2 use crate::cmp
::{self, Ordering}
;
3 use crate::ops
::{ChangeOutputType, ControlFlow, FromResidual, Residual, Try}
;
5 use super::super::try_process
;
6 use super::super::ByRefSized
;
7 use super::super::TrustedRandomAccessNoCoerce
;
8 use super::super::{ArrayChunks, Chain, Cloned, Copied, Cycle, Enumerate, Filter, FilterMap, Fuse}
;
9 use super::super::{FlatMap, Flatten}
;
10 use super::super::{FromIterator, Intersperse, IntersperseWith, Product, Sum, Zip}
;
12 Inspect
, Map
, MapWhile
, Peekable
, Rev
, Scan
, Skip
, SkipWhile
, StepBy
, Take
, TakeWhile
,
15 fn _assert_is_object_safe(_
: &dyn Iterator
<Item
= ()>) {}
17 /// An interface for dealing with iterators.
19 /// This is the main iterator trait. For more about the concept of iterators
20 /// generally, please see the [module-level documentation]. In particular, you
21 /// may want to know how to [implement `Iterator`][impl].
23 /// [module-level documentation]: crate::iter
24 /// [impl]: crate::iter#implementing-iterator
25 #[stable(feature = "rust1", since = "1.0.0")]
26 #[rustc_on_unimplemented(
28 _Self
= "std::ops::RangeTo<Idx>",
29 label
= "if you meant to iterate until a value, add a starting value",
30 note
= "`..end` is a `RangeTo`, which cannot be iterated on; you might have meant to have a \
31 bounded `Range`: `0..end`"
34 _Self
= "std::ops::RangeToInclusive<Idx>",
35 label
= "if you meant to iterate until a value (including it), add a starting value",
36 note
= "`..=end` is a `RangeToInclusive`, which cannot be iterated on; you might have meant \
37 to have a bounded `RangeInclusive`: `0..=end`"
41 label
= "`{Self}` is not an iterator; try calling `.into_iter()` or `.iter()`"
43 on(_Self
= "&[]", label
= "`{Self}` is not an iterator; try calling `.iter()`"),
45 _Self
= "std::vec::Vec<T, A>",
46 label
= "`{Self}` is not an iterator; try calling `.into_iter()` or `.iter()`"
50 label
= "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
53 _Self
= "std::string::String",
54 label
= "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
58 note
= "if you want to iterate between `start` until a value `end`, use the exclusive range \
59 syntax `start..end` or the inclusive range syntax `start..=end`"
61 label
= "`{Self}` is not an iterator",
62 message
= "`{Self}` is not an iterator"
65 #[rustc_diagnostic_item = "Iterator"]
66 #[must_use = "iterators are lazy and do nothing unless consumed"]
68 /// The type of the elements being iterated over.
69 #[stable(feature = "rust1", since = "1.0.0")]
72 /// Advances the iterator and returns the next value.
74 /// Returns [`None`] when iteration is finished. Individual iterator
75 /// implementations may choose to resume iteration, and so calling `next()`
76 /// again may or may not eventually start returning [`Some(Item)`] again at some
79 /// [`Some(Item)`]: Some
86 /// let a = [1, 2, 3];
88 /// let mut iter = a.iter();
90 /// // A call to next() returns the next value...
91 /// assert_eq!(Some(&1), iter.next());
92 /// assert_eq!(Some(&2), iter.next());
93 /// assert_eq!(Some(&3), iter.next());
95 /// // ... and then None once it's over.
96 /// assert_eq!(None, iter.next());
98 /// // More calls may or may not return `None`. Here, they always will.
99 /// assert_eq!(None, iter.next());
100 /// assert_eq!(None, iter.next());
103 #[stable(feature = "rust1", since = "1.0.0")]
104 fn next(&mut self) -> Option
<Self::Item
>;
106 /// Advances the iterator and returns an array containing the next `N` values.
108 /// If there are not enough elements to fill the array then `Err` is returned
109 /// containing an iterator over the remaining elements.
116 /// #![feature(iter_next_chunk)]
118 /// let mut iter = "lorem".chars();
120 /// assert_eq!(iter.next_chunk().unwrap(), ['l', 'o']); // N is inferred as 2
121 /// assert_eq!(iter.next_chunk().unwrap(), ['r', 'e', 'm']); // N is inferred as 3
122 /// assert_eq!(iter.next_chunk::<4>().unwrap_err().as_slice(), &[]); // N is explicitly 4
125 /// Split a string and get the first three items.
128 /// #![feature(iter_next_chunk)]
130 /// let quote = "not all those who wander are lost";
131 /// let [first, second, third] = quote.split_whitespace().next_chunk().unwrap();
132 /// assert_eq!(first, "not");
133 /// assert_eq!(second, "all");
134 /// assert_eq!(third, "those");
137 #[unstable(feature = "iter_next_chunk", reason = "recently added", issue = "98326")]
138 fn next_chunk
<const N
: usize>(
140 ) -> Result
<[Self::Item
; N
], array
::IntoIter
<Self::Item
, N
>>
144 array
::iter_next_chunk(self)
147 /// Returns the bounds on the remaining length of the iterator.
149 /// Specifically, `size_hint()` returns a tuple where the first element
150 /// is the lower bound, and the second element is the upper bound.
152 /// The second half of the tuple that is returned is an <code>[Option]<[usize]></code>.
153 /// A [`None`] here means that either there is no known upper bound, or the
154 /// upper bound is larger than [`usize`].
156 /// # Implementation notes
158 /// It is not enforced that an iterator implementation yields the declared
159 /// number of elements. A buggy iterator may yield less than the lower bound
160 /// or more than the upper bound of elements.
162 /// `size_hint()` is primarily intended to be used for optimizations such as
163 /// reserving space for the elements of the iterator, but must not be
164 /// trusted to e.g., omit bounds checks in unsafe code. An incorrect
165 /// implementation of `size_hint()` should not lead to memory safety
168 /// That said, the implementation should provide a correct estimation,
169 /// because otherwise it would be a violation of the trait's protocol.
171 /// The default implementation returns <code>(0, [None])</code> which is correct for any
179 /// let a = [1, 2, 3];
180 /// let mut iter = a.iter();
182 /// assert_eq!((3, Some(3)), iter.size_hint());
183 /// let _ = iter.next();
184 /// assert_eq!((2, Some(2)), iter.size_hint());
187 /// A more complex example:
190 /// // The even numbers in the range of zero to nine.
191 /// let iter = (0..10).filter(|x| x % 2 == 0);
193 /// // We might iterate from zero to ten times. Knowing that it's five
194 /// // exactly wouldn't be possible without executing filter().
195 /// assert_eq!((0, Some(10)), iter.size_hint());
197 /// // Let's add five more numbers with chain()
198 /// let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20);
200 /// // now both bounds are increased by five
201 /// assert_eq!((5, Some(15)), iter.size_hint());
204 /// Returning `None` for an upper bound:
207 /// // an infinite iterator has no upper bound
208 /// // and the maximum possible lower bound
211 /// assert_eq!((usize::MAX, None), iter.size_hint());
214 #[stable(feature = "rust1", since = "1.0.0")]
215 fn size_hint(&self) -> (usize, Option
<usize>) {
219 /// Consumes the iterator, counting the number of iterations and returning it.
221 /// This method will call [`next`] repeatedly until [`None`] is encountered,
222 /// returning the number of times it saw [`Some`]. Note that [`next`] has to be
223 /// called at least once even if the iterator does not have any elements.
225 /// [`next`]: Iterator::next
227 /// # Overflow Behavior
229 /// The method does no guarding against overflows, so counting elements of
230 /// an iterator with more than [`usize::MAX`] elements either produces the
231 /// wrong result or panics. If debug assertions are enabled, a panic is
236 /// This function might panic if the iterator has more than [`usize::MAX`]
244 /// let a = [1, 2, 3];
245 /// assert_eq!(a.iter().count(), 3);
247 /// let a = [1, 2, 3, 4, 5];
248 /// assert_eq!(a.iter().count(), 5);
251 #[stable(feature = "rust1", since = "1.0.0")]
252 fn count(self) -> usize
258 #[rustc_inherit_overflow_checks]
259 |count
, _
| count
+ 1,
263 /// Consumes the iterator, returning the last element.
265 /// This method will evaluate the iterator until it returns [`None`]. While
266 /// doing so, it keeps track of the current element. After [`None`] is
267 /// returned, `last()` will then return the last element it saw.
274 /// let a = [1, 2, 3];
275 /// assert_eq!(a.iter().last(), Some(&3));
277 /// let a = [1, 2, 3, 4, 5];
278 /// assert_eq!(a.iter().last(), Some(&5));
281 #[stable(feature = "rust1", since = "1.0.0")]
282 fn last(self) -> Option
<Self::Item
>
287 fn some
<T
>(_
: Option
<T
>, x
: T
) -> Option
<T
> {
291 self.fold(None
, some
)
294 /// Advances the iterator by `n` elements.
296 /// This method will eagerly skip `n` elements by calling [`next`] up to `n`
297 /// times until [`None`] is encountered.
299 /// `advance_by(n)` will return [`Ok(())`][Ok] if the iterator successfully advances by
300 /// `n` elements, or [`Err(k)`][Err] if [`None`] is encountered, where `k` is the number
301 /// of elements the iterator is advanced by before running out of elements (i.e. the
302 /// length of the iterator). Note that `k` is always less than `n`.
304 /// Calling `advance_by(0)` can do meaningful work, for example [`Flatten`]
305 /// can advance its outer iterator until it finds an inner iterator that is not empty, which
306 /// then often allows it to return a more accurate `size_hint()` than in its initial state.
308 /// [`Flatten`]: crate::iter::Flatten
309 /// [`next`]: Iterator::next
316 /// #![feature(iter_advance_by)]
318 /// let a = [1, 2, 3, 4];
319 /// let mut iter = a.iter();
321 /// assert_eq!(iter.advance_by(2), Ok(()));
322 /// assert_eq!(iter.next(), Some(&3));
323 /// assert_eq!(iter.advance_by(0), Ok(()));
324 /// assert_eq!(iter.advance_by(100), Err(1)); // only `&4` was skipped
327 #[unstable(feature = "iter_advance_by", reason = "recently added", issue = "77404")]
328 fn advance_by(&mut self, n
: usize) -> Result
<(), usize> {
330 self.next().ok_or(i
)?
;
335 /// Returns the `n`th element of the iterator.
337 /// Like most indexing operations, the count starts from zero, so `nth(0)`
338 /// returns the first value, `nth(1)` the second, and so on.
340 /// Note that all preceding elements, as well as the returned element, will be
341 /// consumed from the iterator. That means that the preceding elements will be
342 /// discarded, and also that calling `nth(0)` multiple times on the same iterator
343 /// will return different elements.
345 /// `nth()` will return [`None`] if `n` is greater than or equal to the length of the
353 /// let a = [1, 2, 3];
354 /// assert_eq!(a.iter().nth(1), Some(&2));
357 /// Calling `nth()` multiple times doesn't rewind the iterator:
360 /// let a = [1, 2, 3];
362 /// let mut iter = a.iter();
364 /// assert_eq!(iter.nth(1), Some(&2));
365 /// assert_eq!(iter.nth(1), None);
368 /// Returning `None` if there are less than `n + 1` elements:
371 /// let a = [1, 2, 3];
372 /// assert_eq!(a.iter().nth(10), None);
375 #[stable(feature = "rust1", since = "1.0.0")]
376 fn nth(&mut self, n
: usize) -> Option
<Self::Item
> {
377 self.advance_by(n
).ok()?
;
381 /// Creates an iterator starting at the same point, but stepping by
382 /// the given amount at each iteration.
384 /// Note 1: The first element of the iterator will always be returned,
385 /// regardless of the step given.
387 /// Note 2: The time at which ignored elements are pulled is not fixed.
388 /// `StepBy` behaves like the sequence `self.next()`, `self.nth(step-1)`,
389 /// `self.nth(step-1)`, …, but is also free to behave like the sequence
390 /// `advance_n_and_return_first(&mut self, step)`,
391 /// `advance_n_and_return_first(&mut self, step)`, …
392 /// Which way is used may change for some iterators for performance reasons.
393 /// The second way will advance the iterator earlier and may consume more items.
395 /// `advance_n_and_return_first` is the equivalent of:
397 /// fn advance_n_and_return_first<I>(iter: &mut I, n: usize) -> Option<I::Item>
401 /// let next = iter.next();
411 /// The method will panic if the given step is `0`.
418 /// let a = [0, 1, 2, 3, 4, 5];
419 /// let mut iter = a.iter().step_by(2);
421 /// assert_eq!(iter.next(), Some(&0));
422 /// assert_eq!(iter.next(), Some(&2));
423 /// assert_eq!(iter.next(), Some(&4));
424 /// assert_eq!(iter.next(), None);
427 #[stable(feature = "iterator_step_by", since = "1.28.0")]
428 fn step_by(self, step
: usize) -> StepBy
<Self>
432 StepBy
::new(self, step
)
435 /// Takes two iterators and creates a new iterator over both in sequence.
437 /// `chain()` will return a new iterator which will first iterate over
438 /// values from the first iterator and then over values from the second
441 /// In other words, it links two iterators together, in a chain. 🔗
443 /// [`once`] is commonly used to adapt a single value into a chain of
444 /// other kinds of iteration.
451 /// let a1 = [1, 2, 3];
452 /// let a2 = [4, 5, 6];
454 /// let mut iter = a1.iter().chain(a2.iter());
456 /// assert_eq!(iter.next(), Some(&1));
457 /// assert_eq!(iter.next(), Some(&2));
458 /// assert_eq!(iter.next(), Some(&3));
459 /// assert_eq!(iter.next(), Some(&4));
460 /// assert_eq!(iter.next(), Some(&5));
461 /// assert_eq!(iter.next(), Some(&6));
462 /// assert_eq!(iter.next(), None);
465 /// Since the argument to `chain()` uses [`IntoIterator`], we can pass
466 /// anything that can be converted into an [`Iterator`], not just an
467 /// [`Iterator`] itself. For example, slices (`&[T]`) implement
468 /// [`IntoIterator`], and so can be passed to `chain()` directly:
471 /// let s1 = &[1, 2, 3];
472 /// let s2 = &[4, 5, 6];
474 /// let mut iter = s1.iter().chain(s2);
476 /// assert_eq!(iter.next(), Some(&1));
477 /// assert_eq!(iter.next(), Some(&2));
478 /// assert_eq!(iter.next(), Some(&3));
479 /// assert_eq!(iter.next(), Some(&4));
480 /// assert_eq!(iter.next(), Some(&5));
481 /// assert_eq!(iter.next(), Some(&6));
482 /// assert_eq!(iter.next(), None);
485 /// If you work with Windows API, you may wish to convert [`OsStr`] to `Vec<u16>`:
489 /// fn os_str_to_utf16(s: &std::ffi::OsStr) -> Vec<u16> {
490 /// use std::os::windows::ffi::OsStrExt;
491 /// s.encode_wide().chain(std::iter::once(0)).collect()
495 /// [`once`]: crate::iter::once
496 /// [`OsStr`]: ../../std/ffi/struct.OsStr.html
498 #[stable(feature = "rust1", since = "1.0.0")]
499 fn chain
<U
>(self, other
: U
) -> Chain
<Self, U
::IntoIter
>
502 U
: IntoIterator
<Item
= Self::Item
>,
504 Chain
::new(self, other
.into_iter())
507 /// 'Zips up' two iterators into a single iterator of pairs.
509 /// `zip()` returns a new iterator that will iterate over two other
510 /// iterators, returning a tuple where the first element comes from the
511 /// first iterator, and the second element comes from the second iterator.
513 /// In other words, it zips two iterators together, into a single one.
515 /// If either iterator returns [`None`], [`next`] from the zipped iterator
516 /// will return [`None`].
517 /// If the zipped iterator has no more elements to return then each further attempt to advance
518 /// it will first try to advance the first iterator at most one time and if it still yielded an item
519 /// try to advance the second iterator at most one time.
521 /// To 'undo' the result of zipping up two iterators, see [`unzip`].
523 /// [`unzip`]: Iterator::unzip
530 /// let a1 = [1, 2, 3];
531 /// let a2 = [4, 5, 6];
533 /// let mut iter = a1.iter().zip(a2.iter());
535 /// assert_eq!(iter.next(), Some((&1, &4)));
536 /// assert_eq!(iter.next(), Some((&2, &5)));
537 /// assert_eq!(iter.next(), Some((&3, &6)));
538 /// assert_eq!(iter.next(), None);
541 /// Since the argument to `zip()` uses [`IntoIterator`], we can pass
542 /// anything that can be converted into an [`Iterator`], not just an
543 /// [`Iterator`] itself. For example, slices (`&[T]`) implement
544 /// [`IntoIterator`], and so can be passed to `zip()` directly:
547 /// let s1 = &[1, 2, 3];
548 /// let s2 = &[4, 5, 6];
550 /// let mut iter = s1.iter().zip(s2);
552 /// assert_eq!(iter.next(), Some((&1, &4)));
553 /// assert_eq!(iter.next(), Some((&2, &5)));
554 /// assert_eq!(iter.next(), Some((&3, &6)));
555 /// assert_eq!(iter.next(), None);
558 /// `zip()` is often used to zip an infinite iterator to a finite one.
559 /// This works because the finite iterator will eventually return [`None`],
560 /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate`]:
563 /// let enumerate: Vec<_> = "foo".chars().enumerate().collect();
565 /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect();
567 /// assert_eq!((0, 'f'), enumerate[0]);
568 /// assert_eq!((0, 'f'), zipper[0]);
570 /// assert_eq!((1, 'o'), enumerate[1]);
571 /// assert_eq!((1, 'o'), zipper[1]);
573 /// assert_eq!((2, 'o'), enumerate[2]);
574 /// assert_eq!((2, 'o'), zipper[2]);
577 /// If both iterators have roughly equivalent syntax, it may be more readable to use [`zip`]:
580 /// use std::iter::zip;
582 /// let a = [1, 2, 3];
583 /// let b = [2, 3, 4];
585 /// let mut zipped = zip(
586 /// a.into_iter().map(|x| x * 2).skip(1),
587 /// b.into_iter().map(|x| x * 2).skip(1),
590 /// assert_eq!(zipped.next(), Some((4, 6)));
591 /// assert_eq!(zipped.next(), Some((6, 8)));
592 /// assert_eq!(zipped.next(), None);
598 /// # let a = [1, 2, 3];
599 /// # let b = [2, 3, 4];
601 /// let mut zipped = a
605 /// .zip(b.into_iter().map(|x| x * 2).skip(1));
607 /// # assert_eq!(zipped.next(), Some((4, 6)));
608 /// # assert_eq!(zipped.next(), Some((6, 8)));
609 /// # assert_eq!(zipped.next(), None);
612 /// [`enumerate`]: Iterator::enumerate
613 /// [`next`]: Iterator::next
614 /// [`zip`]: crate::iter::zip
616 #[stable(feature = "rust1", since = "1.0.0")]
617 fn zip
<U
>(self, other
: U
) -> Zip
<Self, U
::IntoIter
>
622 Zip
::new(self, other
.into_iter())
625 /// Creates a new iterator which places a copy of `separator` between adjacent
626 /// items of the original iterator.
628 /// In case `separator` does not implement [`Clone`] or needs to be
629 /// computed every time, use [`intersperse_with`].
636 /// #![feature(iter_intersperse)]
638 /// let mut a = [0, 1, 2].iter().intersperse(&100);
639 /// assert_eq!(a.next(), Some(&0)); // The first element from `a`.
640 /// assert_eq!(a.next(), Some(&100)); // The separator.
641 /// assert_eq!(a.next(), Some(&1)); // The next element from `a`.
642 /// assert_eq!(a.next(), Some(&100)); // The separator.
643 /// assert_eq!(a.next(), Some(&2)); // The last element from `a`.
644 /// assert_eq!(a.next(), None); // The iterator is finished.
647 /// `intersperse` can be very useful to join an iterator's items using a common element:
649 /// #![feature(iter_intersperse)]
651 /// let hello = ["Hello", "World", "!"].iter().copied().intersperse(" ").collect::<String>();
652 /// assert_eq!(hello, "Hello World !");
655 /// [`Clone`]: crate::clone::Clone
656 /// [`intersperse_with`]: Iterator::intersperse_with
658 #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
659 fn intersperse(self, separator
: Self::Item
) -> Intersperse
<Self>
664 Intersperse
::new(self, separator
)
667 /// Creates a new iterator which places an item generated by `separator`
668 /// between adjacent items of the original iterator.
670 /// The closure will be called exactly once each time an item is placed
671 /// between two adjacent items from the underlying iterator; specifically,
672 /// the closure is not called if the underlying iterator yields less than
673 /// two items and after the last item is yielded.
675 /// If the iterator's item implements [`Clone`], it may be easier to use
683 /// #![feature(iter_intersperse)]
685 /// #[derive(PartialEq, Debug)]
686 /// struct NotClone(usize);
688 /// let v = [NotClone(0), NotClone(1), NotClone(2)];
689 /// let mut it = v.into_iter().intersperse_with(|| NotClone(99));
691 /// assert_eq!(it.next(), Some(NotClone(0))); // The first element from `v`.
692 /// assert_eq!(it.next(), Some(NotClone(99))); // The separator.
693 /// assert_eq!(it.next(), Some(NotClone(1))); // The next element from `v`.
694 /// assert_eq!(it.next(), Some(NotClone(99))); // The separator.
695 /// assert_eq!(it.next(), Some(NotClone(2))); // The last element from `v`.
696 /// assert_eq!(it.next(), None); // The iterator is finished.
699 /// `intersperse_with` can be used in situations where the separator needs
702 /// #![feature(iter_intersperse)]
704 /// let src = ["Hello", "to", "all", "people", "!!"].iter().copied();
706 /// // The closure mutably borrows its context to generate an item.
707 /// let mut happy_emojis = [" ❤️ ", " 😀 "].iter().copied();
708 /// let separator = || happy_emojis.next().unwrap_or(" 🦀 ");
710 /// let result = src.intersperse_with(separator).collect::<String>();
711 /// assert_eq!(result, "Hello ❤️ to 😀 all 🦀 people 🦀 !!");
713 /// [`Clone`]: crate::clone::Clone
714 /// [`intersperse`]: Iterator::intersperse
716 #[unstable(feature = "iter_intersperse", reason = "recently added", issue = "79524")]
717 fn intersperse_with
<G
>(self, separator
: G
) -> IntersperseWith
<Self, G
>
720 G
: FnMut() -> Self::Item
,
722 IntersperseWith
::new(self, separator
)
725 /// Takes a closure and creates an iterator which calls that closure on each
728 /// `map()` transforms one iterator into another, by means of its argument:
729 /// something that implements [`FnMut`]. It produces a new iterator which
730 /// calls this closure on each element of the original iterator.
732 /// If you are good at thinking in types, you can think of `map()` like this:
733 /// If you have an iterator that gives you elements of some type `A`, and
734 /// you want an iterator of some other type `B`, you can use `map()`,
735 /// passing a closure that takes an `A` and returns a `B`.
737 /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is
738 /// lazy, it is best used when you're already working with other iterators.
739 /// If you're doing some sort of looping for a side effect, it's considered
740 /// more idiomatic to use [`for`] than `map()`.
742 /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
743 /// [`FnMut`]: crate::ops::FnMut
750 /// let a = [1, 2, 3];
752 /// let mut iter = a.iter().map(|x| 2 * x);
754 /// assert_eq!(iter.next(), Some(2));
755 /// assert_eq!(iter.next(), Some(4));
756 /// assert_eq!(iter.next(), Some(6));
757 /// assert_eq!(iter.next(), None);
760 /// If you're doing some sort of side effect, prefer [`for`] to `map()`:
763 /// # #![allow(unused_must_use)]
764 /// // don't do this:
765 /// (0..5).map(|x| println!("{x}"));
767 /// // it won't even execute, as it is lazy. Rust will warn you about this.
769 /// // Instead, use for:
775 #[stable(feature = "rust1", since = "1.0.0")]
776 fn map
<B
, F
>(self, f
: F
) -> Map
<Self, F
>
779 F
: FnMut(Self::Item
) -> B
,
784 /// Calls a closure on each element of an iterator.
786 /// This is equivalent to using a [`for`] loop on the iterator, although
787 /// `break` and `continue` are not possible from a closure. It's generally
788 /// more idiomatic to use a `for` loop, but `for_each` may be more legible
789 /// when processing items at the end of longer iterator chains. In some
790 /// cases `for_each` may also be faster than a loop, because it will use
791 /// internal iteration on adapters like `Chain`.
793 /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
800 /// use std::sync::mpsc::channel;
802 /// let (tx, rx) = channel();
803 /// (0..5).map(|x| x * 2 + 1)
804 /// .for_each(move |x| tx.send(x).unwrap());
806 /// let v: Vec<_> = rx.iter().collect();
807 /// assert_eq!(v, vec![1, 3, 5, 7, 9]);
810 /// For such a small example, a `for` loop may be cleaner, but `for_each`
811 /// might be preferable to keep a functional style with longer iterators:
814 /// (0..5).flat_map(|x| x * 100 .. x * 110)
816 /// .filter(|&(i, x)| (i + x) % 3 == 0)
817 /// .for_each(|(i, x)| println!("{i}:{x}"));
820 #[stable(feature = "iterator_for_each", since = "1.21.0")]
821 fn for_each
<F
>(self, f
: F
)
824 F
: FnMut(Self::Item
),
827 fn call
<T
>(mut f
: impl FnMut(T
)) -> impl FnMut((), T
) {
828 move |(), item
| f(item
)
831 self.fold((), call(f
));
834 /// Creates an iterator which uses a closure to determine if an element
835 /// should be yielded.
837 /// Given an element the closure must return `true` or `false`. The returned
838 /// iterator will yield only the elements for which the closure returns
846 /// let a = [0i32, 1, 2];
848 /// let mut iter = a.iter().filter(|x| x.is_positive());
850 /// assert_eq!(iter.next(), Some(&1));
851 /// assert_eq!(iter.next(), Some(&2));
852 /// assert_eq!(iter.next(), None);
855 /// Because the closure passed to `filter()` takes a reference, and many
856 /// iterators iterate over references, this leads to a possibly confusing
857 /// situation, where the type of the closure is a double reference:
860 /// let a = [0, 1, 2];
862 /// let mut iter = a.iter().filter(|x| **x > 1); // need two *s!
864 /// assert_eq!(iter.next(), Some(&2));
865 /// assert_eq!(iter.next(), None);
868 /// It's common to instead use destructuring on the argument to strip away
872 /// let a = [0, 1, 2];
874 /// let mut iter = a.iter().filter(|&x| *x > 1); // both & and *
876 /// assert_eq!(iter.next(), Some(&2));
877 /// assert_eq!(iter.next(), None);
883 /// let a = [0, 1, 2];
885 /// let mut iter = a.iter().filter(|&&x| x > 1); // two &s
887 /// assert_eq!(iter.next(), Some(&2));
888 /// assert_eq!(iter.next(), None);
893 /// Note that `iter.filter(f).next()` is equivalent to `iter.find(f)`.
895 #[stable(feature = "rust1", since = "1.0.0")]
896 fn filter
<P
>(self, predicate
: P
) -> Filter
<Self, P
>
899 P
: FnMut(&Self::Item
) -> bool
,
901 Filter
::new(self, predicate
)
904 /// Creates an iterator that both filters and maps.
906 /// The returned iterator yields only the `value`s for which the supplied
907 /// closure returns `Some(value)`.
909 /// `filter_map` can be used to make chains of [`filter`] and [`map`] more
910 /// concise. The example below shows how a `map().filter().map()` can be
911 /// shortened to a single call to `filter_map`.
913 /// [`filter`]: Iterator::filter
914 /// [`map`]: Iterator::map
921 /// let a = ["1", "two", "NaN", "four", "5"];
923 /// let mut iter = a.iter().filter_map(|s| s.parse().ok());
925 /// assert_eq!(iter.next(), Some(1));
926 /// assert_eq!(iter.next(), Some(5));
927 /// assert_eq!(iter.next(), None);
930 /// Here's the same example, but with [`filter`] and [`map`]:
933 /// let a = ["1", "two", "NaN", "four", "5"];
934 /// let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap());
935 /// assert_eq!(iter.next(), Some(1));
936 /// assert_eq!(iter.next(), Some(5));
937 /// assert_eq!(iter.next(), None);
940 #[stable(feature = "rust1", since = "1.0.0")]
941 fn filter_map
<B
, F
>(self, f
: F
) -> FilterMap
<Self, F
>
944 F
: FnMut(Self::Item
) -> Option
<B
>,
946 FilterMap
::new(self, f
)
949 /// Creates an iterator which gives the current iteration count as well as
952 /// The iterator returned yields pairs `(i, val)`, where `i` is the
953 /// current index of iteration and `val` is the value returned by the
956 /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a
957 /// different sized integer, the [`zip`] function provides similar
960 /// # Overflow Behavior
962 /// The method does no guarding against overflows, so enumerating more than
963 /// [`usize::MAX`] elements either produces the wrong result or panics. If
964 /// debug assertions are enabled, a panic is guaranteed.
968 /// The returned iterator might panic if the to-be-returned index would
969 /// overflow a [`usize`].
971 /// [`zip`]: Iterator::zip
976 /// let a = ['a', 'b', 'c'];
978 /// let mut iter = a.iter().enumerate();
980 /// assert_eq!(iter.next(), Some((0, &'a')));
981 /// assert_eq!(iter.next(), Some((1, &'b')));
982 /// assert_eq!(iter.next(), Some((2, &'c')));
983 /// assert_eq!(iter.next(), None);
986 #[stable(feature = "rust1", since = "1.0.0")]
987 fn enumerate(self) -> Enumerate
<Self>
994 /// Creates an iterator which can use the [`peek`] and [`peek_mut`] methods
995 /// to look at the next element of the iterator without consuming it. See
996 /// their documentation for more information.
998 /// Note that the underlying iterator is still advanced when [`peek`] or
999 /// [`peek_mut`] are called for the first time: In order to retrieve the
1000 /// next element, [`next`] is called on the underlying iterator, hence any
1001 /// side effects (i.e. anything other than fetching the next value) of
1002 /// the [`next`] method will occur.
1010 /// let xs = [1, 2, 3];
1012 /// let mut iter = xs.iter().peekable();
1014 /// // peek() lets us see into the future
1015 /// assert_eq!(iter.peek(), Some(&&1));
1016 /// assert_eq!(iter.next(), Some(&1));
1018 /// assert_eq!(iter.next(), Some(&2));
1020 /// // we can peek() multiple times, the iterator won't advance
1021 /// assert_eq!(iter.peek(), Some(&&3));
1022 /// assert_eq!(iter.peek(), Some(&&3));
1024 /// assert_eq!(iter.next(), Some(&3));
1026 /// // after the iterator is finished, so is peek()
1027 /// assert_eq!(iter.peek(), None);
1028 /// assert_eq!(iter.next(), None);
1031 /// Using [`peek_mut`] to mutate the next item without advancing the
1035 /// let xs = [1, 2, 3];
1037 /// let mut iter = xs.iter().peekable();
1039 /// // `peek_mut()` lets us see into the future
1040 /// assert_eq!(iter.peek_mut(), Some(&mut &1));
1041 /// assert_eq!(iter.peek_mut(), Some(&mut &1));
1042 /// assert_eq!(iter.next(), Some(&1));
1044 /// if let Some(mut p) = iter.peek_mut() {
1045 /// assert_eq!(*p, &2);
1046 /// // put a value into the iterator
1050 /// // The value reappears as the iterator continues
1051 /// assert_eq!(iter.collect::<Vec<_>>(), vec![&1000, &3]);
1053 /// [`peek`]: Peekable::peek
1054 /// [`peek_mut`]: Peekable::peek_mut
1055 /// [`next`]: Iterator::next
1057 #[stable(feature = "rust1", since = "1.0.0")]
1058 fn peekable(self) -> Peekable
<Self>
1065 /// Creates an iterator that [`skip`]s elements based on a predicate.
1067 /// [`skip`]: Iterator::skip
1069 /// `skip_while()` takes a closure as an argument. It will call this
1070 /// closure on each element of the iterator, and ignore elements
1071 /// until it returns `false`.
1073 /// After `false` is returned, `skip_while()`'s job is over, and the
1074 /// rest of the elements are yielded.
1081 /// let a = [-1i32, 0, 1];
1083 /// let mut iter = a.iter().skip_while(|x| x.is_negative());
1085 /// assert_eq!(iter.next(), Some(&0));
1086 /// assert_eq!(iter.next(), Some(&1));
1087 /// assert_eq!(iter.next(), None);
1090 /// Because the closure passed to `skip_while()` takes a reference, and many
1091 /// iterators iterate over references, this leads to a possibly confusing
1092 /// situation, where the type of the closure argument is a double reference:
1095 /// let a = [-1, 0, 1];
1097 /// let mut iter = a.iter().skip_while(|x| **x < 0); // need two *s!
1099 /// assert_eq!(iter.next(), Some(&0));
1100 /// assert_eq!(iter.next(), Some(&1));
1101 /// assert_eq!(iter.next(), None);
1104 /// Stopping after an initial `false`:
1107 /// let a = [-1, 0, 1, -2];
1109 /// let mut iter = a.iter().skip_while(|x| **x < 0);
1111 /// assert_eq!(iter.next(), Some(&0));
1112 /// assert_eq!(iter.next(), Some(&1));
1114 /// // while this would have been false, since we already got a false,
1115 /// // skip_while() isn't used any more
1116 /// assert_eq!(iter.next(), Some(&-2));
1118 /// assert_eq!(iter.next(), None);
1121 #[doc(alias = "drop_while")]
1122 #[stable(feature = "rust1", since = "1.0.0")]
1123 fn skip_while
<P
>(self, predicate
: P
) -> SkipWhile
<Self, P
>
1126 P
: FnMut(&Self::Item
) -> bool
,
1128 SkipWhile
::new(self, predicate
)
1131 /// Creates an iterator that yields elements based on a predicate.
1133 /// `take_while()` takes a closure as an argument. It will call this
1134 /// closure on each element of the iterator, and yield elements
1135 /// while it returns `true`.
1137 /// After `false` is returned, `take_while()`'s job is over, and the
1138 /// rest of the elements are ignored.
1145 /// let a = [-1i32, 0, 1];
1147 /// let mut iter = a.iter().take_while(|x| x.is_negative());
1149 /// assert_eq!(iter.next(), Some(&-1));
1150 /// assert_eq!(iter.next(), None);
1153 /// Because the closure passed to `take_while()` takes a reference, and many
1154 /// iterators iterate over references, this leads to a possibly confusing
1155 /// situation, where the type of the closure is a double reference:
1158 /// let a = [-1, 0, 1];
1160 /// let mut iter = a.iter().take_while(|x| **x < 0); // need two *s!
1162 /// assert_eq!(iter.next(), Some(&-1));
1163 /// assert_eq!(iter.next(), None);
1166 /// Stopping after an initial `false`:
1169 /// let a = [-1, 0, 1, -2];
1171 /// let mut iter = a.iter().take_while(|x| **x < 0);
1173 /// assert_eq!(iter.next(), Some(&-1));
1175 /// // We have more elements that are less than zero, but since we already
1176 /// // got a false, take_while() isn't used any more
1177 /// assert_eq!(iter.next(), None);
1180 /// Because `take_while()` needs to look at the value in order to see if it
1181 /// should be included or not, consuming iterators will see that it is
1185 /// let a = [1, 2, 3, 4];
1186 /// let mut iter = a.iter();
1188 /// let result: Vec<i32> = iter.by_ref()
1189 /// .take_while(|n| **n != 3)
1193 /// assert_eq!(result, &[1, 2]);
1195 /// let result: Vec<i32> = iter.cloned().collect();
1197 /// assert_eq!(result, &[4]);
1200 /// The `3` is no longer there, because it was consumed in order to see if
1201 /// the iteration should stop, but wasn't placed back into the iterator.
1203 #[stable(feature = "rust1", since = "1.0.0")]
1204 fn take_while
<P
>(self, predicate
: P
) -> TakeWhile
<Self, P
>
1207 P
: FnMut(&Self::Item
) -> bool
,
1209 TakeWhile
::new(self, predicate
)
1212 /// Creates an iterator that both yields elements based on a predicate and maps.
1214 /// `map_while()` takes a closure as an argument. It will call this
1215 /// closure on each element of the iterator, and yield elements
1216 /// while it returns [`Some(_)`][`Some`].
1223 /// let a = [-1i32, 4, 0, 1];
1225 /// let mut iter = a.iter().map_while(|x| 16i32.checked_div(*x));
1227 /// assert_eq!(iter.next(), Some(-16));
1228 /// assert_eq!(iter.next(), Some(4));
1229 /// assert_eq!(iter.next(), None);
1232 /// Here's the same example, but with [`take_while`] and [`map`]:
1234 /// [`take_while`]: Iterator::take_while
1235 /// [`map`]: Iterator::map
1238 /// let a = [-1i32, 4, 0, 1];
1240 /// let mut iter = a.iter()
1241 /// .map(|x| 16i32.checked_div(*x))
1242 /// .take_while(|x| x.is_some())
1243 /// .map(|x| x.unwrap());
1245 /// assert_eq!(iter.next(), Some(-16));
1246 /// assert_eq!(iter.next(), Some(4));
1247 /// assert_eq!(iter.next(), None);
1250 /// Stopping after an initial [`None`]:
1253 /// let a = [0, 1, 2, -3, 4, 5, -6];
1255 /// let iter = a.iter().map_while(|x| u32::try_from(*x).ok());
1256 /// let vec = iter.collect::<Vec<_>>();
1258 /// // We have more elements which could fit in u32 (4, 5), but `map_while` returned `None` for `-3`
1259 /// // (as the `predicate` returned `None`) and `collect` stops at the first `None` encountered.
1260 /// assert_eq!(vec, vec![0, 1, 2]);
1263 /// Because `map_while()` needs to look at the value in order to see if it
1264 /// should be included or not, consuming iterators will see that it is
1268 /// let a = [1, 2, -3, 4];
1269 /// let mut iter = a.iter();
1271 /// let result: Vec<u32> = iter.by_ref()
1272 /// .map_while(|n| u32::try_from(*n).ok())
1275 /// assert_eq!(result, &[1, 2]);
1277 /// let result: Vec<i32> = iter.cloned().collect();
1279 /// assert_eq!(result, &[4]);
1282 /// The `-3` is no longer there, because it was consumed in order to see if
1283 /// the iteration should stop, but wasn't placed back into the iterator.
1285 /// Note that unlike [`take_while`] this iterator is **not** fused.
1286 /// It is also not specified what this iterator returns after the first [`None`] is returned.
1287 /// If you need fused iterator, use [`fuse`].
1289 /// [`fuse`]: Iterator::fuse
1291 #[stable(feature = "iter_map_while", since = "1.57.0")]
1292 fn map_while
<B
, P
>(self, predicate
: P
) -> MapWhile
<Self, P
>
1295 P
: FnMut(Self::Item
) -> Option
<B
>,
1297 MapWhile
::new(self, predicate
)
1300 /// Creates an iterator that skips the first `n` elements.
1302 /// `skip(n)` skips elements until `n` elements are skipped or the end of the
1303 /// iterator is reached (whichever happens first). After that, all the remaining
1304 /// elements are yielded. In particular, if the original iterator is too short,
1305 /// then the returned iterator is empty.
1307 /// Rather than overriding this method directly, instead override the `nth` method.
1314 /// let a = [1, 2, 3];
1316 /// let mut iter = a.iter().skip(2);
1318 /// assert_eq!(iter.next(), Some(&3));
1319 /// assert_eq!(iter.next(), None);
1322 #[stable(feature = "rust1", since = "1.0.0")]
1323 fn skip(self, n
: usize) -> Skip
<Self>
1330 /// Creates an iterator that yields the first `n` elements, or fewer
1331 /// if the underlying iterator ends sooner.
1333 /// `take(n)` yields elements until `n` elements are yielded or the end of
1334 /// the iterator is reached (whichever happens first).
1335 /// The returned iterator is a prefix of length `n` if the original iterator
1336 /// contains at least `n` elements, otherwise it contains all of the
1337 /// (fewer than `n`) elements of the original iterator.
1344 /// let a = [1, 2, 3];
1346 /// let mut iter = a.iter().take(2);
1348 /// assert_eq!(iter.next(), Some(&1));
1349 /// assert_eq!(iter.next(), Some(&2));
1350 /// assert_eq!(iter.next(), None);
1353 /// `take()` is often used with an infinite iterator, to make it finite:
1356 /// let mut iter = (0..).take(3);
1358 /// assert_eq!(iter.next(), Some(0));
1359 /// assert_eq!(iter.next(), Some(1));
1360 /// assert_eq!(iter.next(), Some(2));
1361 /// assert_eq!(iter.next(), None);
1364 /// If less than `n` elements are available,
1365 /// `take` will limit itself to the size of the underlying iterator:
1369 /// let mut iter = v.into_iter().take(5);
1370 /// assert_eq!(iter.next(), Some(1));
1371 /// assert_eq!(iter.next(), Some(2));
1372 /// assert_eq!(iter.next(), None);
1375 #[stable(feature = "rust1", since = "1.0.0")]
1376 fn take(self, n
: usize) -> Take
<Self>
1383 /// An iterator adapter similar to [`fold`] that holds internal state and
1384 /// produces a new iterator.
1386 /// [`fold`]: Iterator::fold
1388 /// `scan()` takes two arguments: an initial value which seeds the internal
1389 /// state, and a closure with two arguments, the first being a mutable
1390 /// reference to the internal state and the second an iterator element.
1391 /// The closure can assign to the internal state to share state between
1394 /// On iteration, the closure will be applied to each element of the
1395 /// iterator and the return value from the closure, an [`Option`], is
1396 /// yielded by the iterator.
1403 /// let a = [1, 2, 3];
1405 /// let mut iter = a.iter().scan(1, |state, &x| {
1406 /// // each iteration, we'll multiply the state by the element
1407 /// *state = *state * x;
1409 /// // then, we'll yield the negation of the state
1413 /// assert_eq!(iter.next(), Some(-1));
1414 /// assert_eq!(iter.next(), Some(-2));
1415 /// assert_eq!(iter.next(), Some(-6));
1416 /// assert_eq!(iter.next(), None);
1419 #[stable(feature = "rust1", since = "1.0.0")]
1420 fn scan
<St
, B
, F
>(self, initial_state
: St
, f
: F
) -> Scan
<Self, St
, F
>
1423 F
: FnMut(&mut St
, Self::Item
) -> Option
<B
>,
1425 Scan
::new(self, initial_state
, f
)
1428 /// Creates an iterator that works like map, but flattens nested structure.
1430 /// The [`map`] adapter is very useful, but only when the closure
1431 /// argument produces values. If it produces an iterator instead, there's
1432 /// an extra layer of indirection. `flat_map()` will remove this extra layer
1435 /// You can think of `flat_map(f)` as the semantic equivalent
1436 /// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`.
1438 /// Another way of thinking about `flat_map()`: [`map`]'s closure returns
1439 /// one item for each element, and `flat_map()`'s closure returns an
1440 /// iterator for each element.
1442 /// [`map`]: Iterator::map
1443 /// [`flatten`]: Iterator::flatten
1450 /// let words = ["alpha", "beta", "gamma"];
1452 /// // chars() returns an iterator
1453 /// let merged: String = words.iter()
1454 /// .flat_map(|s| s.chars())
1456 /// assert_eq!(merged, "alphabetagamma");
1459 #[stable(feature = "rust1", since = "1.0.0")]
1460 fn flat_map
<U
, F
>(self, f
: F
) -> FlatMap
<Self, U
, F
>
1464 F
: FnMut(Self::Item
) -> U
,
1466 FlatMap
::new(self, f
)
1469 /// Creates an iterator that flattens nested structure.
1471 /// This is useful when you have an iterator of iterators or an iterator of
1472 /// things that can be turned into iterators and you want to remove one
1473 /// level of indirection.
1480 /// let data = vec![vec![1, 2, 3, 4], vec![5, 6]];
1481 /// let flattened = data.into_iter().flatten().collect::<Vec<u8>>();
1482 /// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]);
1485 /// Mapping and then flattening:
1488 /// let words = ["alpha", "beta", "gamma"];
1490 /// // chars() returns an iterator
1491 /// let merged: String = words.iter()
1492 /// .map(|s| s.chars())
1495 /// assert_eq!(merged, "alphabetagamma");
1498 /// You can also rewrite this in terms of [`flat_map()`], which is preferable
1499 /// in this case since it conveys intent more clearly:
1502 /// let words = ["alpha", "beta", "gamma"];
1504 /// // chars() returns an iterator
1505 /// let merged: String = words.iter()
1506 /// .flat_map(|s| s.chars())
1508 /// assert_eq!(merged, "alphabetagamma");
1511 /// Flattening only removes one level of nesting at a time:
1514 /// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]];
1516 /// let d2 = d3.iter().flatten().collect::<Vec<_>>();
1517 /// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]);
1519 /// let d1 = d3.iter().flatten().flatten().collect::<Vec<_>>();
1520 /// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]);
1523 /// Here we see that `flatten()` does not perform a "deep" flatten.
1524 /// Instead, only one level of nesting is removed. That is, if you
1525 /// `flatten()` a three-dimensional array, the result will be
1526 /// two-dimensional and not one-dimensional. To get a one-dimensional
1527 /// structure, you have to `flatten()` again.
1529 /// [`flat_map()`]: Iterator::flat_map
1531 #[stable(feature = "iterator_flatten", since = "1.29.0")]
1532 fn flatten(self) -> Flatten
<Self>
1535 Self::Item
: IntoIterator
,
1540 /// Creates an iterator which ends after the first [`None`].
1542 /// After an iterator returns [`None`], future calls may or may not yield
1543 /// [`Some(T)`] again. `fuse()` adapts an iterator, ensuring that after a
1544 /// [`None`] is given, it will always return [`None`] forever.
1546 /// Note that the [`Fuse`] wrapper is a no-op on iterators that implement
1547 /// the [`FusedIterator`] trait. `fuse()` may therefore behave incorrectly
1548 /// if the [`FusedIterator`] trait is improperly implemented.
1550 /// [`Some(T)`]: Some
1551 /// [`FusedIterator`]: crate::iter::FusedIterator
1558 /// // an iterator which alternates between Some and None
1559 /// struct Alternate {
1563 /// impl Iterator for Alternate {
1564 /// type Item = i32;
1566 /// fn next(&mut self) -> Option<i32> {
1567 /// let val = self.state;
1568 /// self.state = self.state + 1;
1570 /// // if it's even, Some(i32), else None
1571 /// if val % 2 == 0 {
1579 /// let mut iter = Alternate { state: 0 };
1581 /// // we can see our iterator going back and forth
1582 /// assert_eq!(iter.next(), Some(0));
1583 /// assert_eq!(iter.next(), None);
1584 /// assert_eq!(iter.next(), Some(2));
1585 /// assert_eq!(iter.next(), None);
1587 /// // however, once we fuse it...
1588 /// let mut iter = iter.fuse();
1590 /// assert_eq!(iter.next(), Some(4));
1591 /// assert_eq!(iter.next(), None);
1593 /// // it will always return `None` after the first time.
1594 /// assert_eq!(iter.next(), None);
1595 /// assert_eq!(iter.next(), None);
1596 /// assert_eq!(iter.next(), None);
1599 #[stable(feature = "rust1", since = "1.0.0")]
1600 fn fuse(self) -> Fuse
<Self>
1607 /// Does something with each element of an iterator, passing the value on.
1609 /// When using iterators, you'll often chain several of them together.
1610 /// While working on such code, you might want to check out what's
1611 /// happening at various parts in the pipeline. To do that, insert
1612 /// a call to `inspect()`.
1614 /// It's more common for `inspect()` to be used as a debugging tool than to
1615 /// exist in your final code, but applications may find it useful in certain
1616 /// situations when errors need to be logged before being discarded.
1623 /// let a = [1, 4, 2, 3];
1625 /// // this iterator sequence is complex.
1626 /// let sum = a.iter()
1628 /// .filter(|x| x % 2 == 0)
1629 /// .fold(0, |sum, i| sum + i);
1631 /// println!("{sum}");
1633 /// // let's add some inspect() calls to investigate what's happening
1634 /// let sum = a.iter()
1636 /// .inspect(|x| println!("about to filter: {x}"))
1637 /// .filter(|x| x % 2 == 0)
1638 /// .inspect(|x| println!("made it through filter: {x}"))
1639 /// .fold(0, |sum, i| sum + i);
1641 /// println!("{sum}");
1644 /// This will print:
1648 /// about to filter: 1
1649 /// about to filter: 4
1650 /// made it through filter: 4
1651 /// about to filter: 2
1652 /// made it through filter: 2
1653 /// about to filter: 3
1657 /// Logging errors before discarding them:
1660 /// let lines = ["1", "2", "a"];
1662 /// let sum: i32 = lines
1664 /// .map(|line| line.parse::<i32>())
1665 /// .inspect(|num| {
1666 /// if let Err(ref e) = *num {
1667 /// println!("Parsing error: {e}");
1670 /// .filter_map(Result::ok)
1673 /// println!("Sum: {sum}");
1676 /// This will print:
1679 /// Parsing error: invalid digit found in string
1683 #[stable(feature = "rust1", since = "1.0.0")]
1684 fn inspect
<F
>(self, f
: F
) -> Inspect
<Self, F
>
1687 F
: FnMut(&Self::Item
),
1689 Inspect
::new(self, f
)
1692 /// Borrows an iterator, rather than consuming it.
1694 /// This is useful to allow applying iterator adapters while still
1695 /// retaining ownership of the original iterator.
1702 /// let mut words = ["hello", "world", "of", "Rust"].into_iter();
1704 /// // Take the first two words.
1705 /// let hello_world: Vec<_> = words.by_ref().take(2).collect();
1706 /// assert_eq!(hello_world, vec!["hello", "world"]);
1708 /// // Collect the rest of the words.
1709 /// // We can only do this because we used `by_ref` earlier.
1710 /// let of_rust: Vec<_> = words.collect();
1711 /// assert_eq!(of_rust, vec!["of", "Rust"]);
1713 #[stable(feature = "rust1", since = "1.0.0")]
1714 fn by_ref(&mut self) -> &mut Self
1721 /// Transforms an iterator into a collection.
1723 /// `collect()` can take anything iterable, and turn it into a relevant
1724 /// collection. This is one of the more powerful methods in the standard
1725 /// library, used in a variety of contexts.
1727 /// The most basic pattern in which `collect()` is used is to turn one
1728 /// collection into another. You take a collection, call [`iter`] on it,
1729 /// do a bunch of transformations, and then `collect()` at the end.
1731 /// `collect()` can also create instances of types that are not typical
1732 /// collections. For example, a [`String`] can be built from [`char`]s,
1733 /// and an iterator of [`Result<T, E>`][`Result`] items can be collected
1734 /// into `Result<Collection<T>, E>`. See the examples below for more.
1736 /// Because `collect()` is so general, it can cause problems with type
1737 /// inference. As such, `collect()` is one of the few times you'll see
1738 /// the syntax affectionately known as the 'turbofish': `::<>`. This
1739 /// helps the inference algorithm understand specifically which collection
1740 /// you're trying to collect into.
1747 /// let a = [1, 2, 3];
1749 /// let doubled: Vec<i32> = a.iter()
1750 /// .map(|&x| x * 2)
1753 /// assert_eq!(vec![2, 4, 6], doubled);
1756 /// Note that we needed the `: Vec<i32>` on the left-hand side. This is because
1757 /// we could collect into, for example, a [`VecDeque<T>`] instead:
1759 /// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html
1762 /// use std::collections::VecDeque;
1764 /// let a = [1, 2, 3];
1766 /// let doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect();
1768 /// assert_eq!(2, doubled[0]);
1769 /// assert_eq!(4, doubled[1]);
1770 /// assert_eq!(6, doubled[2]);
1773 /// Using the 'turbofish' instead of annotating `doubled`:
1776 /// let a = [1, 2, 3];
1778 /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>();
1780 /// assert_eq!(vec![2, 4, 6], doubled);
1783 /// Because `collect()` only cares about what you're collecting into, you can
1784 /// still use a partial type hint, `_`, with the turbofish:
1787 /// let a = [1, 2, 3];
1789 /// let doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>();
1791 /// assert_eq!(vec![2, 4, 6], doubled);
1794 /// Using `collect()` to make a [`String`]:
1797 /// let chars = ['g', 'd', 'k', 'k', 'n'];
1799 /// let hello: String = chars.iter()
1800 /// .map(|&x| x as u8)
1801 /// .map(|x| (x + 1) as char)
1804 /// assert_eq!("hello", hello);
1807 /// If you have a list of [`Result<T, E>`][`Result`]s, you can use `collect()` to
1808 /// see if any of them failed:
1811 /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")];
1813 /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect();
1815 /// // gives us the first error
1816 /// assert_eq!(Err("nope"), result);
1818 /// let results = [Ok(1), Ok(3)];
1820 /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect();
1822 /// // gives us the list of answers
1823 /// assert_eq!(Ok(vec![1, 3]), result);
1826 /// [`iter`]: Iterator::next
1827 /// [`String`]: ../../std/string/struct.String.html
1828 /// [`char`]: type@char
1830 #[stable(feature = "rust1", since = "1.0.0")]
1831 #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"]
1832 fn collect
<B
: FromIterator
<Self::Item
>>(self) -> B
1836 FromIterator
::from_iter(self)
1839 /// Fallibly transforms an iterator into a collection, short circuiting if
1840 /// a failure is encountered.
1842 /// `try_collect()` is a variation of [`collect()`][`collect`] that allows fallible
1843 /// conversions during collection. Its main use case is simplifying conversions from
1844 /// iterators yielding [`Option<T>`][`Option`] into `Option<Collection<T>>`, or similarly for other [`Try`]
1845 /// types (e.g. [`Result`]).
1847 /// Importantly, `try_collect()` doesn't require that the outer [`Try`] type also implements [`FromIterator`];
1848 /// only the inner type produced on `Try::Output` must implement it. Concretely,
1849 /// this means that collecting into `ControlFlow<_, Vec<i32>>` is valid because `Vec<i32>` implements
1850 /// [`FromIterator`], even though [`ControlFlow`] doesn't.
1852 /// Also, if a failure is encountered during `try_collect()`, the iterator is still valid and
1853 /// may continue to be used, in which case it will continue iterating starting after the element that
1854 /// triggered the failure. See the last example below for an example of how this works.
1857 /// Successfully collecting an iterator of `Option<i32>` into `Option<Vec<i32>>`:
1859 /// #![feature(iterator_try_collect)]
1861 /// let u = vec![Some(1), Some(2), Some(3)];
1862 /// let v = u.into_iter().try_collect::<Vec<i32>>();
1863 /// assert_eq!(v, Some(vec![1, 2, 3]));
1866 /// Failing to collect in the same way:
1868 /// #![feature(iterator_try_collect)]
1870 /// let u = vec![Some(1), Some(2), None, Some(3)];
1871 /// let v = u.into_iter().try_collect::<Vec<i32>>();
1872 /// assert_eq!(v, None);
1875 /// A similar example, but with `Result`:
1877 /// #![feature(iterator_try_collect)]
1879 /// let u: Vec<Result<i32, ()>> = vec![Ok(1), Ok(2), Ok(3)];
1880 /// let v = u.into_iter().try_collect::<Vec<i32>>();
1881 /// assert_eq!(v, Ok(vec![1, 2, 3]));
1883 /// let u = vec![Ok(1), Ok(2), Err(()), Ok(3)];
1884 /// let v = u.into_iter().try_collect::<Vec<i32>>();
1885 /// assert_eq!(v, Err(()));
1888 /// Finally, even [`ControlFlow`] works, despite the fact that it
1889 /// doesn't implement [`FromIterator`]. Note also that the iterator can
1890 /// continue to be used, even if a failure is encountered:
1893 /// #![feature(iterator_try_collect)]
1895 /// use core::ops::ControlFlow::{Break, Continue};
1897 /// let u = [Continue(1), Continue(2), Break(3), Continue(4), Continue(5)];
1898 /// let mut it = u.into_iter();
1900 /// let v = it.try_collect::<Vec<_>>();
1901 /// assert_eq!(v, Break(3));
1903 /// let v = it.try_collect::<Vec<_>>();
1904 /// assert_eq!(v, Continue(vec![4, 5]));
1907 /// [`collect`]: Iterator::collect
1909 #[unstable(feature = "iterator_try_collect", issue = "94047")]
1910 fn try_collect
<B
>(&mut self) -> ChangeOutputType
<Self::Item
, B
>
1913 <Self as Iterator
>::Item
: Try
,
1914 <<Self as Iterator
>::Item
as Try
>::Residual
: Residual
<B
>,
1915 B
: FromIterator
<<Self::Item
as Try
>::Output
>,
1917 try_process(ByRefSized(self), |i
| i
.collect())
1920 /// Collects all the items from an iterator into a collection.
1922 /// This method consumes the iterator and adds all its items to the
1923 /// passed collection. The collection is then returned, so the call chain
1924 /// can be continued.
1926 /// This is useful when you already have a collection and wants to add
1927 /// the iterator items to it.
1929 /// This method is a convenience method to call [Extend::extend](trait.Extend.html),
1930 /// but instead of being called on a collection, it's called on an iterator.
1937 /// #![feature(iter_collect_into)]
1939 /// let a = [1, 2, 3];
1940 /// let mut vec: Vec::<i32> = vec![0, 1];
1942 /// a.iter().map(|&x| x * 2).collect_into(&mut vec);
1943 /// a.iter().map(|&x| x * 10).collect_into(&mut vec);
1945 /// assert_eq!(vec![0, 1, 2, 4, 6, 10, 20, 30], vec);
1948 /// `Vec` can have a manual set capacity to avoid reallocating it:
1951 /// #![feature(iter_collect_into)]
1953 /// let a = [1, 2, 3];
1954 /// let mut vec: Vec::<i32> = Vec::with_capacity(6);
1956 /// a.iter().map(|&x| x * 2).collect_into(&mut vec);
1957 /// a.iter().map(|&x| x * 10).collect_into(&mut vec);
1959 /// assert_eq!(6, vec.capacity());
1960 /// println!("{:?}", vec);
1963 /// The returned mutable reference can be used to continue the call chain:
1966 /// #![feature(iter_collect_into)]
1968 /// let a = [1, 2, 3];
1969 /// let mut vec: Vec::<i32> = Vec::with_capacity(6);
1971 /// let count = a.iter().collect_into(&mut vec).iter().count();
1973 /// assert_eq!(count, vec.len());
1974 /// println!("Vec len is {}", count);
1976 /// let count = a.iter().collect_into(&mut vec).iter().count();
1978 /// assert_eq!(count, vec.len());
1979 /// println!("Vec len now is {}", count);
1982 #[unstable(feature = "iter_collect_into", reason = "new API", issue = "94780")]
1983 fn collect_into
<E
: Extend
<Self::Item
>>(self, collection
: &mut E
) -> &mut E
1987 collection
.extend(self);
1991 /// Consumes an iterator, creating two collections from it.
1993 /// The predicate passed to `partition()` can return `true`, or `false`.
1994 /// `partition()` returns a pair, all of the elements for which it returned
1995 /// `true`, and all of the elements for which it returned `false`.
1997 /// See also [`is_partitioned()`] and [`partition_in_place()`].
1999 /// [`is_partitioned()`]: Iterator::is_partitioned
2000 /// [`partition_in_place()`]: Iterator::partition_in_place
2007 /// let a = [1, 2, 3];
2009 /// let (even, odd): (Vec<_>, Vec<_>) = a
2011 /// .partition(|n| n % 2 == 0);
2013 /// assert_eq!(even, vec![2]);
2014 /// assert_eq!(odd, vec![1, 3]);
2016 #[stable(feature = "rust1", since = "1.0.0")]
2017 fn partition
<B
, F
>(self, f
: F
) -> (B
, B
)
2020 B
: Default
+ Extend
<Self::Item
>,
2021 F
: FnMut(&Self::Item
) -> bool
,
2024 fn extend
<'a
, T
, B
: Extend
<T
>>(
2025 mut f
: impl FnMut(&T
) -> bool
+ 'a
,
2028 ) -> impl FnMut((), T
) + 'a
{
2033 right
.extend_one(x
);
2038 let mut left
: B
= Default
::default();
2039 let mut right
: B
= Default
::default();
2041 self.fold((), extend(f
, &mut left
, &mut right
));
2046 /// Reorders the elements of this iterator *in-place* according to the given predicate,
2047 /// such that all those that return `true` precede all those that return `false`.
2048 /// Returns the number of `true` elements found.
2050 /// The relative order of partitioned items is not maintained.
2052 /// # Current implementation
2054 /// Current algorithms tries finding the first element for which the predicate evaluates
2055 /// to false, and the last element for which it evaluates to true and repeatedly swaps them.
2057 /// Time complexity: *O*(*n*)
2059 /// See also [`is_partitioned()`] and [`partition()`].
2061 /// [`is_partitioned()`]: Iterator::is_partitioned
2062 /// [`partition()`]: Iterator::partition
2067 /// #![feature(iter_partition_in_place)]
2069 /// let mut a = [1, 2, 3, 4, 5, 6, 7];
2071 /// // Partition in-place between evens and odds
2072 /// let i = a.iter_mut().partition_in_place(|&n| n % 2 == 0);
2074 /// assert_eq!(i, 3);
2075 /// assert!(a[..i].iter().all(|&n| n % 2 == 0)); // evens
2076 /// assert!(a[i..].iter().all(|&n| n % 2 == 1)); // odds
2078 #[unstable(feature = "iter_partition_in_place", reason = "new API", issue = "62543")]
2079 fn partition_in_place
<'a
, T
: 'a
, P
>(mut self, ref mut predicate
: P
) -> usize
2081 Self: Sized
+ DoubleEndedIterator
<Item
= &'a
mut T
>,
2082 P
: FnMut(&T
) -> bool
,
2084 // FIXME: should we worry about the count overflowing? The only way to have more than
2085 // `usize::MAX` mutable references is with ZSTs, which aren't useful to partition...
2087 // These closure "factory" functions exist to avoid genericity in `Self`.
2091 predicate
: &'a
mut impl FnMut(&T
) -> bool
,
2092 true_count
: &'a
mut usize,
2093 ) -> impl FnMut(&&mut T
) -> bool
+ 'a
{
2095 let p
= predicate(&**x
);
2096 *true_count
+= p
as usize;
2102 fn is_true
<T
>(predicate
: &mut impl FnMut(&T
) -> bool
) -> impl FnMut(&&mut T
) -> bool
+ '_
{
2103 move |x
| predicate(&**x
)
2106 // Repeatedly find the first `false` and swap it with the last `true`.
2107 let mut true_count
= 0;
2108 while let Some(head
) = self.find(is_false(predicate
, &mut true_count
)) {
2109 if let Some(tail
) = self.rfind(is_true(predicate
)) {
2110 crate::mem
::swap(head
, tail
);
2119 /// Checks if the elements of this iterator are partitioned according to the given predicate,
2120 /// such that all those that return `true` precede all those that return `false`.
2122 /// See also [`partition()`] and [`partition_in_place()`].
2124 /// [`partition()`]: Iterator::partition
2125 /// [`partition_in_place()`]: Iterator::partition_in_place
2130 /// #![feature(iter_is_partitioned)]
2132 /// assert!("Iterator".chars().is_partitioned(char::is_uppercase));
2133 /// assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase));
2135 #[unstable(feature = "iter_is_partitioned", reason = "new API", issue = "62544")]
2136 fn is_partitioned
<P
>(mut self, mut predicate
: P
) -> bool
2139 P
: FnMut(Self::Item
) -> bool
,
2141 // Either all items test `true`, or the first clause stops at `false`
2142 // and we check that there are no more `true` items after that.
2143 self.all(&mut predicate
) || !self.any(predicate
)
2146 /// An iterator method that applies a function as long as it returns
2147 /// successfully, producing a single, final value.
2149 /// `try_fold()` takes two arguments: an initial value, and a closure with
2150 /// two arguments: an 'accumulator', and an element. The closure either
2151 /// returns successfully, with the value that the accumulator should have
2152 /// for the next iteration, or it returns failure, with an error value that
2153 /// is propagated back to the caller immediately (short-circuiting).
2155 /// The initial value is the value the accumulator will have on the first
2156 /// call. If applying the closure succeeded against every element of the
2157 /// iterator, `try_fold()` returns the final accumulator as success.
2159 /// Folding is useful whenever you have a collection of something, and want
2160 /// to produce a single value from it.
2162 /// # Note to Implementors
2164 /// Several of the other (forward) methods have default implementations in
2165 /// terms of this one, so try to implement this explicitly if it can
2166 /// do something better than the default `for` loop implementation.
2168 /// In particular, try to have this call `try_fold()` on the internal parts
2169 /// from which this iterator is composed. If multiple calls are needed,
2170 /// the `?` operator may be convenient for chaining the accumulator value
2171 /// along, but beware any invariants that need to be upheld before those
2172 /// early returns. This is a `&mut self` method, so iteration needs to be
2173 /// resumable after hitting an error here.
2180 /// let a = [1, 2, 3];
2182 /// // the checked sum of all of the elements of the array
2183 /// let sum = a.iter().try_fold(0i8, |acc, &x| acc.checked_add(x));
2185 /// assert_eq!(sum, Some(6));
2188 /// Short-circuiting:
2191 /// let a = [10, 20, 30, 100, 40, 50];
2192 /// let mut it = a.iter();
2194 /// // This sum overflows when adding the 100 element
2195 /// let sum = it.try_fold(0i8, |acc, &x| acc.checked_add(x));
2196 /// assert_eq!(sum, None);
2198 /// // Because it short-circuited, the remaining elements are still
2199 /// // available through the iterator.
2200 /// assert_eq!(it.len(), 2);
2201 /// assert_eq!(it.next(), Some(&40));
2204 /// While you cannot `break` from a closure, the [`ControlFlow`] type allows
2208 /// use std::ops::ControlFlow;
2210 /// let triangular = (1..30).try_fold(0_i8, |prev, x| {
2211 /// if let Some(next) = prev.checked_add(x) {
2212 /// ControlFlow::Continue(next)
2214 /// ControlFlow::Break(prev)
2217 /// assert_eq!(triangular, ControlFlow::Break(120));
2219 /// let triangular = (1..30).try_fold(0_u64, |prev, x| {
2220 /// if let Some(next) = prev.checked_add(x) {
2221 /// ControlFlow::Continue(next)
2223 /// ControlFlow::Break(prev)
2226 /// assert_eq!(triangular, ControlFlow::Continue(435));
2229 #[stable(feature = "iterator_try_fold", since = "1.27.0")]
2230 fn try_fold
<B
, F
, R
>(&mut self, init
: B
, mut f
: F
) -> R
2233 F
: FnMut(B
, Self::Item
) -> R
,
2236 let mut accum
= init
;
2237 while let Some(x
) = self.next() {
2238 accum
= f(accum
, x
)?
;
2243 /// An iterator method that applies a fallible function to each item in the
2244 /// iterator, stopping at the first error and returning that error.
2246 /// This can also be thought of as the fallible form of [`for_each()`]
2247 /// or as the stateless version of [`try_fold()`].
2249 /// [`for_each()`]: Iterator::for_each
2250 /// [`try_fold()`]: Iterator::try_fold
2255 /// use std::fs::rename;
2256 /// use std::io::{stdout, Write};
2257 /// use std::path::Path;
2259 /// let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"];
2261 /// let res = data.iter().try_for_each(|x| writeln!(stdout(), "{x}"));
2262 /// assert!(res.is_ok());
2264 /// let mut it = data.iter().cloned();
2265 /// let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old")));
2266 /// assert!(res.is_err());
2267 /// // It short-circuited, so the remaining items are still in the iterator:
2268 /// assert_eq!(it.next(), Some("stale_bread.json"));
2271 /// The [`ControlFlow`] type can be used with this method for the situations
2272 /// in which you'd use `break` and `continue` in a normal loop:
2275 /// use std::ops::ControlFlow;
2277 /// let r = (2..100).try_for_each(|x| {
2278 /// if 323 % x == 0 {
2279 /// return ControlFlow::Break(x)
2282 /// ControlFlow::Continue(())
2284 /// assert_eq!(r, ControlFlow::Break(17));
2287 #[stable(feature = "iterator_try_fold", since = "1.27.0")]
2288 fn try_for_each
<F
, R
>(&mut self, f
: F
) -> R
2291 F
: FnMut(Self::Item
) -> R
,
2292 R
: Try
<Output
= ()>,
2295 fn call
<T
, R
>(mut f
: impl FnMut(T
) -> R
) -> impl FnMut((), T
) -> R
{
2299 self.try_fold((), call(f
))
2302 /// Folds every element into an accumulator by applying an operation,
2303 /// returning the final result.
2305 /// `fold()` takes two arguments: an initial value, and a closure with two
2306 /// arguments: an 'accumulator', and an element. The closure returns the value that
2307 /// the accumulator should have for the next iteration.
2309 /// The initial value is the value the accumulator will have on the first
2312 /// After applying this closure to every element of the iterator, `fold()`
2313 /// returns the accumulator.
2315 /// This operation is sometimes called 'reduce' or 'inject'.
2317 /// Folding is useful whenever you have a collection of something, and want
2318 /// to produce a single value from it.
2320 /// Note: `fold()`, and similar methods that traverse the entire iterator,
2321 /// might not terminate for infinite iterators, even on traits for which a
2322 /// result is determinable in finite time.
2324 /// Note: [`reduce()`] can be used to use the first element as the initial
2325 /// value, if the accumulator type and item type is the same.
2327 /// Note: `fold()` combines elements in a *left-associative* fashion. For associative
2328 /// operators like `+`, the order the elements are combined in is not important, but for non-associative
2329 /// operators like `-` the order will affect the final result.
2330 /// For a *right-associative* version of `fold()`, see [`DoubleEndedIterator::rfold()`].
2332 /// # Note to Implementors
2334 /// Several of the other (forward) methods have default implementations in
2335 /// terms of this one, so try to implement this explicitly if it can
2336 /// do something better than the default `for` loop implementation.
2338 /// In particular, try to have this call `fold()` on the internal parts
2339 /// from which this iterator is composed.
2346 /// let a = [1, 2, 3];
2348 /// // the sum of all of the elements of the array
2349 /// let sum = a.iter().fold(0, |acc, x| acc + x);
2351 /// assert_eq!(sum, 6);
2354 /// Let's walk through each step of the iteration here:
2356 /// | element | acc | x | result |
2357 /// |---------|-----|---|--------|
2359 /// | 1 | 0 | 1 | 1 |
2360 /// | 2 | 1 | 2 | 3 |
2361 /// | 3 | 3 | 3 | 6 |
2363 /// And so, our final result, `6`.
2365 /// This example demonstrates the left-associative nature of `fold()`:
2366 /// it builds a string, starting with an initial value
2367 /// and continuing with each element from the front until the back:
2370 /// let numbers = [1, 2, 3, 4, 5];
2372 /// let zero = "0".to_string();
2374 /// let result = numbers.iter().fold(zero, |acc, &x| {
2375 /// format!("({acc} + {x})")
2378 /// assert_eq!(result, "(((((0 + 1) + 2) + 3) + 4) + 5)");
2380 /// It's common for people who haven't used iterators a lot to
2381 /// use a `for` loop with a list of things to build up a result. Those
2382 /// can be turned into `fold()`s:
2384 /// [`for`]: ../../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
2387 /// let numbers = [1, 2, 3, 4, 5];
2389 /// let mut result = 0;
2392 /// for i in &numbers {
2393 /// result = result + i;
2397 /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x);
2399 /// // they're the same
2400 /// assert_eq!(result, result2);
2403 /// [`reduce()`]: Iterator::reduce
2404 #[doc(alias = "inject", alias = "foldl")]
2406 #[stable(feature = "rust1", since = "1.0.0")]
2407 fn fold
<B
, F
>(mut self, init
: B
, mut f
: F
) -> B
2410 F
: FnMut(B
, Self::Item
) -> B
,
2412 let mut accum
= init
;
2413 while let Some(x
) = self.next() {
2414 accum
= f(accum
, x
);
2419 /// Reduces the elements to a single one, by repeatedly applying a reducing
2422 /// If the iterator is empty, returns [`None`]; otherwise, returns the
2423 /// result of the reduction.
2425 /// The reducing function is a closure with two arguments: an 'accumulator', and an element.
2426 /// For iterators with at least one element, this is the same as [`fold()`]
2427 /// with the first element of the iterator as the initial accumulator value, folding
2428 /// every subsequent element into it.
2430 /// [`fold()`]: Iterator::fold
2435 /// let reduced: i32 = (1..10).reduce(|acc, e| acc + e).unwrap();
2436 /// assert_eq!(reduced, 45);
2438 /// // Which is equivalent to doing it with `fold`:
2439 /// let folded: i32 = (1..10).fold(0, |acc, e| acc + e);
2440 /// assert_eq!(reduced, folded);
2443 #[stable(feature = "iterator_fold_self", since = "1.51.0")]
2444 fn reduce
<F
>(mut self, f
: F
) -> Option
<Self::Item
>
2447 F
: FnMut(Self::Item
, Self::Item
) -> Self::Item
,
2449 let first
= self.next()?
;
2450 Some(self.fold(first
, f
))
2453 /// Reduces the elements to a single one by repeatedly applying a reducing operation. If the
2454 /// closure returns a failure, the failure is propagated back to the caller immediately.
2456 /// The return type of this method depends on the return type of the closure. If the closure
2457 /// returns `Result<Self::Item, E>`, then this function will return `Result<Option<Self::Item>,
2458 /// E>`. If the closure returns `Option<Self::Item>`, then this function will return
2459 /// `Option<Option<Self::Item>>`.
2461 /// When called on an empty iterator, this function will return either `Some(None)` or
2462 /// `Ok(None)` depending on the type of the provided closure.
2464 /// For iterators with at least one element, this is essentially the same as calling
2465 /// [`try_fold()`] with the first element of the iterator as the initial accumulator value.
2467 /// [`try_fold()`]: Iterator::try_fold
2471 /// Safely calculate the sum of a series of numbers:
2474 /// #![feature(iterator_try_reduce)]
2476 /// let numbers: Vec<usize> = vec![10, 20, 5, 23, 0];
2477 /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
2478 /// assert_eq!(sum, Some(Some(58)));
2481 /// Determine when a reduction short circuited:
2484 /// #![feature(iterator_try_reduce)]
2486 /// let numbers = vec![1, 2, 3, usize::MAX, 4, 5];
2487 /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
2488 /// assert_eq!(sum, None);
2491 /// Determine when a reduction was not performed because there are no elements:
2494 /// #![feature(iterator_try_reduce)]
2496 /// let numbers: Vec<usize> = Vec::new();
2497 /// let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
2498 /// assert_eq!(sum, Some(None));
2501 /// Use a [`Result`] instead of an [`Option`]:
2504 /// #![feature(iterator_try_reduce)]
2506 /// let numbers = vec!["1", "2", "3", "4", "5"];
2507 /// let max: Result<Option<_>, <usize as std::str::FromStr>::Err> =
2508 /// numbers.into_iter().try_reduce(|x, y| {
2509 /// if x.parse::<usize>()? > y.parse::<usize>()? { Ok(x) } else { Ok(y) }
2511 /// assert_eq!(max, Ok(Some("5")));
2514 #[unstable(feature = "iterator_try_reduce", reason = "new API", issue = "87053")]
2515 fn try_reduce
<F
, R
>(&mut self, f
: F
) -> ChangeOutputType
<R
, Option
<R
::Output
>>
2518 F
: FnMut(Self::Item
, Self::Item
) -> R
,
2519 R
: Try
<Output
= Self::Item
>,
2520 R
::Residual
: Residual
<Option
<Self::Item
>>,
2522 let first
= match self.next() {
2524 None
=> return Try
::from_output(None
),
2527 match self.try_fold(first
, f
).branch() {
2528 ControlFlow
::Break(r
) => FromResidual
::from_residual(r
),
2529 ControlFlow
::Continue(i
) => Try
::from_output(Some(i
)),
2533 /// Tests if every element of the iterator matches a predicate.
2535 /// `all()` takes a closure that returns `true` or `false`. It applies
2536 /// this closure to each element of the iterator, and if they all return
2537 /// `true`, then so does `all()`. If any of them return `false`, it
2538 /// returns `false`.
2540 /// `all()` is short-circuiting; in other words, it will stop processing
2541 /// as soon as it finds a `false`, given that no matter what else happens,
2542 /// the result will also be `false`.
2544 /// An empty iterator returns `true`.
2551 /// let a = [1, 2, 3];
2553 /// assert!(a.iter().all(|&x| x > 0));
2555 /// assert!(!a.iter().all(|&x| x > 2));
2558 /// Stopping at the first `false`:
2561 /// let a = [1, 2, 3];
2563 /// let mut iter = a.iter();
2565 /// assert!(!iter.all(|&x| x != 2));
2567 /// // we can still use `iter`, as there are more elements.
2568 /// assert_eq!(iter.next(), Some(&3));
2571 #[stable(feature = "rust1", since = "1.0.0")]
2572 fn all
<F
>(&mut self, f
: F
) -> bool
2575 F
: FnMut(Self::Item
) -> bool
,
2578 fn check
<T
>(mut f
: impl FnMut(T
) -> bool
) -> impl FnMut((), T
) -> ControlFlow
<()> {
2580 if f(x
) { ControlFlow::CONTINUE }
else { ControlFlow::BREAK }
2583 self.try_fold((), check(f
)) == ControlFlow
::CONTINUE
2586 /// Tests if any element of the iterator matches a predicate.
2588 /// `any()` takes a closure that returns `true` or `false`. It applies
2589 /// this closure to each element of the iterator, and if any of them return
2590 /// `true`, then so does `any()`. If they all return `false`, it
2591 /// returns `false`.
2593 /// `any()` is short-circuiting; in other words, it will stop processing
2594 /// as soon as it finds a `true`, given that no matter what else happens,
2595 /// the result will also be `true`.
2597 /// An empty iterator returns `false`.
2604 /// let a = [1, 2, 3];
2606 /// assert!(a.iter().any(|&x| x > 0));
2608 /// assert!(!a.iter().any(|&x| x > 5));
2611 /// Stopping at the first `true`:
2614 /// let a = [1, 2, 3];
2616 /// let mut iter = a.iter();
2618 /// assert!(iter.any(|&x| x != 2));
2620 /// // we can still use `iter`, as there are more elements.
2621 /// assert_eq!(iter.next(), Some(&2));
2624 #[stable(feature = "rust1", since = "1.0.0")]
2625 fn any
<F
>(&mut self, f
: F
) -> bool
2628 F
: FnMut(Self::Item
) -> bool
,
2631 fn check
<T
>(mut f
: impl FnMut(T
) -> bool
) -> impl FnMut((), T
) -> ControlFlow
<()> {
2633 if f(x
) { ControlFlow::BREAK }
else { ControlFlow::CONTINUE }
2637 self.try_fold((), check(f
)) == ControlFlow
::BREAK
2640 /// Searches for an element of an iterator that satisfies a predicate.
2642 /// `find()` takes a closure that returns `true` or `false`. It applies
2643 /// this closure to each element of the iterator, and if any of them return
2644 /// `true`, then `find()` returns [`Some(element)`]. If they all return
2645 /// `false`, it returns [`None`].
2647 /// `find()` is short-circuiting; in other words, it will stop processing
2648 /// as soon as the closure returns `true`.
2650 /// Because `find()` takes a reference, and many iterators iterate over
2651 /// references, this leads to a possibly confusing situation where the
2652 /// argument is a double reference. You can see this effect in the
2653 /// examples below, with `&&x`.
2655 /// [`Some(element)`]: Some
2662 /// let a = [1, 2, 3];
2664 /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2));
2666 /// assert_eq!(a.iter().find(|&&x| x == 5), None);
2669 /// Stopping at the first `true`:
2672 /// let a = [1, 2, 3];
2674 /// let mut iter = a.iter();
2676 /// assert_eq!(iter.find(|&&x| x == 2), Some(&2));
2678 /// // we can still use `iter`, as there are more elements.
2679 /// assert_eq!(iter.next(), Some(&3));
2682 /// Note that `iter.find(f)` is equivalent to `iter.filter(f).next()`.
2684 #[stable(feature = "rust1", since = "1.0.0")]
2685 fn find
<P
>(&mut self, predicate
: P
) -> Option
<Self::Item
>
2688 P
: FnMut(&Self::Item
) -> bool
,
2691 fn check
<T
>(mut predicate
: impl FnMut(&T
) -> bool
) -> impl FnMut((), T
) -> ControlFlow
<T
> {
2693 if predicate(&x
) { ControlFlow::Break(x) }
else { ControlFlow::CONTINUE }
2697 self.try_fold((), check(predicate
)).break_value()
2700 /// Applies function to the elements of iterator and returns
2701 /// the first non-none result.
2703 /// `iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`.
2708 /// let a = ["lol", "NaN", "2", "5"];
2710 /// let first_number = a.iter().find_map(|s| s.parse().ok());
2712 /// assert_eq!(first_number, Some(2));
2715 #[stable(feature = "iterator_find_map", since = "1.30.0")]
2716 fn find_map
<B
, F
>(&mut self, f
: F
) -> Option
<B
>
2719 F
: FnMut(Self::Item
) -> Option
<B
>,
2722 fn check
<T
, B
>(mut f
: impl FnMut(T
) -> Option
<B
>) -> impl FnMut((), T
) -> ControlFlow
<B
> {
2723 move |(), x
| match f(x
) {
2724 Some(x
) => ControlFlow
::Break(x
),
2725 None
=> ControlFlow
::CONTINUE
,
2729 self.try_fold((), check(f
)).break_value()
2732 /// Applies function to the elements of iterator and returns
2733 /// the first true result or the first error.
2735 /// The return type of this method depends on the return type of the closure.
2736 /// If you return `Result<bool, E>` from the closure, you'll get a `Result<Option<Self::Item>; E>`.
2737 /// If you return `Option<bool>` from the closure, you'll get an `Option<Option<Self::Item>>`.
2742 /// #![feature(try_find)]
2744 /// let a = ["1", "2", "lol", "NaN", "5"];
2746 /// let is_my_num = |s: &str, search: i32| -> Result<bool, std::num::ParseIntError> {
2747 /// Ok(s.parse::<i32>()? == search)
2750 /// let result = a.iter().try_find(|&&s| is_my_num(s, 2));
2751 /// assert_eq!(result, Ok(Some(&"2")));
2753 /// let result = a.iter().try_find(|&&s| is_my_num(s, 5));
2754 /// assert!(result.is_err());
2757 /// This also supports other types which implement `Try`, not just `Result`.
2759 /// #![feature(try_find)]
2761 /// use std::num::NonZeroU32;
2762 /// let a = [3, 5, 7, 4, 9, 0, 11];
2763 /// let result = a.iter().try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two()));
2764 /// assert_eq!(result, Some(Some(&4)));
2765 /// let result = a.iter().take(3).try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two()));
2766 /// assert_eq!(result, Some(None));
2767 /// let result = a.iter().rev().try_find(|&&x| NonZeroU32::new(x).map(|y| y.is_power_of_two()));
2768 /// assert_eq!(result, None);
2771 #[unstable(feature = "try_find", reason = "new API", issue = "63178")]
2772 fn try_find
<F
, R
>(&mut self, f
: F
) -> ChangeOutputType
<R
, Option
<Self::Item
>>
2775 F
: FnMut(&Self::Item
) -> R
,
2776 R
: Try
<Output
= bool
>,
2777 R
::Residual
: Residual
<Option
<Self::Item
>>,
2781 mut f
: impl FnMut(&I
) -> V
,
2782 ) -> impl FnMut((), I
) -> ControlFlow
<R
::TryType
>
2784 V
: Try
<Output
= bool
, Residual
= R
>,
2785 R
: Residual
<Option
<I
>>,
2787 move |(), x
| match f(&x
).branch() {
2788 ControlFlow
::Continue(false) => ControlFlow
::CONTINUE
,
2789 ControlFlow
::Continue(true) => ControlFlow
::Break(Try
::from_output(Some(x
))),
2790 ControlFlow
::Break(r
) => ControlFlow
::Break(FromResidual
::from_residual(r
)),
2794 match self.try_fold((), check(f
)) {
2795 ControlFlow
::Break(x
) => x
,
2796 ControlFlow
::Continue(()) => Try
::from_output(None
),
2800 /// Searches for an element in an iterator, returning its index.
2802 /// `position()` takes a closure that returns `true` or `false`. It applies
2803 /// this closure to each element of the iterator, and if one of them
2804 /// returns `true`, then `position()` returns [`Some(index)`]. If all of
2805 /// them return `false`, it returns [`None`].
2807 /// `position()` is short-circuiting; in other words, it will stop
2808 /// processing as soon as it finds a `true`.
2810 /// # Overflow Behavior
2812 /// The method does no guarding against overflows, so if there are more
2813 /// than [`usize::MAX`] non-matching elements, it either produces the wrong
2814 /// result or panics. If debug assertions are enabled, a panic is
2819 /// This function might panic if the iterator has more than `usize::MAX`
2820 /// non-matching elements.
2822 /// [`Some(index)`]: Some
2829 /// let a = [1, 2, 3];
2831 /// assert_eq!(a.iter().position(|&x| x == 2), Some(1));
2833 /// assert_eq!(a.iter().position(|&x| x == 5), None);
2836 /// Stopping at the first `true`:
2839 /// let a = [1, 2, 3, 4];
2841 /// let mut iter = a.iter();
2843 /// assert_eq!(iter.position(|&x| x >= 2), Some(1));
2845 /// // we can still use `iter`, as there are more elements.
2846 /// assert_eq!(iter.next(), Some(&3));
2848 /// // The returned index depends on iterator state
2849 /// assert_eq!(iter.position(|&x| x == 4), Some(0));
2853 #[stable(feature = "rust1", since = "1.0.0")]
2854 fn position
<P
>(&mut self, predicate
: P
) -> Option
<usize>
2857 P
: FnMut(Self::Item
) -> bool
,
2861 mut predicate
: impl FnMut(T
) -> bool
,
2862 ) -> impl FnMut(usize, T
) -> ControlFlow
<usize, usize> {
2863 #[rustc_inherit_overflow_checks]
2865 if predicate(x
) { ControlFlow::Break(i) }
else { ControlFlow::Continue(i + 1) }
2869 self.try_fold(0, check(predicate
)).break_value()
2872 /// Searches for an element in an iterator from the right, returning its
2875 /// `rposition()` takes a closure that returns `true` or `false`. It applies
2876 /// this closure to each element of the iterator, starting from the end,
2877 /// and if one of them returns `true`, then `rposition()` returns
2878 /// [`Some(index)`]. If all of them return `false`, it returns [`None`].
2880 /// `rposition()` is short-circuiting; in other words, it will stop
2881 /// processing as soon as it finds a `true`.
2883 /// [`Some(index)`]: Some
2890 /// let a = [1, 2, 3];
2892 /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2));
2894 /// assert_eq!(a.iter().rposition(|&x| x == 5), None);
2897 /// Stopping at the first `true`:
2900 /// let a = [-1, 2, 3, 4];
2902 /// let mut iter = a.iter();
2904 /// assert_eq!(iter.rposition(|&x| x >= 2), Some(3));
2906 /// // we can still use `iter`, as there are more elements.
2907 /// assert_eq!(iter.next(), Some(&-1));
2910 #[stable(feature = "rust1", since = "1.0.0")]
2911 fn rposition
<P
>(&mut self, predicate
: P
) -> Option
<usize>
2913 P
: FnMut(Self::Item
) -> bool
,
2914 Self: Sized
+ ExactSizeIterator
+ DoubleEndedIterator
,
2916 // No need for an overflow check here, because `ExactSizeIterator`
2917 // implies that the number of elements fits into a `usize`.
2920 mut predicate
: impl FnMut(T
) -> bool
,
2921 ) -> impl FnMut(usize, T
) -> ControlFlow
<usize, usize> {
2924 if predicate(x
) { ControlFlow::Break(i) }
else { ControlFlow::Continue(i) }
2929 self.try_rfold(n
, check(predicate
)).break_value()
2932 /// Returns the maximum element of an iterator.
2934 /// If several elements are equally maximum, the last element is
2935 /// returned. If the iterator is empty, [`None`] is returned.
2937 /// Note that [`f32`]/[`f64`] doesn't implement [`Ord`] due to NaN being
2938 /// incomparable. You can work around this by using [`Iterator::reduce`]:
2941 /// [2.4, f32::NAN, 1.3]
2943 /// .reduce(f32::max)
2954 /// let a = [1, 2, 3];
2955 /// let b: Vec<u32> = Vec::new();
2957 /// assert_eq!(a.iter().max(), Some(&3));
2958 /// assert_eq!(b.iter().max(), None);
2961 #[stable(feature = "rust1", since = "1.0.0")]
2962 fn max(self) -> Option
<Self::Item
>
2967 self.max_by(Ord
::cmp
)
2970 /// Returns the minimum element of an iterator.
2972 /// If several elements are equally minimum, the first element is returned.
2973 /// If the iterator is empty, [`None`] is returned.
2975 /// Note that [`f32`]/[`f64`] doesn't implement [`Ord`] due to NaN being
2976 /// incomparable. You can work around this by using [`Iterator::reduce`]:
2979 /// [2.4, f32::NAN, 1.3]
2981 /// .reduce(f32::min)
2992 /// let a = [1, 2, 3];
2993 /// let b: Vec<u32> = Vec::new();
2995 /// assert_eq!(a.iter().min(), Some(&1));
2996 /// assert_eq!(b.iter().min(), None);
2999 #[stable(feature = "rust1", since = "1.0.0")]
3000 fn min(self) -> Option
<Self::Item
>
3005 self.min_by(Ord
::cmp
)
3008 /// Returns the element that gives the maximum value from the
3009 /// specified function.
3011 /// If several elements are equally maximum, the last element is
3012 /// returned. If the iterator is empty, [`None`] is returned.
3017 /// let a = [-3_i32, 0, 1, 5, -10];
3018 /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10);
3021 #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
3022 fn max_by_key
<B
: Ord
, F
>(self, f
: F
) -> Option
<Self::Item
>
3025 F
: FnMut(&Self::Item
) -> B
,
3028 fn key
<T
, B
>(mut f
: impl FnMut(&T
) -> B
) -> impl FnMut(T
) -> (B
, T
) {
3033 fn compare
<T
, B
: Ord
>((x_p
, _
): &(B
, T
), (y_p
, _
): &(B
, T
)) -> Ordering
{
3037 let (_
, x
) = self.map(key(f
)).max_by(compare
)?
;
3041 /// Returns the element that gives the maximum value with respect to the
3042 /// specified comparison function.
3044 /// If several elements are equally maximum, the last element is
3045 /// returned. If the iterator is empty, [`None`] is returned.
3050 /// let a = [-3_i32, 0, 1, 5, -10];
3051 /// assert_eq!(*a.iter().max_by(|x, y| x.cmp(y)).unwrap(), 5);
3054 #[stable(feature = "iter_max_by", since = "1.15.0")]
3055 fn max_by
<F
>(self, compare
: F
) -> Option
<Self::Item
>
3058 F
: FnMut(&Self::Item
, &Self::Item
) -> Ordering
,
3061 fn fold
<T
>(mut compare
: impl FnMut(&T
, &T
) -> Ordering
) -> impl FnMut(T
, T
) -> T
{
3062 move |x
, y
| cmp
::max_by(x
, y
, &mut compare
)
3065 self.reduce(fold(compare
))
3068 /// Returns the element that gives the minimum value from the
3069 /// specified function.
3071 /// If several elements are equally minimum, the first element is
3072 /// returned. If the iterator is empty, [`None`] is returned.
3077 /// let a = [-3_i32, 0, 1, 5, -10];
3078 /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0);
3081 #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
3082 fn min_by_key
<B
: Ord
, F
>(self, f
: F
) -> Option
<Self::Item
>
3085 F
: FnMut(&Self::Item
) -> B
,
3088 fn key
<T
, B
>(mut f
: impl FnMut(&T
) -> B
) -> impl FnMut(T
) -> (B
, T
) {
3093 fn compare
<T
, B
: Ord
>((x_p
, _
): &(B
, T
), (y_p
, _
): &(B
, T
)) -> Ordering
{
3097 let (_
, x
) = self.map(key(f
)).min_by(compare
)?
;
3101 /// Returns the element that gives the minimum value with respect to the
3102 /// specified comparison function.
3104 /// If several elements are equally minimum, the first element is
3105 /// returned. If the iterator is empty, [`None`] is returned.
3110 /// let a = [-3_i32, 0, 1, 5, -10];
3111 /// assert_eq!(*a.iter().min_by(|x, y| x.cmp(y)).unwrap(), -10);
3114 #[stable(feature = "iter_min_by", since = "1.15.0")]
3115 fn min_by
<F
>(self, compare
: F
) -> Option
<Self::Item
>
3118 F
: FnMut(&Self::Item
, &Self::Item
) -> Ordering
,
3121 fn fold
<T
>(mut compare
: impl FnMut(&T
, &T
) -> Ordering
) -> impl FnMut(T
, T
) -> T
{
3122 move |x
, y
| cmp
::min_by(x
, y
, &mut compare
)
3125 self.reduce(fold(compare
))
3128 /// Reverses an iterator's direction.
3130 /// Usually, iterators iterate from left to right. After using `rev()`,
3131 /// an iterator will instead iterate from right to left.
3133 /// This is only possible if the iterator has an end, so `rev()` only
3134 /// works on [`DoubleEndedIterator`]s.
3139 /// let a = [1, 2, 3];
3141 /// let mut iter = a.iter().rev();
3143 /// assert_eq!(iter.next(), Some(&3));
3144 /// assert_eq!(iter.next(), Some(&2));
3145 /// assert_eq!(iter.next(), Some(&1));
3147 /// assert_eq!(iter.next(), None);
3150 #[doc(alias = "reverse")]
3151 #[stable(feature = "rust1", since = "1.0.0")]
3152 fn rev(self) -> Rev
<Self>
3154 Self: Sized
+ DoubleEndedIterator
,
3159 /// Converts an iterator of pairs into a pair of containers.
3161 /// `unzip()` consumes an entire iterator of pairs, producing two
3162 /// collections: one from the left elements of the pairs, and one
3163 /// from the right elements.
3165 /// This function is, in some sense, the opposite of [`zip`].
3167 /// [`zip`]: Iterator::zip
3174 /// let a = [(1, 2), (3, 4), (5, 6)];
3176 /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip();
3178 /// assert_eq!(left, [1, 3, 5]);
3179 /// assert_eq!(right, [2, 4, 6]);
3181 /// // you can also unzip multiple nested tuples at once
3182 /// let a = [(1, (2, 3)), (4, (5, 6))];
3184 /// let (x, (y, z)): (Vec<_>, (Vec<_>, Vec<_>)) = a.iter().cloned().unzip();
3185 /// assert_eq!(x, [1, 4]);
3186 /// assert_eq!(y, [2, 5]);
3187 /// assert_eq!(z, [3, 6]);
3189 #[stable(feature = "rust1", since = "1.0.0")]
3190 fn unzip
<A
, B
, FromA
, FromB
>(self) -> (FromA
, FromB
)
3192 FromA
: Default
+ Extend
<A
>,
3193 FromB
: Default
+ Extend
<B
>,
3194 Self: Sized
+ Iterator
<Item
= (A
, B
)>,
3196 let mut unzipped
: (FromA
, FromB
) = Default
::default();
3197 unzipped
.extend(self);
3201 /// Creates an iterator which copies all of its elements.
3203 /// This is useful when you have an iterator over `&T`, but you need an
3204 /// iterator over `T`.
3211 /// let a = [1, 2, 3];
3213 /// let v_copied: Vec<_> = a.iter().copied().collect();
3215 /// // copied is the same as .map(|&x| x)
3216 /// let v_map: Vec<_> = a.iter().map(|&x| x).collect();
3218 /// assert_eq!(v_copied, vec![1, 2, 3]);
3219 /// assert_eq!(v_map, vec![1, 2, 3]);
3221 #[stable(feature = "iter_copied", since = "1.36.0")]
3222 fn copied
<'a
, T
: 'a
>(self) -> Copied
<Self>
3224 Self: Sized
+ Iterator
<Item
= &'a T
>,
3230 /// Creates an iterator which [`clone`]s all of its elements.
3232 /// This is useful when you have an iterator over `&T`, but you need an
3233 /// iterator over `T`.
3235 /// There is no guarantee whatsoever about the `clone` method actually
3236 /// being called *or* optimized away. So code should not depend on
3239 /// [`clone`]: Clone::clone
3246 /// let a = [1, 2, 3];
3248 /// let v_cloned: Vec<_> = a.iter().cloned().collect();
3250 /// // cloned is the same as .map(|&x| x), for integers
3251 /// let v_map: Vec<_> = a.iter().map(|&x| x).collect();
3253 /// assert_eq!(v_cloned, vec![1, 2, 3]);
3254 /// assert_eq!(v_map, vec![1, 2, 3]);
3257 /// To get the best performance, try to clone late:
3260 /// let a = [vec![0_u8, 1, 2], vec![3, 4], vec![23]];
3261 /// // don't do this:
3262 /// let slower: Vec<_> = a.iter().cloned().filter(|s| s.len() == 1).collect();
3263 /// assert_eq!(&[vec![23]], &slower[..]);
3264 /// // instead call `cloned` late
3265 /// let faster: Vec<_> = a.iter().filter(|s| s.len() == 1).cloned().collect();
3266 /// assert_eq!(&[vec![23]], &faster[..]);
3268 #[stable(feature = "rust1", since = "1.0.0")]
3269 fn cloned
<'a
, T
: 'a
>(self) -> Cloned
<Self>
3271 Self: Sized
+ Iterator
<Item
= &'a T
>,
3277 /// Repeats an iterator endlessly.
3279 /// Instead of stopping at [`None`], the iterator will instead start again,
3280 /// from the beginning. After iterating again, it will start at the
3281 /// beginning again. And again. And again. Forever. Note that in case the
3282 /// original iterator is empty, the resulting iterator will also be empty.
3289 /// let a = [1, 2, 3];
3291 /// let mut it = a.iter().cycle();
3293 /// assert_eq!(it.next(), Some(&1));
3294 /// assert_eq!(it.next(), Some(&2));
3295 /// assert_eq!(it.next(), Some(&3));
3296 /// assert_eq!(it.next(), Some(&1));
3297 /// assert_eq!(it.next(), Some(&2));
3298 /// assert_eq!(it.next(), Some(&3));
3299 /// assert_eq!(it.next(), Some(&1));
3301 #[stable(feature = "rust1", since = "1.0.0")]
3303 fn cycle(self) -> Cycle
<Self>
3305 Self: Sized
+ Clone
,
3310 /// Returns an iterator over `N` elements of the iterator at a time.
3312 /// The chunks do not overlap. If `N` does not divide the length of the
3313 /// iterator, then the last up to `N-1` elements will be omitted and can be
3314 /// retrieved from the [`.into_remainder()`][ArrayChunks::into_remainder]
3315 /// function of the iterator.
3319 /// Panics if `N` is 0.
3326 /// #![feature(iter_array_chunks)]
3328 /// let mut iter = "lorem".chars().array_chunks();
3329 /// assert_eq!(iter.next(), Some(['l', 'o']));
3330 /// assert_eq!(iter.next(), Some(['r', 'e']));
3331 /// assert_eq!(iter.next(), None);
3332 /// assert_eq!(iter.into_remainder().unwrap().as_slice(), &['m']);
3336 /// #![feature(iter_array_chunks)]
3338 /// let data = [1, 1, 2, -2, 6, 0, 3, 1];
3339 /// // ^-----^ ^------^
3340 /// for [x, y, z] in data.iter().array_chunks() {
3341 /// assert_eq!(x + y + z, 4);
3345 #[unstable(feature = "iter_array_chunks", reason = "recently added", issue = "100450")]
3346 fn array_chunks
<const N
: usize>(self) -> ArrayChunks
<Self, N
>
3350 ArrayChunks
::new(self)
3353 /// Sums the elements of an iterator.
3355 /// Takes each element, adds them together, and returns the result.
3357 /// An empty iterator returns the zero value of the type.
3361 /// When calling `sum()` and a primitive integer type is being returned, this
3362 /// method will panic if the computation overflows and debug assertions are
3370 /// let a = [1, 2, 3];
3371 /// let sum: i32 = a.iter().sum();
3373 /// assert_eq!(sum, 6);
3375 #[stable(feature = "iter_arith", since = "1.11.0")]
3376 fn sum
<S
>(self) -> S
3384 /// Iterates over the entire iterator, multiplying all the elements
3386 /// An empty iterator returns the one value of the type.
3390 /// When calling `product()` and a primitive integer type is being returned,
3391 /// method will panic if the computation overflows and debug assertions are
3397 /// fn factorial(n: u32) -> u32 {
3398 /// (1..=n).product()
3400 /// assert_eq!(factorial(0), 1);
3401 /// assert_eq!(factorial(1), 1);
3402 /// assert_eq!(factorial(5), 120);
3404 #[stable(feature = "iter_arith", since = "1.11.0")]
3405 fn product
<P
>(self) -> P
3408 P
: Product
<Self::Item
>,
3410 Product
::product(self)
3413 /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those
3419 /// use std::cmp::Ordering;
3421 /// assert_eq!([1].iter().cmp([1].iter()), Ordering::Equal);
3422 /// assert_eq!([1].iter().cmp([1, 2].iter()), Ordering::Less);
3423 /// assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater);
3425 #[stable(feature = "iter_order", since = "1.5.0")]
3426 fn cmp
<I
>(self, other
: I
) -> Ordering
3428 I
: IntoIterator
<Item
= Self::Item
>,
3432 self.cmp_by(other
, |x
, y
| x
.cmp(&y
))
3435 /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those
3436 /// of another with respect to the specified comparison function.
3443 /// #![feature(iter_order_by)]
3445 /// use std::cmp::Ordering;
3447 /// let xs = [1, 2, 3, 4];
3448 /// let ys = [1, 4, 9, 16];
3450 /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| x.cmp(&y)), Ordering::Less);
3451 /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (x * x).cmp(&y)), Ordering::Equal);
3452 /// assert_eq!(xs.iter().cmp_by(&ys, |&x, &y| (2 * x).cmp(&y)), Ordering::Greater);
3454 #[unstable(feature = "iter_order_by", issue = "64295")]
3455 fn cmp_by
<I
, F
>(self, other
: I
, cmp
: F
) -> Ordering
3459 F
: FnMut(Self::Item
, I
::Item
) -> Ordering
,
3462 fn compare
<X
, Y
, F
>(mut cmp
: F
) -> impl FnMut(X
, Y
) -> ControlFlow
<Ordering
>
3464 F
: FnMut(X
, Y
) -> Ordering
,
3466 move |x
, y
| match cmp(x
, y
) {
3467 Ordering
::Equal
=> ControlFlow
::CONTINUE
,
3468 non_eq
=> ControlFlow
::Break(non_eq
),
3472 match iter_compare(self, other
.into_iter(), compare(cmp
)) {
3473 ControlFlow
::Continue(ord
) => ord
,
3474 ControlFlow
::Break(ord
) => ord
,
3478 /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those
3484 /// use std::cmp::Ordering;
3486 /// assert_eq!([1.].iter().partial_cmp([1.].iter()), Some(Ordering::Equal));
3487 /// assert_eq!([1.].iter().partial_cmp([1., 2.].iter()), Some(Ordering::Less));
3488 /// assert_eq!([1., 2.].iter().partial_cmp([1.].iter()), Some(Ordering::Greater));
3490 /// assert_eq!([f64::NAN].iter().partial_cmp([1.].iter()), None);
3492 #[stable(feature = "iter_order", since = "1.5.0")]
3493 fn partial_cmp
<I
>(self, other
: I
) -> Option
<Ordering
>
3496 Self::Item
: PartialOrd
<I
::Item
>,
3499 self.partial_cmp_by(other
, |x
, y
| x
.partial_cmp(&y
))
3502 /// [Lexicographically](Ord#lexicographical-comparison) compares the elements of this [`Iterator`] with those
3503 /// of another with respect to the specified comparison function.
3510 /// #![feature(iter_order_by)]
3512 /// use std::cmp::Ordering;
3514 /// let xs = [1.0, 2.0, 3.0, 4.0];
3515 /// let ys = [1.0, 4.0, 9.0, 16.0];
3518 /// xs.iter().partial_cmp_by(&ys, |&x, &y| x.partial_cmp(&y)),
3519 /// Some(Ordering::Less)
3522 /// xs.iter().partial_cmp_by(&ys, |&x, &y| (x * x).partial_cmp(&y)),
3523 /// Some(Ordering::Equal)
3526 /// xs.iter().partial_cmp_by(&ys, |&x, &y| (2.0 * x).partial_cmp(&y)),
3527 /// Some(Ordering::Greater)
3530 #[unstable(feature = "iter_order_by", issue = "64295")]
3531 fn partial_cmp_by
<I
, F
>(self, other
: I
, partial_cmp
: F
) -> Option
<Ordering
>
3535 F
: FnMut(Self::Item
, I
::Item
) -> Option
<Ordering
>,
3538 fn compare
<X
, Y
, F
>(mut partial_cmp
: F
) -> impl FnMut(X
, Y
) -> ControlFlow
<Option
<Ordering
>>
3540 F
: FnMut(X
, Y
) -> Option
<Ordering
>,
3542 move |x
, y
| match partial_cmp(x
, y
) {
3543 Some(Ordering
::Equal
) => ControlFlow
::CONTINUE
,
3544 non_eq
=> ControlFlow
::Break(non_eq
),
3548 match iter_compare(self, other
.into_iter(), compare(partial_cmp
)) {
3549 ControlFlow
::Continue(ord
) => Some(ord
),
3550 ControlFlow
::Break(ord
) => ord
,
3554 /// Determines if the elements of this [`Iterator`] are equal to those of
3560 /// assert_eq!([1].iter().eq([1].iter()), true);
3561 /// assert_eq!([1].iter().eq([1, 2].iter()), false);
3563 #[stable(feature = "iter_order", since = "1.5.0")]
3564 fn eq
<I
>(self, other
: I
) -> bool
3567 Self::Item
: PartialEq
<I
::Item
>,
3570 self.eq_by(other
, |x
, y
| x
== y
)
3573 /// Determines if the elements of this [`Iterator`] are equal to those of
3574 /// another with respect to the specified equality function.
3581 /// #![feature(iter_order_by)]
3583 /// let xs = [1, 2, 3, 4];
3584 /// let ys = [1, 4, 9, 16];
3586 /// assert!(xs.iter().eq_by(&ys, |&x, &y| x * x == y));
3588 #[unstable(feature = "iter_order_by", issue = "64295")]
3589 fn eq_by
<I
, F
>(self, other
: I
, eq
: F
) -> bool
3593 F
: FnMut(Self::Item
, I
::Item
) -> bool
,
3596 fn compare
<X
, Y
, F
>(mut eq
: F
) -> impl FnMut(X
, Y
) -> ControlFlow
<()>
3598 F
: FnMut(X
, Y
) -> bool
,
3601 if eq(x
, y
) { ControlFlow::CONTINUE }
else { ControlFlow::BREAK }
3605 match iter_compare(self, other
.into_iter(), compare(eq
)) {
3606 ControlFlow
::Continue(ord
) => ord
== Ordering
::Equal
,
3607 ControlFlow
::Break(()) => false,
3611 /// Determines if the elements of this [`Iterator`] are unequal to those of
3617 /// assert_eq!([1].iter().ne([1].iter()), false);
3618 /// assert_eq!([1].iter().ne([1, 2].iter()), true);
3620 #[stable(feature = "iter_order", since = "1.5.0")]
3621 fn ne
<I
>(self, other
: I
) -> bool
3624 Self::Item
: PartialEq
<I
::Item
>,
3630 /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison)
3631 /// less than those of another.
3636 /// assert_eq!([1].iter().lt([1].iter()), false);
3637 /// assert_eq!([1].iter().lt([1, 2].iter()), true);
3638 /// assert_eq!([1, 2].iter().lt([1].iter()), false);
3639 /// assert_eq!([1, 2].iter().lt([1, 2].iter()), false);
3641 #[stable(feature = "iter_order", since = "1.5.0")]
3642 fn lt
<I
>(self, other
: I
) -> bool
3645 Self::Item
: PartialOrd
<I
::Item
>,
3648 self.partial_cmp(other
) == Some(Ordering
::Less
)
3651 /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison)
3652 /// less or equal to those of another.
3657 /// assert_eq!([1].iter().le([1].iter()), true);
3658 /// assert_eq!([1].iter().le([1, 2].iter()), true);
3659 /// assert_eq!([1, 2].iter().le([1].iter()), false);
3660 /// assert_eq!([1, 2].iter().le([1, 2].iter()), true);
3662 #[stable(feature = "iter_order", since = "1.5.0")]
3663 fn le
<I
>(self, other
: I
) -> bool
3666 Self::Item
: PartialOrd
<I
::Item
>,
3669 matches
!(self.partial_cmp(other
), Some(Ordering
::Less
| Ordering
::Equal
))
3672 /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison)
3673 /// greater than those of another.
3678 /// assert_eq!([1].iter().gt([1].iter()), false);
3679 /// assert_eq!([1].iter().gt([1, 2].iter()), false);
3680 /// assert_eq!([1, 2].iter().gt([1].iter()), true);
3681 /// assert_eq!([1, 2].iter().gt([1, 2].iter()), false);
3683 #[stable(feature = "iter_order", since = "1.5.0")]
3684 fn gt
<I
>(self, other
: I
) -> bool
3687 Self::Item
: PartialOrd
<I
::Item
>,
3690 self.partial_cmp(other
) == Some(Ordering
::Greater
)
3693 /// Determines if the elements of this [`Iterator`] are [lexicographically](Ord#lexicographical-comparison)
3694 /// greater than or equal to those of another.
3699 /// assert_eq!([1].iter().ge([1].iter()), true);
3700 /// assert_eq!([1].iter().ge([1, 2].iter()), false);
3701 /// assert_eq!([1, 2].iter().ge([1].iter()), true);
3702 /// assert_eq!([1, 2].iter().ge([1, 2].iter()), true);
3704 #[stable(feature = "iter_order", since = "1.5.0")]
3705 fn ge
<I
>(self, other
: I
) -> bool
3708 Self::Item
: PartialOrd
<I
::Item
>,
3711 matches
!(self.partial_cmp(other
), Some(Ordering
::Greater
| Ordering
::Equal
))
3714 /// Checks if the elements of this iterator are sorted.
3716 /// That is, for each element `a` and its following element `b`, `a <= b` must hold. If the
3717 /// iterator yields exactly zero or one element, `true` is returned.
3719 /// Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition
3720 /// implies that this function returns `false` if any two consecutive items are not
3726 /// #![feature(is_sorted)]
3728 /// assert!([1, 2, 2, 9].iter().is_sorted());
3729 /// assert!(![1, 3, 2, 4].iter().is_sorted());
3730 /// assert!([0].iter().is_sorted());
3731 /// assert!(std::iter::empty::<i32>().is_sorted());
3732 /// assert!(![0.0, 1.0, f32::NAN].iter().is_sorted());
3735 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3736 fn is_sorted(self) -> bool
3739 Self::Item
: PartialOrd
,
3741 self.is_sorted_by(PartialOrd
::partial_cmp
)
3744 /// Checks if the elements of this iterator are sorted using the given comparator function.
3746 /// Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare`
3747 /// function to determine the ordering of two elements. Apart from that, it's equivalent to
3748 /// [`is_sorted`]; see its documentation for more information.
3753 /// #![feature(is_sorted)]
3755 /// assert!([1, 2, 2, 9].iter().is_sorted_by(|a, b| a.partial_cmp(b)));
3756 /// assert!(![1, 3, 2, 4].iter().is_sorted_by(|a, b| a.partial_cmp(b)));
3757 /// assert!([0].iter().is_sorted_by(|a, b| a.partial_cmp(b)));
3758 /// assert!(std::iter::empty::<i32>().is_sorted_by(|a, b| a.partial_cmp(b)));
3759 /// assert!(![0.0, 1.0, f32::NAN].iter().is_sorted_by(|a, b| a.partial_cmp(b)));
3762 /// [`is_sorted`]: Iterator::is_sorted
3763 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3764 fn is_sorted_by
<F
>(mut self, compare
: F
) -> bool
3767 F
: FnMut(&Self::Item
, &Self::Item
) -> Option
<Ordering
>,
3772 mut compare
: impl FnMut(&T
, &T
) -> Option
<Ordering
> + 'a
,
3773 ) -> impl FnMut(T
) -> bool
+ 'a
{
3775 if let Some(Ordering
::Greater
) | None
= compare(&last
, &curr
) {
3783 let mut last
= match self.next() {
3785 None
=> return true,
3788 self.all(check(&mut last
, compare
))
3791 /// Checks if the elements of this iterator are sorted using the given key extraction
3794 /// Instead of comparing the iterator's elements directly, this function compares the keys of
3795 /// the elements, as determined by `f`. Apart from that, it's equivalent to [`is_sorted`]; see
3796 /// its documentation for more information.
3798 /// [`is_sorted`]: Iterator::is_sorted
3803 /// #![feature(is_sorted)]
3805 /// assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len()));
3806 /// assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs()));
3809 #[unstable(feature = "is_sorted", reason = "new API", issue = "53485")]
3810 fn is_sorted_by_key
<F
, K
>(self, f
: F
) -> bool
3813 F
: FnMut(Self::Item
) -> K
,
3816 self.map(f
).is_sorted()
3819 /// See [TrustedRandomAccess][super::super::TrustedRandomAccess]
3820 // The unusual name is to avoid name collisions in method resolution
3824 #[unstable(feature = "trusted_random_access", issue = "none")]
3825 unsafe fn __iterator_get_unchecked(&mut self, _idx
: usize) -> Self::Item
3827 Self: TrustedRandomAccessNoCoerce
,
3829 unreachable
!("Always specialized");
3833 /// Compares two iterators element-wise using the given function.
3835 /// If `ControlFlow::CONTINUE` is returned from the function, the comparison moves on to the next
3836 /// elements of both iterators. Returning `ControlFlow::Break(x)` short-circuits the iteration and
3837 /// returns `ControlFlow::Break(x)`. If one of the iterators runs out of elements,
3838 /// `ControlFlow::Continue(ord)` is returned where `ord` is the result of comparing the lengths of
3841 /// Isolates the logic shared by ['cmp_by'](Iterator::cmp_by),
3842 /// ['partial_cmp_by'](Iterator::partial_cmp_by), and ['eq_by'](Iterator::eq_by).
3844 fn iter_compare
<A
, B
, F
, T
>(mut a
: A
, mut b
: B
, f
: F
) -> ControlFlow
<T
, Ordering
>
3848 F
: FnMut(A
::Item
, B
::Item
) -> ControlFlow
<T
>,
3851 fn compare
<'a
, B
, X
, T
>(
3853 mut f
: impl FnMut(X
, B
::Item
) -> ControlFlow
<T
> + 'a
,
3854 ) -> impl FnMut(X
) -> ControlFlow
<ControlFlow
<T
, Ordering
>> + 'a
3858 move |x
| match b
.next() {
3859 None
=> ControlFlow
::Break(ControlFlow
::Continue(Ordering
::Greater
)),
3860 Some(y
) => f(x
, y
).map_break(ControlFlow
::Break
),
3864 match a
.try_for_each(compare(&mut b
, f
)) {
3865 ControlFlow
::Continue(()) => ControlFlow
::Continue(match b
.next() {
3866 None
=> Ordering
::Equal
,
3867 Some(_
) => Ordering
::Less
,
3869 ControlFlow
::Break(x
) => x
,
3873 #[stable(feature = "rust1", since = "1.0.0")]
3874 impl<I
: Iterator
+ ?Sized
> Iterator
for &mut I
{
3875 type Item
= I
::Item
;
3877 fn next(&mut self) -> Option
<I
::Item
> {
3880 fn size_hint(&self) -> (usize, Option
<usize>) {
3881 (**self).size_hint()
3883 fn advance_by(&mut self, n
: usize) -> Result
<(), usize> {
3884 (**self).advance_by(n
)
3886 fn nth(&mut self, n
: usize) -> Option
<Self::Item
> {