn size_hint(&self) -> (usize, Option<usize>) {
1185 let len = self.len - self.index;
1190 fn nth(&mut self, n: usize) -> Option<Self::Item> {
1191 let delta = cmp::min(n, self.len - self.index);
1192 let end = self.index + delta;
1193 while self.index < end {
1196 if A::may_have_side_effect() {
1197 unsafe { self.a.get_unchecked(i); }
1199 if B::may_have_side_effect() {
1200 unsafe { self.b.get_unchecked(i); }
1204 self.super_nth(n - delta)
1208 fn next_back(&mut self) -> Option<(A::Item, B::Item)>
1209 where A: DoubleEndedIterator + ExactSizeIterator,
1210 B: DoubleEndedIterator + ExactSizeIterator
1212 // Adjust a, b to equal length
1213 if A::may_have_side_effect() {
1214 let sz = self.a.len();
1216 for _ in 0..sz - cmp::max(self.len, self.index) {
1221 if B::may_have_side_effect() {
1222 let sz = self.b.len();
1224 for _ in 0..sz - self.len {
1229 if self.index < self.len {
1233 Some((self.a.get_unchecked(i), self.b.get_unchecked(i)))
1241 #[stable(feature = "rust1", since = "1.0.0")]
1242 impl<A, B> ExactSizeIterator for Zip<A, B>
1243 where A: ExactSizeIterator, B: ExactSizeIterator {}
1246 unsafe impl<A, B> TrustedRandomAccess for Zip<A, B>
1247 where A: TrustedRandomAccess,
1248 B: TrustedRandomAccess,
1250 unsafe fn get_unchecked(&mut self, i: usize) -> (A::Item, B::Item) {
1251 (self.a.get_unchecked(i), self.b.get_unchecked(i))
1254 fn may_have_side_effect() -> bool {
1255 A::may_have_side_effect() || B::may_have_side_effect()
1259 #[stable(feature = "fused", since = "1.26.0")]
1260 impl<A, B> FusedIterator for Zip<A, B>
1261 where A: FusedIterator, B: FusedIterator, {}
1263 #[unstable(feature = "trusted_len", issue = "37572")]
1264 unsafe impl<A, B> TrustedLen for Zip<A, B>
1265 where A: TrustedLen, B: TrustedLen,
1268 /// An iterator that maps the values of `iter` with `f`.
1270 /// This `struct` is created by the [`map`] method on [`Iterator`]. See its
1271 /// documentation for more.
1273 /// [`map`]: trait.Iterator.html#method.map
1274 /// [`Iterator`]: trait.Iterator.html
1276 /// # Notes about side effects
1278 /// The [`map`] iterator implements [`DoubleEndedIterator`], meaning that
1279 /// you can also [`map`] backwards:
1282 /// let v: Vec<i32> = vec![1, 2, 3].into_iter().map(|x| x + 1).rev().collect();
1284 /// assert_eq!(v, [4, 3, 2]);
1287 /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html
1289 /// But if your closure has state, iterating backwards may act in a way you do
1290 /// not expect. Let's go through an example. First, in the forward direction:
1295 /// for pair in vec!['a', 'b', 'c'].into_iter()
1296 /// .map(|letter| { c += 1; (letter, c) }) {
1297 /// println!("{:?}", pair);
1301 /// This will print "('a', 1), ('b', 2), ('c', 3)".
1303 /// Now consider this twist where we add a call to `rev`. This version will
1304 /// print `('c', 1), ('b', 2), ('a', 3)`. Note that the letters are reversed,
1305 /// but the values of the counter still go in order. This is because `map()` is
1306 /// still being called lazily on each item, but we are popping items off the
1307 /// back of the vector now, instead of shifting them from the front.
1312 /// for pair in vec!['a', 'b', 'c'].into_iter()
1313 /// .map(|letter| { c += 1; (letter, c) })
1315 /// println!("{:?}", pair);
1318 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1319 #[stable(feature = "rust1", since = "1.0.0")]
1321 pub struct Map<I, F> {
1326 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1327 impl<I: fmt::Debug, F> fmt::Debug for Map<I, F> {
1328 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1329 f.debug_struct("Map")
1330 .field("iter", &self.iter)
1335 #[stable(feature = "rust1", since = "1.0.0")]
1336 impl<B, I: Iterator, F> Iterator for Map<I, F> where F: FnMut(I::Item) -> B {
1340 fn next(&mut self) -> Option<B> {
1341 self.iter.next().map(&mut self.f)
1345 fn size_hint(&self) -> (usize, Option<usize>) {
1346 self.iter.size_hint()
1349 fn try_fold<Acc, G, R>(&mut self, init: Acc, mut g: G) -> R where
1350 Self: Sized, G: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1352 let f = &mut self.f;
1353 self.iter.try_fold(init, move |acc, elt| g(acc, f(elt)))
1356 fn fold<Acc, G>(self, init: Acc, mut g: G) -> Acc
1357 where G: FnMut(Acc, Self::Item) -> Acc,
1360 self.iter.fold(init, move |acc, elt| g(acc, f(elt)))
1364 #[stable(feature = "rust1", since = "1.0.0")]
1365 impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F> where
1366 F: FnMut(I::Item) -> B,
1369 fn next_back(&mut self) -> Option<B> {
1370 self.iter.next_back().map(&mut self.f)
1373 fn try_rfold<Acc, G, R>(&mut self, init: Acc, mut g: G) -> R where
1374 Self: Sized, G: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1376 let f = &mut self.f;
1377 self.iter.try_rfold(init, move |acc, elt| g(acc, f(elt)))
1380 fn rfold<Acc, G>(self, init: Acc, mut g: G) -> Acc
1381 where G: FnMut(Acc, Self::Item) -> Acc,
1384 self.iter.rfold(init, move |acc, elt| g(acc, f(elt)))
1388 #[stable(feature = "rust1", since = "1.0.0")]
1389 impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F>
1390 where F: FnMut(I::Item) -> B
1392 fn len(&self) -> usize {
1396 fn is_empty(&self) -> bool {
1397 self.iter.is_empty()
1401 #[stable(feature = "fused", since = "1.26.0")]
1402 impl<B, I: FusedIterator, F> FusedIterator for Map<I, F>
1403 where F: FnMut(I::Item) -> B {}
1405 #[unstable(feature = "trusted_len", issue = "37572")]
1406 unsafe impl<B, I, F> TrustedLen for Map<I, F>
1407 where I: TrustedLen,
1408 F: FnMut(I::Item) -> B {}
1411 unsafe impl<B, I, F> TrustedRandomAccess for Map<I, F>
1412 where I: TrustedRandomAccess,
1413 F: FnMut(I::Item) -> B,
1415 unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
1416 (self.f)(self.iter.get_unchecked(i))
1419 fn may_have_side_effect() -> bool { true }
1422 /// An iterator that filters the elements of `iter` with `predicate`.
1424 /// This `struct` is created by the [`filter`] method on [`Iterator`]. See its
1425 /// documentation for more.
1427 /// [`filter`]: trait.Iterator.html#method.filter
1428 /// [`Iterator`]: trait.Iterator.html
1429 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1430 #[stable(feature = "rust1", since = "1.0.0")]
1432 pub struct Filter<I, P> {
1437 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1438 impl<I: fmt::Debug, P> fmt::Debug for Filter<I, P> {
1439 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1440 f.debug_struct("Filter")
1441 .field("iter", &self.iter)
1446 #[stable(feature = "rust1", since = "1.0.0")]
1447 impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {
1448 type Item = I::Item;
1451 fn next(&mut self) -> Option<I::Item> {
1452 for x in &mut self.iter {
1453 if (self.predicate)(&x) {
1461 fn size_hint(&self) -> (usize, Option<usize>) {
1462 let (_, upper) = self.iter.size_hint();
1463 (0, upper) // can't know a lower bound, due to the predicate
1466 // this special case allows the compiler to make `.filter(_).count()`
1467 // branchless. Barring perfect branch prediction (which is unattainable in
1468 // the general case), this will be much faster in >90% of cases (containing
1469 // virtually all real workloads) and only a tiny bit slower in the rest.
1471 // Having this specialization thus allows us to write `.filter(p).count()`
1472 // where we would otherwise write `.map(|x| p(x) as usize).sum()`, which is
1473 // less readable and also less backwards-compatible to Rust before 1.10.
1475 // Using the branchless version will also simplify the LLVM byte code, thus
1476 // leaving more budget for LLVM optimizations.
1478 fn count(mut self) -> usize {
1480 for x in &mut self.iter {
1481 count += (self.predicate)(&x) as usize;
1487 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1488 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1490 let predicate = &mut self.predicate;
1491 self.iter.try_fold(init, move |acc, item| if predicate(&item) {
1499 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1500 where Fold: FnMut(Acc, Self::Item) -> Acc,
1502 let mut predicate = self.predicate;
1503 self.iter.fold(init, move |acc, item| if predicate(&item) {
1511 #[stable(feature = "rust1", since = "1.0.0")]
1512 impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
1513 where P: FnMut(&I::Item) -> bool,
1516 fn next_back(&mut self) -> Option<I::Item> {
1517 for x in self.iter.by_ref().rev() {
1518 if (self.predicate)(&x) {
1526 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1527 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1529 let predicate = &mut self.predicate;
1530 self.iter.try_rfold(init, move |acc, item| if predicate(&item) {
1538 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1539 where Fold: FnMut(Acc, Self::Item) -> Acc,
1541 let mut predicate = self.predicate;
1542 self.iter.rfold(init, move |acc, item| if predicate(&item) {
1550 #[stable(feature = "fused", since = "1.26.0")]
1551 impl<I: FusedIterator, P> FusedIterator for Filter<I, P>
1552 where P: FnMut(&I::Item) -> bool {}
1554 /// An iterator that uses `f` to both filter and map elements from `iter`.
1556 /// This `struct` is created by the [`filter_map`] method on [`Iterator`]. See its
1557 /// documentation for more.
1559 /// [`filter_map`]: trait.Iterator.html#method.filter_map
1560 /// [`Iterator`]: trait.Iterator.html
1561 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1562 #[stable(feature = "rust1", since = "1.0.0")]
1564 pub struct FilterMap<I, F> {
1569 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1570 impl<I: fmt::Debug, F> fmt::Debug for FilterMap<I, F> {
1571 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1572 f.debug_struct("FilterMap")
1573 .field("iter", &self.iter)
1578 #[stable(feature = "rust1", since = "1.0.0")]
1579 impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
1580 where F: FnMut(I::Item) -> Option<B>,
1585 fn next(&mut self) -> Option<B> {
1586 for x in self.iter.by_ref() {
1587 if let Some(y) = (self.f)(x) {
1595 fn size_hint(&self) -> (usize, Option<usize>) {
1596 let (_, upper) = self.iter.size_hint();
1597 (0, upper) // can't know a lower bound, due to the predicate
1601 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1602 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1604 let f = &mut self.f;
1605 self.iter.try_fold(init, move |acc, item| match f(item) {
1606 Some(x) => fold(acc, x),
1607 None => Try::from_ok(acc),
1612 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1613 where Fold: FnMut(Acc, Self::Item) -> Acc,
1616 self.iter.fold(init, move |acc, item| match f(item) {
1617 Some(x) => fold(acc, x),
1623 #[stable(feature = "rust1", since = "1.0.0")]
1624 impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
1625 where F: FnMut(I::Item) -> Option<B>,
1628 fn next_back(&mut self) -> Option<B> {
1629 for x in self.iter.by_ref().rev() {
1630 if let Some(y) = (self.f)(x) {
1638 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1639 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1641 let f = &mut self.f;
1642 self.iter.try_rfold(init, move |acc, item| match f(item) {
1643 Some(x) => fold(acc, x),
1644 None => Try::from_ok(acc),
1649 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1650 where Fold: FnMut(Acc, Self::Item) -> Acc,
1653 self.iter.rfold(init, move |acc, item| match f(item) {
1654 Some(x) => fold(acc, x),
1660 #[stable(feature = "fused", since = "1.26.0")]
1661 impl<B, I: FusedIterator, F> FusedIterator for FilterMap<I, F>
1662 where F: FnMut(I::Item) -> Option<B> {}
1664 /// An iterator that yields the current count and the element during iteration.
1666 /// This `struct` is created by the [`enumerate`] method on [`Iterator`]. See its
1667 /// documentation for more.
1669 /// [`enumerate`]: trait.Iterator.html#method.enumerate
1670 /// [`Iterator`]: trait.Iterator.html
1671 #[derive(Clone, Debug)]
1672 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1673 #[stable(feature = "rust1", since = "1.0.0")]
1674 pub struct Enumerate<I> {
1679 #[stable(feature = "rust1", since = "1.0.0")]
1680 impl<I> Iterator for Enumerate<I> where I: Iterator {
1681 type Item = (usize, <I as Iterator>::Item);
1683 /// # Overflow Behavior
1685 /// The method does no guarding against overflows, so enumerating more than
1686 /// `usize::MAX` elements either produces the wrong result or panics. If
1687 /// debug assertions are enabled, a panic is guaranteed.
1691 /// Might panic if the index of the element overflows a `usize`.
1693 #[rustc_inherit_overflow_checks]
1694 fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
1695 self.iter.next().map(|a| {
1696 let ret = (self.count, a);
1697 // Possible undefined overflow.
1704 fn size_hint(&self) -> (usize, Option<usize>) {
1705 self.iter.size_hint()
1709 #[rustc_inherit_overflow_checks]
1710 fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> {
1711 self.iter.nth(n).map(|a| {
1712 let i = self.count + n;
1719 fn count(self) -> usize {
1724 #[rustc_inherit_overflow_checks]
1725 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1726 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1728 let count = &mut self.count;
1729 self.iter.try_fold(init, move |acc, item| {
1730 let acc = fold(acc, (*count, item));
1737 #[rustc_inherit_overflow_checks]
1738 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1739 where Fold: FnMut(Acc, Self::Item) -> Acc,
1741 let mut count = self.count;
1742 self.iter.fold(init, move |acc, item| {
1743 let acc = fold(acc, (count, item));
1750 #[stable(feature = "rust1", since = "1.0.0")]
1751 impl<I> DoubleEndedIterator for Enumerate<I> where
1752 I: ExactSizeIterator + DoubleEndedIterator
1755 fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
1756 self.iter.next_back().map(|a| {
1757 let len = self.iter.len();
1758 // Can safely add, `ExactSizeIterator` promises that the number of
1759 // elements fits into a `usize`.
1760 (self.count + len, a)
1765 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1766 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1768 // Can safely add and subtract the count, as `ExactSizeIterator` promises
1769 // that the number of elements fits into a `usize`.
1770 let mut count = self.count + self.iter.len();
1771 self.iter.try_rfold(init, move |acc, item| {
1773 fold(acc, (count, item))
1778 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1779 where Fold: FnMut(Acc, Self::Item) -> Acc,
1781 // Can safely add and subtract the count, as `ExactSizeIterator` promises
1782 // that the number of elements fits into a `usize`.
1783 let mut count = self.count + self.iter.len();
1784 self.iter.rfold(init, move |acc, item| {
1786 fold(acc, (count, item))
1791 #[stable(feature = "rust1", since = "1.0.0")]
1792 impl<I> ExactSizeIterator for Enumerate<I> where I: ExactSizeIterator {
1793 fn len(&self) -> usize {
1797 fn is_empty(&self) -> bool {
1798 self.iter.is_empty()
1803 unsafe impl<I> TrustedRandomAccess for Enumerate<I>
1804 where I: TrustedRandomAccess
1806 unsafe fn get_unchecked(&mut self, i: usize) -> (usize, I::Item) {
1807 (self.count + i, self.iter.get_unchecked(i))
1810 fn may_have_side_effect() -> bool {
1811 I::may_have_side_effect()
1815 #[stable(feature = "fused", since = "1.26.0")]
1816 impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {}
1818 #[unstable(feature = "trusted_len", issue = "37572")]
1819 unsafe impl<I> TrustedLen for Enumerate<I>
1820 where I: TrustedLen,
1824 /// An iterator with a `peek()` that returns an optional reference to the next
1827 /// This `struct` is created by the [`peekable`] method on [`Iterator`]. See its
1828 /// documentation for more.
1830 /// [`peekable`]: trait.Iterator.html#method.peekable
1831 /// [`Iterator`]: trait.Iterator.html
1832 #[derive(Clone, Debug)]
1833 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1834 #[stable(feature = "rust1", since = "1.0.0")]
1835 pub struct Peekable<I: Iterator> {
1837 /// Remember a peeked value, even if it was None.
1838 peeked: Option<Option<I::Item>>,
1841 // Peekable must remember if a None has been seen in the `.peek()` method.
1842 // It ensures that `.peek(); .peek();` or `.peek(); .next();` only advances the
1843 // underlying iterator at most once. This does not by itself make the iterator
1845 #[stable(feature = "rust1", since = "1.0.0")]
1846 impl<I: Iterator> Iterator for Peekable<I> {
1847 type Item = I::Item;
1850 fn next(&mut self) -> Option<I::Item> {
1851 match self.peeked.take() {
1853 None => self.iter.next(),
1858 #[rustc_inherit_overflow_checks]
1859 fn count(mut self) -> usize {
1860 match self.peeked.take() {
1862 Some(Some(_)) => 1 + self.iter.count(),
1863 None => self.iter.count(),
1868 fn nth(&mut self, n: usize) -> Option<I::Item> {
1869 // FIXME(#43234): merge these when borrow-checking gets better.
1871 match self.peeked.take() {
1873 None => self.iter.nth(n),
1876 match self.peeked.take() {
1878 Some(Some(_)) => self.iter.nth(n - 1),
1879 None => self.iter.nth(n),
1885 fn last(mut self) -> Option<I::Item> {
1886 let peek_opt = match self.peeked.take() {
1887 Some(None) => return None,
1891 self.iter.last().or(peek_opt)
1895 fn size_hint(&self) -> (usize, Option<usize>) {
1896 let peek_len = match self.peeked {
1897 Some(None) => return (0, Some(0)),
1901 let (lo, hi) = self.iter.size_hint();
1902 let lo = lo.saturating_add(peek_len);
1903 let hi = hi.and_then(|x| x.checked_add(peek_len));
1908 fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where
1909 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
1911 let acc = match self.peeked.take() {
1912 Some(None) => return Try::from_ok(init),
1913 Some(Some(v)) => f(init, v)?,
1916 self.iter.try_fold(acc, f)
1920 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1921 where Fold: FnMut(Acc, Self::Item) -> Acc,
1923 let acc = match self.peeked {
1924 Some(None) => return init,
1925 Some(Some(v)) => fold(init, v),
1928 self.iter.fold(acc, fold)
1932 #[stable(feature = "rust1", since = "1.0.0")]
1933 impl<I: ExactSizeIterator> ExactSizeIterator for Peekable<I> {}
1935 #[stable(feature = "fused", since = "1.26.0")]
1936 impl<I: FusedIterator> FusedIterator for Peekable<I> {}
1938 impl<I: Iterator> Peekable<I> {
1939 /// Returns a reference to the next() value without advancing the iterator.
1941 /// Like [`next`], if there is a value, it is wrapped in a `Some(T)`.
1942 /// But if the iteration is over, `None` is returned.
1944 /// [`next`]: trait.Iterator.html#tymethod.next
1946 /// Because `peek()` returns a reference, and many iterators iterate over
1947 /// references, there can be a possibly confusing situation where the
1948 /// return value is a double reference. You can see this effect in the
1956 /// let xs = [1, 2, 3];
1958 /// let mut iter = xs.iter().peekable();
1960 /// // peek() lets us see into the future
1961 /// assert_eq!(iter.peek(), Some(&&1));
1962 /// assert_eq!(iter.next(), Some(&1));
1964 /// assert_eq!(iter.next(), Some(&2));
1966 /// // The iterator does not advance even if we `peek` multiple times
1967 /// assert_eq!(iter.peek(), Some(&&3));
1968 /// assert_eq!(iter.peek(), Some(&&3));
1970 /// assert_eq!(iter.next(), Some(&3));
1972 /// // After the iterator is finished, so is `peek()`
1973 /// assert_eq!(iter.peek(), None);
1974 /// assert_eq!(iter.next(), None);
1977 #[stable(feature = "rust1", since = "1.0.0")]
1978 pub fn peek(&mut self) -> Option<&I::Item> {
1979 if self.peeked.is_none() {
1980 self.peeked = Some(self.iter.next());
1983 Some(Some(ref value)) => Some(value),
1985 _ => unreachable!(),
1990 /// An iterator that rejects elements while `predicate` is true.
1992 /// This `struct` is created by the [`skip_while`] method on [`Iterator`]. See its
1993 /// documentation for more.
1995 /// [`skip_while`]: trait.Iterator.html#method.skip_while
1996 /// [`Iterator`]: trait.Iterator.html
1997 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1998 #[stable(feature = "rust1", since = "1.0.0")]
2000 pub struct SkipWhile<I, P> {
2006 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2007 impl<I: fmt::Debug, P> fmt::Debug for SkipWhile<I, P> {
2008 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2009 f.debug_struct("SkipWhile")
2010 .field("iter", &self.iter)
2011 .field("flag", &self.flag)
2016 #[stable(feature = "rust1", since = "1.0.0")]
2017 impl<I: Iterator, P> Iterator for SkipWhile<I, P>
2018 where P: FnMut(&I::Item) -> bool
2020 type Item = I::Item;
2023 fn next(&mut self) -> Option<I::Item> {
2024 let flag = &mut self.flag;
2025 let pred = &mut self.predicate;
2026 self.iter.find(move |x| {
2027 if *flag || !pred(x) {
2037 fn size_hint(&self) -> (usize, Option<usize>) {
2038 let (_, upper) = self.iter.size_hint();
2039 (0, upper) // can't know a lower bound, due to the predicate
2043 fn try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
2044 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2048 Some(v) => init = fold(init, v)?,
2049 None => return Try::from_ok(init),
2052 self.iter.try_fold(init, fold)
2056 fn fold<Acc, Fold>(mut self, mut init: Acc, mut fold: Fold) -> Acc
2057 where Fold: FnMut(Acc, Self::Item) -> Acc,
2061 Some(v) => init = fold(init, v),
2062 None => return init,
2065 self.iter.fold(init, fold)
2069 #[stable(feature = "fused", since = "1.26.0")]
2070 impl<I, P> FusedIterator for SkipWhile<I, P>
2071 where I: FusedIterator, P: FnMut(&I::Item) -> bool {}
2073 /// An iterator that only accepts elements while `predicate` is true.
2075 /// This `struct` is created by the [`take_while`] method on [`Iterator`]. See its
2076 /// documentation for more.
2078 /// [`take_while`]: trait.Iterator.html#method.take_while
2079 /// [`Iterator`]: trait.Iterator.html
2080 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2081 #[stable(feature = "rust1", since = "1.0.0")]
2083 pub struct TakeWhile<I, P> {
2089 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2090 impl<I: fmt::Debug, P> fmt::Debug for TakeWhile<I, P> {
2091 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2092 f.debug_struct("TakeWhile")
2093 .field("iter", &self.iter)
2094 .field("flag", &self.flag)
2099 #[stable(feature = "rust1", since = "1.0.0")]
2100 impl<I: Iterator, P> Iterator for TakeWhile<I, P>
2101 where P: FnMut(&I::Item) -> bool
2103 type Item = I::Item;
2106 fn next(&mut self) -> Option<I::Item> {
2110 self.iter.next().and_then(|x| {
2111 if (self.predicate)(&x) {
2122 fn size_hint(&self) -> (usize, Option<usize>) {
2123 let (_, upper) = self.iter.size_hint();
2124 (0, upper) // can't know a lower bound, due to the predicate
2128 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2129 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2134 let flag = &mut self.flag;
2135 let p = &mut self.predicate;
2136 self.iter.try_fold(init, move |acc, x|{
2138 LoopState::from_try(fold(acc, x))
2141 LoopState::Break(Try::from_ok(acc))
2148 #[stable(feature = "fused", since = "1.26.0")]
2149 impl<I, P> FusedIterator for TakeWhile<I, P>
2150 where I: FusedIterator, P: FnMut(&I::Item) -> bool {}
2152 /// An iterator that skips over `n` elements of `iter`.
2154 /// This `struct` is created by the [`skip`] method on [`Iterator`]. See its
2155 /// documentation for more.
2157 /// [`skip`]: trait.Iterator.html#method.skip
2158 /// [`Iterator`]: trait.Iterator.html
2159 #[derive(Clone, Debug)]
2160 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2161 #[stable(feature = "rust1", since = "1.0.0")]
2162 pub struct Skip<I> {
2167 #[stable(feature = "rust1", since = "1.0.0")]
2168 impl<I> Iterator for Skip<I> where I: Iterator {
2169 type Item = <I as Iterator>::Item;
2172 fn next(&mut self) -> Option<I::Item> {
2178 self.iter.nth(old_n)
2183 fn nth(&mut self, n: usize) -> Option<I::Item> {
2184 // Can't just add n + self.n due to overflow.
2188 let to_skip = self.n;
2191 if self.iter.nth(to_skip-1).is_none() {
2199 fn count(self) -> usize {
2200 self.iter.count().saturating_sub(self.n)
2204 fn last(mut self) -> Option<I::Item> {
2208 let next = self.next();
2210 // recurse. n should be 0.
2211 self.last().or(next)
2219 fn size_hint(&self) -> (usize, Option<usize>) {
2220 let (lower, upper) = self.iter.size_hint();
2222 let lower = lower.saturating_sub(self.n);
2223 let upper = upper.map(|x| x.saturating_sub(self.n));
2229 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2230 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2236 if self.iter.nth(n - 1).is_none() {
2237 return Try::from_ok(init);
2240 self.iter.try_fold(init, fold)
2244 fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
2245 where Fold: FnMut(Acc, Self::Item) -> Acc,
2249 if self.iter.nth(self.n - 1).is_none() {
2253 self.iter.fold(init, fold)
2257 #[stable(feature = "rust1", since = "1.0.0")]
2258 impl<I> ExactSizeIterator for Skip<I> where I: ExactSizeIterator {}
2260 #[stable(feature = "double_ended_skip_iterator", since = "1.9.0")]
2261 impl<I> DoubleEndedIterator for Skip<I> where I: DoubleEndedIterator + ExactSizeIterator {
2262 fn next_back(&mut self) -> Option<Self::Item> {
2264 self.iter.next_back()
2270 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2271 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2273 let mut n = self.len();
2277 self.iter.try_rfold(init, move |acc, x| {
2279 let r = fold(acc, x);
2280 if n == 0 { LoopState::Break(r) }
2281 else { LoopState::from_try(r) }
2287 #[stable(feature = "fused", since = "1.26.0")]
2288 impl<I> FusedIterator for Skip<I> where I: FusedIterator {}
2290 /// An iterator that only iterates over the first `n` iterations of `iter`.
2292 /// This `struct` is created by the [`take`] method on [`Iterator`]. See its
2293 /// documentation for more.
2295 /// [`take`]: trait.Iterator.html#method.take
2296 /// [`Iterator`]: trait.Iterator.html
2297 #[derive(Clone, Debug)]
2298 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2299 #[stable(feature = "rust1", since = "1.0.0")]
2300 pub struct Take<I> {
2305 #[stable(feature = "rust1", since = "1.0.0")]
2306 impl<I> Iterator for Take<I> where I: Iterator{
2307 type Item = <I as Iterator>::Item;
2310 fn next(&mut self) -> Option<<I as Iterator>::Item> {
2320 fn nth(&mut self, n: usize) -> Option<I::Item> {
2326 self.iter.nth(self.n - 1);
2334 fn size_hint(&self) -> (usize, Option<usize>) {
2335 let (lower, upper) = self.iter.size_hint();
2337 let lower = cmp::min(lower, self.n);
2339 let upper = match upper {
2340 Some(x) if x < self.n => Some(x),
2348 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2349 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2354 let n = &mut self.n;
2355 self.iter.try_fold(init, move |acc, x| {
2357 let r = fold(acc, x);
2358 if *n == 0 { LoopState::Break(r) }
2359 else { LoopState::from_try(r) }
2365 #[stable(feature = "rust1", since = "1.0.0")]
2366 impl<I> ExactSizeIterator for Take<I> where I: ExactSizeIterator {}
2368 #[stable(feature = "fused", since = "1.26.0")]
2369 impl<I> FusedIterator for Take<I> where I: FusedIterator {}
2371 #[unstable(feature = "trusted_len", issue = "37572")]
2372 unsafe impl<I: TrustedLen> TrustedLen for Take<I> {}
2374 /// An iterator to maintain state while iterating another iterator.
2376 /// This `struct` is created by the [`scan`] method on [`Iterator`]. See its
2377 /// documentation for more.
2379 /// [`scan`]: trait.Iterator.html#method.scan
2380 /// [`Iterator`]: trait.Iterator.html
2381 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2382 #[stable(feature = "rust1", since = "1.0.0")]
2384 pub struct Scan<I, St, F> {
2390 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2391 impl<I: fmt::Debug, St: fmt::Debug, F> fmt::Debug for Scan<I, St, F> {
2392 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2393 f.debug_struct("Scan")
2394 .field("iter", &self.iter)
2395 .field("state", &self.state)
2400 #[stable(feature = "rust1", since = "1.0.0")]
2401 impl<B, I, St, F> Iterator for Scan<I, St, F> where
2403 F: FnMut(&mut St, I::Item) -> Option<B>,
2408 fn next(&mut self) -> Option<B> {
2409 self.iter.next().and_then(|a| (self.f)(&mut self.state, a))
2413 fn size_hint(&self) -> (usize, Option<usize>) {
2414 let (_, upper) = self.iter.size_hint();
2415 (0, upper) // can't know a lower bound, due to the scan function
2419 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2420 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2422 let state = &mut self.state;
2423 let f = &mut self.f;
2424 self.iter.try_fold(init, move |acc, x| {
2426 None => LoopState::Break(Try::from_ok(acc)),
2427 Some(x) => LoopState::from_try(fold(acc, x)),
2433 /// An iterator that maps each element to an iterator, and yields the elements
2434 /// of the produced iterators.
2436 /// This `struct` is created by the [`flat_map`] method on [`Iterator`]. See its
2437 /// documentation for more.
2439 /// [`flat_map`]: trait.Iterator.html#method.flat_map
2440 /// [`Iterator`]: trait.Iterator.html
2441 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2442 #[stable(feature = "rust1", since = "1.0.0")]
2443 pub struct FlatMap<I, U: IntoIterator, F> {
2444 inner: FlattenCompat<Map<I, F>, <U as IntoIterator>::IntoIter>
2447 #[stable(feature = "rust1", since = "1.0.0")]
2448 impl<I: Clone, U: Clone + IntoIterator, F: Clone> Clone for FlatMap<I, U, F>
2449 where <U as IntoIterator>::IntoIter: Clone
2451 fn clone(&self) -> Self { FlatMap { inner: self.inner.clone() } }
2454 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2455 impl<I: fmt::Debug, U: IntoIterator, F> fmt::Debug for FlatMap<I, U, F>
2456 where U::IntoIter: fmt::Debug
2458 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2459 f.debug_struct("FlatMap").field("inner", &self.inner).finish()
2463 #[stable(feature = "rust1", since = "1.0.0")]
2464 impl<I: Iterator, U: IntoIterator, F> Iterator for FlatMap<I, U, F>
2465 where F: FnMut(I::Item) -> U,
2467 type Item = U::Item;
2470 fn next(&mut self) -> Option<U::Item> { self.inner.next() }
2473 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
2476 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2477 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2479 self.inner.try_fold(init, fold)
2483 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2484 where Fold: FnMut(Acc, Self::Item) -> Acc,
2486 self.inner.fold(init, fold)
2490 #[stable(feature = "rust1", since = "1.0.0")]
2491 impl<I: DoubleEndedIterator, U, F> DoubleEndedIterator for FlatMap<I, U, F>
2492 where F: FnMut(I::Item) -> U,
2494 U::IntoIter: DoubleEndedIterator
2497 fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }
2500 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2501 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2503 self.inner.try_rfold(init, fold)
2507 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2508 where Fold: FnMut(Acc, Self::Item) -> Acc,
2510 self.inner.rfold(init, fold)
2514 #[stable(feature = "fused", since = "1.26.0")]
2515 impl<I, U, F> FusedIterator for FlatMap<I, U, F>
2516 where I: FusedIterator, U: IntoIterator, F: FnMut(I::Item) -> U {}
2518 /// An iterator that flattens one level of nesting in an iterator of things
2519 /// that can be turned into iterators.
2521 /// This `struct` is created by the [`flatten`] method on [`Iterator`]. See its
2522 /// documentation for more.
2524 /// [`flatten`]: trait.Iterator.html#method.flatten
2525 /// [`Iterator`]: trait.Iterator.html
2526 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2527 #[unstable(feature = "iterator_flatten", issue = "48213")]
2528 pub struct Flatten<I: Iterator>
2529 where I::Item: IntoIterator {
2530 inner: FlattenCompat<I, <I::Item as IntoIterator>::IntoIter>,
2533 #[unstable(feature = "iterator_flatten", issue = "48213")]
2534 impl<I, U> fmt::Debug for Flatten<I>
2535 where I: Iterator + fmt::Debug, U: Iterator + fmt::Debug,
2536 I::Item: IntoIterator<IntoIter = U, Item = U::Item>,
2538 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2539 f.debug_struct("Flatten").field("inner", &self.inner).finish()
2543 #[unstable(feature = "iterator_flatten", issue = "48213")]
2544 impl<I, U> Clone for Flatten<I>
2545 where I: Iterator + Clone, U: Iterator + Clone,
2546 I::Item: IntoIterator<IntoIter = U, Item = U::Item>,
2548 fn clone(&self) -> Self { Flatten { inner: self.inner.clone() } }
2551 #[unstable(feature = "iterator_flatten", issue = "48213")]
2552 impl<I, U> Iterator for Flatten<I>
2553 where I: Iterator, U: Iterator,
2554 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2556 type Item = U::Item;
2559 fn next(&mut self) -> Option<U::Item> { self.inner.next() }
2562 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
2565 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2566 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2568 self.inner.try_fold(init, fold)
2572 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2573 where Fold: FnMut(Acc, Self::Item) -> Acc,
2575 self.inner.fold(init, fold)
2579 #[unstable(feature = "iterator_flatten", issue = "48213")]
2580 impl<I, U> DoubleEndedIterator for Flatten<I>
2581 where I: DoubleEndedIterator, U: DoubleEndedIterator,
2582 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2585 fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }
2588 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2589 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2591 self.inner.try_rfold(init, fold)
2595 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2596 where Fold: FnMut(Acc, Self::Item) -> Acc,
2598 self.inner.rfold(init, fold)
2602 #[unstable(feature = "iterator_flatten", issue = "48213")]
2603 impl<I, U> FusedIterator for Flatten<I>
2604 where I: FusedIterator, U: Iterator,
2605 I::Item: IntoIterator<IntoIter = U, Item = U::Item> {}
2607 /// Adapts an iterator by flattening it, for use in `flatten()` and `flat_map()`.
2608 fn flatten_compat<I, U>(iter: I) -> FlattenCompat<I, U> {
2609 FlattenCompat { iter, frontiter: None, backiter: None }
2612 /// Real logic of both `Flatten` and `FlatMap` which simply delegate to
2614 #[derive(Clone, Debug)]
2615 struct FlattenCompat<I, U> {
2617 frontiter: Option<U>,
2618 backiter: Option<U>,
2621 impl<I, U> Iterator for FlattenCompat<I, U>
2622 where I: Iterator, U: Iterator,
2623 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2625 type Item = U::Item;
2628 fn next(&mut self) -> Option<U::Item> {
2630 if let Some(ref mut inner) = self.frontiter {
2631 if let elt@Some(_) = inner.next() { return elt }
2633 match self.iter.next() {
2634 None => return self.backiter.as_mut().and_then(|it| it.next()),
2635 Some(inner) => self.frontiter = Some(inner.into_iter()),
2641 fn size_hint(&self) -> (usize, Option<usize>) {
2642 let (flo, fhi) = self.frontiter.as_ref().map_or((0, Some(0)), |it| it.size_hint());
2643 let (blo, bhi) = self.backiter.as_ref().map_or((0, Some(0)), |it| it.size_hint());
2644 let lo = flo.saturating_add(blo);
2645 match (self.iter.size_hint(), fhi, bhi) {
2646 ((0, Some(0)), Some(a), Some(b)) => (lo, a.checked_add(b)),
2652 fn try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
2653 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2655 if let Some(ref mut front) = self.frontiter {
2656 init = front.try_fold(init, &mut fold)?;
2658 self.frontiter = None;
2661 let frontiter = &mut self.frontiter;
2662 init = self.iter.try_fold(init, |acc, x| {
2663 let mut mid = x.into_iter();
2664 let r = mid.try_fold(acc, &mut fold);
2665 *frontiter = Some(mid);
2669 self.frontiter = None;
2671 if let Some(ref mut back) = self.backiter {
2672 init = back.try_fold(init, &mut fold)?;
2674 self.backiter = None;
2680 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
2681 where Fold: FnMut(Acc, Self::Item) -> Acc,
2683 self.frontiter.into_iter()
2684 .chain(self.iter.map(IntoIterator::into_iter))
2685 .chain(self.backiter)
2686 .fold(init, |acc, iter| iter.fold(acc, &mut fold))
2690 impl<I, U> DoubleEndedIterator for FlattenCompat<I, U>
2691 where I: DoubleEndedIterator, U: DoubleEndedIterator,
2692 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2695 fn next_back(&mut self) -> Option<U::Item> {
2697 if let Some(ref mut inner) = self.backiter {
2698 if let elt@Some(_) = inner.next_back() { return elt }
2700 match self.iter.next_back() {
2701 None => return self.frontiter.as_mut().and_then(|it| it.next_back()),
2702 next => self.backiter = next.map(IntoIterator::into_iter),
2708 fn try_rfold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
2709 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2711 if let Some(ref mut back) = self.backiter {
2712 init = back.try_rfold(init, &mut fold)?;
2714 self.backiter = None;
2717 let backiter = &mut self.backiter;
2718 init = self.iter.try_rfold(init, |acc, x| {
2719 let mut mid = x.into_iter();
2720 let r = mid.try_rfold(acc, &mut fold);
2721 *backiter = Some(mid);
2725 self.backiter = None;
2727 if let Some(ref mut front) = self.frontiter {
2728 init = front.try_rfold(init, &mut fold)?;
2730 self.frontiter = None;
2736 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
2737 where Fold: FnMut(Acc, Self::Item) -> Acc,
2739 self.frontiter.into_iter()
2740 .chain(self.iter.map(IntoIterator::into_iter))
2741 .chain(self.backiter)
2742 .rfold(init, |acc, iter| iter.rfold(acc, &mut fold))
2746 /// An iterator that yields `None` forever after the underlying iterator
2747 /// yields `None` once.
2749 /// This `struct` is created by the [`fuse`] method on [`Iterator`]. See its
2750 /// documentation for more.
2752 /// [`fuse`]: trait.Iterator.html#method.fuse
2753 /// [`Iterator`]: trait.Iterator.html
2754 #[derive(Clone, Debug)]
2755 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2756 #[stable(feature = "rust1", since = "1.0.0")]
2757 pub struct Fuse<I> {
2762 #[stable(feature = "fused", since = "1.26.0")]
2763 impl<I> FusedIterator for Fuse<I> where I: Iterator {}
2765 #[stable(feature = "rust1", since = "1.0.0")]
2766 impl<I> Iterator for Fuse<I> where I: Iterator {
2767 type Item = <I as Iterator>::Item;
2770 default fn next(&mut self) -> Option<<I as Iterator>::Item> {
2774 let next = self.iter.next();
2775 self.done = next.is_none();
2781 default fn nth(&mut self, n: usize) -> Option<I::Item> {
2785 let nth = self.iter.nth(n);
2786 self.done = nth.is_none();
2792 default fn last(self) -> Option<I::Item> {
2801 default fn count(self) -> usize {
2810 default fn size_hint(&self) -> (usize, Option<usize>) {
2814 self.iter.size_hint()
2819 default fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2820 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2825 let acc = self.iter.try_fold(init, fold)?;
2832 default fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2833 where Fold: FnMut(Acc, Self::Item) -> Acc,
2838 self.iter.fold(init, fold)
2843 #[stable(feature = "rust1", since = "1.0.0")]
2844 impl<I> DoubleEndedIterator for Fuse<I> where I: DoubleEndedIterator {
2846 default fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
2850 let next = self.iter.next_back();
2851 self.done = next.is_none();
2857 default fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2858 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2863 let acc = self.iter.try_rfold(init, fold)?;
2870 default fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2871 where Fold: FnMut(Acc, Self::Item) -> Acc,
2876 self.iter.rfold(init, fold)
2881 unsafe impl<I> TrustedRandomAccess for Fuse<I>
2882 where I: TrustedRandomAccess,
2884 unsafe fn get_unchecked(&mut self, i: usize) -> I::Item {
2885 self.iter.get_unchecked(i)
2888 fn may_have_side_effect() -> bool {
2889 I::may_have_side_effect()
2893 #[stable(feature = "fused", since = "1.26.0")]
2894 impl<I> Iterator for Fuse<I> where I: FusedIterator {
2896 fn next(&mut self) -> Option<<I as Iterator>::Item> {
2901 fn nth(&mut self, n: usize) -> Option<I::Item> {
2906 fn last(self) -> Option<I::Item> {
2911 fn count(self) -> usize {
2916 fn size_hint(&self) -> (usize, Option<usize>) {
2917 self.iter.size_hint()
2921 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2922 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2924 self.iter.try_fold(init, fold)
2928 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2929 where Fold: FnMut(Acc, Self::Item) -> Acc,
2931 self.iter.fold(init, fold)
2935 #[stable(feature = "fused", since = "1.26.0")]
2936 impl<I> DoubleEndedIterator for Fuse<I>
2937 where I: DoubleEndedIterator + FusedIterator
2940 fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
2941 self.iter.next_back()
2945 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2946 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2948 self.iter.try_rfold(init, fold)
2952 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2953 where Fold: FnMut(Acc, Self::Item) -> Acc,
2955 self.iter.rfold(init, fold)
2960 #[stable(feature = "rust1", since = "1.0.0")]
2961 impl<I> ExactSizeIterator for Fuse<I> where I: ExactSizeIterator {
2962 fn len(&self) -> usize {
2966 fn is_empty(&self) -> bool {
2967 self.iter.is_empty()
2971 /// An iterator that calls a function with a reference to each element before
2974 /// This `struct` is created by the [`inspect`] method on [`Iterator`]. See its
2975 /// documentation for more.
2977 /// [`inspect`]: trait.Iterator.html#method.inspect
2978 /// [`Iterator`]: trait.Iterator.html
2979 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2980 #[stable(feature = "rust1", since = "1.0.0")]
2982 pub struct Inspect<I, F> {
2987 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2988 impl<I: fmt::Debug, F> fmt::Debug for Inspect<I, F> {
2989 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2990 f.debug_struct("Inspect")
2991 .field("iter", &self.iter)
2996 impl<I: Iterator, F> Inspect<I, F> where F: FnMut(&I::Item) {
2998 fn do_inspect(&mut self, elt: Option<I::Item>) -> Option<I::Item> {
2999 if let Some(ref a) = elt {
3007 #[stable(feature = "rust1", since = "1.0.0")]
3008 impl<I: Iterator, F> Iterator for Inspect<I, F> where F: FnMut(&I::Item) {
3009 type Item = I::Item;
3012 fn next(&mut self) -> Option<I::Item> {
3013 let next = self.iter.next();
3014 self.do_inspect(next)
3018 fn size_hint(&self) -> (usize, Option<usize>) {
3019 self.iter.size_hint()
3023 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
3024 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
3026 let f = &mut self.f;
3027 self.iter.try_fold(init, move |acc, item| { f(&item); fold(acc, item) })
3031 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
3032 where Fold: FnMut(Acc, Self::Item) -> Acc,
3035 self.iter.fold(init, move |acc, item| { f(&item); fold(acc, item) })
3039 #[stable(feature = "rust1", since = "1.0.0")]
3040 impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
3041 where F: FnMut(&I::Item),
3044 fn next_back(&mut self) -> Option<I::Item> {
3045 let next = self.iter.next_back();
3046 self.do_inspect(next)
3050 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
3051 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
3053 let f = &mut self.f;
3054 self.iter.try_rfold(init, move |acc, item| { f(&item); fold(acc, item) })
3058 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
3059 where Fold: FnMut(Acc, Self::Item) -> Acc,
3062 self.iter.rfold(init, move |acc, item| { f(&item); fold(acc, item) })
3066 #[stable(feature = "rust1", since = "1.0.0")]
3067 impl<I: ExactSizeIterator, F> ExactSizeIterator for Inspect<I, F>
3068 where F: FnMut(&I::Item)
3070 fn len(&self) -> usize {
3074 fn is_empty(&self) -> bool {
3075 self.iter.is_empty()
3079 #[stable(feature = "fused", since = "1.26.0")]
3080 impl<I: FusedIterator, F> FusedIterator for Inspect<I, F>
3081 where F: FnMut(&I::Item) {}