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 #[unstable(feature = "iterator_repeat_with", issue = "48169")]
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 #[unstable(feature = "iterator_step_by",
677 reason = "unstable replacement of Range::step_by",
679 #[derive(Clone, Debug)]
680 pub struct StepBy<I> {
686 #[unstable(feature = "iterator_step_by",
687 reason = "unstable replacement of Range::step_by",
689 impl<I> Iterator for StepBy<I> where I: Iterator {
693 fn next(&mut self) -> Option<Self::Item> {
695 self.first_take = false;
698 self.iter.nth(self.step)
703 fn size_hint(&self) -> (usize, Option<usize>) {
704 let inner_hint = self.iter.size_hint();
707 let f = |n| if n == 0 { 0 } else { 1 + (n-1)/(self.step+1) };
708 (f(inner_hint.0), inner_hint.1.map(f))
710 let f = |n| n / (self.step+1);
711 (f(inner_hint.0), inner_hint.1.map(f))
716 fn nth(&mut self, mut n: usize) -> Option<Self::Item> {
718 self.first_take = false;
719 let first = self.iter.next();
725 // n and self.step are indices, we need to add 1 to get the amount of elements
726 // When calling `.nth`, we need to subtract 1 again to convert back to an index
727 // step + 1 can't overflow because `.step_by` sets `self.step` to `step - 1`
728 let mut step = self.step + 1;
729 // n + 1 could overflow
730 // thus, if n is usize::MAX, instead of adding one, we call .nth(step)
732 self.iter.nth(step - 1);
739 let mul = n.checked_mul(step);
740 if unsafe { intrinsics::likely(mul.is_some()) } {
741 return self.iter.nth(mul.unwrap() - 1);
743 let div_n = usize::MAX / n;
744 let div_step = usize::MAX / step;
745 let nth_n = div_n * n;
746 let nth_step = div_step * step;
747 let nth = if nth_n > nth_step {
754 self.iter.nth(nth - 1);
759 // StepBy can only make the iterator shorter, so the len will still fit.
760 #[unstable(feature = "iterator_step_by",
761 reason = "unstable replacement of Range::step_by",
763 impl<I> ExactSizeIterator for StepBy<I> where I: ExactSizeIterator {}
765 /// An iterator that strings two iterators together.
767 /// This `struct` is created by the [`chain`] method on [`Iterator`]. See its
768 /// documentation for more.
770 /// [`chain`]: trait.Iterator.html#method.chain
771 /// [`Iterator`]: trait.Iterator.html
772 #[derive(Clone, Debug)]
773 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
774 #[stable(feature = "rust1", since = "1.0.0")]
775 pub struct Chain<A, B> {
781 // The iterator protocol specifies that iteration ends with the return value
782 // `None` from `.next()` (or `.next_back()`) and it is unspecified what
783 // further calls return. The chain adaptor must account for this since it uses
786 // It uses three states:
788 // - Both: `a` and `b` are remaining
789 // - Front: `a` remaining
790 // - Back: `b` remaining
792 // The fourth state (neither iterator is remaining) only occurs after Chain has
793 // returned None once, so we don't need to store this state.
794 #[derive(Clone, Debug)]
796 // both front and back iterator are remaining
798 // only front is remaining
800 // only back is remaining
804 #[stable(feature = "rust1", since = "1.0.0")]
805 impl<A, B> Iterator for Chain<A, B> where
807 B: Iterator<Item = A::Item>
812 fn next(&mut self) -> Option<A::Item> {
814 ChainState::Both => match self.a.next() {
815 elt @ Some(..) => elt,
817 self.state = ChainState::Back;
821 ChainState::Front => self.a.next(),
822 ChainState::Back => self.b.next(),
827 #[rustc_inherit_overflow_checks]
828 fn count(self) -> usize {
830 ChainState::Both => self.a.count() + self.b.count(),
831 ChainState::Front => self.a.count(),
832 ChainState::Back => self.b.count(),
836 fn try_fold<Acc, F, R>(&mut self, init: Acc, mut f: F) -> R where
837 Self: Sized, F: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
839 let mut accum = init;
841 ChainState::Both | ChainState::Front => {
842 accum = self.a.try_fold(accum, &mut f)?;
843 if let ChainState::Both = self.state {
844 self.state = ChainState::Back;
849 if let ChainState::Back = self.state {
850 accum = self.b.try_fold(accum, &mut f)?;
855 fn fold<Acc, F>(self, init: Acc, mut f: F) -> Acc
856 where F: FnMut(Acc, Self::Item) -> Acc,
858 let mut accum = init;
860 ChainState::Both | ChainState::Front => {
861 accum = self.a.fold(accum, &mut f);
866 ChainState::Both | ChainState::Back => {
867 accum = self.b.fold(accum, &mut f);
875 fn nth(&mut self, mut n: usize) -> Option<A::Item> {
877 ChainState::Both | ChainState::Front => {
878 for x in self.a.by_ref() {
884 if let ChainState::Both = self.state {
885 self.state = ChainState::Back;
888 ChainState::Back => {}
890 if let ChainState::Back = self.state {
898 fn find<P>(&mut self, mut predicate: P) -> Option<Self::Item> where
899 P: FnMut(&Self::Item) -> bool,
902 ChainState::Both => match self.a.find(&mut predicate) {
904 self.state = ChainState::Back;
905 self.b.find(predicate)
909 ChainState::Front => self.a.find(predicate),
910 ChainState::Back => self.b.find(predicate),
915 fn last(self) -> Option<A::Item> {
917 ChainState::Both => {
918 // Must exhaust a before b.
919 let a_last = self.a.last();
920 let b_last = self.b.last();
923 ChainState::Front => self.a.last(),
924 ChainState::Back => self.b.last()
929 fn size_hint(&self) -> (usize, Option<usize>) {
930 let (a_lower, a_upper) = self.a.size_hint();
931 let (b_lower, b_upper) = self.b.size_hint();
933 let lower = a_lower.saturating_add(b_lower);
935 let upper = match (a_upper, b_upper) {
936 (Some(x), Some(y)) => x.checked_add(y),
944 #[stable(feature = "rust1", since = "1.0.0")]
945 impl<A, B> DoubleEndedIterator for Chain<A, B> where
946 A: DoubleEndedIterator,
947 B: DoubleEndedIterator<Item=A::Item>,
950 fn next_back(&mut self) -> Option<A::Item> {
952 ChainState::Both => match self.b.next_back() {
953 elt @ Some(..) => elt,
955 self.state = ChainState::Front;
959 ChainState::Front => self.a.next_back(),
960 ChainState::Back => self.b.next_back(),
964 fn try_rfold<Acc, F, R>(&mut self, init: Acc, mut f: F) -> R where
965 Self: Sized, F: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
967 let mut accum = init;
969 ChainState::Both | ChainState::Back => {
970 accum = self.b.try_rfold(accum, &mut f)?;
971 if let ChainState::Both = self.state {
972 self.state = ChainState::Front;
977 if let ChainState::Front = self.state {
978 accum = self.a.try_rfold(accum, &mut f)?;
983 fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
984 where F: FnMut(Acc, Self::Item) -> Acc,
986 let mut accum = init;
988 ChainState::Both | ChainState::Back => {
989 accum = self.b.rfold(accum, &mut f);
994 ChainState::Both | ChainState::Front => {
995 accum = self.a.rfold(accum, &mut f);
1004 // Note: *both* must be fused to handle double-ended iterators.
1005 #[stable(feature = "fused", since = "1.26.0")]
1006 impl<A, B> FusedIterator for Chain<A, B>
1007 where A: FusedIterator,
1008 B: FusedIterator<Item=A::Item>,
1011 #[unstable(feature = "trusted_len", issue = "37572")]
1012 unsafe impl<A, B> TrustedLen for Chain<A, B>
1013 where A: TrustedLen, B: TrustedLen<Item=A::Item>,
1016 /// An iterator that iterates two other iterators simultaneously.
1018 /// This `struct` is created by the [`zip`] method on [`Iterator`]. See its
1019 /// documentation for more.
1021 /// [`zip`]: trait.Iterator.html#method.zip
1022 /// [`Iterator`]: trait.Iterator.html
1023 #[derive(Clone, Debug)]
1024 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1025 #[stable(feature = "rust1", since = "1.0.0")]
1026 pub struct Zip<A, B> {
1029 // index and len are only used by the specialized version of zip
1034 #[stable(feature = "rust1", since = "1.0.0")]
1035 impl<A, B> Iterator for Zip<A, B> where A: Iterator, B: Iterator
1037 type Item = (A::Item, B::Item);
1040 fn next(&mut self) -> Option<Self::Item> {
1045 fn size_hint(&self) -> (usize, Option<usize>) {
1046 ZipImpl::size_hint(self)
1050 fn nth(&mut self, n: usize) -> Option<Self::Item> {
1051 ZipImpl::nth(self, n)
1055 #[stable(feature = "rust1", since = "1.0.0")]
1056 impl<A, B> DoubleEndedIterator for Zip<A, B> where
1057 A: DoubleEndedIterator + ExactSizeIterator,
1058 B: DoubleEndedIterator + ExactSizeIterator,
1061 fn next_back(&mut self) -> Option<(A::Item, B::Item)> {
1062 ZipImpl::next_back(self)
1066 // Zip specialization trait
1068 trait ZipImpl<A, B> {
1070 fn new(a: A, b: B) -> Self;
1071 fn next(&mut self) -> Option<Self::Item>;
1072 fn size_hint(&self) -> (usize, Option<usize>);
1073 fn nth(&mut self, n: usize) -> Option<Self::Item>;
1074 fn super_nth(&mut self, mut n: usize) -> Option<Self::Item> {
1075 while let Some(x) = self.next() {
1076 if n == 0 { return Some(x) }
1081 fn next_back(&mut self) -> Option<Self::Item>
1082 where A: DoubleEndedIterator + ExactSizeIterator,
1083 B: DoubleEndedIterator + ExactSizeIterator;
1088 impl<A, B> ZipImpl<A, B> for Zip<A, B>
1089 where A: Iterator, B: Iterator
1091 type Item = (A::Item, B::Item);
1092 default fn new(a: A, b: B) -> Self {
1102 default fn next(&mut self) -> Option<(A::Item, B::Item)> {
1103 self.a.next().and_then(|x| {
1104 self.b.next().and_then(|y| {
1111 default fn nth(&mut self, n: usize) -> Option<Self::Item> {
1116 default fn next_back(&mut self) -> Option<(A::Item, B::Item)>
1117 where A: DoubleEndedIterator + ExactSizeIterator,
1118 B: DoubleEndedIterator + ExactSizeIterator
1120 let a_sz = self.a.len();
1121 let b_sz = self.b.len();
1123 // Adjust a, b to equal length
1125 for _ in 0..a_sz - b_sz { self.a.next_back(); }
1127 for _ in 0..b_sz - a_sz { self.b.next_back(); }
1130 match (self.a.next_back(), self.b.next_back()) {
1131 (Some(x), Some(y)) => Some((x, y)),
1132 (None, None) => None,
1133 _ => unreachable!(),
1138 default fn size_hint(&self) -> (usize, Option<usize>) {
1139 let (a_lower, a_upper) = self.a.size_hint();
1140 let (b_lower, b_upper) = self.b.size_hint();
1142 let lower = cmp::min(a_lower, b_lower);
1144 let upper = match (a_upper, b_upper) {
1145 (Some(x), Some(y)) => Some(cmp::min(x,y)),
1146 (Some(x), None) => Some(x),
1147 (None, Some(y)) => Some(y),
1148 (None, None) => None
1156 impl<A, B> ZipImpl<A, B> for Zip<A, B>
1157 where A: TrustedRandomAccess, B: TrustedRandomAccess
1159 fn new(a: A, b: B) -> Self {
1160 let len = cmp::min(a.len(), b.len());
1170 fn next(&mut self) -> Option<(A::Item, B::Item)> {
1171 if self.index < self.len {
1175 Some((self.a.get_unchecked(i), self.b.get_unchecked(i)))
1177 } else if A::may_have_side_effect() && self.index < self.a.len() {
1178 // match the base implementation's potential side effects
1180 self.a.get_unchecked(self.index);
1190 fn size_hint(&self) -> (usize, Option<usize>) {
1191 let len = self.len - self.index;
1196 fn nth(&mut self, n: usize) -> Option<Self::Item> {
1197 let delta = cmp::min(n, self.len - self.index);
1198 let end = self.index + delta;
1199 while self.index < end {
1202 if A::may_have_side_effect() {
1203 unsafe { self.a.get_unchecked(i); }
1205 if B::may_have_side_effect() {
1206 unsafe { self.b.get_unchecked(i); }
1210 self.super_nth(n - delta)
1214 fn next_back(&mut self) -> Option<(A::Item, B::Item)>
1215 where A: DoubleEndedIterator + ExactSizeIterator,
1216 B: DoubleEndedIterator + ExactSizeIterator
1218 // Adjust a, b to equal length
1219 if A::may_have_side_effect() {
1220 let sz = self.a.len();
1222 for _ in 0..sz - cmp::max(self.len, self.index) {
1227 if B::may_have_side_effect() {
1228 let sz = self.b.len();
1230 for _ in 0..sz - self.len {
1235 if self.index < self.len {
1239 Some((self.a.get_unchecked(i), self.b.get_unchecked(i)))
1247 #[stable(feature = "rust1", since = "1.0.0")]
1248 impl<A, B> ExactSizeIterator for Zip<A, B>
1249 where A: ExactSizeIterator, B: ExactSizeIterator {}
1252 unsafe impl<A, B> TrustedRandomAccess for Zip<A, B>
1253 where A: TrustedRandomAccess,
1254 B: TrustedRandomAccess,
1256 unsafe fn get_unchecked(&mut self, i: usize) -> (A::Item, B::Item) {
1257 (self.a.get_unchecked(i), self.b.get_unchecked(i))
1260 fn may_have_side_effect() -> bool {
1261 A::may_have_side_effect() || B::may_have_side_effect()
1265 #[stable(feature = "fused", since = "1.26.0")]
1266 impl<A, B> FusedIterator for Zip<A, B>
1267 where A: FusedIterator, B: FusedIterator, {}
1269 #[unstable(feature = "trusted_len", issue = "37572")]
1270 unsafe impl<A, B> TrustedLen for Zip<A, B>
1271 where A: TrustedLen, B: TrustedLen,
1274 /// An iterator that maps the values of `iter` with `f`.
1276 /// This `struct` is created by the [`map`] method on [`Iterator`]. See its
1277 /// documentation for more.
1279 /// [`map`]: trait.Iterator.html#method.map
1280 /// [`Iterator`]: trait.Iterator.html
1282 /// # Notes about side effects
1284 /// The [`map`] iterator implements [`DoubleEndedIterator`], meaning that
1285 /// you can also [`map`] backwards:
1288 /// let v: Vec<i32> = vec![1, 2, 3].into_iter().map(|x| x + 1).rev().collect();
1290 /// assert_eq!(v, [4, 3, 2]);
1293 /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html
1295 /// But if your closure has state, iterating backwards may act in a way you do
1296 /// not expect. Let's go through an example. First, in the forward direction:
1301 /// for pair in vec!['a', 'b', 'c'].into_iter()
1302 /// .map(|letter| { c += 1; (letter, c) }) {
1303 /// println!("{:?}", pair);
1307 /// This will print "('a', 1), ('b', 2), ('c', 3)".
1309 /// Now consider this twist where we add a call to `rev`. This version will
1310 /// print `('c', 1), ('b', 2), ('a', 3)`. Note that the letters are reversed,
1311 /// but the values of the counter still go in order. This is because `map()` is
1312 /// still being called lazily on each item, but we are popping items off the
1313 /// back of the vector now, instead of shifting them from the front.
1318 /// for pair in vec!['a', 'b', 'c'].into_iter()
1319 /// .map(|letter| { c += 1; (letter, c) })
1321 /// println!("{:?}", pair);
1324 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1325 #[stable(feature = "rust1", since = "1.0.0")]
1327 pub struct Map<I, F> {
1332 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1333 impl<I: fmt::Debug, F> fmt::Debug for Map<I, F> {
1334 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1335 f.debug_struct("Map")
1336 .field("iter", &self.iter)
1341 #[stable(feature = "rust1", since = "1.0.0")]
1342 impl<B, I: Iterator, F> Iterator for Map<I, F> where F: FnMut(I::Item) -> B {
1346 fn next(&mut self) -> Option<B> {
1347 self.iter.next().map(&mut self.f)
1351 fn size_hint(&self) -> (usize, Option<usize>) {
1352 self.iter.size_hint()
1355 fn try_fold<Acc, G, R>(&mut self, init: Acc, mut g: G) -> R where
1356 Self: Sized, G: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1358 let f = &mut self.f;
1359 self.iter.try_fold(init, move |acc, elt| g(acc, f(elt)))
1362 fn fold<Acc, G>(self, init: Acc, mut g: G) -> Acc
1363 where G: FnMut(Acc, Self::Item) -> Acc,
1366 self.iter.fold(init, move |acc, elt| g(acc, f(elt)))
1370 #[stable(feature = "rust1", since = "1.0.0")]
1371 impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F> where
1372 F: FnMut(I::Item) -> B,
1375 fn next_back(&mut self) -> Option<B> {
1376 self.iter.next_back().map(&mut self.f)
1379 fn try_rfold<Acc, G, R>(&mut self, init: Acc, mut g: G) -> R where
1380 Self: Sized, G: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1382 let f = &mut self.f;
1383 self.iter.try_rfold(init, move |acc, elt| g(acc, f(elt)))
1386 fn rfold<Acc, G>(self, init: Acc, mut g: G) -> Acc
1387 where G: FnMut(Acc, Self::Item) -> Acc,
1390 self.iter.rfold(init, move |acc, elt| g(acc, f(elt)))
1394 #[stable(feature = "rust1", since = "1.0.0")]
1395 impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F>
1396 where F: FnMut(I::Item) -> B
1398 fn len(&self) -> usize {
1402 fn is_empty(&self) -> bool {
1403 self.iter.is_empty()
1407 #[stable(feature = "fused", since = "1.26.0")]
1408 impl<B, I: FusedIterator, F> FusedIterator for Map<I, F>
1409 where F: FnMut(I::Item) -> B {}
1411 #[unstable(feature = "trusted_len", issue = "37572")]
1412 unsafe impl<B, I, F> TrustedLen for Map<I, F>
1413 where I: TrustedLen,
1414 F: FnMut(I::Item) -> B {}
1417 unsafe impl<B, I, F> TrustedRandomAccess for Map<I, F>
1418 where I: TrustedRandomAccess,
1419 F: FnMut(I::Item) -> B,
1421 unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
1422 (self.f)(self.iter.get_unchecked(i))
1425 fn may_have_side_effect() -> bool { true }
1428 /// An iterator that filters the elements of `iter` with `predicate`.
1430 /// This `struct` is created by the [`filter`] method on [`Iterator`]. See its
1431 /// documentation for more.
1433 /// [`filter`]: trait.Iterator.html#method.filter
1434 /// [`Iterator`]: trait.Iterator.html
1435 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1436 #[stable(feature = "rust1", since = "1.0.0")]
1438 pub struct Filter<I, P> {
1443 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1444 impl<I: fmt::Debug, P> fmt::Debug for Filter<I, P> {
1445 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1446 f.debug_struct("Filter")
1447 .field("iter", &self.iter)
1452 #[stable(feature = "rust1", since = "1.0.0")]
1453 impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {
1454 type Item = I::Item;
1457 fn next(&mut self) -> Option<I::Item> {
1458 for x in &mut self.iter {
1459 if (self.predicate)(&x) {
1467 fn size_hint(&self) -> (usize, Option<usize>) {
1468 let (_, upper) = self.iter.size_hint();
1469 (0, upper) // can't know a lower bound, due to the predicate
1472 // this special case allows the compiler to make `.filter(_).count()`
1473 // branchless. Barring perfect branch prediction (which is unattainable in
1474 // the general case), this will be much faster in >90% of cases (containing
1475 // virtually all real workloads) and only a tiny bit slower in the rest.
1477 // Having this specialization thus allows us to write `.filter(p).count()`
1478 // where we would otherwise write `.map(|x| p(x) as usize).sum()`, which is
1479 // less readable and also less backwards-compatible to Rust before 1.10.
1481 // Using the branchless version will also simplify the LLVM byte code, thus
1482 // leaving more budget for LLVM optimizations.
1484 fn count(mut self) -> usize {
1486 for x in &mut self.iter {
1487 count += (self.predicate)(&x) as usize;
1493 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1494 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1496 let predicate = &mut self.predicate;
1497 self.iter.try_fold(init, move |acc, item| if predicate(&item) {
1505 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1506 where Fold: FnMut(Acc, Self::Item) -> Acc,
1508 let mut predicate = self.predicate;
1509 self.iter.fold(init, move |acc, item| if predicate(&item) {
1517 #[stable(feature = "rust1", since = "1.0.0")]
1518 impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
1519 where P: FnMut(&I::Item) -> bool,
1522 fn next_back(&mut self) -> Option<I::Item> {
1523 for x in self.iter.by_ref().rev() {
1524 if (self.predicate)(&x) {
1532 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1533 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1535 let predicate = &mut self.predicate;
1536 self.iter.try_rfold(init, move |acc, item| if predicate(&item) {
1544 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1545 where Fold: FnMut(Acc, Self::Item) -> Acc,
1547 let mut predicate = self.predicate;
1548 self.iter.rfold(init, move |acc, item| if predicate(&item) {
1556 #[stable(feature = "fused", since = "1.26.0")]
1557 impl<I: FusedIterator, P> FusedIterator for Filter<I, P>
1558 where P: FnMut(&I::Item) -> bool {}
1560 /// An iterator that uses `f` to both filter and map elements from `iter`.
1562 /// This `struct` is created by the [`filter_map`] method on [`Iterator`]. See its
1563 /// documentation for more.
1565 /// [`filter_map`]: trait.Iterator.html#method.filter_map
1566 /// [`Iterator`]: trait.Iterator.html
1567 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1568 #[stable(feature = "rust1", since = "1.0.0")]
1570 pub struct FilterMap<I, F> {
1575 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1576 impl<I: fmt::Debug, F> fmt::Debug for FilterMap<I, F> {
1577 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1578 f.debug_struct("FilterMap")
1579 .field("iter", &self.iter)
1584 #[stable(feature = "rust1", since = "1.0.0")]
1585 impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
1586 where F: FnMut(I::Item) -> Option<B>,
1591 fn next(&mut self) -> Option<B> {
1592 for x in self.iter.by_ref() {
1593 if let Some(y) = (self.f)(x) {
1601 fn size_hint(&self) -> (usize, Option<usize>) {
1602 let (_, upper) = self.iter.size_hint();
1603 (0, upper) // can't know a lower bound, due to the predicate
1607 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1608 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1610 let f = &mut self.f;
1611 self.iter.try_fold(init, move |acc, item| match f(item) {
1612 Some(x) => fold(acc, x),
1613 None => Try::from_ok(acc),
1618 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1619 where Fold: FnMut(Acc, Self::Item) -> Acc,
1622 self.iter.fold(init, move |acc, item| match f(item) {
1623 Some(x) => fold(acc, x),
1629 #[stable(feature = "rust1", since = "1.0.0")]
1630 impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
1631 where F: FnMut(I::Item) -> Option<B>,
1634 fn next_back(&mut self) -> Option<B> {
1635 for x in self.iter.by_ref().rev() {
1636 if let Some(y) = (self.f)(x) {
1644 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1645 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1647 let f = &mut self.f;
1648 self.iter.try_rfold(init, move |acc, item| match f(item) {
1649 Some(x) => fold(acc, x),
1650 None => Try::from_ok(acc),
1655 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1656 where Fold: FnMut(Acc, Self::Item) -> Acc,
1659 self.iter.rfold(init, move |acc, item| match f(item) {
1660 Some(x) => fold(acc, x),
1666 #[stable(feature = "fused", since = "1.26.0")]
1667 impl<B, I: FusedIterator, F> FusedIterator for FilterMap<I, F>
1668 where F: FnMut(I::Item) -> Option<B> {}
1670 /// An iterator that yields the current count and the element during iteration.
1672 /// This `struct` is created by the [`enumerate`] method on [`Iterator`]. See its
1673 /// documentation for more.
1675 /// [`enumerate`]: trait.Iterator.html#method.enumerate
1676 /// [`Iterator`]: trait.Iterator.html
1677 #[derive(Clone, Debug)]
1678 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1679 #[stable(feature = "rust1", since = "1.0.0")]
1680 pub struct Enumerate<I> {
1685 #[stable(feature = "rust1", since = "1.0.0")]
1686 impl<I> Iterator for Enumerate<I> where I: Iterator {
1687 type Item = (usize, <I as Iterator>::Item);
1689 /// # Overflow Behavior
1691 /// The method does no guarding against overflows, so enumerating more than
1692 /// `usize::MAX` elements either produces the wrong result or panics. If
1693 /// debug assertions are enabled, a panic is guaranteed.
1697 /// Might panic if the index of the element overflows a `usize`.
1699 #[rustc_inherit_overflow_checks]
1700 fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
1701 self.iter.next().map(|a| {
1702 let ret = (self.count, a);
1703 // Possible undefined overflow.
1710 fn size_hint(&self) -> (usize, Option<usize>) {
1711 self.iter.size_hint()
1715 #[rustc_inherit_overflow_checks]
1716 fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> {
1717 self.iter.nth(n).map(|a| {
1718 let i = self.count + n;
1725 fn count(self) -> usize {
1730 #[rustc_inherit_overflow_checks]
1731 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1732 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1734 let count = &mut self.count;
1735 self.iter.try_fold(init, move |acc, item| {
1736 let acc = fold(acc, (*count, item));
1743 #[rustc_inherit_overflow_checks]
1744 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1745 where Fold: FnMut(Acc, Self::Item) -> Acc,
1747 let mut count = self.count;
1748 self.iter.fold(init, move |acc, item| {
1749 let acc = fold(acc, (count, item));
1756 #[stable(feature = "rust1", since = "1.0.0")]
1757 impl<I> DoubleEndedIterator for Enumerate<I> where
1758 I: ExactSizeIterator + DoubleEndedIterator
1761 fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
1762 self.iter.next_back().map(|a| {
1763 let len = self.iter.len();
1764 // Can safely add, `ExactSizeIterator` promises that the number of
1765 // elements fits into a `usize`.
1766 (self.count + len, a)
1771 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1772 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1774 // Can safely add and subtract the count, as `ExactSizeIterator` promises
1775 // that the number of elements fits into a `usize`.
1776 let mut count = self.count + self.iter.len();
1777 self.iter.try_rfold(init, move |acc, item| {
1779 fold(acc, (count, item))
1784 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1785 where Fold: FnMut(Acc, Self::Item) -> Acc,
1787 // Can safely add and subtract the count, as `ExactSizeIterator` promises
1788 // that the number of elements fits into a `usize`.
1789 let mut count = self.count + self.iter.len();
1790 self.iter.rfold(init, move |acc, item| {
1792 fold(acc, (count, item))
1797 #[stable(feature = "rust1", since = "1.0.0")]
1798 impl<I> ExactSizeIterator for Enumerate<I> where I: ExactSizeIterator {
1799 fn len(&self) -> usize {
1803 fn is_empty(&self) -> bool {
1804 self.iter.is_empty()
1809 unsafe impl<I> TrustedRandomAccess for Enumerate<I>
1810 where I: TrustedRandomAccess
1812 unsafe fn get_unchecked(&mut self, i: usize) -> (usize, I::Item) {
1813 (self.count + i, self.iter.get_unchecked(i))
1816 fn may_have_side_effect() -> bool {
1817 I::may_have_side_effect()
1821 #[stable(feature = "fused", since = "1.26.0")]
1822 impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {}
1824 #[unstable(feature = "trusted_len", issue = "37572")]
1825 unsafe impl<I> TrustedLen for Enumerate<I>
1826 where I: TrustedLen,
1830 /// An iterator with a `peek()` that returns an optional reference to the next
1833 /// This `struct` is created by the [`peekable`] method on [`Iterator`]. See its
1834 /// documentation for more.
1836 /// [`peekable`]: trait.Iterator.html#method.peekable
1837 /// [`Iterator`]: trait.Iterator.html
1838 #[derive(Clone, Debug)]
1839 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1840 #[stable(feature = "rust1", since = "1.0.0")]
1841 pub struct Peekable<I: Iterator> {
1843 /// Remember a peeked value, even if it was None.
1844 peeked: Option<Option<I::Item>>,
1847 // Peekable must remember if a None has been seen in the `.peek()` method.
1848 // It ensures that `.peek(); .peek();` or `.peek(); .next();` only advances the
1849 // underlying iterator at most once. This does not by itself make the iterator
1851 #[stable(feature = "rust1", since = "1.0.0")]
1852 impl<I: Iterator> Iterator for Peekable<I> {
1853 type Item = I::Item;
1856 fn next(&mut self) -> Option<I::Item> {
1857 match self.peeked.take() {
1859 None => self.iter.next(),
1864 #[rustc_inherit_overflow_checks]
1865 fn count(mut self) -> usize {
1866 match self.peeked.take() {
1868 Some(Some(_)) => 1 + self.iter.count(),
1869 None => self.iter.count(),
1874 fn nth(&mut self, n: usize) -> Option<I::Item> {
1875 // FIXME(#6393): merge these when borrow-checking gets better.
1877 match self.peeked.take() {
1879 None => self.iter.nth(n),
1882 match self.peeked.take() {
1884 Some(Some(_)) => self.iter.nth(n - 1),
1885 None => self.iter.nth(n),
1891 fn last(mut self) -> Option<I::Item> {
1892 let peek_opt = match self.peeked.take() {
1893 Some(None) => return None,
1897 self.iter.last().or(peek_opt)
1901 fn size_hint(&self) -> (usize, Option<usize>) {
1902 let peek_len = match self.peeked {
1903 Some(None) => return (0, Some(0)),
1907 let (lo, hi) = self.iter.size_hint();
1908 let lo = lo.saturating_add(peek_len);
1909 let hi = hi.and_then(|x| x.checked_add(peek_len));
1914 fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where
1915 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
1917 let acc = match self.peeked.take() {
1918 Some(None) => return Try::from_ok(init),
1919 Some(Some(v)) => f(init, v)?,
1922 self.iter.try_fold(acc, f)
1926 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1927 where Fold: FnMut(Acc, Self::Item) -> Acc,
1929 let acc = match self.peeked {
1930 Some(None) => return init,
1931 Some(Some(v)) => fold(init, v),
1934 self.iter.fold(acc, fold)
1938 #[stable(feature = "rust1", since = "1.0.0")]
1939 impl<I: ExactSizeIterator> ExactSizeIterator for Peekable<I> {}
1941 #[stable(feature = "fused", since = "1.26.0")]
1942 impl<I: FusedIterator> FusedIterator for Peekable<I> {}
1944 impl<I: Iterator> Peekable<I> {
1945 /// Returns a reference to the next() value without advancing the iterator.
1947 /// Like [`next`], if there is a value, it is wrapped in a `Some(T)`.
1948 /// But if the iteration is over, `None` is returned.
1950 /// [`next`]: trait.Iterator.html#tymethod.next
1952 /// Because `peek()` returns a reference, and many iterators iterate over
1953 /// references, there can be a possibly confusing situation where the
1954 /// return value is a double reference. You can see this effect in the
1962 /// let xs = [1, 2, 3];
1964 /// let mut iter = xs.iter().peekable();
1966 /// // peek() lets us see into the future
1967 /// assert_eq!(iter.peek(), Some(&&1));
1968 /// assert_eq!(iter.next(), Some(&1));
1970 /// assert_eq!(iter.next(), Some(&2));
1972 /// // The iterator does not advance even if we `peek` multiple times
1973 /// assert_eq!(iter.peek(), Some(&&3));
1974 /// assert_eq!(iter.peek(), Some(&&3));
1976 /// assert_eq!(iter.next(), Some(&3));
1978 /// // After the iterator is finished, so is `peek()`
1979 /// assert_eq!(iter.peek(), None);
1980 /// assert_eq!(iter.next(), None);
1983 #[stable(feature = "rust1", since = "1.0.0")]
1984 pub fn peek(&mut self) -> Option<&I::Item> {
1985 if self.peeked.is_none() {
1986 self.peeked = Some(self.iter.next());
1989 Some(Some(ref value)) => Some(value),
1991 _ => unreachable!(),
1996 /// An iterator that rejects elements while `predicate` is true.
1998 /// This `struct` is created by the [`skip_while`] method on [`Iterator`]. See its
1999 /// documentation for more.
2001 /// [`skip_while`]: trait.Iterator.html#method.skip_while
2002 /// [`Iterator`]: trait.Iterator.html
2003 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2004 #[stable(feature = "rust1", since = "1.0.0")]
2006 pub struct SkipWhile<I, P> {
2012 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2013 impl<I: fmt::Debug, P> fmt::Debug for SkipWhile<I, P> {
2014 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2015 f.debug_struct("SkipWhile")
2016 .field("iter", &self.iter)
2017 .field("flag", &self.flag)
2022 #[stable(feature = "rust1", since = "1.0.0")]
2023 impl<I: Iterator, P> Iterator for SkipWhile<I, P>
2024 where P: FnMut(&I::Item) -> bool
2026 type Item = I::Item;
2029 fn next(&mut self) -> Option<I::Item> {
2030 let flag = &mut self.flag;
2031 let pred = &mut self.predicate;
2032 self.iter.find(move |x| {
2033 if *flag || !pred(x) {
2043 fn size_hint(&self) -> (usize, Option<usize>) {
2044 let (_, upper) = self.iter.size_hint();
2045 (0, upper) // can't know a lower bound, due to the predicate
2049 fn try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
2050 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2054 Some(v) => init = fold(init, v)?,
2055 None => return Try::from_ok(init),
2058 self.iter.try_fold(init, fold)
2062 fn fold<Acc, Fold>(mut self, mut init: Acc, mut fold: Fold) -> Acc
2063 where Fold: FnMut(Acc, Self::Item) -> Acc,
2067 Some(v) => init = fold(init, v),
2068 None => return init,
2071 self.iter.fold(init, fold)
2075 #[stable(feature = "fused", since = "1.26.0")]
2076 impl<I, P> FusedIterator for SkipWhile<I, P>
2077 where I: FusedIterator, P: FnMut(&I::Item) -> bool {}
2079 /// An iterator that only accepts elements while `predicate` is true.
2081 /// This `struct` is created by the [`take_while`] method on [`Iterator`]. See its
2082 /// documentation for more.
2084 /// [`take_while`]: trait.Iterator.html#method.take_while
2085 /// [`Iterator`]: trait.Iterator.html
2086 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2087 #[stable(feature = "rust1", since = "1.0.0")]
2089 pub struct TakeWhile<I, P> {
2095 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2096 impl<I: fmt::Debug, P> fmt::Debug for TakeWhile<I, P> {
2097 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2098 f.debug_struct("TakeWhile")
2099 .field("iter", &self.iter)
2100 .field("flag", &self.flag)
2105 #[stable(feature = "rust1", since = "1.0.0")]
2106 impl<I: Iterator, P> Iterator for TakeWhile<I, P>
2107 where P: FnMut(&I::Item) -> bool
2109 type Item = I::Item;
2112 fn next(&mut self) -> Option<I::Item> {
2116 self.iter.next().and_then(|x| {
2117 if (self.predicate)(&x) {
2128 fn size_hint(&self) -> (usize, Option<usize>) {
2129 let (_, upper) = self.iter.size_hint();
2130 (0, upper) // can't know a lower bound, due to the predicate
2134 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2135 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2140 let flag = &mut self.flag;
2141 let p = &mut self.predicate;
2142 self.iter.try_fold(init, move |acc, x|{
2144 LoopState::from_try(fold(acc, x))
2147 LoopState::Break(Try::from_ok(acc))
2154 #[stable(feature = "fused", since = "1.26.0")]
2155 impl<I, P> FusedIterator for TakeWhile<I, P>
2156 where I: FusedIterator, P: FnMut(&I::Item) -> bool {}
2158 /// An iterator that skips over `n` elements of `iter`.
2160 /// This `struct` is created by the [`skip`] method on [`Iterator`]. See its
2161 /// documentation for more.
2163 /// [`skip`]: trait.Iterator.html#method.skip
2164 /// [`Iterator`]: trait.Iterator.html
2165 #[derive(Clone, Debug)]
2166 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2167 #[stable(feature = "rust1", since = "1.0.0")]
2168 pub struct Skip<I> {
2173 #[stable(feature = "rust1", since = "1.0.0")]
2174 impl<I> Iterator for Skip<I> where I: Iterator {
2175 type Item = <I as Iterator>::Item;
2178 fn next(&mut self) -> Option<I::Item> {
2184 self.iter.nth(old_n)
2189 fn nth(&mut self, n: usize) -> Option<I::Item> {
2190 // Can't just add n + self.n due to overflow.
2194 let to_skip = self.n;
2197 if self.iter.nth(to_skip-1).is_none() {
2205 fn count(self) -> usize {
2206 self.iter.count().saturating_sub(self.n)
2210 fn last(mut self) -> Option<I::Item> {
2214 let next = self.next();
2216 // recurse. n should be 0.
2217 self.last().or(next)
2225 fn size_hint(&self) -> (usize, Option<usize>) {
2226 let (lower, upper) = self.iter.size_hint();
2228 let lower = lower.saturating_sub(self.n);
2229 let upper = upper.map(|x| x.saturating_sub(self.n));
2235 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2236 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2242 if self.iter.nth(n - 1).is_none() {
2243 return Try::from_ok(init);
2246 self.iter.try_fold(init, fold)
2250 fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
2251 where Fold: FnMut(Acc, Self::Item) -> Acc,
2255 if self.iter.nth(self.n - 1).is_none() {
2259 self.iter.fold(init, fold)
2263 #[stable(feature = "rust1", since = "1.0.0")]
2264 impl<I> ExactSizeIterator for Skip<I> where I: ExactSizeIterator {}
2266 #[stable(feature = "double_ended_skip_iterator", since = "1.9.0")]
2267 impl<I> DoubleEndedIterator for Skip<I> where I: DoubleEndedIterator + ExactSizeIterator {
2268 fn next_back(&mut self) -> Option<Self::Item> {
2270 self.iter.next_back()
2276 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2277 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2279 let mut n = self.len();
2283 self.iter.try_rfold(init, move |acc, x| {
2285 let r = fold(acc, x);
2286 if n == 0 { LoopState::Break(r) }
2287 else { LoopState::from_try(r) }
2293 #[stable(feature = "fused", since = "1.26.0")]
2294 impl<I> FusedIterator for Skip<I> where I: FusedIterator {}
2296 /// An iterator that only iterates over the first `n` iterations of `iter`.
2298 /// This `struct` is created by the [`take`] method on [`Iterator`]. See its
2299 /// documentation for more.
2301 /// [`take`]: trait.Iterator.html#method.take
2302 /// [`Iterator`]: trait.Iterator.html
2303 #[derive(Clone, Debug)]
2304 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2305 #[stable(feature = "rust1", since = "1.0.0")]
2306 pub struct Take<I> {
2311 #[stable(feature = "rust1", since = "1.0.0")]
2312 impl<I> Iterator for Take<I> where I: Iterator{
2313 type Item = <I as Iterator>::Item;
2316 fn next(&mut self) -> Option<<I as Iterator>::Item> {
2326 fn nth(&mut self, n: usize) -> Option<I::Item> {
2332 self.iter.nth(self.n - 1);
2340 fn size_hint(&self) -> (usize, Option<usize>) {
2341 let (lower, upper) = self.iter.size_hint();
2343 let lower = cmp::min(lower, self.n);
2345 let upper = match upper {
2346 Some(x) if x < self.n => Some(x),
2354 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2355 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2360 let n = &mut self.n;
2361 self.iter.try_fold(init, move |acc, x| {
2363 let r = fold(acc, x);
2364 if *n == 0 { LoopState::Break(r) }
2365 else { LoopState::from_try(r) }
2371 #[stable(feature = "rust1", since = "1.0.0")]
2372 impl<I> ExactSizeIterator for Take<I> where I: ExactSizeIterator {}
2374 #[stable(feature = "fused", since = "1.26.0")]
2375 impl<I> FusedIterator for Take<I> where I: FusedIterator {}
2377 #[unstable(feature = "trusted_len", issue = "37572")]
2378 unsafe impl<I: TrustedLen> TrustedLen for Take<I> {}
2380 /// An iterator to maintain state while iterating another iterator.
2382 /// This `struct` is created by the [`scan`] method on [`Iterator`]. See its
2383 /// documentation for more.
2385 /// [`scan`]: trait.Iterator.html#method.scan
2386 /// [`Iterator`]: trait.Iterator.html
2387 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2388 #[stable(feature = "rust1", since = "1.0.0")]
2390 pub struct Scan<I, St, F> {
2396 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2397 impl<I: fmt::Debug, St: fmt::Debug, F> fmt::Debug for Scan<I, St, F> {
2398 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2399 f.debug_struct("Scan")
2400 .field("iter", &self.iter)
2401 .field("state", &self.state)
2406 #[stable(feature = "rust1", since = "1.0.0")]
2407 impl<B, I, St, F> Iterator for Scan<I, St, F> where
2409 F: FnMut(&mut St, I::Item) -> Option<B>,
2414 fn next(&mut self) -> Option<B> {
2415 self.iter.next().and_then(|a| (self.f)(&mut self.state, a))
2419 fn size_hint(&self) -> (usize, Option<usize>) {
2420 let (_, upper) = self.iter.size_hint();
2421 (0, upper) // can't know a lower bound, due to the scan function
2425 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2426 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2428 let state = &mut self.state;
2429 let f = &mut self.f;
2430 self.iter.try_fold(init, move |acc, x| {
2432 None => LoopState::Break(Try::from_ok(acc)),
2433 Some(x) => LoopState::from_try(fold(acc, x)),
2439 /// An iterator that maps each element to an iterator, and yields the elements
2440 /// of the produced iterators.
2442 /// This `struct` is created by the [`flat_map`] method on [`Iterator`]. See its
2443 /// documentation for more.
2445 /// [`flat_map`]: trait.Iterator.html#method.flat_map
2446 /// [`Iterator`]: trait.Iterator.html
2447 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2448 #[stable(feature = "rust1", since = "1.0.0")]
2449 pub struct FlatMap<I, U: IntoIterator, F> {
2450 inner: FlattenCompat<Map<I, F>, <U as IntoIterator>::IntoIter>
2453 #[stable(feature = "rust1", since = "1.0.0")]
2454 impl<I: Clone, U: Clone + IntoIterator, F: Clone> Clone for FlatMap<I, U, F>
2455 where <U as IntoIterator>::IntoIter: Clone
2457 fn clone(&self) -> Self { FlatMap { inner: self.inner.clone() } }
2460 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2461 impl<I: fmt::Debug, U: IntoIterator, F> fmt::Debug for FlatMap<I, U, F>
2462 where U::IntoIter: fmt::Debug
2464 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2465 f.debug_struct("FlatMap").field("inner", &self.inner).finish()
2469 #[stable(feature = "rust1", since = "1.0.0")]
2470 impl<I: Iterator, U: IntoIterator, F> Iterator for FlatMap<I, U, F>
2471 where F: FnMut(I::Item) -> U,
2473 type Item = U::Item;
2476 fn next(&mut self) -> Option<U::Item> { self.inner.next() }
2479 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
2482 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2483 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2485 self.inner.try_fold(init, fold)
2489 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2490 where Fold: FnMut(Acc, Self::Item) -> Acc,
2492 self.inner.fold(init, fold)
2496 #[stable(feature = "rust1", since = "1.0.0")]
2497 impl<I: DoubleEndedIterator, U, F> DoubleEndedIterator for FlatMap<I, U, F>
2498 where F: FnMut(I::Item) -> U,
2500 U::IntoIter: DoubleEndedIterator
2503 fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }
2506 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2507 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2509 self.inner.try_rfold(init, fold)
2513 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2514 where Fold: FnMut(Acc, Self::Item) -> Acc,
2516 self.inner.rfold(init, fold)
2520 #[stable(feature = "fused", since = "1.26.0")]
2521 impl<I, U, F> FusedIterator for FlatMap<I, U, F>
2522 where I: FusedIterator, U: IntoIterator, F: FnMut(I::Item) -> U {}
2524 /// An iterator that flattens one level of nesting in an iterator of things
2525 /// that can be turned into iterators.
2527 /// This `struct` is created by the [`flatten`] method on [`Iterator`]. See its
2528 /// documentation for more.
2530 /// [`flatten`]: trait.Iterator.html#method.flatten
2531 /// [`Iterator`]: trait.Iterator.html
2532 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2533 #[unstable(feature = "iterator_flatten", issue = "48213")]
2534 pub struct Flatten<I: Iterator>
2535 where I::Item: IntoIterator {
2536 inner: FlattenCompat<I, <I::Item as IntoIterator>::IntoIter>,
2539 #[unstable(feature = "iterator_flatten", issue = "48213")]
2540 impl<I, U> fmt::Debug for Flatten<I>
2541 where I: Iterator + fmt::Debug, U: Iterator + fmt::Debug,
2542 I::Item: IntoIterator<IntoIter = U, Item = U::Item>,
2544 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2545 f.debug_struct("Flatten").field("inner", &self.inner).finish()
2549 #[unstable(feature = "iterator_flatten", issue = "48213")]
2550 impl<I, U> Clone for Flatten<I>
2551 where I: Iterator + Clone, U: Iterator + Clone,
2552 I::Item: IntoIterator<IntoIter = U, Item = U::Item>,
2554 fn clone(&self) -> Self { Flatten { inner: self.inner.clone() } }
2557 #[unstable(feature = "iterator_flatten", issue = "48213")]
2558 impl<I, U> Iterator for Flatten<I>
2559 where I: Iterator, U: Iterator,
2560 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2562 type Item = U::Item;
2565 fn next(&mut self) -> Option<U::Item> { self.inner.next() }
2568 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
2571 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2572 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2574 self.inner.try_fold(init, fold)
2578 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2579 where Fold: FnMut(Acc, Self::Item) -> Acc,
2581 self.inner.fold(init, fold)
2585 #[unstable(feature = "iterator_flatten", issue = "48213")]
2586 impl<I, U> DoubleEndedIterator for Flatten<I>
2587 where I: DoubleEndedIterator, U: DoubleEndedIterator,
2588 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2591 fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }
2594 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2595 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2597 self.inner.try_rfold(init, fold)
2601 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2602 where Fold: FnMut(Acc, Self::Item) -> Acc,
2604 self.inner.rfold(init, fold)
2608 #[stable(feature = "fused", since = "1.26.0")]
2609 impl<I, U> FusedIterator for Flatten<I>
2610 where I: FusedIterator, U: Iterator,
2611 I::Item: IntoIterator<IntoIter = U, Item = U::Item> {}
2613 /// Adapts an iterator by flattening it, for use in `flatten()` and `flat_map()`.
2614 fn flatten_compat<I, U>(iter: I) -> FlattenCompat<I, U> {
2615 FlattenCompat { iter, frontiter: None, backiter: None }
2618 /// Real logic of both `Flatten` and `FlatMap` which simply delegate to
2620 #[derive(Clone, Debug)]
2621 struct FlattenCompat<I, U> {
2623 frontiter: Option<U>,
2624 backiter: Option<U>,
2627 impl<I, U> Iterator for FlattenCompat<I, U>
2628 where I: Iterator, U: Iterator,
2629 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2631 type Item = U::Item;
2634 fn next(&mut self) -> Option<U::Item> {
2636 if let Some(ref mut inner) = self.frontiter {
2637 if let elt@Some(_) = inner.next() { return elt }
2639 match self.iter.next() {
2640 None => return self.backiter.as_mut().and_then(|it| it.next()),
2641 Some(inner) => self.frontiter = Some(inner.into_iter()),
2647 fn size_hint(&self) -> (usize, Option<usize>) {
2648 let (flo, fhi) = self.frontiter.as_ref().map_or((0, Some(0)), |it| it.size_hint());
2649 let (blo, bhi) = self.backiter.as_ref().map_or((0, Some(0)), |it| it.size_hint());
2650 let lo = flo.saturating_add(blo);
2651 match (self.iter.size_hint(), fhi, bhi) {
2652 ((0, Some(0)), Some(a), Some(b)) => (lo, a.checked_add(b)),
2658 fn try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
2659 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2661 if let Some(ref mut front) = self.frontiter {
2662 init = front.try_fold(init, &mut fold)?;
2664 self.frontiter = None;
2667 let frontiter = &mut self.frontiter;
2668 init = self.iter.try_fold(init, |acc, x| {
2669 let mut mid = x.into_iter();
2670 let r = mid.try_fold(acc, &mut fold);
2671 *frontiter = Some(mid);
2675 self.frontiter = None;
2677 if let Some(ref mut back) = self.backiter {
2678 init = back.try_fold(init, &mut fold)?;
2680 self.backiter = None;
2686 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
2687 where Fold: FnMut(Acc, Self::Item) -> Acc,
2689 self.frontiter.into_iter()
2690 .chain(self.iter.map(IntoIterator::into_iter))
2691 .chain(self.backiter)
2692 .fold(init, |acc, iter| iter.fold(acc, &mut fold))
2696 impl<I, U> DoubleEndedIterator for FlattenCompat<I, U>
2697 where I: DoubleEndedIterator, U: DoubleEndedIterator,
2698 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2701 fn next_back(&mut self) -> Option<U::Item> {
2703 if let Some(ref mut inner) = self.backiter {
2704 if let elt@Some(_) = inner.next_back() { return elt }
2706 match self.iter.next_back() {
2707 None => return self.frontiter.as_mut().and_then(|it| it.next_back()),
2708 next => self.backiter = next.map(IntoIterator::into_iter),
2714 fn try_rfold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
2715 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2717 if let Some(ref mut back) = self.backiter {
2718 init = back.try_rfold(init, &mut fold)?;
2720 self.backiter = None;
2723 let backiter = &mut self.backiter;
2724 init = self.iter.try_rfold(init, |acc, x| {
2725 let mut mid = x.into_iter();
2726 let r = mid.try_rfold(acc, &mut fold);
2727 *backiter = Some(mid);
2731 self.backiter = None;
2733 if let Some(ref mut front) = self.frontiter {
2734 init = front.try_rfold(init, &mut fold)?;
2736 self.frontiter = None;
2742 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
2743 where Fold: FnMut(Acc, Self::Item) -> Acc,
2745 self.frontiter.into_iter()
2746 .chain(self.iter.map(IntoIterator::into_iter))
2747 .chain(self.backiter)
2748 .rfold(init, |acc, iter| iter.rfold(acc, &mut fold))
2752 /// An iterator that yields `None` forever after the underlying iterator
2753 /// yields `None` once.
2755 /// This `struct` is created by the [`fuse`] method on [`Iterator`]. See its
2756 /// documentation for more.
2758 /// [`fuse`]: trait.Iterator.html#method.fuse
2759 /// [`Iterator`]: trait.Iterator.html
2760 #[derive(Clone, Debug)]
2761 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2762 #[stable(feature = "rust1", since = "1.0.0")]
2763 pub struct Fuse<I> {
2768 #[stable(feature = "fused", since = "1.26.0")]
2769 impl<I> FusedIterator for Fuse<I> where I: Iterator {}
2771 #[stable(feature = "rust1", since = "1.0.0")]
2772 impl<I> Iterator for Fuse<I> where I: Iterator {
2773 type Item = <I as Iterator>::Item;
2776 default fn next(&mut self) -> Option<<I as Iterator>::Item> {
2780 let next = self.iter.next();
2781 self.done = next.is_none();
2787 default fn nth(&mut self, n: usize) -> Option<I::Item> {
2791 let nth = self.iter.nth(n);
2792 self.done = nth.is_none();
2798 default fn last(self) -> Option<I::Item> {
2807 default fn count(self) -> usize {
2816 default fn size_hint(&self) -> (usize, Option<usize>) {
2820 self.iter.size_hint()
2825 default fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2826 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2831 let acc = self.iter.try_fold(init, fold)?;
2838 default fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2839 where Fold: FnMut(Acc, Self::Item) -> Acc,
2844 self.iter.fold(init, fold)
2849 #[stable(feature = "rust1", since = "1.0.0")]
2850 impl<I> DoubleEndedIterator for Fuse<I> where I: DoubleEndedIterator {
2852 default fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
2856 let next = self.iter.next_back();
2857 self.done = next.is_none();
2863 default fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2864 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2869 let acc = self.iter.try_rfold(init, fold)?;
2876 default fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2877 where Fold: FnMut(Acc, Self::Item) -> Acc,
2882 self.iter.rfold(init, fold)
2887 unsafe impl<I> TrustedRandomAccess for Fuse<I>
2888 where I: TrustedRandomAccess,
2890 unsafe fn get_unchecked(&mut self, i: usize) -> I::Item {
2891 self.iter.get_unchecked(i)
2894 fn may_have_side_effect() -> bool {
2895 I::may_have_side_effect()
2899 #[stable(feature = "fused", since = "1.26.0")]
2900 impl<I> Iterator for Fuse<I> where I: FusedIterator {
2902 fn next(&mut self) -> Option<<I as Iterator>::Item> {
2907 fn nth(&mut self, n: usize) -> Option<I::Item> {
2912 fn last(self) -> Option<I::Item> {
2917 fn count(self) -> usize {
2922 fn size_hint(&self) -> (usize, Option<usize>) {
2923 self.iter.size_hint()
2927 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2928 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2930 self.iter.try_fold(init, fold)
2934 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2935 where Fold: FnMut(Acc, Self::Item) -> Acc,
2937 self.iter.fold(init, fold)
2941 #[stable(feature = "fused", since = "1.26.0")]
2942 impl<I> DoubleEndedIterator for Fuse<I>
2943 where I: DoubleEndedIterator + FusedIterator
2946 fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
2947 self.iter.next_back()
2951 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2952 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2954 self.iter.try_rfold(init, fold)
2958 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2959 where Fold: FnMut(Acc, Self::Item) -> Acc,
2961 self.iter.rfold(init, fold)
2966 #[stable(feature = "rust1", since = "1.0.0")]
2967 impl<I> ExactSizeIterator for Fuse<I> where I: ExactSizeIterator {
2968 fn len(&self) -> usize {
2972 fn is_empty(&self) -> bool {
2973 self.iter.is_empty()
2977 /// An iterator that calls a function with a reference to each element before
2980 /// This `struct` is created by the [`inspect`] method on [`Iterator`]. See its
2981 /// documentation for more.
2983 /// [`inspect`]: trait.Iterator.html#method.inspect
2984 /// [`Iterator`]: trait.Iterator.html
2985 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2986 #[stable(feature = "rust1", since = "1.0.0")]
2988 pub struct Inspect<I, F> {
2993 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2994 impl<I: fmt::Debug, F> fmt::Debug for Inspect<I, F> {
2995 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2996 f.debug_struct("Inspect")
2997 .field("iter", &self.iter)
3002 impl<I: Iterator, F> Inspect<I, F> where F: FnMut(&I::Item) {
3004 fn do_inspect(&mut self, elt: Option<I::Item>) -> Option<I::Item> {
3005 if let Some(ref a) = elt {
3013 #[stable(feature = "rust1", since = "1.0.0")]
3014 impl<I: Iterator, F> Iterator for Inspect<I, F> where F: FnMut(&I::Item) {
3015 type Item = I::Item;
3018 fn next(&mut self) -> Option<I::Item> {
3019 let next = self.iter.next();
3020 self.do_inspect(next)
3024 fn size_hint(&self) -> (usize, Option<usize>) {
3025 self.iter.size_hint()
3029 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
3030 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
3032 let f = &mut self.f;
3033 self.iter.try_fold(init, move |acc, item| { f(&item); fold(acc, item) })
3037 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
3038 where Fold: FnMut(Acc, Self::Item) -> Acc,
3041 self.iter.fold(init, move |acc, item| { f(&item); fold(acc, item) })
3045 #[stable(feature = "rust1", since = "1.0.0")]
3046 impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
3047 where F: FnMut(&I::Item),
3050 fn next_back(&mut self) -> Option<I::Item> {
3051 let next = self.iter.next_back();
3052 self.do_inspect(next)
3056 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
3057 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
3059 let f = &mut self.f;
3060 self.iter.try_rfold(init, move |acc, item| { f(&item); fold(acc, item) })
3064 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
3065 where Fold: FnMut(Acc, Self::Item) -> Acc,
3068 self.iter.rfold(init, move |acc, item| { f(&item); fold(acc, item) })
3072 #[stable(feature = "rust1", since = "1.0.0")]
3073 impl<I: ExactSizeIterator, F> ExactSizeIterator for Inspect<I, F>
3074 where F: FnMut(&I::Item)
3076 fn len(&self) -> usize {
3080 fn is_empty(&self) -> bool {
3081 self.iter.is_empty()
3085 #[stable(feature = "fused", since = "1.26.0")]
3086 impl<I: FusedIterator, F> FusedIterator for Inspect<I, F>
3087 where F: FnMut(&I::Item) {}