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;
322 use ops::{self, Try};
327 #[stable(feature = "rust1", since = "1.0.0")]
328 pub use self::iterator::Iterator;
330 #[unstable(feature = "step_trait",
331 reason = "likely to be replaced by finer-grained traits",
333 pub use self::range::Step;
335 #[stable(feature = "rust1", since = "1.0.0")]
336 pub use self::sources::{Repeat, repeat};
337 #[stable(feature = "iterator_repeat_with", since = "1.28.0")]
338 pub use self::sources::{RepeatWith, repeat_with};
339 #[stable(feature = "iter_empty", since = "1.2.0")]
340 pub use self::sources::{Empty, empty};
341 #[stable(feature = "iter_once", since = "1.2.0")]
342 pub use self::sources::{Once, once};
344 #[stable(feature = "rust1", since = "1.0.0")]
345 pub use self::traits::{FromIterator, IntoIterator, DoubleEndedIterator, Extend};
346 #[stable(feature = "rust1", since = "1.0.0")]
347 pub use self::traits::{ExactSizeIterator, Sum, Product};
348 #[stable(feature = "fused", since = "1.26.0")]
349 pub use self::traits::FusedIterator;
350 #[unstable(feature = "trusted_len", issue = "37572")]
351 pub use self::traits::TrustedLen;
358 /// Used to make try_fold closures more like normal loops
360 enum LoopState<C, B> {
365 impl<C, B> Try for LoopState<C, B> {
369 fn into_result(self) -> Result<Self::Ok, Self::Error> {
371 LoopState::Continue(y) => Ok(y),
372 LoopState::Break(x) => Err(x),
376 fn from_error(v: Self::Error) -> Self { LoopState::Break(v) }
378 fn from_ok(v: Self::Ok) -> Self { LoopState::Continue(v) }
381 impl<C, B> LoopState<C, B> {
383 fn break_value(self) -> Option<B> {
385 LoopState::Continue(..) => None,
386 LoopState::Break(x) => Some(x),
391 impl<R: Try> LoopState<R::Ok, R> {
393 fn from_try(r: R) -> Self {
394 match Try::into_result(r) {
395 Ok(v) => LoopState::Continue(v),
396 Err(v) => LoopState::Break(Try::from_error(v)),
400 fn into_try(self) -> R {
402 LoopState::Continue(v) => Try::from_ok(v),
403 LoopState::Break(v) => v,
408 /// A double-ended iterator with the direction inverted.
410 /// This `struct` is created by the [`rev`] method on [`Iterator`]. See its
411 /// documentation for more.
413 /// [`rev`]: trait.Iterator.html#method.rev
414 /// [`Iterator`]: trait.Iterator.html
415 #[derive(Clone, Debug)]
416 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
417 #[stable(feature = "rust1", since = "1.0.0")]
422 #[stable(feature = "rust1", since = "1.0.0")]
423 impl<I> Iterator for Rev<I> where I: DoubleEndedIterator {
424 type Item = <I as Iterator>::Item;
427 fn next(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next_back() }
429 fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
431 fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R where
432 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
434 self.iter.try_rfold(init, f)
437 fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
438 where F: FnMut(Acc, Self::Item) -> Acc,
440 self.iter.rfold(init, f)
444 fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
445 where P: FnMut(&Self::Item) -> bool
447 self.iter.rfind(predicate)
451 fn rposition<P>(&mut self, predicate: P) -> Option<usize> where
452 P: FnMut(Self::Item) -> bool
454 self.iter.position(predicate)
458 #[stable(feature = "rust1", since = "1.0.0")]
459 impl<I> DoubleEndedIterator for Rev<I> where I: DoubleEndedIterator {
461 fn next_back(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next() }
463 fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
464 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
466 self.iter.try_fold(init, f)
469 fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
470 where F: FnMut(Acc, Self::Item) -> Acc,
472 self.iter.fold(init, f)
475 fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
476 where P: FnMut(&Self::Item) -> bool
478 self.iter.find(predicate)
482 #[stable(feature = "rust1", since = "1.0.0")]
483 impl<I> ExactSizeIterator for Rev<I>
484 where I: ExactSizeIterator + DoubleEndedIterator
486 fn len(&self) -> usize {
490 fn is_empty(&self) -> bool {
495 #[stable(feature = "fused", since = "1.26.0")]
496 impl<I> FusedIterator for Rev<I>
497 where I: FusedIterator + DoubleEndedIterator {}
499 #[unstable(feature = "trusted_len", issue = "37572")]
500 unsafe impl<I> TrustedLen for Rev<I>
501 where I: TrustedLen + DoubleEndedIterator {}
503 /// An iterator that clones the elements of an underlying iterator.
505 /// This `struct` is created by the [`cloned`] method on [`Iterator`]. See its
506 /// documentation for more.
508 /// [`cloned`]: trait.Iterator.html#method.cloned
509 /// [`Iterator`]: trait.Iterator.html
510 #[stable(feature = "iter_cloned", since = "1.1.0")]
511 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
512 #[derive(Clone, Debug)]
513 pub struct Cloned<I> {
517 #[stable(feature = "iter_cloned", since = "1.1.0")]
518 impl<'a, I, T: 'a> Iterator for Cloned<I>
519 where I: Iterator<Item=&'a T>, T: Clone
523 fn next(&mut self) -> Option<T> {
524 self.it.next().cloned()
527 fn size_hint(&self) -> (usize, Option<usize>) {
531 fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where
532 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
534 self.it.try_fold(init, move |acc, elt| f(acc, elt.clone()))
537 fn fold<Acc, F>(self, init: Acc, mut f: F) -> Acc
538 where F: FnMut(Acc, Self::Item) -> Acc,
540 self.it.fold(init, move |acc, elt| f(acc, elt.clone()))
544 #[stable(feature = "iter_cloned", since = "1.1.0")]
545 impl<'a, I, T: 'a> DoubleEndedIterator for Cloned<I>
546 where I: DoubleEndedIterator<Item=&'a T>, T: Clone
548 fn next_back(&mut self) -> Option<T> {
549 self.it.next_back().cloned()
552 fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R where
553 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
555 self.it.try_rfold(init, move |acc, elt| f(acc, elt.clone()))
558 fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
559 where F: FnMut(Acc, Self::Item) -> Acc,
561 self.it.rfold(init, move |acc, elt| f(acc, elt.clone()))
565 #[stable(feature = "iter_cloned", since = "1.1.0")]
566 impl<'a, I, T: 'a> ExactSizeIterator for Cloned<I>
567 where I: ExactSizeIterator<Item=&'a T>, T: Clone
569 fn len(&self) -> usize {
573 fn is_empty(&self) -> bool {
578 #[stable(feature = "fused", since = "1.26.0")]
579 impl<'a, I, T: 'a> FusedIterator for Cloned<I>
580 where I: FusedIterator<Item=&'a T>, T: Clone
584 unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
585 where I: TrustedRandomAccess<Item=&'a T>, T: Clone
587 default unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
588 self.it.get_unchecked(i).clone()
592 default fn may_have_side_effect() -> bool { true }
596 unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
597 where I: TrustedRandomAccess<Item=&'a T>, T: Copy
599 unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
600 *self.it.get_unchecked(i)
604 fn may_have_side_effect() -> bool { false }
607 #[unstable(feature = "trusted_len", issue = "37572")]
608 unsafe impl<'a, I, T: 'a> TrustedLen for Cloned<I>
609 where I: TrustedLen<Item=&'a T>,
613 /// An iterator that repeats endlessly.
615 /// This `struct` is created by the [`cycle`] method on [`Iterator`]. See its
616 /// documentation for more.
618 /// [`cycle`]: trait.Iterator.html#method.cycle
619 /// [`Iterator`]: trait.Iterator.html
620 #[derive(Clone, Debug)]
621 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
622 #[stable(feature = "rust1", since = "1.0.0")]
623 pub struct Cycle<I> {
628 #[stable(feature = "rust1", since = "1.0.0")]
629 impl<I> Iterator for Cycle<I> where I: Clone + Iterator {
630 type Item = <I as Iterator>::Item;
633 fn next(&mut self) -> Option<<I as Iterator>::Item> {
634 match self.iter.next() {
635 None => { self.iter = self.orig.clone(); self.iter.next() }
641 fn size_hint(&self) -> (usize, Option<usize>) {
642 // the cycle iterator is either empty or infinite
643 match self.orig.size_hint() {
644 sz @ (0, Some(0)) => sz,
646 _ => (usize::MAX, None)
651 #[stable(feature = "fused", since = "1.26.0")]
652 impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {}
654 /// An iterator for stepping iterators by a custom amount.
656 /// This `struct` is created by the [`step_by`] method on [`Iterator`]. See
657 /// its documentation for more.
659 /// [`step_by`]: trait.Iterator.html#method.step_by
660 /// [`Iterator`]: trait.Iterator.html
661 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
662 #[stable(feature = "iterator_step_by", since = "1.28.0")]
663 #[derive(Clone, Debug)]
664 pub struct StepBy<I> {
670 #[stable(feature = "iterator_step_by", since = "1.28.0")]
671 impl<I> Iterator for StepBy<I> where I: Iterator {
675 fn next(&mut self) -> Option<Self::Item> {
676 <Self as StepBySpecIterator>::spec_next(self)
680 fn size_hint(&self) -> (usize, Option<usize>) {
681 let inner_hint = self.iter.size_hint();
684 let f = |n| if n == 0 { 0 } else { 1 + (n-1)/(self.step+1) };
685 (f(inner_hint.0), inner_hint.1.map(f))
687 let f = |n| n / (self.step+1);
688 (f(inner_hint.0), inner_hint.1.map(f))
693 fn nth(&mut self, mut n: usize) -> Option<Self::Item> {
695 self.first_take = false;
696 let first = self.iter.next();
702 // n and self.step are indices, we need to add 1 to get the amount of elements
703 // When calling `.nth`, we need to subtract 1 again to convert back to an index
704 // step + 1 can't overflow because `.step_by` sets `self.step` to `step - 1`
705 let mut step = self.step + 1;
706 // n + 1 could overflow
707 // thus, if n is usize::MAX, instead of adding one, we call .nth(step)
709 self.iter.nth(step - 1);
716 let mul = n.checked_mul(step);
717 if unsafe { intrinsics::likely(mul.is_some()) } {
718 return self.iter.nth(mul.unwrap() - 1);
720 let div_n = usize::MAX / n;
721 let div_step = usize::MAX / step;
722 let nth_n = div_n * n;
723 let nth_step = div_step * step;
724 let nth = if nth_n > nth_step {
731 self.iter.nth(nth - 1);
736 // hidden trait for specializing iterator methods
737 // could be generalized but is currently only used for StepBy
738 trait StepBySpecIterator {
740 fn spec_next(&mut self) -> Option<Self::Item>;
743 impl<I> StepBySpecIterator for StepBy<I>
750 default fn spec_next(&mut self) -> Option<I::Item> {
752 self.first_take = false;
755 self.iter.nth(self.step)
760 impl<T> StepBySpecIterator for StepBy<ops::Range<T>>
765 fn spec_next(&mut self) -> Option<Self::Item> {
766 self.first_take = false;
767 if !(self.iter.start < self.iter.end) {
770 // add 1 to self.step to get original step size back
771 // it was decremented for the general case on construction
772 if let Some(n) = self.iter.start.add_usize(self.step+1) {
773 let next = mem::replace(&mut self.iter.start, n);
776 let last = self.iter.start.clone();
777 self.iter.start = self.iter.end.clone();
783 impl<T> StepBySpecIterator for StepBy<ops::RangeInclusive<T>>
788 fn spec_next(&mut self) -> Option<Self::Item> {
789 self.first_take = false;
790 if !(self.iter.start <= self.iter.end) {
793 // add 1 to self.step to get original step size back
794 // it was decremented for the general case on construction
795 if let Some(n) = self.iter.start.add_usize(self.step+1) {
796 let next = mem::replace(&mut self.iter.start, n);
799 let last = self.iter.start.replace_one();
800 self.iter.end.replace_zero();
806 // StepBy can only make the iterator shorter, so the len will still fit.
807 #[stable(feature = "iterator_step_by", since = "1.28.0")]
808 impl<I> ExactSizeIterator for StepBy<I> where I: ExactSizeIterator {}
810 /// An iterator that strings two iterators together.
812 /// This `struct` is created by the [`chain`] method on [`Iterator`]. See its
813 /// documentation for more.
815 /// [`chain`]: trait.Iterator.html#method.chain
816 /// [`Iterator`]: trait.Iterator.html
817 #[derive(Clone, Debug)]
818 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
819 #[stable(feature = "rust1", since = "1.0.0")]
820 pub struct Chain<A, B> {
826 // The iterator protocol specifies that iteration ends with the return value
827 // `None` from `.next()` (or `.next_back()`) and it is unspecified what
828 // further calls return. The chain adaptor must account for this since it uses
831 // It uses three states:
833 // - Both: `a` and `b` are remaining
834 // - Front: `a` remaining
835 // - Back: `b` remaining
837 // The fourth state (neither iterator is remaining) only occurs after Chain has
838 // returned None once, so we don't need to store this state.
839 #[derive(Clone, Debug)]
841 // both front and back iterator are remaining
843 // only front is remaining
845 // only back is remaining
849 #[stable(feature = "rust1", since = "1.0.0")]
850 impl<A, B> Iterator for Chain<A, B> where
852 B: Iterator<Item = A::Item>
857 fn next(&mut self) -> Option<A::Item> {
859 ChainState::Both => match self.a.next() {
860 elt @ Some(..) => elt,
862 self.state = ChainState::Back;
866 ChainState::Front => self.a.next(),
867 ChainState::Back => self.b.next(),
872 #[rustc_inherit_overflow_checks]
873 fn count(self) -> usize {
875 ChainState::Both => self.a.count() + self.b.count(),
876 ChainState::Front => self.a.count(),
877 ChainState::Back => self.b.count(),
881 fn try_fold<Acc, F, R>(&mut self, init: Acc, mut f: F) -> R where
882 Self: Sized, F: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
884 let mut accum = init;
886 ChainState::Both | ChainState::Front => {
887 accum = self.a.try_fold(accum, &mut f)?;
888 if let ChainState::Both = self.state {
889 self.state = ChainState::Back;
894 if let ChainState::Back = self.state {
895 accum = self.b.try_fold(accum, &mut f)?;
900 fn fold<Acc, F>(self, init: Acc, mut f: F) -> Acc
901 where F: FnMut(Acc, Self::Item) -> Acc,
903 let mut accum = init;
905 ChainState::Both | ChainState::Front => {
906 accum = self.a.fold(accum, &mut f);
911 ChainState::Both | ChainState::Back => {
912 accum = self.b.fold(accum, &mut f);
920 fn nth(&mut self, mut n: usize) -> Option<A::Item> {
922 ChainState::Both | ChainState::Front => {
923 for x in self.a.by_ref() {
929 if let ChainState::Both = self.state {
930 self.state = ChainState::Back;
933 ChainState::Back => {}
935 if let ChainState::Back = self.state {
943 fn find<P>(&mut self, mut predicate: P) -> Option<Self::Item> where
944 P: FnMut(&Self::Item) -> bool,
947 ChainState::Both => match self.a.find(&mut predicate) {
949 self.state = ChainState::Back;
950 self.b.find(predicate)
954 ChainState::Front => self.a.find(predicate),
955 ChainState::Back => self.b.find(predicate),
960 fn last(self) -> Option<A::Item> {
962 ChainState::Both => {
963 // Must exhaust a before b.
964 let a_last = self.a.last();
965 let b_last = self.b.last();
968 ChainState::Front => self.a.last(),
969 ChainState::Back => self.b.last()
974 fn size_hint(&self) -> (usize, Option<usize>) {
975 let (a_lower, a_upper) = self.a.size_hint();
976 let (b_lower, b_upper) = self.b.size_hint();
978 let lower = a_lower.saturating_add(b_lower);
980 let upper = match (a_upper, b_upper) {
981 (Some(x), Some(y)) => x.checked_add(y),
989 #[stable(feature = "rust1", since = "1.0.0")]
990 impl<A, B> DoubleEndedIterator for Chain<A, B> where
991 A: DoubleEndedIterator,
992 B: DoubleEndedIterator<Item=A::Item>,
995 fn next_back(&mut self) -> Option<A::Item> {
997 ChainState::Both => match self.b.next_back() {
998 elt @ Some(..) => elt,
1000 self.state = ChainState::Front;
1004 ChainState::Front => self.a.next_back(),
1005 ChainState::Back => self.b.next_back(),
1009 fn try_rfold<Acc, F, R>(&mut self, init: Acc, mut f: F) -> R where
1010 Self: Sized, F: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1012 let mut accum = init;
1014 ChainState::Both | ChainState::Back => {
1015 accum = self.b.try_rfold(accum, &mut f)?;
1016 if let ChainState::Both = self.state {
1017 self.state = ChainState::Front;
1022 if let ChainState::Front = self.state {
1023 accum = self.a.try_rfold(accum, &mut f)?;
1028 fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
1029 where F: FnMut(Acc, Self::Item) -> Acc,
1031 let mut accum = init;
1033 ChainState::Both | ChainState::Back => {
1034 accum = self.b.rfold(accum, &mut f);
1039 ChainState::Both | ChainState::Front => {
1040 accum = self.a.rfold(accum, &mut f);
1049 // Note: *both* must be fused to handle double-ended iterators.
1050 #[stable(feature = "fused", since = "1.26.0")]
1051 impl<A, B> FusedIterator for Chain<A, B>
1052 where A: FusedIterator,
1053 B: FusedIterator<Item=A::Item>,
1056 #[unstable(feature = "trusted_len", issue = "37572")]
1057 unsafe impl<A, B> TrustedLen for Chain<A, B>
1058 where A: TrustedLen, B: TrustedLen<Item=A::Item>,
1061 /// An iterator that iterates two other iterators simultaneously.
1063 /// This `struct` is created by the [`zip`] method on [`Iterator`]. See its
1064 /// documentation for more.
1066 /// [`zip`]: trait.Iterator.html#method.zip
1067 /// [`Iterator`]: trait.Iterator.html
1068 #[derive(Clone, Debug)]
1069 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1070 #[stable(feature = "rust1", since = "1.0.0")]
1071 pub struct Zip<A, B> {
1074 // index and len are only used by the specialized version of zip
1079 #[stable(feature = "rust1", since = "1.0.0")]
1080 impl<A, B> Iterator for Zip<A, B> where A: Iterator, B: Iterator
1082 type Item = (A::Item, B::Item);
1085 fn next(&mut self) -> Option<Self::Item> {
1090 fn size_hint(&self) -> (usize, Option<usize>) {
1091 ZipImpl::size_hint(self)
1095 fn nth(&mut self, n: usize) -> Option<Self::Item> {
1096 ZipImpl::nth(self, n)
1100 #[stable(feature = "rust1", since = "1.0.0")]
1101 impl<A, B> DoubleEndedIterator for Zip<A, B> where
1102 A: DoubleEndedIterator + ExactSizeIterator,
1103 B: DoubleEndedIterator + ExactSizeIterator,
1106 fn next_back(&mut self) -> Option<(A::Item, B::Item)> {
1107 ZipImpl::next_back(self)
1111 // Zip specialization trait
1113 trait ZipImpl<A, B> {
1115 fn new(a: A, b: B) -> Self;
1116 fn next(&mut self) -> Option<Self::Item>;
1117 fn size_hint(&self) -> (usize, Option<usize>);
1118 fn nth(&mut self, n: usize) -> Option<Self::Item>;
1119 fn super_nth(&mut self, mut n: usize) -> Option<Self::Item> {
1120 while let Some(x) = self.next() {
1121 if n == 0 { return Some(x) }
1126 fn next_back(&mut self) -> Option<Self::Item>
1127 where A: DoubleEndedIterator + ExactSizeIterator,
1128 B: DoubleEndedIterator + ExactSizeIterator;
1133 impl<A, B> ZipImpl<A, B> for Zip<A, B>
1134 where A: Iterator, B: Iterator
1136 type Item = (A::Item, B::Item);
1137 default fn new(a: A, b: B) -> Self {
1147 default fn next(&mut self) -> Option<(A::Item, B::Item)> {
1148 self.a.next().and_then(|x| {
1149 self.b.next().and_then(|y| {
1156 default fn nth(&mut self, n: usize) -> Option<Self::Item> {
1161 default fn next_back(&mut self) -> Option<(A::Item, B::Item)>
1162 where A: DoubleEndedIterator + ExactSizeIterator,
1163 B: DoubleEndedIterator + ExactSizeIterator
1165 let a_sz = self.a.len();
1166 let b_sz = self.b.len();
1168 // Adjust a, b to equal length
1170 for _ in 0..a_sz - b_sz { self.a.next_back(); }
1172 for _ in 0..b_sz - a_sz { self.b.next_back(); }
1175 match (self.a.next_back(), self.b.next_back()) {
1176 (Some(x), Some(y)) => Some((x, y)),
1177 (None, None) => None,
1178 _ => unreachable!(),
1183 default fn size_hint(&self) -> (usize, Option<usize>) {
1184 let (a_lower, a_upper) = self.a.size_hint();
1185 let (b_lower, b_upper) = self.b.size_hint();
1187 let lower = cmp::min(a_lower, b_lower);
1189 let upper = match (a_upper, b_upper) {
1190 (Some(x), Some(y)) => Some(cmp::min(x,y)),
1191 (Some(x), None) => Some(x),
1192 (None, Some(y)) => Some(y),
1193 (None, None) => None
1201 impl<A, B> ZipImpl<A, B> for Zip<A, B>
1202 where A: TrustedRandomAccess, B: TrustedRandomAccess
1204 fn new(a: A, b: B) -> Self {
1205 let len = cmp::min(a.len(), b.len());
1215 fn next(&mut self) -> Option<(A::Item, B::Item)> {
1216 if self.index < self.len {
1220 Some((self.a.get_unchecked(i), self.b.get_unchecked(i)))
1222 } else if A::may_have_side_effect() && self.index < self.a.len() {
1223 // match the base implementation's potential side effects
1225 self.a.get_unchecked(self.index);
1235 fn size_hint(&self) -> (usize, Option<usize>) {
1236 let len = self.len - self.index;
1241 fn nth(&mut self, n: usize) -> Option<Self::Item> {
1242 let delta = cmp::min(n, self.len - self.index);
1243 let end = self.index + delta;
1244 while self.index < end {
1247 if A::may_have_side_effect() {
1248 unsafe { self.a.get_unchecked(i); }
1250 if B::may_have_side_effect() {
1251 unsafe { self.b.get_unchecked(i); }
1255 self.super_nth(n - delta)
1259 fn next_back(&mut self) -> Option<(A::Item, B::Item)>
1260 where A: DoubleEndedIterator + ExactSizeIterator,
1261 B: DoubleEndedIterator + ExactSizeIterator
1263 // Adjust a, b to equal length
1264 if A::may_have_side_effect() {
1265 let sz = self.a.len();
1267 for _ in 0..sz - cmp::max(self.len, self.index) {
1272 if B::may_have_side_effect() {
1273 let sz = self.b.len();
1275 for _ in 0..sz - self.len {
1280 if self.index < self.len {
1284 Some((self.a.get_unchecked(i), self.b.get_unchecked(i)))
1292 #[stable(feature = "rust1", since = "1.0.0")]
1293 impl<A, B> ExactSizeIterator for Zip<A, B>
1294 where A: ExactSizeIterator, B: ExactSizeIterator {}
1297 unsafe impl<A, B> TrustedRandomAccess for Zip<A, B>
1298 where A: TrustedRandomAccess,
1299 B: TrustedRandomAccess,
1301 unsafe fn get_unchecked(&mut self, i: usize) -> (A::Item, B::Item) {
1302 (self.a.get_unchecked(i), self.b.get_unchecked(i))
1305 fn may_have_side_effect() -> bool {
1306 A::may_have_side_effect() || B::may_have_side_effect()
1310 #[stable(feature = "fused", since = "1.26.0")]
1311 impl<A, B> FusedIterator for Zip<A, B>
1312 where A: FusedIterator, B: FusedIterator, {}
1314 #[unstable(feature = "trusted_len", issue = "37572")]
1315 unsafe impl<A, B> TrustedLen for Zip<A, B>
1316 where A: TrustedLen, B: TrustedLen,
1319 /// An iterator that maps the values of `iter` with `f`.
1321 /// This `struct` is created by the [`map`] method on [`Iterator`]. See its
1322 /// documentation for more.
1324 /// [`map`]: trait.Iterator.html#method.map
1325 /// [`Iterator`]: trait.Iterator.html
1327 /// # Notes about side effects
1329 /// The [`map`] iterator implements [`DoubleEndedIterator`], meaning that
1330 /// you can also [`map`] backwards:
1333 /// let v: Vec<i32> = vec![1, 2, 3].into_iter().map(|x| x + 1).rev().collect();
1335 /// assert_eq!(v, [4, 3, 2]);
1338 /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html
1340 /// But if your closure has state, iterating backwards may act in a way you do
1341 /// not expect. Let's go through an example. First, in the forward direction:
1346 /// for pair in vec!['a', 'b', 'c'].into_iter()
1347 /// .map(|letter| { c += 1; (letter, c) }) {
1348 /// println!("{:?}", pair);
1352 /// This will print "('a', 1), ('b', 2), ('c', 3)".
1354 /// Now consider this twist where we add a call to `rev`. This version will
1355 /// print `('c', 1), ('b', 2), ('a', 3)`. Note that the letters are reversed,
1356 /// but the values of the counter still go in order. This is because `map()` is
1357 /// still being called lazily on each item, but we are popping items off the
1358 /// back of the vector now, instead of shifting them from the front.
1363 /// for pair in vec!['a', 'b', 'c'].into_iter()
1364 /// .map(|letter| { c += 1; (letter, c) })
1366 /// println!("{:?}", pair);
1369 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1370 #[stable(feature = "rust1", since = "1.0.0")]
1372 pub struct Map<I, F> {
1377 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1378 impl<I: fmt::Debug, F> fmt::Debug for Map<I, F> {
1379 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1380 f.debug_struct("Map")
1381 .field("iter", &self.iter)
1386 #[stable(feature = "rust1", since = "1.0.0")]
1387 impl<B, I: Iterator, F> Iterator for Map<I, F> where F: FnMut(I::Item) -> B {
1391 fn next(&mut self) -> Option<B> {
1392 self.iter.next().map(&mut self.f)
1396 fn size_hint(&self) -> (usize, Option<usize>) {
1397 self.iter.size_hint()
1400 fn try_fold<Acc, G, R>(&mut self, init: Acc, mut g: G) -> R where
1401 Self: Sized, G: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1403 let f = &mut self.f;
1404 self.iter.try_fold(init, move |acc, elt| g(acc, f(elt)))
1407 fn fold<Acc, G>(self, init: Acc, mut g: G) -> Acc
1408 where G: FnMut(Acc, Self::Item) -> Acc,
1411 self.iter.fold(init, move |acc, elt| g(acc, f(elt)))
1415 #[stable(feature = "rust1", since = "1.0.0")]
1416 impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F> where
1417 F: FnMut(I::Item) -> B,
1420 fn next_back(&mut self) -> Option<B> {
1421 self.iter.next_back().map(&mut self.f)
1424 fn try_rfold<Acc, G, R>(&mut self, init: Acc, mut g: G) -> R where
1425 Self: Sized, G: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1427 let f = &mut self.f;
1428 self.iter.try_rfold(init, move |acc, elt| g(acc, f(elt)))
1431 fn rfold<Acc, G>(self, init: Acc, mut g: G) -> Acc
1432 where G: FnMut(Acc, Self::Item) -> Acc,
1435 self.iter.rfold(init, move |acc, elt| g(acc, f(elt)))
1439 #[stable(feature = "rust1", since = "1.0.0")]
1440 impl<B, I: ExactSizeIterator, F> ExactSizeIterator for Map<I, F>
1441 where F: FnMut(I::Item) -> B
1443 fn len(&self) -> usize {
1447 fn is_empty(&self) -> bool {
1448 self.iter.is_empty()
1452 #[stable(feature = "fused", since = "1.26.0")]
1453 impl<B, I: FusedIterator, F> FusedIterator for Map<I, F>
1454 where F: FnMut(I::Item) -> B {}
1456 #[unstable(feature = "trusted_len", issue = "37572")]
1457 unsafe impl<B, I, F> TrustedLen for Map<I, F>
1458 where I: TrustedLen,
1459 F: FnMut(I::Item) -> B {}
1462 unsafe impl<B, I, F> TrustedRandomAccess for Map<I, F>
1463 where I: TrustedRandomAccess,
1464 F: FnMut(I::Item) -> B,
1466 unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
1467 (self.f)(self.iter.get_unchecked(i))
1470 fn may_have_side_effect() -> bool { true }
1473 /// An iterator that filters the elements of `iter` with `predicate`.
1475 /// This `struct` is created by the [`filter`] method on [`Iterator`]. See its
1476 /// documentation for more.
1478 /// [`filter`]: trait.Iterator.html#method.filter
1479 /// [`Iterator`]: trait.Iterator.html
1480 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1481 #[stable(feature = "rust1", since = "1.0.0")]
1483 pub struct Filter<I, P> {
1488 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1489 impl<I: fmt::Debug, P> fmt::Debug for Filter<I, P> {
1490 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1491 f.debug_struct("Filter")
1492 .field("iter", &self.iter)
1497 #[stable(feature = "rust1", since = "1.0.0")]
1498 impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool {
1499 type Item = I::Item;
1502 fn next(&mut self) -> Option<I::Item> {
1503 for x in &mut self.iter {
1504 if (self.predicate)(&x) {
1512 fn size_hint(&self) -> (usize, Option<usize>) {
1513 let (_, upper) = self.iter.size_hint();
1514 (0, upper) // can't know a lower bound, due to the predicate
1517 // this special case allows the compiler to make `.filter(_).count()`
1518 // branchless. Barring perfect branch prediction (which is unattainable in
1519 // the general case), this will be much faster in >90% of cases (containing
1520 // virtually all real workloads) and only a tiny bit slower in the rest.
1522 // Having this specialization thus allows us to write `.filter(p).count()`
1523 // where we would otherwise write `.map(|x| p(x) as usize).sum()`, which is
1524 // less readable and also less backwards-compatible to Rust before 1.10.
1526 // Using the branchless version will also simplify the LLVM byte code, thus
1527 // leaving more budget for LLVM optimizations.
1529 fn count(mut self) -> usize {
1531 for x in &mut self.iter {
1532 count += (self.predicate)(&x) as usize;
1538 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1539 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1541 let predicate = &mut self.predicate;
1542 self.iter.try_fold(init, move |acc, item| if predicate(&item) {
1550 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1551 where Fold: FnMut(Acc, Self::Item) -> Acc,
1553 let mut predicate = self.predicate;
1554 self.iter.fold(init, move |acc, item| if predicate(&item) {
1562 #[stable(feature = "rust1", since = "1.0.0")]
1563 impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
1564 where P: FnMut(&I::Item) -> bool,
1567 fn next_back(&mut self) -> Option<I::Item> {
1568 for x in self.iter.by_ref().rev() {
1569 if (self.predicate)(&x) {
1577 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1578 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1580 let predicate = &mut self.predicate;
1581 self.iter.try_rfold(init, move |acc, item| if predicate(&item) {
1589 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1590 where Fold: FnMut(Acc, Self::Item) -> Acc,
1592 let mut predicate = self.predicate;
1593 self.iter.rfold(init, move |acc, item| if predicate(&item) {
1601 #[stable(feature = "fused", since = "1.26.0")]
1602 impl<I: FusedIterator, P> FusedIterator for Filter<I, P>
1603 where P: FnMut(&I::Item) -> bool {}
1605 /// An iterator that uses `f` to both filter and map elements from `iter`.
1607 /// This `struct` is created by the [`filter_map`] method on [`Iterator`]. See its
1608 /// documentation for more.
1610 /// [`filter_map`]: trait.Iterator.html#method.filter_map
1611 /// [`Iterator`]: trait.Iterator.html
1612 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1613 #[stable(feature = "rust1", since = "1.0.0")]
1615 pub struct FilterMap<I, F> {
1620 #[stable(feature = "core_impl_debug", since = "1.9.0")]
1621 impl<I: fmt::Debug, F> fmt::Debug for FilterMap<I, F> {
1622 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1623 f.debug_struct("FilterMap")
1624 .field("iter", &self.iter)
1629 #[stable(feature = "rust1", since = "1.0.0")]
1630 impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
1631 where F: FnMut(I::Item) -> Option<B>,
1636 fn next(&mut self) -> Option<B> {
1637 for x in self.iter.by_ref() {
1638 if let Some(y) = (self.f)(x) {
1646 fn size_hint(&self) -> (usize, Option<usize>) {
1647 let (_, upper) = self.iter.size_hint();
1648 (0, upper) // can't know a lower bound, due to the predicate
1652 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1653 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1655 let f = &mut self.f;
1656 self.iter.try_fold(init, move |acc, item| match f(item) {
1657 Some(x) => fold(acc, x),
1658 None => Try::from_ok(acc),
1663 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1664 where Fold: FnMut(Acc, Self::Item) -> Acc,
1667 self.iter.fold(init, move |acc, item| match f(item) {
1668 Some(x) => fold(acc, x),
1674 #[stable(feature = "rust1", since = "1.0.0")]
1675 impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
1676 where F: FnMut(I::Item) -> Option<B>,
1679 fn next_back(&mut self) -> Option<B> {
1680 for x in self.iter.by_ref().rev() {
1681 if let Some(y) = (self.f)(x) {
1689 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1690 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1692 let f = &mut self.f;
1693 self.iter.try_rfold(init, move |acc, item| match f(item) {
1694 Some(x) => fold(acc, x),
1695 None => Try::from_ok(acc),
1700 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1701 where Fold: FnMut(Acc, Self::Item) -> Acc,
1704 self.iter.rfold(init, move |acc, item| match f(item) {
1705 Some(x) => fold(acc, x),
1711 #[stable(feature = "fused", since = "1.26.0")]
1712 impl<B, I: FusedIterator, F> FusedIterator for FilterMap<I, F>
1713 where F: FnMut(I::Item) -> Option<B> {}
1715 /// An iterator that yields the current count and the element during iteration.
1717 /// This `struct` is created by the [`enumerate`] method on [`Iterator`]. See its
1718 /// documentation for more.
1720 /// [`enumerate`]: trait.Iterator.html#method.enumerate
1721 /// [`Iterator`]: trait.Iterator.html
1722 #[derive(Clone, Debug)]
1723 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1724 #[stable(feature = "rust1", since = "1.0.0")]
1725 pub struct Enumerate<I> {
1730 #[stable(feature = "rust1", since = "1.0.0")]
1731 impl<I> Iterator for Enumerate<I> where I: Iterator {
1732 type Item = (usize, <I as Iterator>::Item);
1734 /// # Overflow Behavior
1736 /// The method does no guarding against overflows, so enumerating more than
1737 /// `usize::MAX` elements either produces the wrong result or panics. If
1738 /// debug assertions are enabled, a panic is guaranteed.
1742 /// Might panic if the index of the element overflows a `usize`.
1744 #[rustc_inherit_overflow_checks]
1745 fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
1746 self.iter.next().map(|a| {
1747 let ret = (self.count, a);
1748 // Possible undefined overflow.
1755 fn size_hint(&self) -> (usize, Option<usize>) {
1756 self.iter.size_hint()
1760 #[rustc_inherit_overflow_checks]
1761 fn nth(&mut self, n: usize) -> Option<(usize, I::Item)> {
1762 self.iter.nth(n).map(|a| {
1763 let i = self.count + n;
1770 fn count(self) -> usize {
1775 #[rustc_inherit_overflow_checks]
1776 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1777 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1779 let count = &mut self.count;
1780 self.iter.try_fold(init, move |acc, item| {
1781 let acc = fold(acc, (*count, item));
1788 #[rustc_inherit_overflow_checks]
1789 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1790 where Fold: FnMut(Acc, Self::Item) -> Acc,
1792 let mut count = self.count;
1793 self.iter.fold(init, move |acc, item| {
1794 let acc = fold(acc, (count, item));
1801 #[stable(feature = "rust1", since = "1.0.0")]
1802 impl<I> DoubleEndedIterator for Enumerate<I> where
1803 I: ExactSizeIterator + DoubleEndedIterator
1806 fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
1807 self.iter.next_back().map(|a| {
1808 let len = self.iter.len();
1809 // Can safely add, `ExactSizeIterator` promises that the number of
1810 // elements fits into a `usize`.
1811 (self.count + len, a)
1816 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
1817 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
1819 // Can safely add and subtract the count, as `ExactSizeIterator` promises
1820 // that the number of elements fits into a `usize`.
1821 let mut count = self.count + self.iter.len();
1822 self.iter.try_rfold(init, move |acc, item| {
1824 fold(acc, (count, item))
1829 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1830 where Fold: FnMut(Acc, Self::Item) -> Acc,
1832 // Can safely add and subtract the count, as `ExactSizeIterator` promises
1833 // that the number of elements fits into a `usize`.
1834 let mut count = self.count + self.iter.len();
1835 self.iter.rfold(init, move |acc, item| {
1837 fold(acc, (count, item))
1842 #[stable(feature = "rust1", since = "1.0.0")]
1843 impl<I> ExactSizeIterator for Enumerate<I> where I: ExactSizeIterator {
1844 fn len(&self) -> usize {
1848 fn is_empty(&self) -> bool {
1849 self.iter.is_empty()
1854 unsafe impl<I> TrustedRandomAccess for Enumerate<I>
1855 where I: TrustedRandomAccess
1857 unsafe fn get_unchecked(&mut self, i: usize) -> (usize, I::Item) {
1858 (self.count + i, self.iter.get_unchecked(i))
1861 fn may_have_side_effect() -> bool {
1862 I::may_have_side_effect()
1866 #[stable(feature = "fused", since = "1.26.0")]
1867 impl<I> FusedIterator for Enumerate<I> where I: FusedIterator {}
1869 #[unstable(feature = "trusted_len", issue = "37572")]
1870 unsafe impl<I> TrustedLen for Enumerate<I>
1871 where I: TrustedLen,
1875 /// An iterator with a `peek()` that returns an optional reference to the next
1878 /// This `struct` is created by the [`peekable`] method on [`Iterator`]. See its
1879 /// documentation for more.
1881 /// [`peekable`]: trait.Iterator.html#method.peekable
1882 /// [`Iterator`]: trait.Iterator.html
1883 #[derive(Clone, Debug)]
1884 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
1885 #[stable(feature = "rust1", since = "1.0.0")]
1886 pub struct Peekable<I: Iterator> {
1888 /// Remember a peeked value, even if it was None.
1889 peeked: Option<Option<I::Item>>,
1892 // Peekable must remember if a None has been seen in the `.peek()` method.
1893 // It ensures that `.peek(); .peek();` or `.peek(); .next();` only advances the
1894 // underlying iterator at most once. This does not by itself make the iterator
1896 #[stable(feature = "rust1", since = "1.0.0")]
1897 impl<I: Iterator> Iterator for Peekable<I> {
1898 type Item = I::Item;
1901 fn next(&mut self) -> Option<I::Item> {
1902 match self.peeked.take() {
1904 None => self.iter.next(),
1909 #[rustc_inherit_overflow_checks]
1910 fn count(mut self) -> usize {
1911 match self.peeked.take() {
1913 Some(Some(_)) => 1 + self.iter.count(),
1914 None => self.iter.count(),
1919 fn nth(&mut self, n: usize) -> Option<I::Item> {
1920 // FIXME(#43234): merge these when borrow-checking gets better.
1922 match self.peeked.take() {
1924 None => self.iter.nth(n),
1927 match self.peeked.take() {
1929 Some(Some(_)) => self.iter.nth(n - 1),
1930 None => self.iter.nth(n),
1936 fn last(mut self) -> Option<I::Item> {
1937 let peek_opt = match self.peeked.take() {
1938 Some(None) => return None,
1942 self.iter.last().or(peek_opt)
1946 fn size_hint(&self) -> (usize, Option<usize>) {
1947 let peek_len = match self.peeked {
1948 Some(None) => return (0, Some(0)),
1952 let (lo, hi) = self.iter.size_hint();
1953 let lo = lo.saturating_add(peek_len);
1954 let hi = hi.and_then(|x| x.checked_add(peek_len));
1959 fn try_fold<B, F, R>(&mut self, init: B, mut f: F) -> R where
1960 Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Ok=B>
1962 let acc = match self.peeked.take() {
1963 Some(None) => return Try::from_ok(init),
1964 Some(Some(v)) => f(init, v)?,
1967 self.iter.try_fold(acc, f)
1971 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
1972 where Fold: FnMut(Acc, Self::Item) -> Acc,
1974 let acc = match self.peeked {
1975 Some(None) => return init,
1976 Some(Some(v)) => fold(init, v),
1979 self.iter.fold(acc, fold)
1983 #[stable(feature = "rust1", since = "1.0.0")]
1984 impl<I: ExactSizeIterator> ExactSizeIterator for Peekable<I> {}
1986 #[stable(feature = "fused", since = "1.26.0")]
1987 impl<I: FusedIterator> FusedIterator for Peekable<I> {}
1989 impl<I: Iterator> Peekable<I> {
1990 /// Returns a reference to the next() value without advancing the iterator.
1992 /// Like [`next`], if there is a value, it is wrapped in a `Some(T)`.
1993 /// But if the iteration is over, `None` is returned.
1995 /// [`next`]: trait.Iterator.html#tymethod.next
1997 /// Because `peek()` returns a reference, and many iterators iterate over
1998 /// references, there can be a possibly confusing situation where the
1999 /// return value is a double reference. You can see this effect in the
2007 /// let xs = [1, 2, 3];
2009 /// let mut iter = xs.iter().peekable();
2011 /// // peek() lets us see into the future
2012 /// assert_eq!(iter.peek(), Some(&&1));
2013 /// assert_eq!(iter.next(), Some(&1));
2015 /// assert_eq!(iter.next(), Some(&2));
2017 /// // The iterator does not advance even if we `peek` multiple times
2018 /// assert_eq!(iter.peek(), Some(&&3));
2019 /// assert_eq!(iter.peek(), Some(&&3));
2021 /// assert_eq!(iter.next(), Some(&3));
2023 /// // After the iterator is finished, so is `peek()`
2024 /// assert_eq!(iter.peek(), None);
2025 /// assert_eq!(iter.next(), None);
2028 #[stable(feature = "rust1", since = "1.0.0")]
2029 pub fn peek(&mut self) -> Option<&I::Item> {
2030 if self.peeked.is_none() {
2031 self.peeked = Some(self.iter.next());
2034 Some(Some(ref value)) => Some(value),
2036 _ => unreachable!(),
2041 /// An iterator that rejects elements while `predicate` is true.
2043 /// This `struct` is created by the [`skip_while`] method on [`Iterator`]. See its
2044 /// documentation for more.
2046 /// [`skip_while`]: trait.Iterator.html#method.skip_while
2047 /// [`Iterator`]: trait.Iterator.html
2048 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2049 #[stable(feature = "rust1", since = "1.0.0")]
2051 pub struct SkipWhile<I, P> {
2057 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2058 impl<I: fmt::Debug, P> fmt::Debug for SkipWhile<I, P> {
2059 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2060 f.debug_struct("SkipWhile")
2061 .field("iter", &self.iter)
2062 .field("flag", &self.flag)
2067 #[stable(feature = "rust1", since = "1.0.0")]
2068 impl<I: Iterator, P> Iterator for SkipWhile<I, P>
2069 where P: FnMut(&I::Item) -> bool
2071 type Item = I::Item;
2074 fn next(&mut self) -> Option<I::Item> {
2075 let flag = &mut self.flag;
2076 let pred = &mut self.predicate;
2077 self.iter.find(move |x| {
2078 if *flag || !pred(x) {
2088 fn size_hint(&self) -> (usize, Option<usize>) {
2089 let (_, upper) = self.iter.size_hint();
2090 (0, upper) // can't know a lower bound, due to the predicate
2094 fn try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
2095 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2099 Some(v) => init = fold(init, v)?,
2100 None => return Try::from_ok(init),
2103 self.iter.try_fold(init, fold)
2107 fn fold<Acc, Fold>(mut self, mut init: Acc, mut fold: Fold) -> Acc
2108 where Fold: FnMut(Acc, Self::Item) -> Acc,
2112 Some(v) => init = fold(init, v),
2113 None => return init,
2116 self.iter.fold(init, fold)
2120 #[stable(feature = "fused", since = "1.26.0")]
2121 impl<I, P> FusedIterator for SkipWhile<I, P>
2122 where I: FusedIterator, P: FnMut(&I::Item) -> bool {}
2124 /// An iterator that only accepts elements while `predicate` is true.
2126 /// This `struct` is created by the [`take_while`] method on [`Iterator`]. See its
2127 /// documentation for more.
2129 /// [`take_while`]: trait.Iterator.html#method.take_while
2130 /// [`Iterator`]: trait.Iterator.html
2131 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2132 #[stable(feature = "rust1", since = "1.0.0")]
2134 pub struct TakeWhile<I, P> {
2140 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2141 impl<I: fmt::Debug, P> fmt::Debug for TakeWhile<I, P> {
2142 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2143 f.debug_struct("TakeWhile")
2144 .field("iter", &self.iter)
2145 .field("flag", &self.flag)
2150 #[stable(feature = "rust1", since = "1.0.0")]
2151 impl<I: Iterator, P> Iterator for TakeWhile<I, P>
2152 where P: FnMut(&I::Item) -> bool
2154 type Item = I::Item;
2157 fn next(&mut self) -> Option<I::Item> {
2161 self.iter.next().and_then(|x| {
2162 if (self.predicate)(&x) {
2173 fn size_hint(&self) -> (usize, Option<usize>) {
2174 let (_, upper) = self.iter.size_hint();
2175 (0, upper) // can't know a lower bound, due to the predicate
2179 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2180 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2185 let flag = &mut self.flag;
2186 let p = &mut self.predicate;
2187 self.iter.try_fold(init, move |acc, x|{
2189 LoopState::from_try(fold(acc, x))
2192 LoopState::Break(Try::from_ok(acc))
2199 #[stable(feature = "fused", since = "1.26.0")]
2200 impl<I, P> FusedIterator for TakeWhile<I, P>
2201 where I: FusedIterator, P: FnMut(&I::Item) -> bool {}
2203 /// An iterator that skips over `n` elements of `iter`.
2205 /// This `struct` is created by the [`skip`] method on [`Iterator`]. See its
2206 /// documentation for more.
2208 /// [`skip`]: trait.Iterator.html#method.skip
2209 /// [`Iterator`]: trait.Iterator.html
2210 #[derive(Clone, Debug)]
2211 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2212 #[stable(feature = "rust1", since = "1.0.0")]
2213 pub struct Skip<I> {
2218 #[stable(feature = "rust1", since = "1.0.0")]
2219 impl<I> Iterator for Skip<I> where I: Iterator {
2220 type Item = <I as Iterator>::Item;
2223 fn next(&mut self) -> Option<I::Item> {
2229 self.iter.nth(old_n)
2234 fn nth(&mut self, n: usize) -> Option<I::Item> {
2235 // Can't just add n + self.n due to overflow.
2239 let to_skip = self.n;
2242 if self.iter.nth(to_skip-1).is_none() {
2250 fn count(self) -> usize {
2251 self.iter.count().saturating_sub(self.n)
2255 fn last(mut self) -> Option<I::Item> {
2259 let next = self.next();
2261 // recurse. n should be 0.
2262 self.last().or(next)
2270 fn size_hint(&self) -> (usize, Option<usize>) {
2271 let (lower, upper) = self.iter.size_hint();
2273 let lower = lower.saturating_sub(self.n);
2274 let upper = upper.map(|x| x.saturating_sub(self.n));
2280 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2281 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2287 if self.iter.nth(n - 1).is_none() {
2288 return Try::from_ok(init);
2291 self.iter.try_fold(init, fold)
2295 fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
2296 where Fold: FnMut(Acc, Self::Item) -> Acc,
2300 if self.iter.nth(self.n - 1).is_none() {
2304 self.iter.fold(init, fold)
2308 #[stable(feature = "rust1", since = "1.0.0")]
2309 impl<I> ExactSizeIterator for Skip<I> where I: ExactSizeIterator {}
2311 #[stable(feature = "double_ended_skip_iterator", since = "1.9.0")]
2312 impl<I> DoubleEndedIterator for Skip<I> where I: DoubleEndedIterator + ExactSizeIterator {
2313 fn next_back(&mut self) -> Option<Self::Item> {
2315 self.iter.next_back()
2321 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2322 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2324 let mut n = self.len();
2328 self.iter.try_rfold(init, move |acc, x| {
2330 let r = fold(acc, x);
2331 if n == 0 { LoopState::Break(r) }
2332 else { LoopState::from_try(r) }
2338 #[stable(feature = "fused", since = "1.26.0")]
2339 impl<I> FusedIterator for Skip<I> where I: FusedIterator {}
2341 /// An iterator that only iterates over the first `n` iterations of `iter`.
2343 /// This `struct` is created by the [`take`] method on [`Iterator`]. See its
2344 /// documentation for more.
2346 /// [`take`]: trait.Iterator.html#method.take
2347 /// [`Iterator`]: trait.Iterator.html
2348 #[derive(Clone, Debug)]
2349 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2350 #[stable(feature = "rust1", since = "1.0.0")]
2351 pub struct Take<I> {
2356 #[stable(feature = "rust1", since = "1.0.0")]
2357 impl<I> Iterator for Take<I> where I: Iterator{
2358 type Item = <I as Iterator>::Item;
2361 fn next(&mut self) -> Option<<I as Iterator>::Item> {
2371 fn nth(&mut self, n: usize) -> Option<I::Item> {
2377 self.iter.nth(self.n - 1);
2385 fn size_hint(&self) -> (usize, Option<usize>) {
2386 let (lower, upper) = self.iter.size_hint();
2388 let lower = cmp::min(lower, self.n);
2390 let upper = match upper {
2391 Some(x) if x < self.n => Some(x),
2399 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2400 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2405 let n = &mut self.n;
2406 self.iter.try_fold(init, move |acc, x| {
2408 let r = fold(acc, x);
2409 if *n == 0 { LoopState::Break(r) }
2410 else { LoopState::from_try(r) }
2416 #[stable(feature = "rust1", since = "1.0.0")]
2417 impl<I> ExactSizeIterator for Take<I> where I: ExactSizeIterator {}
2419 #[stable(feature = "fused", since = "1.26.0")]
2420 impl<I> FusedIterator for Take<I> where I: FusedIterator {}
2422 #[unstable(feature = "trusted_len", issue = "37572")]
2423 unsafe impl<I: TrustedLen> TrustedLen for Take<I> {}
2425 /// An iterator to maintain state while iterating another iterator.
2427 /// This `struct` is created by the [`scan`] method on [`Iterator`]. See its
2428 /// documentation for more.
2430 /// [`scan`]: trait.Iterator.html#method.scan
2431 /// [`Iterator`]: trait.Iterator.html
2432 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2433 #[stable(feature = "rust1", since = "1.0.0")]
2435 pub struct Scan<I, St, F> {
2441 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2442 impl<I: fmt::Debug, St: fmt::Debug, F> fmt::Debug for Scan<I, St, F> {
2443 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2444 f.debug_struct("Scan")
2445 .field("iter", &self.iter)
2446 .field("state", &self.state)
2451 #[stable(feature = "rust1", since = "1.0.0")]
2452 impl<B, I, St, F> Iterator for Scan<I, St, F> where
2454 F: FnMut(&mut St, I::Item) -> Option<B>,
2459 fn next(&mut self) -> Option<B> {
2460 self.iter.next().and_then(|a| (self.f)(&mut self.state, a))
2464 fn size_hint(&self) -> (usize, Option<usize>) {
2465 let (_, upper) = self.iter.size_hint();
2466 (0, upper) // can't know a lower bound, due to the scan function
2470 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
2471 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2473 let state = &mut self.state;
2474 let f = &mut self.f;
2475 self.iter.try_fold(init, move |acc, x| {
2477 None => LoopState::Break(Try::from_ok(acc)),
2478 Some(x) => LoopState::from_try(fold(acc, x)),
2484 /// An iterator that maps each element to an iterator, and yields the elements
2485 /// of the produced iterators.
2487 /// This `struct` is created by the [`flat_map`] method on [`Iterator`]. See its
2488 /// documentation for more.
2490 /// [`flat_map`]: trait.Iterator.html#method.flat_map
2491 /// [`Iterator`]: trait.Iterator.html
2492 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2493 #[stable(feature = "rust1", since = "1.0.0")]
2494 pub struct FlatMap<I, U: IntoIterator, F> {
2495 inner: FlattenCompat<Map<I, F>, <U as IntoIterator>::IntoIter>
2498 #[stable(feature = "rust1", since = "1.0.0")]
2499 impl<I: Clone, U: Clone + IntoIterator, F: Clone> Clone for FlatMap<I, U, F>
2500 where <U as IntoIterator>::IntoIter: Clone
2502 fn clone(&self) -> Self { FlatMap { inner: self.inner.clone() } }
2505 #[stable(feature = "core_impl_debug", since = "1.9.0")]
2506 impl<I: fmt::Debug, U: IntoIterator, F> fmt::Debug for FlatMap<I, U, F>
2507 where U::IntoIter: fmt::Debug
2509 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2510 f.debug_struct("FlatMap").field("inner", &self.inner).finish()
2514 #[stable(feature = "rust1", since = "1.0.0")]
2515 impl<I: Iterator, U: IntoIterator, F> Iterator for FlatMap<I, U, F>
2516 where F: FnMut(I::Item) -> U,
2518 type Item = U::Item;
2521 fn next(&mut self) -> Option<U::Item> { self.inner.next() }
2524 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
2527 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2528 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2530 self.inner.try_fold(init, fold)
2534 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2535 where Fold: FnMut(Acc, Self::Item) -> Acc,
2537 self.inner.fold(init, fold)
2541 #[stable(feature = "rust1", since = "1.0.0")]
2542 impl<I: DoubleEndedIterator, U, F> DoubleEndedIterator for FlatMap<I, U, F>
2543 where F: FnMut(I::Item) -> U,
2545 U::IntoIter: DoubleEndedIterator
2548 fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }
2551 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2552 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2554 self.inner.try_rfold(init, fold)
2558 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2559 where Fold: FnMut(Acc, Self::Item) -> Acc,
2561 self.inner.rfold(init, fold)
2565 #[stable(feature = "fused", since = "1.26.0")]
2566 impl<I, U, F> FusedIterator for FlatMap<I, U, F>
2567 where I: FusedIterator, U: IntoIterator, F: FnMut(I::Item) -> U {}
2569 /// An iterator that flattens one level of nesting in an iterator of things
2570 /// that can be turned into iterators.
2572 /// This `struct` is created by the [`flatten`] method on [`Iterator`]. See its
2573 /// documentation for more.
2575 /// [`flatten`]: trait.Iterator.html#method.flatten
2576 /// [`Iterator`]: trait.Iterator.html
2577 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2578 #[stable(feature = "iterator_flatten", since = "1.29")]
2579 pub struct Flatten<I: Iterator>
2580 where I::Item: IntoIterator {
2581 inner: FlattenCompat<I, <I::Item as IntoIterator>::IntoIter>,
2584 #[stable(feature = "iterator_flatten", since = "1.29")]
2585 impl<I, U> fmt::Debug for Flatten<I>
2586 where I: Iterator + fmt::Debug, U: Iterator + fmt::Debug,
2587 I::Item: IntoIterator<IntoIter = U, Item = U::Item>,
2589 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
2590 f.debug_struct("Flatten").field("inner", &self.inner).finish()
2594 #[stable(feature = "iterator_flatten", since = "1.29")]
2595 impl<I, U> Clone for Flatten<I>
2596 where I: Iterator + Clone, U: Iterator + Clone,
2597 I::Item: IntoIterator<IntoIter = U, Item = U::Item>,
2599 fn clone(&self) -> Self { Flatten { inner: self.inner.clone() } }
2602 #[stable(feature = "iterator_flatten", since = "1.29")]
2603 impl<I, U> Iterator for Flatten<I>
2604 where I: Iterator, U: Iterator,
2605 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2607 type Item = U::Item;
2610 fn next(&mut self) -> Option<U::Item> { self.inner.next() }
2613 fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
2616 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2617 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2619 self.inner.try_fold(init, fold)
2623 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2624 where Fold: FnMut(Acc, Self::Item) -> Acc,
2626 self.inner.fold(init, fold)
2630 #[stable(feature = "iterator_flatten", since = "1.29")]
2631 impl<I, U> DoubleEndedIterator for Flatten<I>
2632 where I: DoubleEndedIterator, U: DoubleEndedIterator,
2633 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2636 fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }
2639 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2640 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2642 self.inner.try_rfold(init, fold)
2646 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2647 where Fold: FnMut(Acc, Self::Item) -> Acc,
2649 self.inner.rfold(init, fold)
2653 #[stable(feature = "iterator_flatten", since = "1.29")]
2654 impl<I, U> FusedIterator for Flatten<I>
2655 where I: FusedIterator, U: Iterator,
2656 I::Item: IntoIterator<IntoIter = U, Item = U::Item> {}
2658 /// Adapts an iterator by flattening it, for use in `flatten()` and `flat_map()`.
2659 fn flatten_compat<I, U>(iter: I) -> FlattenCompat<I, U> {
2660 FlattenCompat { iter, frontiter: None, backiter: None }
2663 /// Real logic of both `Flatten` and `FlatMap` which simply delegate to
2665 #[derive(Clone, Debug)]
2666 struct FlattenCompat<I, U> {
2668 frontiter: Option<U>,
2669 backiter: Option<U>,
2672 impl<I, U> Iterator for FlattenCompat<I, U>
2673 where I: Iterator, U: Iterator,
2674 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2676 type Item = U::Item;
2679 fn next(&mut self) -> Option<U::Item> {
2681 if let Some(ref mut inner) = self.frontiter {
2682 if let elt@Some(_) = inner.next() { return elt }
2684 match self.iter.next() {
2685 None => return self.backiter.as_mut().and_then(|it| it.next()),
2686 Some(inner) => self.frontiter = Some(inner.into_iter()),
2692 fn size_hint(&self) -> (usize, Option<usize>) {
2693 let (flo, fhi) = self.frontiter.as_ref().map_or((0, Some(0)), |it| it.size_hint());
2694 let (blo, bhi) = self.backiter.as_ref().map_or((0, Some(0)), |it| it.size_hint());
2695 let lo = flo.saturating_add(blo);
2696 match (self.iter.size_hint(), fhi, bhi) {
2697 ((0, Some(0)), Some(a), Some(b)) => (lo, a.checked_add(b)),
2703 fn try_fold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
2704 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2706 if let Some(ref mut front) = self.frontiter {
2707 init = front.try_fold(init, &mut fold)?;
2709 self.frontiter = None;
2712 let frontiter = &mut self.frontiter;
2713 init = self.iter.try_fold(init, |acc, x| {
2714 let mut mid = x.into_iter();
2715 let r = mid.try_fold(acc, &mut fold);
2716 *frontiter = Some(mid);
2720 self.frontiter = None;
2722 if let Some(ref mut back) = self.backiter {
2723 init = back.try_fold(init, &mut fold)?;
2725 self.backiter = None;
2731 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
2732 where Fold: FnMut(Acc, Self::Item) -> Acc,
2734 self.frontiter.into_iter()
2735 .chain(self.iter.map(IntoIterator::into_iter))
2736 .chain(self.backiter)
2737 .fold(init, |acc, iter| iter.fold(acc, &mut fold))
2741 impl<I, U> DoubleEndedIterator for FlattenCompat<I, U>
2742 where I: DoubleEndedIterator, U: DoubleEndedIterator,
2743 I::Item: IntoIterator<IntoIter = U, Item = U::Item>
2746 fn next_back(&mut self) -> Option<U::Item> {
2748 if let Some(ref mut inner) = self.backiter {
2749 if let elt@Some(_) = inner.next_back() { return elt }
2751 match self.iter.next_back() {
2752 None => return self.frontiter.as_mut().and_then(|it| it.next_back()),
2753 next => self.backiter = next.map(IntoIterator::into_iter),
2759 fn try_rfold<Acc, Fold, R>(&mut self, mut init: Acc, mut fold: Fold) -> R where
2760 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2762 if let Some(ref mut back) = self.backiter {
2763 init = back.try_rfold(init, &mut fold)?;
2765 self.backiter = None;
2768 let backiter = &mut self.backiter;
2769 init = self.iter.try_rfold(init, |acc, x| {
2770 let mut mid = x.into_iter();
2771 let r = mid.try_rfold(acc, &mut fold);
2772 *backiter = Some(mid);
2776 self.backiter = None;
2778 if let Some(ref mut front) = self.frontiter {
2779 init = front.try_rfold(init, &mut fold)?;
2781 self.frontiter = None;
2787 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
2788 where Fold: FnMut(Acc, Self::Item) -> Acc,
2790 self.frontiter.into_iter()
2791 .chain(self.iter.map(IntoIterator::into_iter))
2792 .chain(self.backiter)
2793 .rfold(init, |acc, iter| iter.rfold(acc, &mut fold))
2797 /// An iterator that yields `None` forever after the underlying iterator
2798 /// yields `None` once.
2800 /// This `struct` is created by the [`fuse`] method on [`Iterator`]. See its
2801 /// documentation for more.
2803 /// [`fuse`]: trait.Iterator.html#method.fuse
2804 /// [`Iterator`]: trait.Iterator.html
2805 #[derive(Clone, Debug)]
2806 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
2807 #[stable(feature = "rust1", since = "1.0.0")]
2808 pub struct Fuse<I> {
2813 #[stable(feature = "fused", since = "1.26.0")]
2814 impl<I> FusedIterator for Fuse<I> where I: Iterator {}
2816 #[stable(feature = "rust1", since = "1.0.0")]
2817 impl<I> Iterator for Fuse<I> where I: Iterator {
2818 type Item = <I as Iterator>::Item;
2821 default fn next(&mut self) -> Option<<I as Iterator>::Item> {
2825 let next = self.iter.next();
2826 self.done = next.is_none();
2832 default fn nth(&mut self, n: usize) -> Option<I::Item> {
2836 let nth = self.iter.nth(n);
2837 self.done = nth.is_none();
2843 default fn last(self) -> Option<I::Item> {
2852 default fn count(self) -> usize {
2861 default fn size_hint(&self) -> (usize, Option<usize>) {
2865 self.iter.size_hint()
2870 default fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2871 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2876 let acc = self.iter.try_fold(init, fold)?;
2883 default fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2884 where Fold: FnMut(Acc, Self::Item) -> Acc,
2889 self.iter.fold(init, fold)
2894 #[stable(feature = "rust1", since = "1.0.0")]
2895 impl<I> DoubleEndedIterator for Fuse<I> where I: DoubleEndedIterator {
2897 default fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
2901 let next = self.iter.next_back();
2902 self.done = next.is_none();
2908 default fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2909 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2914 let acc = self.iter.try_rfold(init, fold)?;
2921 default fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2922 where Fold: FnMut(Acc, Self::Item) -> Acc,
2927 self.iter.rfold(init, fold)
2932 unsafe impl<I> TrustedRandomAccess for Fuse<I>
2933 where I: TrustedRandomAccess,
2935 unsafe fn get_unchecked(&mut self, i: usize) -> I::Item {
2936 self.iter.get_unchecked(i)
2939 fn may_have_side_effect() -> bool {
2940 I::may_have_side_effect()
2944 #[stable(feature = "fused", since = "1.26.0")]
2945 impl<I> Iterator for Fuse<I> where I: FusedIterator {
2947 fn next(&mut self) -> Option<<I as Iterator>::Item> {
2952 fn nth(&mut self, n: usize) -> Option<I::Item> {
2957 fn last(self) -> Option<I::Item> {
2962 fn count(self) -> usize {
2967 fn size_hint(&self) -> (usize, Option<usize>) {
2968 self.iter.size_hint()
2972 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2973 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2975 self.iter.try_fold(init, fold)
2979 fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
2980 where Fold: FnMut(Acc, Self::Item) -> Acc,
2982 self.iter.fold(init, fold)
2986 #[stable(feature = "fused", since = "1.26.0")]
2987 impl<I> DoubleEndedIterator for Fuse<I>
2988 where I: DoubleEndedIterator + FusedIterator
2991 fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
2992 self.iter.next_back()
2996 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
2997 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
2999 self.iter.try_rfold(init, fold)
3003 fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
3004 where Fold: FnMut(Acc, Self::Item) -> Acc,
3006 self.iter.rfold(init, fold)
3011 #[stable(feature = "rust1", since = "1.0.0")]
3012 impl<I> ExactSizeIterator for Fuse<I> where I: ExactSizeIterator {
3013 fn len(&self) -> usize {
3017 fn is_empty(&self) -> bool {
3018 self.iter.is_empty()
3022 /// An iterator that calls a function with a reference to each element before
3025 /// This `struct` is created by the [`inspect`] method on [`Iterator`]. See its
3026 /// documentation for more.
3028 /// [`inspect`]: trait.Iterator.html#method.inspect
3029 /// [`Iterator`]: trait.Iterator.html
3030 #[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
3031 #[stable(feature = "rust1", since = "1.0.0")]
3033 pub struct Inspect<I, F> {
3038 #[stable(feature = "core_impl_debug", since = "1.9.0")]
3039 impl<I: fmt::Debug, F> fmt::Debug for Inspect<I, F> {
3040 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
3041 f.debug_struct("Inspect")
3042 .field("iter", &self.iter)
3047 impl<I: Iterator, F> Inspect<I, F> where F: FnMut(&I::Item) {
3049 fn do_inspect(&mut self, elt: Option<I::Item>) -> Option<I::Item> {
3050 if let Some(ref a) = elt {
3058 #[stable(feature = "rust1", since = "1.0.0")]
3059 impl<I: Iterator, F> Iterator for Inspect<I, F> where F: FnMut(&I::Item) {
3060 type Item = I::Item;
3063 fn next(&mut self) -> Option<I::Item> {
3064 let next = self.iter.next();
3065 self.do_inspect(next)
3069 fn size_hint(&self) -> (usize, Option<usize>) {
3070 self.iter.size_hint()
3074 fn try_fold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
3075 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
3077 let f = &mut self.f;
3078 self.iter.try_fold(init, move |acc, item| { f(&item); fold(acc, item) })
3082 fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
3083 where Fold: FnMut(Acc, Self::Item) -> Acc,
3086 self.iter.fold(init, move |acc, item| { f(&item); fold(acc, item) })
3090 #[stable(feature = "rust1", since = "1.0.0")]
3091 impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
3092 where F: FnMut(&I::Item),
3095 fn next_back(&mut self) -> Option<I::Item> {
3096 let next = self.iter.next_back();
3097 self.do_inspect(next)
3101 fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, mut fold: Fold) -> R where
3102 Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
3104 let f = &mut self.f;
3105 self.iter.try_rfold(init, move |acc, item| { f(&item); fold(acc, item) })
3109 fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
3110 where Fold: FnMut(Acc, Self::Item) -> Acc,
3113 self.iter.rfold(init, move |acc, item| { f(&item); fold(acc, item) })
3117 #[stable(feature = "rust1", since = "1.0.0")]
3118 impl<I: ExactSizeIterator, F> ExactSizeIterator for Inspect<I, F>
3119 where F: FnMut(&I::Item)
3121 fn len(&self) -> usize {
3125 fn is_empty(&self) -> bool {
3126 self.iter.is_empty()
3130 #[stable(feature = "fused", since = "1.26.0")]
3131 impl<I: FusedIterator, F> FusedIterator for Inspect<I, F>
3132 where F: FnMut(&I::Item) {}