Iterator in std::iter - Rust
Description: A trait for dealing with iterators.

## Iterator

# Trait Iterator

1.0.0 · Source

    pub trait Iterator {
        type Item;

    Show 76 methods    // Required method
        fn next(&mut self) -> Option<Self::Item>;

        // Provided methods
        fn next_chunk<const N: usize>(
            &mut self,
        ) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>
           where Self: Sized { ... }
        fn size_hint(&self) -> (usize, Option<usize>) { ... }
        fn count(self) -> usize
           where Self: Sized { ... }
        fn last(self) -> Option<Self::Item>
           where Self: Sized { ... }
        fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> { ... }
        fn nth(&mut self, n: usize) -> Option<Self::Item> { ... }
        fn step_by(self, step: usize) -> StepBy<Self> ⓘ
           where Self: Sized { ... }
        fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> ⓘ
           where Self: Sized,
                 U: IntoIterator<Item = Self::Item> { ... }
        fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> ⓘ
           where Self: Sized,
                 U: IntoIterator { ... }
        fn intersperse(self, separator: Self::Item) -> Intersperse<Self> ⓘ
           where Self: Sized,
                 Self::Item: Clone { ... }
        fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> ⓘ
           where Self: Sized,
                 G: FnMut() -> Self::Item { ... }
        fn map<B, F>(self, f: F) -> Map<Self, F> ⓘ
           where Self: Sized,
                 F: FnMut(Self::Item) -> B { ... }
        fn for_each<F>(self, f: F)
           where Self: Sized,
                 F: FnMut(Self::Item) { ... }
        fn filter<P>(self, predicate: P) -> Filter<Self, P> ⓘ
           where Self: Sized,
                 P: FnMut(&Self::Item) -> bool { ... }
        fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> ⓘ
           where Self: Sized,
                 F: FnMut(Self::Item) -> Option<B> { ... }
        fn enumerate(self) -> Enumerate<Self> ⓘ
           where Self: Sized { ... }
        fn peekable(self) -> Peekable<Self> ⓘ
           where Self: Sized { ... }
        fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> ⓘ
           where Self: Sized,
                 P: FnMut(&Self::Item) -> bool { ... }
        fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> ⓘ
           where Self: Sized,
                 P: FnMut(&Self::Item) -> bool { ... }
        fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> ⓘ
           where Self: Sized,
                 P: FnMut(Self::Item) -> Option<B> { ... }
        fn skip(self, n: usize) -> Skip<Self> ⓘ
           where Self: Sized { ... }
        fn take(self, n: usize) -> Take<Self> ⓘ
           where Self: Sized { ... }
        fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> ⓘ
           where Self: Sized,
                 F: FnMut(&mut St, Self::Item) -> Option<B> { ... }
        fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> ⓘ
           where Self: Sized,
                 U: IntoIterator,
                 F: FnMut(Self::Item) -> U { ... }
        fn flatten(self) -> Flatten<Self> ⓘ
           where Self: Sized,
                 Self::Item: IntoIterator { ... }
        fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N> ⓘ
           where Self: Sized,
                 F: FnMut(&[Self::Item; N]) -> R { ... }
        fn fuse(self) -> Fuse<Self> ⓘ
           where Self: Sized { ... }
        fn inspect<F>(self, f: F) -> Inspect<Self, F> ⓘ
           where Self: Sized,
                 F: FnMut(&Self::Item) { ... }
        fn by_ref(&mut self) -> &mut Self
           where Self: Sized { ... }
        fn collect<B>(self) -> B
           where B: FromIterator<Self::Item>,
                 Self: Sized { ... }
        fn try_collect<B>(
            &mut self,
        ) -> <<Self::Item as Try>::Residual as Residual<B>>::TryType
           where Self: Sized,
                 Self::Item: Try,
                 <Self::Item as Try>::Residual: Residual<B>,
                 B: FromIterator<<Self::Item as Try>::Output> { ... }
        fn collect_into<E>(self, collection: &mut E) -> &mut E
           where E: Extend<Self::Item>,
                 Self: Sized { ... }
        fn partition<B, F>(self, f: F) -> (B, B)
           where Self: Sized,
                 B: Default + Extend<Self::Item>,
                 F: FnMut(&Self::Item) -> bool { ... }
        fn partition_in_place<'a, T, P>(self, predicate: P) -> usize
           where T: 'a,
                 Self: Sized + DoubleEndedIterator<Item = &'a mut T>,
                 P: FnMut(&T) -> bool { ... }
        fn is_partitioned<P>(self, predicate: P) -> bool
           where Self: Sized,
                 P: FnMut(Self::Item) -> bool { ... }
        fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
           where Self: Sized,
                 F: FnMut(B, Self::Item) -> R,
                 R: Try<Output = B> { ... }
        fn try_for_each<F, R>(&mut self, f: F) -> R
           where Self: Sized,
                 F: FnMut(Self::Item) -> R,
                 R: Try<Output = ()> { ... }
        fn fold<B, F>(self, init: B, f: F) -> B
           where Self: Sized,
                 F: FnMut(B, Self::Item) -> B { ... }
        fn reduce<F>(self, f: F) -> Option<Self::Item>
           where Self: Sized,
                 F: FnMut(Self::Item, Self::Item) -> Self::Item { ... }
        fn try_reduce<R>(
            &mut self,
            f: impl FnMut(Self::Item, Self::Item) -> R,
        ) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType
           where Self: Sized,
                 R: Try<Output = Self::Item>,
                 <R as Try>::Residual: Residual<Option<Self::Item>> { ... }
        fn all<F>(&mut self, f: F) -> bool
           where Self: Sized,
                 F: FnMut(Self::Item) -> bool { ... }
        fn any<F>(&mut self, f: F) -> bool
           where Self: Sized,
                 F: FnMut(Self::Item) -> bool { ... }
        fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
           where Self: Sized,
                 P: FnMut(&Self::Item) -> bool { ... }
        fn find_map<B, F>(&mut self, f: F) -> Option<B>
           where Self: Sized,
                 F: FnMut(Self::Item) -> Option<B> { ... }
        fn try_find<R>(
            &mut self,
            f: impl FnMut(&Self::Item) -> R,
        ) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType
           where Self: Sized,
                 R: Try<Output = bool>,
                 <R as Try>::Residual: Residual<Option<Self::Item>> { ... }
        fn position<P>(&mut self, predicate: P) -> Option<usize>
           where Self: Sized,
                 P: FnMut(Self::Item) -> bool { ... }
        fn rposition<P>(&mut self, predicate: P) -> Option<usize>
           where P: FnMut(Self::Item) -> bool,
                 Self: Sized + ExactSizeIterator + DoubleEndedIterator { ... }
        fn max(self) -> Option<Self::Item>
           where Self: Sized,
                 Self::Item: Ord { ... }
        fn min(self) -> Option<Self::Item>
           where Self: Sized,
                 Self::Item: Ord { ... }
        fn max_by_key<B, F>(self, f: F) -> Option<Self::Item>
           where B: Ord,
                 Self: Sized,
                 F: FnMut(&Self::Item) -> B { ... }
        fn max_by<F>(self, compare: F) -> Option<Self::Item>
           where Self: Sized,
                 F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
        fn min_by_key<B, F>(self, f: F) -> Option<Self::Item>
           where B: Ord,
                 Self: Sized,
                 F: FnMut(&Self::Item) -> B { ... }
        fn min_by<F>(self, compare: F) -> Option<Self::Item>
           where Self: Sized,
                 F: FnMut(&Self::Item, &Self::Item) -> Ordering { ... }
        fn rev(self) -> Rev<Self> ⓘ
           where Self: Sized + DoubleEndedIterator { ... }
        fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
           where FromA: Default + Extend<A>,
                 FromB: Default + Extend<B>,
                 Self: Sized + Iterator<Item = (A, B)> { ... }
        fn copied<'a, T>(self) -> Copied<Self> ⓘ
           where T: Copy + 'a,
                 Self: Sized + Iterator<Item = &'a T> { ... }
        fn cloned<'a, T>(self) -> Cloned<Self> ⓘ
           where T: Clone + 'a,
                 Self: Sized + Iterator<Item = &'a T> { ... }
        fn cycle(self) -> Cycle<Self> ⓘ
           where Self: Sized + Clone { ... }
        fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N> ⓘ
           where Self: Sized { ... }
        fn sum<S>(self) -> S
           where Self: Sized,
                 S: Sum<Self::Item> { ... }
        fn product<P>(self) -> P
           where Self: Sized,
                 P: Product<Self::Item> { ... }
        fn cmp<I>(self, other: I) -> Ordering
           where I: IntoIterator<Item = Self::Item>,
                 Self::Item: Ord,
                 Self: Sized { ... }
        fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
           where Self: Sized,
                 I: IntoIterator,
                 F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Ordering { ... }
        fn partial_cmp<I>(self, other: I) -> Option<Ordering>
           where I: IntoIterator,
                 Self::Item: PartialOrd<<I as IntoIterator>::Item>,
                 Self: Sized { ... }
        fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>
           where Self: Sized,
                 I: IntoIterator,
                 F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering> { ... }
        fn eq<I>(self, other: I) -> bool
           where I: IntoIterator,
                 Self::Item: PartialEq<<I as IntoIterator>::Item>,
                 Self: Sized { ... }
        fn eq_by<I, F>(self, other: I, eq: F) -> bool
           where Self: Sized,
                 I: IntoIterator,
                 F: FnMut(Self::Item, <I as IntoIterator>::Item) -> bool { ... }
        fn ne<I>(self, other: I) -> bool
           where I: IntoIterator,
                 Self::Item: PartialEq<<I as IntoIterator>::Item>,
                 Self: Sized { ... }
        fn lt<I>(self, other: I) -> bool
           where I: IntoIterator,
                 Self::Item: PartialOrd<<I as IntoIterator>::Item>,
                 Self: Sized { ... }
        fn le<I>(self, other: I) -> bool
           where I: IntoIterator,
                 Self::Item: PartialOrd<<I as IntoIterator>::Item>,
                 Self: Sized { ... }
        fn gt<I>(self, other: I) -> bool
           where I: IntoIterator,
                 Self::Item: PartialOrd<<I as IntoIterator>::Item>,
                 Self: Sized { ... }
        fn ge<I>(self, other: I) -> bool
           where I: IntoIterator,
                 Self::Item: PartialOrd<<I as IntoIterator>::Item>,
                 Self: Sized { ... }
        fn is_sorted(self) -> bool
           where Self: Sized,
                 Self::Item: PartialOrd { ... }
        fn is_sorted_by<F>(self, compare: F) -> bool
           where Self: Sized,
                 F: FnMut(&Self::Item, &Self::Item) -> bool { ... }
        fn is_sorted_by_key<F, K>(self, f: F) -> bool
           where Self: Sized,
                 F: FnMut(Self::Item) -> K,
                 K: PartialOrd { ... }
    }

Expand description

A trait for dealing with iterators.

This is the main iterator trait. For more about the concept of iterators generally, please see the module-level documentation. In particular, you may want to know how to implement `Iterator`.

## Required Associated Types§

1.0.0 · Source

#### type Item

The type of the elements being iterated over.

## Required Methods§

1.0.0 · Source

#### fn next(&mut self) -> Option<Self::Item>

Advances the iterator and returns the next value.

Returns `None` when iteration is finished. Individual iterator implementations may choose to resume iteration, and so calling `next()` again may or may not eventually start returning `Some(Item)` again at some point.

##### §Examples

    let a = [1, 2, 3];

    let mut iter = a.into_iter();

    // A call to next() returns the next value...
    assert_eq!(Some(1), iter.next());
    assert_eq!(Some(2), iter.next());
    assert_eq!(Some(3), iter.next());

    // ... and then None once it's over.
    assert_eq!(None, iter.next());

    // More calls may or may not return `None`. Here, they always will.
    assert_eq!(None, iter.next());
    assert_eq!(None, iter.next());

## Provided Methods§

Source

#### fn next_chunk<const N: usize>( &mut self, ) -> Result<[Self::Item; N], IntoIter<Self::Item, N>>
where Self: Sized,

🔬This is a nightly-only experimental API. (`iter_next_chunk` #98326)

Advances the iterator and returns an array containing the next `N` values.

If there are not enough elements to fill the array then `Err` is returned containing an iterator over the remaining elements.

##### §Examples

Basic usage:

    #![feature(iter_next_chunk)]

    let mut iter = "lorem".chars();

    assert_eq!(iter.next_chunk().unwrap(), ['l', 'o']);              // N is inferred as 2
    assert_eq!(iter.next_chunk().unwrap(), ['r', 'e', 'm']);         // N is inferred as 3
    assert_eq!(iter.next_chunk::<4>().unwrap_err().as_slice(), &[]); // N is explicitly 4

Split a string and get the first three items.

    #![feature(iter_next_chunk)]

    let quote = "not all those who wander are lost";
    let [first, second, third] = quote.split_whitespace().next_chunk().unwrap();
    assert_eq!(first, "not");
    assert_eq!(second, "all");
    assert_eq!(third, "those");

1.0.0 · Source

#### fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the iterator.

Specifically, `size_hint()` returns a tuple where the first element is the lower bound, and the second element is the upper bound.

The second half of the tuple that is returned is an `Option<usize>`. A `None` here means that either there is no known upper bound, or the upper bound is larger than `usize`.

##### §Implementation notes

It is not enforced that an iterator implementation yields the declared number of elements. A buggy iterator may yield less than the lower bound or more than the upper bound of elements.

`size_hint()` is primarily intended to be used for optimizations such as reserving space for the elements of the iterator, but must not be trusted to e.g., omit bounds checks in unsafe code. An incorrect implementation of `size_hint()` should not lead to memory safety violations.

That said, the implementation should provide a correct estimation, because otherwise it would be a violation of the trait’s protocol.

The default implementation returns `(0, None)` which is correct for any iterator.

##### §Examples

Basic usage:

    let a = [1, 2, 3];
    let mut iter = a.iter();

    assert_eq!((3, Some(3)), iter.size_hint());
    let _ = iter.next();
    assert_eq!((2, Some(2)), iter.size_hint());

A more complex example:

    // The even numbers in the range of zero to nine.
    let iter = (0..10).filter(|x| x % 2 == 0);

    // We might iterate from zero to ten times. Knowing that it's five
    // exactly wouldn't be possible without executing filter().
    assert_eq!((0, Some(10)), iter.size_hint());

    // Let's add five more numbers with chain()
    let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20);

    // now both bounds are increased by five
    assert_eq!((5, Some(15)), iter.size_hint());

Returning `None` for an upper bound:

    // an infinite iterator has no upper bound
    // and the maximum possible lower bound
    let iter = 0..;

    assert_eq!((usize::MAX, None), iter.size_hint());

1.0.0 · Source

#### fn count(self) -> usize
where Self: Sized,

Consumes the iterator, counting the number of iterations and returning it.

This method will call `next` repeatedly until `None` is encountered, returning the number of times it saw `Some`. Note that `next` has to be called at least once even if the iterator does not have any elements.

##### §Overflow Behavior

The method does no guarding against overflows, so counting elements of an iterator with more than `usize::MAX` elements either produces the wrong result or panics. If overflow checks are enabled, a panic is guaranteed.

##### §Panics

This function might panic if the iterator has more than `usize::MAX` elements.

##### §Examples

    let a = [1, 2, 3];
    assert_eq!(a.iter().count(), 3);

    let a = [1, 2, 3, 4, 5];
    assert_eq!(a.iter().count(), 5);

1.0.0 · Source

#### fn last(self) -> Option<Self::Item>
where Self: Sized,

Consumes the iterator, returning the last element.

This method will evaluate the iterator until it returns `None`. While doing so, it keeps track of the current element. After `None` is returned, `last()` will then return the last element it saw.

##### §Panics

This function might panic if the iterator is infinite.

##### §Examples

    let a = [1, 2, 3];
    assert_eq!(a.into_iter().last(), Some(3));

    let a = [1, 2, 3, 4, 5];
    assert_eq!(a.into_iter().last(), Some(5));

Source

#### fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>>

🔬This is a nightly-only experimental API. (`iter_advance_by` #77404)

Advances the iterator by `n` elements.

This method will eagerly skip `n` elements by calling `next` up to `n` times until `None` is encountered.

`advance_by(n)` will return `Ok(())` if the iterator successfully advances by `n` elements, or a `Err(NonZero<usize>)` with value `k` if `None` is encountered, where `k` is remaining number of steps that could not be advanced because the iterator ran out. If `self` is empty and `n` is non-zero, then this returns `Err(n)`. Otherwise, `k` is always less than `n`.

Calling `advance_by(0)` can do meaningful work, for example `Flatten` can advance its outer iterator until it finds an inner iterator that is not empty, which then often allows it to return a more accurate `size_hint()` than in its initial state.

##### §Examples

    #![feature(iter_advance_by)]

    use std::num::NonZero;

    let a = [1, 2, 3, 4];
    let mut iter = a.into_iter();

    assert_eq!(iter.advance_by(2), Ok(()));
    assert_eq!(iter.next(), Some(3));
    assert_eq!(iter.advance_by(0), Ok(()));
    assert_eq!(iter.advance_by(100), Err(NonZero::new(99).unwrap())); // only `4` was skipped

1.0.0 · Source

#### fn nth(&mut self, n: usize) -> Option<Self::Item>

Returns the `n`th element of the iterator.

Like most indexing operations, the count starts from zero, so `nth(0)` returns the first value, `nth(1)` the second, and so on.

Note that all preceding elements, as well as the returned element, will be consumed from the iterator. That means that the preceding elements will be discarded, and also that calling `nth(0)` multiple times on the same iterator will return different elements.

`nth()` will return `None` if `n` is greater than or equal to the length of the iterator.

##### §Examples

Basic usage:

    let a = [1, 2, 3];
    assert_eq!(a.into_iter().nth(1), Some(2));

Calling `nth()` multiple times doesn’t rewind the iterator:

    let a = [1, 2, 3];

    let mut iter = a.into_iter();

    assert_eq!(iter.nth(1), Some(2));
    assert_eq!(iter.nth(1), None);

Returning `None` if there are less than `n + 1` elements:

    let a = [1, 2, 3];
    assert_eq!(a.into_iter().nth(10), None);

1.28.0 · Source

#### fn step_by(self, step: usize) -> StepBy<Self> ⓘ
where Self: Sized,

Creates an iterator starting at the same point, but stepping by the given amount at each iteration.

Note 1: The first element of the iterator will always be returned, regardless of the step given.

Note 2: The time at which ignored elements are pulled is not fixed. `StepBy` behaves like the sequence `self.next()`, `self.nth(step-1)`, `self.nth(step-1)`, …, but is also free to behave like the sequence `advance_n_and_return_first(&mut self, step)`, `advance_n_and_return_first(&mut self, step)`, … Which way is used may change for some iterators for performance reasons. The second way will advance the iterator earlier and may consume more items.

`advance_n_and_return_first` is the equivalent of:

    fn advance_n_and_return_first<I>(iter: &mut I, n: usize) -> Option<I::Item>
    where
        I: Iterator,
    {
        let next = iter.next();
        if n > 1 {
            iter.nth(n - 2);
        }
        next
    }

##### §Panics

The method will panic if the given step is `0`.

##### §Examples

    let a = [0, 1, 2, 3, 4, 5];
    let mut iter = a.into_iter().step_by(2);

    assert_eq!(iter.next(), Some(0));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), Some(4));
    assert_eq!(iter.next(), None);

1.0.0 · Source

#### fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> ⓘ
where Self: Sized, U: IntoIterator<Item = Self::Item>,

Takes two iterators and creates a new iterator over both in sequence.

`chain()` will return a new iterator which will first iterate over values from the first iterator and then over values from the second iterator.

In other words, it links two iterators together, in a chain. 🔗

`once` is commonly used to adapt a single value into a chain of other kinds of iteration.

##### §Examples

Basic usage:

    let s1 = "abc".chars();
    let s2 = "def".chars();

    let mut iter = s1.chain(s2);

    assert_eq!(iter.next(), Some('a'));
    assert_eq!(iter.next(), Some('b'));
    assert_eq!(iter.next(), Some('c'));
    assert_eq!(iter.next(), Some('d'));
    assert_eq!(iter.next(), Some('e'));
    assert_eq!(iter.next(), Some('f'));
    assert_eq!(iter.next(), None);

Since the argument to `chain()` uses `IntoIterator`, we can pass anything that can be converted into an `Iterator`, not just an `Iterator` itself. For example, arrays (`[T]`) implement `IntoIterator`, and so can be passed to `chain()` directly:

    let a1 = [1, 2, 3];
    let a2 = [4, 5, 6];

    let mut iter = a1.into_iter().chain(a2);

    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), Some(3));
    assert_eq!(iter.next(), Some(4));
    assert_eq!(iter.next(), Some(5));
    assert_eq!(iter.next(), Some(6));
    assert_eq!(iter.next(), None);

If you work with Windows API, you may wish to convert `OsStr` to `Vec<u16>`:

    #[cfg(windows)]
    fn os_str_to_utf16(s: &std::ffi::OsStr) -> Vec<u16> {
        use std::os::windows::ffi::OsStrExt;
        s.encode_wide().chain(std::iter::once(0)).collect()
    }

1.0.0 · Source

#### fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> ⓘ
where Self: Sized, U: IntoIterator,

‘Zips up’ two iterators into a single iterator of pairs.

`zip()` returns a new iterator that will iterate over two other iterators, returning a tuple where the first element comes from the first iterator, and the second element comes from the second iterator.

In other words, it zips two iterators together, into a single one.

If either iterator returns `None`, `next` from the zipped iterator will return `None`. If the zipped iterator has no more elements to return then each further attempt to advance it will first try to advance the first iterator at most one time and if it still yielded an item try to advance the second iterator at most one time.

To ‘undo’ the result of zipping up two iterators, see `unzip`.

##### §Examples

Basic usage:

    let s1 = "abc".chars();
    let s2 = "def".chars();

    let mut iter = s1.zip(s2);

    assert_eq!(iter.next(), Some(('a', 'd')));
    assert_eq!(iter.next(), Some(('b', 'e')));
    assert_eq!(iter.next(), Some(('c', 'f')));
    assert_eq!(iter.next(), None);

Since the argument to `zip()` uses `IntoIterator`, we can pass anything that can be converted into an `Iterator`, not just an `Iterator` itself. For example, arrays (`[T]`) implement `IntoIterator`, and so can be passed to `zip()` directly:

    let a1 = [1, 2, 3];
    let a2 = [4, 5, 6];

    let mut iter = a1.into_iter().zip(a2);

    assert_eq!(iter.next(), Some((1, 4)));
    assert_eq!(iter.next(), Some((2, 5)));
    assert_eq!(iter.next(), Some((3, 6)));
    assert_eq!(iter.next(), None);

`zip()` is often used to zip an infinite iterator to a finite one. This works because the finite iterator will eventually return `None`, ending the zipper. Zipping with `(0..)` can look a lot like `enumerate`:

    let enumerate: Vec<_> = "foo".chars().enumerate().collect();

    let zipper: Vec<_> = (0..).zip("foo".chars()).collect();

    assert_eq!((0, 'f'), enumerate[0]);
    assert_eq!((0, 'f'), zipper[0]);

    assert_eq!((1, 'o'), enumerate[1]);
    assert_eq!((1, 'o'), zipper[1]);

    assert_eq!((2, 'o'), enumerate[2]);
    assert_eq!((2, 'o'), zipper[2]);

If both iterators have roughly equivalent syntax, it may be more readable to use `zip`:

    use std::iter::zip;

    let a = [1, 2, 3];
    let b = [2, 3, 4];

    let mut zipped = zip(
        a.into_iter().map(|x| x * 2).skip(1),
        b.into_iter().map(|x| x * 2).skip(1),
    );

    assert_eq!(zipped.next(), Some((4, 6)));
    assert_eq!(zipped.next(), Some((6, 8)));
    assert_eq!(zipped.next(), None);

compared to:

    let mut zipped = a
        .into_iter()
        .map(|x| x * 2)
        .skip(1)
        .zip(b.into_iter().map(|x| x * 2).skip(1));

Source

#### fn intersperse(self, separator: Self::Item) -> Intersperse<Self> ⓘ
where Self: Sized, Self::Item: Clone,

🔬This is a nightly-only experimental API. (`iter_intersperse` #79524)

Creates a new iterator which places a copy of `separator` between adjacent items of the original iterator.

In case `separator` does not implement `Clone` or needs to be computed every time, use `intersperse_with`.

##### §Examples

Basic usage:

    #![feature(iter_intersperse)]

    let mut a = [0, 1, 2].into_iter().intersperse(100);
    assert_eq!(a.next(), Some(0));   // The first element from `a`.
    assert_eq!(a.next(), Some(100)); // The separator.
    assert_eq!(a.next(), Some(1));   // The next element from `a`.
    assert_eq!(a.next(), Some(100)); // The separator.
    assert_eq!(a.next(), Some(2));   // The last element from `a`.
    assert_eq!(a.next(), None);       // The iterator is finished.

`intersperse` can be very useful to join an iterator’s items using a common element:

    #![feature(iter_intersperse)]

    let words = ["Hello", "World", "!"];
    let hello: String = words.into_iter().intersperse(" ").collect();
    assert_eq!(hello, "Hello World !");

Source

#### fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> ⓘ
where Self: Sized, G: FnMut() -> Self::Item,

🔬This is a nightly-only experimental API. (`iter_intersperse` #79524)

Creates a new iterator which places an item generated by `separator` between adjacent items of the original iterator.

The closure will be called exactly once each time an item is placed between two adjacent items from the underlying iterator; specifically, the closure is not called if the underlying iterator yields less than two items and after the last item is yielded.

If the iterator’s item implements `Clone`, it may be easier to use `intersperse`.

##### §Examples

Basic usage:

    #![feature(iter_intersperse)]

    #[derive(PartialEq, Debug)]
    struct NotClone(usize);

    let v = [NotClone(0), NotClone(1), NotClone(2)];
    let mut it = v.into_iter().intersperse_with(|| NotClone(99));

    assert_eq!(it.next(), Some(NotClone(0)));  // The first element from `v`.
    assert_eq!(it.next(), Some(NotClone(99))); // The separator.
    assert_eq!(it.next(), Some(NotClone(1)));  // The next element from `v`.
    assert_eq!(it.next(), Some(NotClone(99))); // The separator.
    assert_eq!(it.next(), Some(NotClone(2)));  // The last element from `v`.
    assert_eq!(it.next(), None);               // The iterator is finished.

`intersperse_with` can be used in situations where the separator needs to be computed:

    #![feature(iter_intersperse)]

    let src = ["Hello", "to", "all", "people", "!!"].iter().copied();

    // The closure mutably borrows its context to generate an item.
    let mut happy_emojis = [" ❤️ ", " 😀 "].into_iter();
    let separator = || happy_emojis.next().unwrap_or(" 🦀 ");

    let result = src.intersperse_with(separator).collect::<String>();
    assert_eq!(result, "Hello ❤️ to 😀 all 🦀 people 🦀 !!");

1.0.0 · Source

#### fn map<B, F>(self, f: F) -> Map<Self, F> ⓘ
where Self: Sized, F: FnMut(Self::Item) -> B,

Takes a closure and creates an iterator which calls that closure on each element.

`map()` transforms one iterator into another, by means of its argument: something that implements `FnMut`. It produces a new iterator which calls this closure on each element of the original iterator.

If you are good at thinking in types, you can think of `map()` like this: If you have an iterator that gives you elements of some type `A`, and you want an iterator of some other type `B`, you can use `map()`, passing a closure that takes an `A` and returns a `B`.

`map()` is conceptually similar to a `for` loop. However, as `map()` is lazy, it is best used when you’re already working with other iterators. If you’re doing some sort of looping for a side effect, it’s considered more idiomatic to use `for` than `map()`.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    let mut iter = a.iter().map(|x| 2 * x);

    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), Some(4));
    assert_eq!(iter.next(), Some(6));
    assert_eq!(iter.next(), None);

If you’re doing some sort of side effect, prefer `for` to `map()`:

    // don't do this:
    (0..5).map(|x| println!("{x}"));

    // it won't even execute, as it is lazy. Rust will warn you about this.

    // Instead, use a for-loop:
    for x in 0..5 {
        println!("{x}");
    }

1.21.0 · Source

#### fn for_each<F>(self, f: F)
where Self: Sized, F: FnMut(Self::Item),

Calls a closure on each element of an iterator.

This is equivalent to using a `for` loop on the iterator, although `break` and `continue` are not possible from a closure. It’s generally more idiomatic to use a `for` loop, but `for_each` may be more legible when processing items at the end of longer iterator chains. In some cases `for_each` may also be faster than a loop, because it will use internal iteration on adapters like `Chain`.

##### §Examples

Basic usage:

    use std::sync::mpsc::channel;

    let (tx, rx) = channel();
    (0..5).map(|x| x * 2 + 1)
          .for_each(move |x| tx.send(x).unwrap());

    let v: Vec<_> = rx.iter().collect();
    assert_eq!(v, vec![1, 3, 5, 7, 9]);

For such a small example, a `for` loop may be cleaner, but `for_each` might be preferable to keep a functional style with longer iterators:

    (0..5).flat_map(|x| (x * 100)..(x * 110))
          .enumerate()
          .filter(|&(i, x)| (i + x) % 3 == 0)
          .for_each(|(i, x)| println!("{i}:{x}"));

1.0.0 · Source

#### fn filter<P>(self, predicate: P) -> Filter<Self, P> ⓘ
where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator which uses a closure to determine if an element should be yielded.

Given an element the closure must return `true` or `false`. The returned iterator will yield only the elements for which the closure returns `true`.

##### §Examples

Basic usage:

    let a = [0i32, 1, 2];

    let mut iter = a.into_iter().filter(|x| x.is_positive());

    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), None);

Because the closure passed to `filter()` takes a reference, and many iterators iterate over references, this leads to a possibly confusing situation, where the type of the closure is a double reference:

    let s = &[0, 1, 2];

    let mut iter = s.iter().filter(|x| **x > 1); // needs two *s!

    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), None);

It’s common to instead use destructuring on the argument to strip away one:

    let s = &[0, 1, 2];

    let mut iter = s.iter().filter(|&x| *x > 1); // both & and *

    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), None);

or both:

    let s = &[0, 1, 2];

    let mut iter = s.iter().filter(|&&x| x > 1); // two &s

    assert_eq!(iter.next(), Some(&2));
    assert_eq!(iter.next(), None);

of these layers.

Note that `iter.filter(f).next()` is equivalent to `iter.find(f)`.

1.0.0 · Source

#### fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> ⓘ
where Self: Sized, F: FnMut(Self::Item) -> Option<B>,

Creates an iterator that both filters and maps.

The returned iterator yields only the `value`s for which the supplied closure returns `Some(value)`.

`filter_map` can be used to make chains of `filter` and `map` more concise. The example below shows how a `map().filter().map()` can be shortened to a single call to `filter_map`.

##### §Examples

Basic usage:

    let a = ["1", "two", "NaN", "four", "5"];

    let mut iter = a.iter().filter_map(|s| s.parse().ok());

    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(5));
    assert_eq!(iter.next(), None);

Here’s the same example, but with `filter` and `map`:

    let a = ["1", "two", "NaN", "four", "5"];
    let mut iter = a.iter().map(|s| s.parse()).filter(|s| s.is_ok()).map(|s| s.unwrap());
    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(5));
    assert_eq!(iter.next(), None);

1.0.0 · Source

#### fn enumerate(self) -> Enumerate<Self> ⓘ
where Self: Sized,

Creates an iterator which gives the current iteration count as well as the next value.

The iterator returned yields pairs `(i, val)`, where `i` is the current index of iteration and `val` is the value returned by the iterator.

`enumerate()` keeps its count as a `usize`. If you want to count by a different sized integer, the `zip` function provides similar functionality.

##### §Overflow Behavior

The method does no guarding against overflows, so enumerating more than `usize::MAX` elements either produces the wrong result or panics. If overflow checks are enabled, a panic is guaranteed.

##### §Panics

The returned iterator might panic if the to-be-returned index would overflow a `usize`.

##### §Examples

    let a = ['a', 'b', 'c'];

    let mut iter = a.into_iter().enumerate();

    assert_eq!(iter.next(), Some((0, 'a')));
    assert_eq!(iter.next(), Some((1, 'b')));
    assert_eq!(iter.next(), Some((2, 'c')));
    assert_eq!(iter.next(), None);

1.0.0 · Source

#### fn peekable(self) -> Peekable<Self> ⓘ
where Self: Sized,

Creates an iterator which can use the `peek` and `peek_mut` methods to look at the next element of the iterator without consuming it. See their documentation for more information.

Note that the underlying iterator is still advanced when `peek` or `peek_mut` are called for the first time: In order to retrieve the next element, `next` is called on the underlying iterator, hence any side effects (i.e. anything other than fetching the next value) of the `next` method will occur.

##### §Examples

Basic usage:

    let xs = [1, 2, 3];

    let mut iter = xs.into_iter().peekable();

    // peek() lets us see into the future
    assert_eq!(iter.peek(), Some(&1));
    assert_eq!(iter.next(), Some(1));

    assert_eq!(iter.next(), Some(2));

    // we can peek() multiple times, the iterator won't advance
    assert_eq!(iter.peek(), Some(&3));
    assert_eq!(iter.peek(), Some(&3));

    assert_eq!(iter.next(), Some(3));

    // after the iterator is finished, so is peek()
    assert_eq!(iter.peek(), None);
    assert_eq!(iter.next(), None);

Using `peek_mut` to mutate the next item without advancing the iterator:

    let xs = [1, 2, 3];

    let mut iter = xs.into_iter().peekable();

    // `peek_mut()` lets us see into the future
    assert_eq!(iter.peek_mut(), Some(&mut 1));
    assert_eq!(iter.peek_mut(), Some(&mut 1));
    assert_eq!(iter.next(), Some(1));

    if let Some(p) = iter.peek_mut() {
        assert_eq!(*p, 2);
        // put a value into the iterator
        *p = 1000;
    }

    // The value reappears as the iterator continues
    assert_eq!(iter.collect::<Vec<_>>(), vec![1000, 3]);

1.0.0 · Source

#### fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> ⓘ
where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that `skip`s elements based on a predicate.

`skip_while()` takes a closure as an argument. It will call this closure on each element of the iterator, and ignore elements until it returns `false`.

After `false` is returned, `skip_while()`’s job is over, and the rest of the elements are yielded.

##### §Examples

Basic usage:

    let a = [-1i32, 0, 1];

    let mut iter = a.into_iter().skip_while(|x| x.is_negative());

    assert_eq!(iter.next(), Some(0));
    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), None);

Because the closure passed to `skip_while()` takes a reference, and many iterators iterate over references, this leads to a possibly confusing situation, where the type of the closure argument is a double reference:

    let s = &[-1, 0, 1];

    let mut iter = s.iter().skip_while(|x| **x < 0); // need two *s!

    assert_eq!(iter.next(), Some(&0));
    assert_eq!(iter.next(), Some(&1));
    assert_eq!(iter.next(), None);

Stopping after an initial `false`:

    let a = [-1, 0, 1, -2];

    let mut iter = a.into_iter().skip_while(|&x| x < 0);

    assert_eq!(iter.next(), Some(0));
    assert_eq!(iter.next(), Some(1));

    // while this would have been false, since we already got a false,
    // skip_while() isn't used any more
    assert_eq!(iter.next(), Some(-2));

    assert_eq!(iter.next(), None);

1.0.0 · Source

#### fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> ⓘ
where Self: Sized, P: FnMut(&Self::Item) -> bool,

Creates an iterator that yields elements based on a predicate.

`take_while()` takes a closure as an argument. It will call this closure on each element of the iterator, and yield elements while it returns `true`.

After `false` is returned, `take_while()`’s job is over, and the rest of the elements are ignored.

##### §Examples

Basic usage:

    let a = [-1i32, 0, 1];

    let mut iter = a.into_iter().take_while(|x| x.is_negative());

    assert_eq!(iter.next(), Some(-1));
    assert_eq!(iter.next(), None);

Because the closure passed to `take_while()` takes a reference, and many iterators iterate over references, this leads to a possibly confusing situation, where the type of the closure is a double reference:

    let s = &[-1, 0, 1];

    let mut iter = s.iter().take_while(|x| **x < 0); // need two *s!

    assert_eq!(iter.next(), Some(&-1));
    assert_eq!(iter.next(), None);

Stopping after an initial `false`:

    let a = [-1, 0, 1, -2];

    let mut iter = a.into_iter().take_while(|&x| x < 0);

    assert_eq!(iter.next(), Some(-1));

    // We have more elements that are less than zero, but since we already
    // got a false, take_while() ignores the remaining elements.
    assert_eq!(iter.next(), None);

Because `take_while()` needs to look at the value in order to see if it should be included or not, consuming iterators will see that it is removed:

    let a = [1, 2, 3, 4];
    let mut iter = a.into_iter();

    let result: Vec<i32> = iter.by_ref().take_while(|&n| n != 3).collect();

    assert_eq!(result, [1, 2]);

    let result: Vec<i32> = iter.collect();

    assert_eq!(result, [4]);

The `3` is no longer there, because it was consumed in order to see if the iteration should stop, but wasn’t placed back into the iterator.

1.57.0 · Source

#### fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> ⓘ
where Self: Sized, P: FnMut(Self::Item) -> Option<B>,

Creates an iterator that both yields elements based on a predicate and maps.

`map_while()` takes a closure as an argument. It will call this closure on each element of the iterator, and yield elements while it returns `Some(_)`.

##### §Examples

Basic usage:

    let a = [-1i32, 4, 0, 1];

    let mut iter = a.into_iter().map_while(|x| 16i32.checked_div(x));

    assert_eq!(iter.next(), Some(-16));
    assert_eq!(iter.next(), Some(4));
    assert_eq!(iter.next(), None);

Here’s the same example, but with `take_while` and `map`:

    let a = [-1i32, 4, 0, 1];

    let mut iter = a.into_iter()
                    .map(|x| 16i32.checked_div(x))
                    .take_while(|x| x.is_some())
                    .map(|x| x.unwrap());

    assert_eq!(iter.next(), Some(-16));
    assert_eq!(iter.next(), Some(4));
    assert_eq!(iter.next(), None);

Stopping after an initial `None`:

    let a = [0, 1, 2, -3, 4, 5, -6];

    let iter = a.into_iter().map_while(|x| u32::try_from(x).ok());
    let vec: Vec<_> = iter.collect();

    // We have more elements that could fit in u32 (such as 4, 5), but `map_while` returned `None` for `-3`
    // (as the `predicate` returned `None`) and `collect` stops at the first `None` encountered.
    assert_eq!(vec, [0, 1, 2]);

Because `map_while()` needs to look at the value in order to see if it should be included or not, consuming iterators will see that it is removed:

    let a = [1, 2, -3, 4];
    let mut iter = a.into_iter();

    let result: Vec<u32> = iter.by_ref()
                               .map_while(|n| u32::try_from(n).ok())
                               .collect();

    assert_eq!(result, [1, 2]);

    let result: Vec<i32> = iter.collect();

    assert_eq!(result, [4]);

The `-3` is no longer there, because it was consumed in order to see if the iteration should stop, but wasn’t placed back into the iterator.

Note that unlike `take_while` this iterator is not fused. It is also not specified what this iterator returns after the first `None` is returned. If you need a fused iterator, use `fuse`.

1.0.0 · Source

#### fn skip(self, n: usize) -> Skip<Self> ⓘ
where Self: Sized,

Creates an iterator that skips the first `n` elements.

`skip(n)` skips elements until `n` elements are skipped or the end of the iterator is reached (whichever happens first). After that, all the remaining elements are yielded. In particular, if the original iterator is too short, then the returned iterator is empty.

Rather than overriding this method directly, instead override the `nth` method.

##### §Examples

    let a = [1, 2, 3];

    let mut iter = a.into_iter().skip(2);

    assert_eq!(iter.next(), Some(3));
    assert_eq!(iter.next(), None);

1.0.0 · Source

#### fn take(self, n: usize) -> Take<Self> ⓘ
where Self: Sized,

Creates an iterator that yields the first `n` elements, or fewer if the underlying iterator ends sooner.

`take(n)` yields elements until `n` elements are yielded or the end of the iterator is reached (whichever happens first). The returned iterator is a prefix of length `n` if the original iterator contains at least `n` elements, otherwise it contains all of the (fewer than `n`) elements of the original iterator.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    let mut iter = a.into_iter().take(2);

    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), None);

`take()` is often used with an infinite iterator, to make it finite:

    let mut iter = (0..).take(3);

    assert_eq!(iter.next(), Some(0));
    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), None);

If less than `n` elements are available, `take` will limit itself to the size of the underlying iterator:

    let v = [1, 2];
    let mut iter = v.into_iter().take(5);
    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), None);

Use `by_ref` to take from the iterator without consuming it, and then continue using the original iterator:

    let mut words = ["hello", "world", "of", "Rust"].into_iter();

    // Take the first two words.
    let hello_world: Vec<_> = words.by_ref().take(2).collect();
    assert_eq!(hello_world, vec!["hello", "world"]);

    // Collect the rest of the words.
    // We can only do this because we used `by_ref` earlier.
    let of_rust: Vec<_> = words.collect();
    assert_eq!(of_rust, vec!["of", "Rust"]);

1.0.0 · Source

#### fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> ⓘ
where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>,

An iterator adapter which, like `fold`, holds internal state, but unlike `fold`, produces a new iterator.

`scan()` takes two arguments: an initial value which seeds the internal state, and a closure with two arguments, the first being a mutable reference to the internal state and the second an iterator element. The closure can assign to the internal state to share state between iterations.

On iteration, the closure will be applied to each element of the iterator and the return value from the closure, an `Option`, is returned by the `next` method. Thus the closure can return `Some(value)` to yield `value`, or `None` to end the iteration.

##### §Examples

    let a = [1, 2, 3, 4];

    let mut iter = a.into_iter().scan(1, |state, x| {
        // each iteration, we'll multiply the state by the element ...
        *state = *state * x;

        // ... and terminate if the state exceeds 6
        if *state > 6 {
            return None;
        }
        // ... else yield the negation of the state
        Some(-*state)
    });

    assert_eq!(iter.next(), Some(-1));
    assert_eq!(iter.next(), Some(-2));
    assert_eq!(iter.next(), Some(-6));
    assert_eq!(iter.next(), None);

1.0.0 · Source

#### fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> ⓘ
where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U,

Creates an iterator that works like map, but flattens nested structure.

The `map` adapter is very useful, but only when the closure argument produces values. If it produces an iterator instead, there’s an extra layer of indirection. `flat_map()` will remove this extra layer on its own.

You can think of `flat_map(f)` as the semantic equivalent of `map`ping, and then `flatten`ing as in `map(f).flatten()`.

Another way of thinking about `flat_map()`: `map`’s closure returns one item for each element, and `flat_map()`’s closure returns an iterator for each element.

##### §Examples

    let words = ["alpha", "beta", "gamma"];

    // chars() returns an iterator
    let merged: String = words.iter()
                              .flat_map(|s| s.chars())
                              .collect();
    assert_eq!(merged, "alphabetagamma");

1.29.0 · Source

#### fn flatten(self) -> Flatten<Self> ⓘ
where Self: Sized, Self::Item: IntoIterator,

Creates an iterator that flattens nested structure.

This is useful when you have an iterator of iterators or an iterator of things that can be turned into iterators and you want to remove one level of indirection.

##### §Examples

Basic usage:

    let data = vec![vec![1, 2, 3, 4], vec![5, 6]];
    let flattened: Vec<_> = data.into_iter().flatten().collect();
    assert_eq!(flattened, [1, 2, 3, 4, 5, 6]);

Mapping and then flattening:

    let words = ["alpha", "beta", "gamma"];

    // chars() returns an iterator
    let merged: String = words.iter()
                              .map(|s| s.chars())
                              .flatten()
                              .collect();
    assert_eq!(merged, "alphabetagamma");

You can also rewrite this in terms of `flat_map()`, which is preferable in this case since it conveys intent more clearly:

    let words = ["alpha", "beta", "gamma"];

    // chars() returns an iterator
    let merged: String = words.iter()
                              .flat_map(|s| s.chars())
                              .collect();
    assert_eq!(merged, "alphabetagamma");

Flattening works on any `IntoIterator` type, including `Option` and `Result`:

    let options = vec![Some(123), Some(321), None, Some(231)];
    let flattened_options: Vec<_> = options.into_iter().flatten().collect();
    assert_eq!(flattened_options, [123, 321, 231]);

    let results = vec![Ok(123), Ok(321), Err(456), Ok(231)];
    let flattened_results: Vec<_> = results.into_iter().flatten().collect();
    assert_eq!(flattened_results, [123, 321, 231]);

Flattening only removes one level of nesting at a time:

    let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]];

    let d2: Vec<_> = d3.into_iter().flatten().collect();
    assert_eq!(d2, [[1, 2], [3, 4], [5, 6], [7, 8]]);

    let d1: Vec<_> = d3.into_iter().flatten().flatten().collect();
    assert_eq!(d1, [1, 2, 3, 4, 5, 6, 7, 8]);

Here we see that `flatten()` does not perform a “deep” flatten. Instead, only one level of nesting is removed. That is, if you `flatten()` a three-dimensional array, the result will be two-dimensional and not one-dimensional. To get a one-dimensional structure, you have to `flatten()` again.

Source

#### fn map_windows<F, R, const N: usize>(self, f: F) -> MapWindows<Self, F, N> ⓘ
where Self: Sized, F: FnMut(&[Self::Item; N]) -> R,

🔬This is a nightly-only experimental API. (`iter_map_windows` #87155)

Calls the given function `f` for each contiguous window of size `N` over `self` and returns an iterator over the outputs of `f`. Like `slice::windows()`, the windows during mapping overlap as well.

In the following example, the closure is called three times with the arguments `&['a', 'b']`, `&['b', 'c']` and `&['c', 'd']` respectively.

    #![feature(iter_map_windows)]

    let strings = "abcd".chars()
        .map_windows(|[x, y]| format!("{}+{}", x, y))
        .collect::<Vec<String>>();

    assert_eq!(strings, vec!["a+b", "b+c", "c+d"]);

Note that the const parameter `N` is usually inferred by the destructured argument in the closure.

The returned iterator yields 𝑘 − `N` + 1 items (where 𝑘 is the number of items yielded by `self`). If 𝑘 is less than `N`, this method yields an empty iterator.

The returned iterator implements `FusedIterator`, because once `self` returns `None`, even if it returns a `Some(T)` again in the next iterations, we cannot put it into a contiguous array buffer, and thus the returned iterator should be fused.

##### §Panics

Panics if `N` is zero. This check will most probably get changed to a compile time error before this method gets stabilized.

ⓘ

    #![feature(iter_map_windows)]

    let iter = std::iter::repeat(0).map_windows(|&[]| ());

##### §Examples

Building the sums of neighboring numbers.

    #![feature(iter_map_windows)]

    let mut it = [1, 3, 8, 1].iter().map_windows(|&[a, b]| a + b);
    assert_eq!(it.next(), Some(4));  // 1 + 3
    assert_eq!(it.next(), Some(11)); // 3 + 8
    assert_eq!(it.next(), Some(9));  // 8 + 1
    assert_eq!(it.next(), None);

Since the elements in the following example implement `Copy`, we can just copy the array and get an iterator over the windows.

    #![feature(iter_map_windows)]

    let mut it = "ferris".chars().map_windows(|w: &[_; 3]| *w);
    assert_eq!(it.next(), Some(['f', 'e', 'r']));
    assert_eq!(it.next(), Some(['e', 'r', 'r']));
    assert_eq!(it.next(), Some(['r', 'r', 'i']));
    assert_eq!(it.next(), Some(['r', 'i', 's']));
    assert_eq!(it.next(), None);

You can also use this function to check the sortedness of an iterator. For the simple case, rather use `Iterator::is_sorted`.

    #![feature(iter_map_windows)]

    let mut it = [0.5, 1.0, 3.5, 3.0, 8.5, 8.5, f32::NAN].iter()
        .map_windows(|[a, b]| a <= b);

    assert_eq!(it.next(), Some(true));  // 0.5 <= 1.0
    assert_eq!(it.next(), Some(true));  // 1.0 <= 3.5
    assert_eq!(it.next(), Some(false)); // 3.5 <= 3.0
    assert_eq!(it.next(), Some(true));  // 3.0 <= 8.5
    assert_eq!(it.next(), Some(true));  // 8.5 <= 8.5
    assert_eq!(it.next(), Some(false)); // 8.5 <= NAN
    assert_eq!(it.next(), None);

For non-fused iterators, they are fused after `map_windows`.

    #![feature(iter_map_windows)]

    #[derive(Default)]
    struct NonFusedIterator {
        state: i32,
    }

    impl Iterator for NonFusedIterator {
        type Item = i32;

        fn next(&mut self) -> Option<i32> {
            let val = self.state;
            self.state = self.state + 1;

            // yields `0..5` first, then only even numbers since `6..`.
            if val < 5 || val % 2 == 0 {
                Some(val)
            } else {
                None
            }
        }
    }

    let mut iter = NonFusedIterator::default();

    // yields 0..5 first.
    assert_eq!(iter.next(), Some(0));
    assert_eq!(iter.next(), Some(1));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), Some(3));
    assert_eq!(iter.next(), Some(4));
    // then we can see our iterator going back and forth
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), Some(6));
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), Some(8));
    assert_eq!(iter.next(), None);

    // however, with `.map_windows()`, it is fused.
    let mut iter = NonFusedIterator::default()
        .map_windows(|arr: &[_; 2]| *arr);

    assert_eq!(iter.next(), Some([0, 1]));
    assert_eq!(iter.next(), Some([1, 2]));
    assert_eq!(iter.next(), Some([2, 3]));
    assert_eq!(iter.next(), Some([3, 4]));
    assert_eq!(iter.next(), None);

    // it will always return `None` after the first time.
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), None);

1.0.0 · Source

#### fn fuse(self) -> Fuse<Self> ⓘ
where Self: Sized,

Creates an iterator which ends after the first `None`.

After an iterator returns `None`, future calls may or may not yield `Some(T)` again. `fuse()` adapts an iterator, ensuring that after a `None` is given, it will always return `None` forever.

Note that the `Fuse` wrapper is a no-op on iterators that implement the `FusedIterator` trait. `fuse()` may therefore behave incorrectly if the `FusedIterator` trait is improperly implemented.

##### §Examples

    // an iterator which alternates between Some and None
    struct Alternate {
        state: i32,
    }

    impl Iterator for Alternate {
        type Item = i32;

        fn next(&mut self) -> Option<i32> {
            let val = self.state;
            self.state = self.state + 1;

            // if it's even, Some(i32), else None
            (val % 2 == 0).then_some(val)
        }
    }

    let mut iter = Alternate { state: 0 };

    // we can see our iterator going back and forth
    assert_eq!(iter.next(), Some(0));
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), None);

    // however, once we fuse it...
    let mut iter = iter.fuse();

    assert_eq!(iter.next(), Some(4));
    assert_eq!(iter.next(), None);

    // it will always return `None` after the first time.
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), None);
    assert_eq!(iter.next(), None);

1.0.0 · Source

#### fn inspect<F>(self, f: F) -> Inspect<Self, F> ⓘ
where Self: Sized, F: FnMut(&Self::Item),

Does something with each element of an iterator, passing the value on.

When using iterators, you’ll often chain several of them together. While working on such code, you might want to check out what’s happening at various parts in the pipeline. To do that, insert a call to `inspect()`.

It’s more common for `inspect()` to be used as a debugging tool than to exist in your final code, but applications may find it useful in certain situations when errors need to be logged before being discarded.

##### §Examples

Basic usage:

    let a = [1, 4, 2, 3];

    // this iterator sequence is complex.
    let sum = a.iter()
        .cloned()
        .filter(|x| x % 2 == 0)
        .fold(0, |sum, i| sum + i);

    println!("{sum}");

    // let's add some inspect() calls to investigate what's happening
    let sum = a.iter()
        .cloned()
        .inspect(|x| println!("about to filter: {x}"))
        .filter(|x| x % 2 == 0)
        .inspect(|x| println!("made it through filter: {x}"))
        .fold(0, |sum, i| sum + i);

    println!("{sum}");

This will print:

    6
    about to filter: 1
    about to filter: 4
    made it through filter: 4
    about to filter: 2
    made it through filter: 2
    about to filter: 3
    6

Logging errors before discarding them:

    let lines = ["1", "2", "a"];

    let sum: i32 = lines
        .iter()
        .map(|line| line.parse::<i32>())
        .inspect(|num| {
            if let Err(ref e) = *num {
                println!("Parsing error: {e}");
            }
        })
        .filter_map(Result::ok)
        .sum();

    println!("Sum: {sum}");

This will print:

    Parsing error: invalid digit found in string
    Sum: 3

1.0.0 · Source

#### fn by_ref(&mut self) -> &mut Self
where Self: Sized,

Creates a “by reference” adapter for this instance of `Iterator`.

Consuming method calls (direct or indirect calls to `next`) on the “by reference” adapter will consume the original iterator, but ownership-taking methods (those with a `self` parameter) only take ownership of the “by reference” iterator.

This is useful for applying ownership-taking methods (such as `take` in the example below) without giving up ownership of the original iterator, so you can use the original iterator afterwards.

Uses `impl<I: Iterator + ?Sized> Iterator for &mut I { type Item = I::Item; ...}`.

##### §Examples

    let mut words = ["hello", "world", "of", "Rust"].into_iter();

    // Take the first two words.
    let hello_world: Vec<_> = words.by_ref().take(2).collect();
    assert_eq!(hello_world, vec!["hello", "world"]);

    // Collect the rest of the words.
    // We can only do this because we used `by_ref` earlier.
    let of_rust: Vec<_> = words.collect();
    assert_eq!(of_rust, vec!["of", "Rust"]);

1.0.0 · Source

#### fn collect<B>(self) -> B
where B: FromIterator<Self::Item>, Self: Sized,

Transforms an iterator into a collection.

`collect()` takes ownership of an iterator and produces whichever collection type you request. The iterator itself carries no knowledge of the eventual container; the target collection is chosen entirely by the type you ask `collect()` to return. This makes `collect()` one of the more powerful methods in the standard library, and it shows up in a wide variety of contexts.

The most basic pattern in which `collect()` is used is to turn one collection into another. You take a collection, call `iter` on it, do a bunch of transformations, and then `collect()` at the end.

`collect()` can also create instances of types that are not typical collections. For example, a `String` can be built from `char`s, and an iterator of `Result<T, E>` items can be collected into `Result<Collection<T>, E>`. See the examples below for more.

Because `collect()` is so general, it can cause problems with type inference. As such, `collect()` is one of the few times you’ll see the syntax affectionately known as the ‘turbofish’: `::<>`. This helps the inference algorithm understand specifically which collection you’re trying to collect into.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    let doubled: Vec<i32> = a.iter()
                             .map(|x| x * 2)
                             .collect();

    assert_eq!(vec![2, 4, 6], doubled);

Note that we needed the `: Vec<i32>` on the left-hand side. This is because we could collect into, for example, a `VecDeque<T>` instead:

    use std::collections::VecDeque;

    let a = [1, 2, 3];

    let doubled: VecDeque<i32> = a.iter().map(|x| x * 2).collect();

    assert_eq!(2, doubled[0]);
    assert_eq!(4, doubled[1]);
    assert_eq!(6, doubled[2]);

Using the ‘turbofish’ instead of annotating `doubled`:

    let a = [1, 2, 3];

    let doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>();

    assert_eq!(vec![2, 4, 6], doubled);

Because `collect()` only cares about what you’re collecting into, you can still use a partial type hint, `_`, with the turbofish:

    let a = [1, 2, 3];

    let doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>();

    assert_eq!(vec![2, 4, 6], doubled);

Using `collect()` to make a `String`:

    let chars = ['g', 'd', 'k', 'k', 'n'];

    let hello: String = chars.into_iter()
        .map(|x| x as u8)
        .map(|x| (x + 1) as char)
        .collect();

    assert_eq!("hello", hello);

If you have a list of `Result<T, E>`s, you can use `collect()` to see if any of them failed:

    let results = [Ok(1), Err("nope"), Ok(3), Err("bad")];

    let result: Result<Vec<_>, &str> = results.into_iter().collect();

    // gives us the first error
    assert_eq!(Err("nope"), result);

    let results = [Ok(1), Ok(3)];

    let result: Result<Vec<_>, &str> = results.into_iter().collect();

    // gives us the list of answers
    assert_eq!(Ok(vec![1, 3]), result);

Source

#### fn try_collect<B>( &mut self, ) -> <<Self::Item as Try>::Residual as Residual<B>>::TryType
where Self: Sized, Self::Item: Try, <Self::Item as Try>::Residual: Residual<B>, B: FromIterator<<Self::Item as Try>::Output>,

🔬This is a nightly-only experimental API. (`iterator_try_collect` #94047)

Fallibly transforms an iterator into a collection, short circuiting if a failure is encountered.

`try_collect()` is a variation of `collect()` that allows fallible conversions during collection. Its main use case is simplifying conversions from iterators yielding `Option<T>` into `Option<Collection<T>>`, or similarly for other `Try` types (e.g. `Result`).

Importantly, `try_collect()` doesn’t require that the outer `Try` type also implements `FromIterator`; only the inner type produced on `Try::Output` must implement it. Concretely, this means that collecting into `ControlFlow<_, Vec<i32>>` is valid because `Vec<i32>` implements `FromIterator`, even though `ControlFlow` doesn’t.

Also, if a failure is encountered during `try_collect()`, the iterator is still valid and may continue to be used, in which case it will continue iterating starting after the element that triggered the failure. See the last example below for an example of how this works.

##### §Examples

Successfully collecting an iterator of `Option<i32>` into `Option<Vec<i32>>`:

    #![feature(iterator_try_collect)]

    let u = vec![Some(1), Some(2), Some(3)];
    let v = u.into_iter().try_collect::<Vec<i32>>();
    assert_eq!(v, Some(vec![1, 2, 3]));

Failing to collect in the same way:

    #![feature(iterator_try_collect)]

    let u = vec![Some(1), Some(2), None, Some(3)];
    let v = u.into_iter().try_collect::<Vec<i32>>();
    assert_eq!(v, None);

A similar example, but with `Result`:

    #![feature(iterator_try_collect)]

    let u: Vec<Result<i32, ()>> = vec![Ok(1), Ok(2), Ok(3)];
    let v = u.into_iter().try_collect::<Vec<i32>>();
    assert_eq!(v, Ok(vec![1, 2, 3]));

    let u = vec![Ok(1), Ok(2), Err(()), Ok(3)];
    let v = u.into_iter().try_collect::<Vec<i32>>();
    assert_eq!(v, Err(()));

Finally, even `ControlFlow` works, despite the fact that it doesn’t implement `FromIterator`. Note also that the iterator can continue to be used, even if a failure is encountered:

    #![feature(iterator_try_collect)]

    use core::ops::ControlFlow::{Break, Continue};

    let u = [Continue(1), Continue(2), Break(3), Continue(4), Continue(5)];
    let mut it = u.into_iter();

    let v = it.try_collect::<Vec<_>>();
    assert_eq!(v, Break(3));

    let v = it.try_collect::<Vec<_>>();
    assert_eq!(v, Continue(vec![4, 5]));

Source

#### fn collect_into<E>(self, collection: &mut E) -> &mut E
where E: Extend<Self::Item>, Self: Sized,

🔬This is a nightly-only experimental API. (`iter_collect_into` #94780)

Collects all the items from an iterator into a collection.

This method consumes the iterator and adds all its items to the passed collection. The collection is then returned, so the call chain can be continued.

This is useful when you already have a collection and want to add the iterator items to it.

This method is a convenience method to call Extend::extend, but instead of being called on a collection, it’s called on an iterator.

##### §Examples

Basic usage:

    #![feature(iter_collect_into)]

    let a = [1, 2, 3];
    let mut vec: Vec::<i32> = vec![0, 1];

    a.iter().map(|x| x * 2).collect_into(&mut vec);
    a.iter().map(|x| x * 10).collect_into(&mut vec);

    assert_eq!(vec, vec![0, 1, 2, 4, 6, 10, 20, 30]);

`Vec` can have a manual set capacity to avoid reallocating it:

    #![feature(iter_collect_into)]

    let a = [1, 2, 3];
    let mut vec: Vec::<i32> = Vec::with_capacity(6);

    a.iter().map(|x| x * 2).collect_into(&mut vec);
    a.iter().map(|x| x * 10).collect_into(&mut vec);

    assert_eq!(6, vec.capacity());
    assert_eq!(vec, vec![2, 4, 6, 10, 20, 30]);

The returned mutable reference can be used to continue the call chain:

    #![feature(iter_collect_into)]

    let a = [1, 2, 3];
    let mut vec: Vec::<i32> = Vec::with_capacity(6);

    let count = a.iter().collect_into(&mut vec).iter().count();

    assert_eq!(count, vec.len());
    assert_eq!(vec, vec![1, 2, 3]);

    let count = a.iter().collect_into(&mut vec).iter().count();

    assert_eq!(count, vec.len());
    assert_eq!(vec, vec![1, 2, 3, 1, 2, 3]);

1.0.0 · Source

#### fn partition<B, F>(self, f: F) -> (B, B)
where Self: Sized, B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool,

Consumes an iterator, creating two collections from it.

The predicate passed to `partition()` can return `true`, or `false`. `partition()` returns a pair, all of the elements for which it returned `true`, and all of the elements for which it returned `false`.

See also `is_partitioned()` and `partition_in_place()`.

##### §Examples

    let a = [1, 2, 3];

    let (even, odd): (Vec<_>, Vec<_>) = a
        .into_iter()
        .partition(|n| n % 2 == 0);

    assert_eq!(even, [2]);
    assert_eq!(odd, [1, 3]);

Source

#### fn partition_in_place<'a, T, P>(self, predicate: P) -> usize
where T: 'a, Self: Sized + DoubleEndedIterator<Item = &'a mut T>, P: FnMut(&T) -> bool,

🔬This is a nightly-only experimental API. (`iter_partition_in_place` #62543)

Reorders the elements of this iterator in-place according to the given predicate, such that all those that return `true` precede all those that return `false`. Returns the number of `true` elements found.

The relative order of partitioned items is not maintained.

##### §Current implementation

The current algorithm tries to find the first element for which the predicate evaluates to false and the last element for which it evaluates to true, and repeatedly swaps them.

Time complexity: O(n)

See also `is_partitioned()` and `partition()`.

##### §Examples

    #![feature(iter_partition_in_place)]

    let mut a = [1, 2, 3, 4, 5, 6, 7];

    // Partition in-place between evens and odds
    let i = a.iter_mut().partition_in_place(|n| n % 2 == 0);

    assert_eq!(i, 3);
    assert!(a[..i].iter().all(|n| n % 2 == 0)); // evens
    assert!(a[i..].iter().all(|n| n % 2 == 1)); // odds

Source

#### fn is_partitioned<P>(self, predicate: P) -> bool
where Self: Sized, P: FnMut(Self::Item) -> bool,

🔬This is a nightly-only experimental API. (`iter_is_partitioned` #62544)

Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return `true` precede all those that return `false`.

See also `partition()` and `partition_in_place()`.

##### §Examples

    #![feature(iter_is_partitioned)]

    assert!("Iterator".chars().is_partitioned(char::is_uppercase));
    assert!(!"IntoIterator".chars().is_partitioned(char::is_uppercase));

1.27.0 · Source

#### fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
where Self: Sized, F: FnMut(B, Self::Item) -> R, R: Try<Output = B>,

An iterator method that applies a function as long as it returns successfully, producing a single, final value.

`try_fold()` takes two arguments: an initial value, and a closure with two arguments: an ‘accumulator’, and an element. The closure either returns successfully, with the value that the accumulator should have for the next iteration, or it returns failure, with an error value that is propagated back to the caller immediately (short-circuiting).

The initial value is the value the accumulator will have on the first call. If applying the closure succeeded against every element of the iterator, `try_fold()` returns the final accumulator as success.

Folding is useful whenever you have a collection of something, and want to produce a single value from it.

##### §Note to Implementors

Several of the other (forward) methods have default implementations in terms of this one, so try to implement this explicitly if it can do something better than the default `for` loop implementation.

In particular, try to have this call `try_fold()` on the internal parts from which this iterator is composed. If multiple calls are needed, the `?` operator may be convenient for chaining the accumulator value along, but beware any invariants that need to be upheld before those early returns. This is a `&mut self` method, so iteration needs to be resumable after hitting an error here.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    // the checked sum of all of the elements of the array
    let sum = a.into_iter().try_fold(0i8, |acc, x| acc.checked_add(x));

    assert_eq!(sum, Some(6));

Short-circuiting:

    let a = [10, 20, 30, 100, 40, 50];
    let mut iter = a.into_iter();

    // This sum overflows when adding the 100 element
    let sum = iter.try_fold(0i8, |acc, x| acc.checked_add(x));
    assert_eq!(sum, None);

    // Because it short-circuited, the remaining elements are still
    // available through the iterator.
    assert_eq!(iter.len(), 2);
    assert_eq!(iter.next(), Some(40));

While you cannot `break` from a closure, the `ControlFlow` type allows a similar idea:

    use std::ops::ControlFlow;

    let triangular = (1..30).try_fold(0_i8, |prev, x| {
        if let Some(next) = prev.checked_add(x) {
            ControlFlow::Continue(next)
        } else {
            ControlFlow::Break(prev)
        }
    });
    assert_eq!(triangular, ControlFlow::Break(120));

    let triangular = (1..30).try_fold(0_u64, |prev, x| {
        if let Some(next) = prev.checked_add(x) {
            ControlFlow::Continue(next)
        } else {
            ControlFlow::Break(prev)
        }
    });
    assert_eq!(triangular, ControlFlow::Continue(435));

1.27.0 · Source

#### fn try_for_each<F, R>(&mut self, f: F) -> R
where Self: Sized, F: FnMut(Self::Item) -> R, R: Try<Output = ()>,

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error.

This can also be thought of as the fallible form of `for_each()` or as the stateless version of `try_fold()`.

##### §Examples

    use std::fs::rename;
    use std::io::{stdout, Write};
    use std::path::Path;

    let data = ["no_tea.txt", "stale_bread.json", "torrential_rain.png"];

    let res = data.iter().try_for_each(|x| writeln!(stdout(), "{x}"));
    assert!(res.is_ok());

    let mut it = data.iter().cloned();
    let res = it.try_for_each(|x| rename(x, Path::new(x).with_extension("old")));
    assert!(res.is_err());
    // It short-circuited, so the remaining items are still in the iterator:
    assert_eq!(it.next(), Some("stale_bread.json"));

The `ControlFlow` type can be used with this method for the situations in which you’d use `break` and `continue` in a normal loop:

    use std::ops::ControlFlow;

    let r = (2..100).try_for_each(|x| {
        if 323 % x == 0 {
            return ControlFlow::Break(x)
        }

        ControlFlow::Continue(())
    });
    assert_eq!(r, ControlFlow::Break(17));

1.0.0 · Source

#### fn fold<B, F>(self, init: B, f: F) -> B
where Self: Sized, F: FnMut(B, Self::Item) -> B,

Folds every element into an accumulator by applying an operation, returning the final result.

`fold()` takes two arguments: an initial value, and a closure with two arguments: an ‘accumulator’, and an element. The closure returns the value that the accumulator should have for the next iteration.

The initial value is the value the accumulator will have on the first call.

After applying this closure to every element of the iterator, `fold()` returns the accumulator.

This operation is sometimes called ‘reduce’ or ‘inject’.

Folding is useful whenever you have a collection of something, and want to produce a single value from it.

Note: `fold()`, and similar methods that traverse the entire iterator, might not terminate for infinite iterators, even on traits for which a result is determinable in finite time.

Note: `reduce()` can be used to use the first element as the initial value, if the accumulator type and item type is the same.

Note: `fold()` combines elements in a left-associative fashion. For associative operators like `+`, the order the elements are combined in is not important, but for non-associative operators like `-` the order will affect the final result. For a right-associative version of `fold()`, see `DoubleEndedIterator::rfold()`.

##### §Note to Implementors

Several of the other (forward) methods have default implementations in terms of this one, so try to implement this explicitly if it can do something better than the default `for` loop implementation.

In particular, try to have this call `fold()` on the internal parts from which this iterator is composed.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    // the sum of all of the elements of the array
    let sum = a.iter().fold(0, |acc, x| acc + x);

    assert_eq!(sum, 6);

Let’s walk through each step of the iteration here:

element | acc | x | result
--- | --- | --- | ---
| 0 |  |
1 | 0 | 1 | 1
2 | 1 | 2 | 3
3 | 3 | 3 | 6

And so, our final result, `6`.

This example demonstrates the left-associative nature of `fold()`: it builds a string, starting with an initial value and continuing with each element from the front until the back:

    let numbers = [1, 2, 3, 4, 5];

    let zero = "0".to_string();

    let result = numbers.iter().fold(zero, |acc, &x| {
        format!("({acc} + {x})")
    });

    assert_eq!(result, "(((((0 + 1) + 2) + 3) + 4) + 5)");

It’s common for people who haven’t used iterators a lot to use a `for` loop with a list of things to build up a result. Those can be turned into `fold()`s:

    let numbers = [1, 2, 3, 4, 5];

    let mut result = 0;

    // for loop:
    for i in &numbers {
        result = result + i;
    }

    // fold:
    let result2 = numbers.iter().fold(0, |acc, &x| acc + x);

    // they're the same
    assert_eq!(result, result2);

1.51.0 · Source

#### fn reduce<F>(self, f: F) -> Option<Self::Item>
where Self: Sized, F: FnMut(Self::Item, Self::Item) -> Self::Item,

Reduces the elements to a single one, by repeatedly applying a reducing operation.

If the iterator is empty, returns `None`; otherwise, returns the result of the reduction.

The reducing function is a closure with two arguments: an ‘accumulator’, and an element. For iterators with at least one element, this is the same as `fold()` with the first element of the iterator as the initial accumulator value, folding every subsequent element into it.

##### §Example

    let reduced: i32 = (1..10).reduce(|acc, e| acc + e).unwrap_or(0);
    assert_eq!(reduced, 45);

    // Which is equivalent to doing it with `fold`:
    let folded: i32 = (1..10).fold(0, |acc, e| acc + e);
    assert_eq!(reduced, folded);

Source

#### fn try_reduce<R>( &mut self, f: impl FnMut(Self::Item, Self::Item) -> R, ) -> <<R as Try>::Residual as Residual<Option<<R as Try>::Output>>>::TryType
where Self: Sized, R: Try<Output = Self::Item>, <R as Try>::Residual: Residual<Option<Self::Item>>,

🔬This is a nightly-only experimental API. (`iterator_try_reduce` #87053)

Reduces the elements to a single one by repeatedly applying a reducing operation. If the closure returns a failure, the failure is propagated back to the caller immediately.

The return type of this method depends on the return type of the closure. If the closure returns `Result<Self::Item, E>`, then this function will return `Result<Option<Self::Item>, E>`. If the closure returns `Option<Self::Item>`, then this function will return `Option<Option<Self::Item>>`.

When called on an empty iterator, this function will return either `Some(None)` or `Ok(None)` depending on the type of the provided closure.

For iterators with at least one element, this is essentially the same as calling `try_fold()` with the first element of the iterator as the initial accumulator value.

##### §Examples

Safely calculate the sum of a series of numbers:

    #![feature(iterator_try_reduce)]

    let numbers: Vec<usize> = vec![10, 20, 5, 23, 0];
    let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
    assert_eq!(sum, Some(Some(58)));

Determine when a reduction short circuited:

    #![feature(iterator_try_reduce)]

    let numbers = vec![1, 2, 3, usize::MAX, 4, 5];
    let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
    assert_eq!(sum, None);

Determine when a reduction was not performed because there are no elements:

    #![feature(iterator_try_reduce)]

    let numbers: Vec<usize> = Vec::new();
    let sum = numbers.into_iter().try_reduce(|x, y| x.checked_add(y));
    assert_eq!(sum, Some(None));

Use a `Result` instead of an `Option`:

    #![feature(iterator_try_reduce)]

    let numbers = vec!["1", "2", "3", "4", "5"];
    let max: Result<Option<_>, <usize as std::str::FromStr>::Err> =
        numbers.into_iter().try_reduce(|x, y| {
            if x.parse::<usize>()? > y.parse::<usize>()? { Ok(x) } else { Ok(y) }
        });
    assert_eq!(max, Ok(Some("5")));

1.0.0 · Source

#### fn all<F>(&mut self, f: F) -> bool
where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if every element of the iterator matches a predicate.

`all()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, and if they all return `true`, then so does `all()`. If any of them return `false`, it returns `false`.

`all()` is short-circuiting; in other words, it will stop processing as soon as it finds a `false`, given that no matter what else happens, the result will also be `false`.

An empty iterator returns `true`.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    assert!(a.into_iter().all(|x| x > 0));

    assert!(!a.into_iter().all(|x| x > 2));

Stopping at the first `false`:

    let a = [1, 2, 3];

    let mut iter = a.into_iter();

    assert!(!iter.all(|x| x != 2));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(3));

1.0.0 · Source

#### fn any<F>(&mut self, f: F) -> bool
where Self: Sized, F: FnMut(Self::Item) -> bool,

Tests if any element of the iterator matches a predicate.

`any()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, and if any of them return `true`, then so does `any()`. If they all return `false`, it returns `false`.

`any()` is short-circuiting; in other words, it will stop processing as soon as it finds a `true`, given that no matter what else happens, the result will also be `true`.

An empty iterator returns `false`.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    assert!(a.into_iter().any(|x| x > 0));

    assert!(!a.into_iter().any(|x| x > 5));

Stopping at the first `true`:

    let a = [1, 2, 3];

    let mut iter = a.into_iter();

    assert!(iter.any(|x| x != 2));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(2));

1.0.0 · Source

#### fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
where Self: Sized, P: FnMut(&Self::Item) -> bool,

Searches for an element of an iterator that satisfies a predicate.

`find()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, and if any of them return `true`, then `find()` returns `Some(element)`. If they all return `false`, it returns `None`.

`find()` is short-circuiting; in other words, it will stop processing as soon as the closure returns `true`.

Because `find()` takes a reference, and many iterators iterate over references, this leads to a possibly confusing situation where the argument is a double reference. You can see this effect in the examples below, with `&&x`.

If you need the index of the element, see `position()`.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    assert_eq!(a.into_iter().find(|&x| x == 2), Some(2));
    assert_eq!(a.into_iter().find(|&x| x == 5), None);

Iterating over references:

    let a = [1, 2, 3];

    // `iter()` yields references i.e. `&i32` and `find()` takes a
    // reference to each element.
    assert_eq!(a.iter().find(|&&x| x == 2), Some(&2));
    assert_eq!(a.iter().find(|&&x| x == 5), None);

Stopping at the first `true`:

    let a = [1, 2, 3];

    let mut iter = a.into_iter();

    assert_eq!(iter.find(|&x| x == 2), Some(2));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(3));

Note that `iter.find(f)` is equivalent to `iter.filter(f).next()`.

1.30.0 · Source

#### fn find_map<B, F>(&mut self, f: F) -> Option<B>
where Self: Sized, F: FnMut(Self::Item) -> Option<B>,

Applies function to the elements of iterator and returns the first non-none result.

`iter.find_map(f)` is equivalent to `iter.filter_map(f).next()`.

##### §Examples

    let a = ["lol", "NaN", "2", "5"];

    let first_number = a.iter().find_map(|s| s.parse().ok());

    assert_eq!(first_number, Some(2));

Source

#### fn try_find<R>( &mut self, f: impl FnMut(&Self::Item) -> R, ) -> <<R as Try>::Residual as Residual<Option<Self::Item>>>::TryType
where Self: Sized, R: Try<Output = bool>, <R as Try>::Residual: Residual<Option<Self::Item>>,

🔬This is a nightly-only experimental API. (`try_find` #63178)

Applies function to the elements of iterator and returns the first true result or the first error.

The return type of this method depends on the return type of the closure. If you return `Result<bool, E>` from the closure, you’ll get a `Result<Option<Self::Item>, E>`. If you return `Option<bool>` from the closure, you’ll get an `Option<Option<Self::Item>>`.

##### §Examples

    #![feature(try_find)]

    let a = ["1", "2", "lol", "NaN", "5"];

    let is_my_num = |s: &str, search: i32| -> Result<bool, std::num::ParseIntError> {
        Ok(s.parse::<i32>()? == search)
    };

    let result = a.into_iter().try_find(|&s| is_my_num(s, 2));
    assert_eq!(result, Ok(Some("2")));

    let result = a.into_iter().try_find(|&s| is_my_num(s, 5));
    assert!(result.is_err());

This also supports other types which implement `Try`, not just `Result`.

    #![feature(try_find)]

    use std::num::NonZero;

    let a = [3, 5, 7, 4, 9, 0, 11u32];
    let result = a.into_iter().try_find(|&x| NonZero::new(x).map(|y| y.is_power_of_two()));
    assert_eq!(result, Some(Some(4)));
    let result = a.into_iter().take(3).try_find(|&x| NonZero::new(x).map(|y| y.is_power_of_two()));
    assert_eq!(result, Some(None));
    let result = a.into_iter().rev().try_find(|&x| NonZero::new(x).map(|y| y.is_power_of_two()));
    assert_eq!(result, None);

1.0.0 · Source

#### fn position<P>(&mut self, predicate: P) -> Option<usize>
where Self: Sized, P: FnMut(Self::Item) -> bool,

Searches for an element in an iterator, returning its index.

`position()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, and if one of them returns `true`, then `position()` returns `Some(index)`. If all of them return `false`, it returns `None`.

`position()` is short-circuiting; in other words, it will stop processing as soon as it finds a `true`.

##### §Overflow Behavior

The method does no guarding against overflows, so if there are more than `usize::MAX` non-matching elements, it either produces the wrong result or panics. If overflow checks are enabled, a panic is guaranteed.

##### §Panics

This function might panic if the iterator has more than `usize::MAX` non-matching elements.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    assert_eq!(a.into_iter().position(|x| x == 2), Some(1));

    assert_eq!(a.into_iter().position(|x| x == 5), None);

Stopping at the first `true`:

    let a = [1, 2, 3, 4];

    let mut iter = a.into_iter();

    assert_eq!(iter.position(|x| x >= 2), Some(1));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(3));

    // The returned index depends on iterator state
    assert_eq!(iter.position(|x| x == 4), Some(0));

1.0.0 · Source

#### fn rposition<P>(&mut self, predicate: P) -> Option<usize>
where P: FnMut(Self::Item) -> bool, Self: Sized + ExactSizeIterator + DoubleEndedIterator,

Searches for an element in an iterator from the right, returning its index.

`rposition()` takes a closure that returns `true` or `false`. It applies this closure to each element of the iterator, starting from the end, and if one of them returns `true`, then `rposition()` returns `Some(index)`. If all of them return `false`, it returns `None`.

`rposition()` is short-circuiting; in other words, it will stop processing as soon as it finds a `true`.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    assert_eq!(a.into_iter().rposition(|x| x == 3), Some(2));

    assert_eq!(a.into_iter().rposition(|x| x == 5), None);

Stopping at the first `true`:

    let a = [-1, 2, 3, 4];

    let mut iter = a.into_iter();

    assert_eq!(iter.rposition(|x| x >= 2), Some(3));

    // we can still use `iter`, as there are more elements.
    assert_eq!(iter.next(), Some(-1));
    assert_eq!(iter.next_back(), Some(3));

1.0.0 · Source

#### fn max(self) -> Option<Self::Item>
where Self: Sized, Self::Item: Ord,

Returns the maximum element of an iterator.

If several elements are equally maximum, the last element is returned. If the iterator is empty, `None` is returned.

Note that `f32`/`f64` doesn’t implement `Ord` due to NaN being incomparable. You can work around this by using `Iterator::reduce`:

    assert_eq!(
        [2.4, f32::NAN, 1.3]
            .into_iter()
            .reduce(f32::max)
            .unwrap_or(0.),
        2.4
    );

##### §Examples

    let a = [1, 2, 3];
    let b: [u32; 0] = [];

    assert_eq!(a.into_iter().max(), Some(3));
    assert_eq!(b.into_iter().max(), None);

1.0.0 · Source

#### fn min(self) -> Option<Self::Item>
where Self: Sized, Self::Item: Ord,

Returns the minimum element of an iterator.

If several elements are equally minimum, the first element is returned. If the iterator is empty, `None` is returned.

Note that `f32`/`f64` doesn’t implement `Ord` due to NaN being incomparable. You can work around this by using `Iterator::reduce`:

    assert_eq!(
        [2.4, f32::NAN, 1.3]
            .into_iter()
            .reduce(f32::min)
            .unwrap_or(0.),
        1.3
    );

##### §Examples

    let a = [1, 2, 3];
    let b: [u32; 0] = [];

    assert_eq!(a.into_iter().min(), Some(1));
    assert_eq!(b.into_iter().min(), None);

1.6.0 · Source

#### fn max_by_key<B, F>(self, f: F) -> Option<Self::Item>
where B: Ord, Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the maximum value from the specified function.

If several elements are equally maximum, the last element is returned. If the iterator is empty, `None` is returned.

##### §Examples

    let a = [-3_i32, 0, 1, 5, -10];
    assert_eq!(a.into_iter().max_by_key(|x| x.abs()).unwrap(), -10);

1.15.0 · Source

#### fn max_by<F>(self, compare: F) -> Option<Self::Item>
where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the maximum value with respect to the specified comparison function.

If several elements are equally maximum, the last element is returned. If the iterator is empty, `None` is returned.

##### §Examples

    let a = [-3_i32, 0, 1, 5, -10];
    assert_eq!(a.into_iter().max_by(|x, y| x.cmp(y)).unwrap(), 5);

1.6.0 · Source

#### fn min_by_key<B, F>(self, f: F) -> Option<Self::Item>
where B: Ord, Self: Sized, F: FnMut(&Self::Item) -> B,

Returns the element that gives the minimum value from the specified function.

If several elements are equally minimum, the first element is returned. If the iterator is empty, `None` is returned.

##### §Examples

    let a = [-3_i32, 0, 1, 5, -10];
    assert_eq!(a.into_iter().min_by_key(|x| x.abs()).unwrap(), 0);

1.15.0 · Source

#### fn min_by<F>(self, compare: F) -> Option<Self::Item>
where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the minimum value with respect to the specified comparison function.

If several elements are equally minimum, the first element is returned. If the iterator is empty, `None` is returned.

##### §Examples

    let a = [-3_i32, 0, 1, 5, -10];
    assert_eq!(a.into_iter().min_by(|x, y| x.cmp(y)).unwrap(), -10);

1.0.0 · Source

#### fn rev(self) -> Rev<Self> ⓘ
where Self: Sized + DoubleEndedIterator,

Reverses an iterator’s direction.

Usually, iterators iterate from left to right. After using `rev()`, an iterator will instead iterate from right to left.

This is only possible if the iterator has an end, so `rev()` only works on `DoubleEndedIterator`s.

##### §Examples

    let a = [1, 2, 3];

    let mut iter = a.into_iter().rev();

    assert_eq!(iter.next(), Some(3));
    assert_eq!(iter.next(), Some(2));
    assert_eq!(iter.next(), Some(1));

    assert_eq!(iter.next(), None);

1.0.0 · Source

#### fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB)
where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Sized + Iterator<Item = (A, B)>,

Converts an iterator of pairs into a pair of containers.

`unzip()` consumes an entire iterator of pairs, producing two collections: one from the left elements of the pairs, and one from the right elements.

This function is, in some sense, the opposite of `zip`.

##### §Examples

    let a = [(1, 2), (3, 4), (5, 6)];

    let (left, right): (Vec<_>, Vec<_>) = a.into_iter().unzip();

    assert_eq!(left, [1, 3, 5]);
    assert_eq!(right, [2, 4, 6]);

    // you can also unzip multiple nested tuples at once
    let a = [(1, (2, 3)), (4, (5, 6))];

    let (x, (y, z)): (Vec<_>, (Vec<_>, Vec<_>)) = a.into_iter().unzip();
    assert_eq!(x, [1, 4]);
    assert_eq!(y, [2, 5]);
    assert_eq!(z, [3, 6]);

1.36.0 · Source

#### fn copied<'a, T>(self) -> Copied<Self> ⓘ
where T: Copy + 'a, Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which copies all of its elements.

This is useful when you have an iterator over `&T`, but you need an iterator over `T`.

##### §Examples

    let a = [1, 2, 3];

    let v_copied: Vec<_> = a.iter().copied().collect();

    // copied is the same as .map(|&x| x)
    let v_map: Vec<_> = a.iter().map(|&x| x).collect();

    assert_eq!(v_copied, [1, 2, 3]);
    assert_eq!(v_map, [1, 2, 3]);

1.0.0 · Source

#### fn cloned<'a, T>(self) -> Cloned<Self> ⓘ
where T: Clone + 'a, Self: Sized + Iterator<Item = &'a T>,

Creates an iterator which `clone`s all of its elements.

This is useful when you have an iterator over `&T`, but you need an iterator over `T`.

There is no guarantee whatsoever about the `clone` method actually being called or optimized away. So code should not depend on either.

##### §Examples

Basic usage:

    let a = [1, 2, 3];

    let v_cloned: Vec<_> = a.iter().cloned().collect();

    // cloned is the same as .map(|&x| x), for integers
    let v_map: Vec<_> = a.iter().map(|&x| x).collect();

    assert_eq!(v_cloned, [1, 2, 3]);
    assert_eq!(v_map, [1, 2, 3]);

To get the best performance, try to clone late:

    let a = [vec![0_u8, 1, 2], vec![3, 4], vec![23]];
    // don't do this:
    let slower: Vec<_> = a.iter().cloned().filter(|s| s.len() == 1).collect();
    assert_eq!(&[vec![23]], &slower[..]);
    // instead call `cloned` late
    let faster: Vec<_> = a.iter().filter(|s| s.len() == 1).cloned().collect();
    assert_eq!(&[vec![23]], &faster[..]);

1.0.0 · Source

#### fn cycle(self) -> Cycle<Self> ⓘ
where Self: Sized + Clone,

Repeats an iterator endlessly.

Instead of stopping at `None`, the iterator will instead start again, from the beginning. After iterating again, it will start at the beginning again. And again. And again. Forever. Note that in case the original iterator is empty, the resulting iterator will also be empty.

##### §Examples

    let a = [1, 2, 3];

    let mut iter = a.into_iter().cycle();

    loop {
        assert_eq!(iter.next(), Some(1));
        assert_eq!(iter.next(), Some(2));
        assert_eq!(iter.next(), Some(3));
    }

Source

#### fn array_chunks<const N: usize>(self) -> ArrayChunks<Self, N> ⓘ
where Self: Sized,

🔬This is a nightly-only experimental API. (`iter_array_chunks` #100450)

Returns an iterator over `N` elements of the iterator at a time.

The chunks do not overlap. If `N` does not divide the length of the iterator, then the last up to `N-1` elements will be omitted and can be retrieved from the `.into_remainder()` function of the iterator.

##### §Panics

Panics if `N` is zero.

##### §Examples

Basic usage:

    #![feature(iter_array_chunks)]

    let mut iter = "lorem".chars().array_chunks();
    assert_eq!(iter.next(), Some(['l', 'o']));
    assert_eq!(iter.next(), Some(['r', 'e']));
    assert_eq!(iter.next(), None);
    assert_eq!(iter.into_remainder().as_slice(), &['m']);

    #![feature(iter_array_chunks)]

    let data = [1, 1, 2, -2, 6, 0, 3, 1];
    //          ^-----^  ^------^
    for [x, y, z] in data.iter().array_chunks() {
        assert_eq!(x + y + z, 4);
    }

1.11.0 · Source

#### fn sum<S>(self) -> S
where Self: Sized, S: Sum<Self::Item>,

Sums the elements of an iterator.

Takes each element, adds them together, and returns the result.

An empty iterator returns the additive identity (“zero”) of the type, which is `0` for integers and `-0.0` for floats.

`sum()` can be used to sum any type implementing `Sum`, including `Option` and `Result`.

##### §Panics

When calling `sum()` and a primitive integer type is being returned, this method will panic if the computation overflows and overflow checks are enabled.

##### §Examples

    let a = [1, 2, 3];
    let sum: i32 = a.iter().sum();

    assert_eq!(sum, 6);

    let b: Vec<f32> = vec![];
    let sum: f32 = b.iter().sum();
    assert_eq!(sum, -0.0_f32);

1.11.0 · Source

#### fn product<P>(self) -> P
where Self: Sized, P: Product<Self::Item>,

Iterates over the entire iterator, multiplying all the elements

An empty iterator returns the one value of the type.

`product()` can be used to multiply any type implementing `Product`, including `Option` and `Result`.

##### §Panics

When calling `product()` and a primitive integer type is being returned, method will panic if the computation overflows and overflow checks are enabled.

##### §Examples

    fn factorial(n: u32) -> u32 {
        (1..=n).product()
    }
    assert_eq!(factorial(0), 1);
    assert_eq!(factorial(1), 1);
    assert_eq!(factorial(5), 120);

1.5.0 · Source

#### fn cmp<I>(self, other: I) -> Ordering
where I: IntoIterator<Item = Self::Item>, Self::Item: Ord, Self: Sized,

Lexicographically compares the elements of this `Iterator` with those of another.

##### §Examples

    use std::cmp::Ordering;

    assert_eq!([1].iter().cmp([1].iter()), Ordering::Equal);
    assert_eq!([1].iter().cmp([1, 2].iter()), Ordering::Less);
    assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater);

Source

#### fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering
where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Ordering,

🔬This is a nightly-only experimental API. (`iter_order_by` #64295)

Lexicographically compares the elements of this `Iterator` with those of another with respect to the specified comparison function.

##### §Examples

    #![feature(iter_order_by)]

    use std::cmp::Ordering;

    let xs = [1, 2, 3, 4];
    let ys = [1, 4, 9, 16];

    assert_eq!(xs.into_iter().cmp_by(ys, |x, y| x.cmp(&y)), Ordering::Less);
    assert_eq!(xs.into_iter().cmp_by(ys, |x, y| (x * x).cmp(&y)), Ordering::Equal);
    assert_eq!(xs.into_iter().cmp_by(ys, |x, y| (2 * x).cmp(&y)), Ordering::Greater);

1.5.0 · Source

#### fn partial_cmp<I>(self, other: I) -> Option<Ordering>
where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Lexicographically compares the `PartialOrd` elements of this `Iterator` with those of another. The comparison works like short-circuit evaluation, returning a result without comparing the remaining elements. As soon as an order can be determined, the evaluation stops and a result is returned.

##### §Examples

    use std::cmp::Ordering;

    assert_eq!([1.].iter().partial_cmp([1.].iter()), Some(Ordering::Equal));
    assert_eq!([1.].iter().partial_cmp([1., 2.].iter()), Some(Ordering::Less));
    assert_eq!([1., 2.].iter().partial_cmp([1.].iter()), Some(Ordering::Greater));

For floating-point numbers, NaN does not have a total order and will result in `None` when compared:

    assert_eq!([f64::NAN].iter().partial_cmp([1.].iter()), None);

The results are determined by the order of evaluation.

    use std::cmp::Ordering;

    assert_eq!([1.0, f64::NAN].iter().partial_cmp([2.0, f64::NAN].iter()), Some(Ordering::Less));
    assert_eq!([2.0, f64::NAN].iter().partial_cmp([1.0, f64::NAN].iter()), Some(Ordering::Greater));
    assert_eq!([f64::NAN, 1.0].iter().partial_cmp([f64::NAN, 2.0].iter()), None);

Source

#### fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering>
where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering>,

🔬This is a nightly-only experimental API. (`iter_order_by` #64295)

Lexicographically compares the elements of this `Iterator` with those of another with respect to the specified comparison function.

##### §Examples

    #![feature(iter_order_by)]

    use std::cmp::Ordering;

    let xs = [1.0, 2.0, 3.0, 4.0];
    let ys = [1.0, 4.0, 9.0, 16.0];

    assert_eq!(
        xs.iter().partial_cmp_by(ys, |x, y| x.partial_cmp(&y)),
        Some(Ordering::Less)
    );
    assert_eq!(
        xs.iter().partial_cmp_by(ys, |x, y| (x * x).partial_cmp(&y)),
        Some(Ordering::Equal)
    );
    assert_eq!(
        xs.iter().partial_cmp_by(ys, |x, y| (2.0 * x).partial_cmp(&y)),
        Some(Ordering::Greater)
    );

1.5.0 · Source

#### fn eq<I>(self, other: I) -> bool
where I: IntoIterator, Self::Item: PartialEq<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are equal to those of another.

##### §Examples

    assert_eq!([1].iter().eq([1].iter()), true);
    assert_eq!([1].iter().eq([1, 2].iter()), false);

Source

#### fn eq_by<I, F>(self, other: I, eq: F) -> bool
where Self: Sized, I: IntoIterator, F: FnMut(Self::Item, <I as IntoIterator>::Item) -> bool,

🔬This is a nightly-only experimental API. (`iter_order_by` #64295)

Determines if the elements of this `Iterator` are equal to those of another with respect to the specified equality function.

##### §Examples

    #![feature(iter_order_by)]

    let xs = [1, 2, 3, 4];
    let ys = [1, 4, 9, 16];

    assert!(xs.iter().eq_by(ys, |x, y| x * x == y));

1.5.0 · Source

#### fn ne<I>(self, other: I) -> bool
where I: IntoIterator, Self::Item: PartialEq<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are not equal to those of another.

##### §Examples

    assert_eq!([1].iter().ne([1].iter()), false);
    assert_eq!([1].iter().ne([1, 2].iter()), true);

1.5.0 · Source

#### fn lt<I>(self, other: I) -> bool
where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are lexicographically less than those of another.

##### §Examples

    assert_eq!([1].iter().lt([1].iter()), false);
    assert_eq!([1].iter().lt([1, 2].iter()), true);
    assert_eq!([1, 2].iter().lt([1].iter()), false);
    assert_eq!([1, 2].iter().lt([1, 2].iter()), false);

1.5.0 · Source

#### fn le<I>(self, other: I) -> bool
where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are lexicographically less or equal to those of another.

##### §Examples

    assert_eq!([1].iter().le([1].iter()), true);
    assert_eq!([1].iter().le([1, 2].iter()), true);
    assert_eq!([1, 2].iter().le([1].iter()), false);
    assert_eq!([1, 2].iter().le([1, 2].iter()), true);

1.5.0 · Source

#### fn gt<I>(self, other: I) -> bool
where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are lexicographically greater than those of another.

##### §Examples

    assert_eq!([1].iter().gt([1].iter()), false);
    assert_eq!([1].iter().gt([1, 2].iter()), false);
    assert_eq!([1, 2].iter().gt([1].iter()), true);
    assert_eq!([1, 2].iter().gt([1, 2].iter()), false);

1.5.0 · Source

#### fn ge<I>(self, other: I) -> bool
where I: IntoIterator, Self::Item: PartialOrd<<I as IntoIterator>::Item>, Self: Sized,

Determines if the elements of this `Iterator` are lexicographically greater than or equal to those of another.

##### §Examples

    assert_eq!([1].iter().ge([1].iter()), true);
    assert_eq!([1].iter().ge([1, 2].iter()), false);
    assert_eq!([1, 2].iter().ge([1].iter()), true);
    assert_eq!([1, 2].iter().ge([1, 2].iter()), true);

1.82.0 · Source

#### fn is_sorted(self) -> bool
where Self: Sized, Self::Item: PartialOrd,

Checks if the elements of this iterator are sorted.

That is, for each element `a` and its following element `b`, `a <= b` must hold. If the iterator yields exactly zero or one element, `true` is returned.

Note that if `Self::Item` is only `PartialOrd`, but not `Ord`, the above definition implies that this function returns `false` if any two consecutive items are not comparable.

##### §Examples

    assert!([1, 2, 2, 9].iter().is_sorted());
    assert!(![1, 3, 2, 4].iter().is_sorted());
    assert!([0].iter().is_sorted());
    assert!(std::iter::empty::<i32>().is_sorted());
    assert!(![0.0, 1.0, f32::NAN].iter().is_sorted());

1.82.0 · Source

#### fn is_sorted_by<F>(self, compare: F) -> bool
where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> bool,

Checks if the elements of this iterator are sorted using the given comparator function.

Instead of using `PartialOrd::partial_cmp`, this function uses the given `compare` function to determine whether two elements are to be considered in sorted order.

##### §Examples

    assert!([1, 2, 2, 9].iter().is_sorted_by(|a, b| a <= b));
    assert!(![1, 2, 2, 9].iter().is_sorted_by(|a, b| a < b));

    assert!([0].iter().is_sorted_by(|a, b| true));
    assert!([0].iter().is_sorted_by(|a, b| false));

    assert!(std::iter::empty::<i32>().is_sorted_by(|a, b| false));
    assert!(std::iter::empty::<i32>().is_sorted_by(|a, b| true));

1.82.0 · Source

#### fn is_sorted_by_key<F, K>(self, f: F) -> bool
where Self: Sized, F: FnMut(Self::Item) -> K, K: PartialOrd,

Checks if the elements of this iterator are sorted using the given key extraction function.

Instead of comparing the iterator’s elements directly, this function compares the keys of the elements, as determined by `f`. Apart from that, it’s equivalent to `is_sorted`; see its documentation for more information.

##### §Examples

    assert!(["c", "bb", "aaa"].iter().is_sorted_by_key(|s| s.len()));
    assert!(![-2i32, -1, 0, 3].iter().is_sorted_by_key(|n| n.abs()));

## Implementors§

1.80.0 · Source§

### impl<'a, I, A> !Iterator for &'a Box<[I], A>
where A: Allocator,

This implementation is required to make sure that the `&Box<[I]>: IntoIterator` implementation doesn’t overlap with `IntoIterator for T where T: Iterator` blanket.

1.80.0 · Source§

### impl<'a, I, A> !Iterator for &'a mut Box<[I], A>
where A: Allocator,

This implementation is required to make sure that the `&mut Box<[I]>: IntoIterator` implementation doesn’t overlap with `IntoIterator for T where T: Iterator` blanket.

1.80.0 · Source§

### impl<I, A> !Iterator for Box<[I], A>
where A: Allocator,

This implementation is required to make sure that the `Box<[I]>: IntoIterator` implementation doesn’t overlap with `IntoIterator for T where T: Iterator` blanket.

1.80.0 · Source§

### impl<T> !Iterator for [T]

Source§

### impl Iterator for core::ffi::c_str::Bytes<'_>

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#### type Item = u8

1.0.0 · Source§

### impl Iterator for std::ascii::EscapeDefault

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#### type Item = u8

1.20.0 · Source§

### impl Iterator for std::char::EscapeDebug

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#### type Item = char

1.0.0 · Source§

### impl Iterator for std::char::EscapeDefault

Source§

#### type Item = char

1.0.0 · Source§

### impl Iterator for std::char::EscapeUnicode

Source§

#### type Item = char

1.0.0 · Source§

### impl Iterator for ToLowercase

Source§

#### type Item = char

1.0.0 · Source§

### impl Iterator for ToUppercase

Source§

#### type Item = char

1.0.0 · Source§

### impl Iterator for Args

Source§

#### type Item = String

1.0.0 · Source§

### impl Iterator for ArgsOs

Source§

#### type Item = OsString

1.0.0 · Source§

### impl Iterator for Vars

Source§

#### type Item = (String, String)

1.0.0 · Source§

### impl Iterator for VarsOs

Source§

#### type Item = (OsString, OsString)

1.0.0 · Source§

### impl Iterator for ReadDir

Source§

#### type Item = Result<DirEntry, Error>

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### impl Iterator for IntoIncoming

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#### type Item = Result<TcpStream, Error>

1.0.0 · Source§

### impl Iterator for std::str::Bytes<'_>

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#### type Item = u8

1.6.0 · Source§

### impl Iterator for std::string::Drain<'_>

Source§

#### type Item = char

Source§

### impl Iterator for IntoChars

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#### type Item = char

Source§

### impl<'a> Iterator for Source<'a>

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#### type Item = &'a (dyn Error + 'static)

1.0.0 · Source§

### impl<'a> Iterator for SplitPaths<'a>

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#### type Item = PathBuf

1.0.0 · Source§

### impl<'a> Iterator for Incoming<'a>

Source§

#### type Item = Result<TcpStream, Error>

1.28.0 · Source§

### impl<'a> Iterator for Ancestors<'a>

Source§

#### type Item = &'a Path

1.0.0 · Source§

### impl<'a> Iterator for Components<'a>

Source§

#### type Item = Component<'a>

1.0.0 · Source§

### impl<'a> Iterator for std::path::Iter<'a>

Source§

#### type Item = &'a OsStr

1.57.0 · Source§

### impl<'a> Iterator for CommandArgs<'a>

Source§

#### type Item = &'a OsStr

1.57.0 · Source§

### impl<'a> Iterator for CommandEnvs<'a>

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#### type Item = (&'a OsStr, Option<&'a OsStr>)

1.60.0 · Source§

### impl<'a> Iterator for EscapeAscii<'a>

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#### type Item = u8

1.0.0 · Source§

### impl<'a> Iterator for CharIndices<'a>

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#### type Item = (usize, char)

1.0.0 · Source§

### impl<'a> Iterator for Chars<'a>

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#### type Item = char

1.8.0 · Source§

### impl<'a> Iterator for EncodeUtf16<'a>

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#### type Item = u16

1.34.0 · Source§

### impl<'a> Iterator for std::str::EscapeDebug<'a>

Source§

#### type Item = char

1.34.0 · Source§

### impl<'a> Iterator for std::str::EscapeDefault<'a>

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#### type Item = char

1.34.0 · Source§

### impl<'a> Iterator for std::str::EscapeUnicode<'a>

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#### type Item = char

1.0.0 · Source§

### impl<'a> Iterator for std::str::Lines<'a>

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#### type Item = &'a str

1.0.0 · Source§

### impl<'a> Iterator for LinesAny<'a>

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#### type Item = &'a str

1.34.0 · Source§

### impl<'a> Iterator for SplitAsciiWhitespace<'a>

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#### type Item = &'a str

1.1.0 · Source§

### impl<'a> Iterator for SplitWhitespace<'a>

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#### type Item = &'a str

1.79.0 · Source§

### impl<'a> Iterator for Utf8Chunks<'a>

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#### type Item = Utf8Chunk<'a>

1.0.0 · Source§

### impl<'a, A> Iterator for std::option::Iter<'a, A>

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#### type Item = &'a A

1.0.0 · Source§

### impl<'a, A> Iterator for std::option::IterMut<'a, A>

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#### type Item = &'a mut A

1.1.0 · Source§

### impl<'a, I, T> Iterator for Cloned<I>
where T: 'a + Clone, I: Iterator<Item = &'a T>,

Source§

#### type Item = T

1.36.0 · Source§

### impl<'a, I, T> Iterator for Copied<I>
where T: 'a + Copy, I: Iterator<Item = &'a T>,

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#### type Item = T

1.0.0 · Source§

### impl<'a, K> Iterator for std::collections::hash_set::Iter<'a, K>

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#### type Item = &'a K

1.0.0 · Source§

### impl<'a, K, A: Allocator> Iterator for std::collections::hash_set::Drain<'a, K, A>

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#### type Item = K

1.0.0 · Source§

### impl<'a, K, V> Iterator for std::collections::btree_map::Iter<'a, K, V>
where K: 'a, V: 'a,

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#### type Item = (&'a K, &'a V)

1.0.0 · Source§

### impl<'a, K, V> Iterator for std::collections::btree_map::IterMut<'a, K, V>

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#### type Item = (&'a K, &'a mut V)

1.0.0 · Source§

### impl<'a, K, V> Iterator for std::collections::btree_map::Keys<'a, K, V>

Source§

#### type Item = &'a K

1.17.0 · Source§

### impl<'a, K, V> Iterator for std::collections::btree_map::Range<'a, K, V>

Source§

#### type Item = (&'a K, &'a V)

1.17.0 · Source§

### impl<'a, K, V> Iterator for RangeMut<'a, K, V>

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#### type Item = (&'a K, &'a mut V)

1.0.0 · Source§

### impl<'a, K, V> Iterator for std::collections::btree_map::Values<'a, K, V>

Source§

#### type Item = &'a V

1.10.0 · Source§

### impl<'a, K, V> Iterator for std::collections::btree_map::ValuesMut<'a, K, V>

Source§

#### type Item = &'a mut V

1.0.0 · Source§

### impl<'a, K, V> Iterator for std::collections::hash_map::Iter<'a, K, V>

Source§

#### type Item = (&'a K, &'a V)

1.0.0 · Source§

### impl<'a, K, V> Iterator for std::collections::hash_map::IterMut<'a, K, V>

Source§

#### type Item = (&'a K, &'a mut V)

1.0.0 · Source§

### impl<'a, K, V> Iterator for std::collections::hash_map::Keys<'a, K, V>

Source§

#### type Item = &'a K

1.0.0 · Source§

### impl<'a, K, V> Iterator for std::collections::hash_map::Values<'a, K, V>

Source§

#### type Item = &'a V

1.10.0 · Source§

### impl<'a, K, V> Iterator for std::collections::hash_map::ValuesMut<'a, K, V>

Source§

#### type Item = &'a mut V

1.6.0 · Source§

### impl<'a, K, V, A: Allocator> Iterator for std::collections::hash_map::Drain<'a, K, V, A>

Source§

#### type Item = (K, V)

1.5.0 · Source§

### impl<'a, P> Iterator for MatchIndices<'a, P>
where P: Pattern,

Source§

#### type Item = (usize, &'a str)

1.2.0 · Source§

### impl<'a, P> Iterator for Matches<'a, P>
where P: Pattern,

Source§

#### type Item = &'a str

1.5.0 · Source§

### impl<'a, P> Iterator for RMatchIndices<'a, P>
where P: Pattern, <P as Pattern>::Searcher<'a>: ReverseSearcher<'a>,

Source§

#### type Item = (usize, &'a str)

1.2.0 · Source§

### impl<'a, P> Iterator for RMatches<'a, P>
where P: Pattern, <P as Pattern>::Searcher<'a>: ReverseSearcher<'a>,

Source§

#### type Item = &'a str

1.0.0 · Source§

### impl<'a, P> Iterator for std::str::RSplit<'a, P>
where P: Pattern, <P as Pattern>::Searcher<'a>: ReverseSearcher<'a>,

Source§

#### type Item = &'a str

1.0.0 · Source§

### impl<'a, P> Iterator for std::str::RSplitN<'a, P>
where P: Pattern, <P as Pattern>::Searcher<'a>: ReverseSearcher<'a>,

Source§

#### type Item = &'a str

1.0.0 · Source§

### impl<'a, P> Iterator for RSplitTerminator<'a, P>
where P: Pattern, <P as Pattern>::Searcher<'a>: ReverseSearcher<'a>,

Source§

#### type Item = &'a str

1.0.0 · Source§

### impl<'a, P> Iterator for std::str::Split<'a, P>
where P: Pattern,

Source§

#### type Item = &'a str

1.51.0 · Source§

### impl<'a, P> Iterator for std::str::SplitInclusive<'a, P>
where P: Pattern,

Source§

#### type Item = &'a str

1.0.0 · Source§

### impl<'a, P> Iterator for std::str::SplitN<'a, P>
where P: Pattern,

Source§

#### type Item = &'a str

1.0.0 · Source§

### impl<'a, P> Iterator for SplitTerminator<'a, P>
where P: Pattern,

Source§

#### type Item = &'a str

1.0.0 · Source§

### impl<'a, T> Iterator for std::collections::binary_heap::Iter<'a, T>

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T> Iterator for std::collections::btree_set::Iter<'a, T>

Source§

#### type Item = &'a T

1.17.0 · Source§

### impl<'a, T> Iterator for std::collections::btree_set::Range<'a, T>

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T> Iterator for std::collections::btree_set::SymmetricDifference<'a, T>
where T: Ord,

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T> Iterator for std::collections::btree_set::Union<'a, T>
where T: Ord,

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T> Iterator for std::collections::linked_list::Iter<'a, T>

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T> Iterator for std::collections::linked_list::IterMut<'a, T>

Source§

#### type Item = &'a mut T

1.0.0 · Source§

### impl<'a, T> Iterator for std::collections::vec_deque::Iter<'a, T>

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T> Iterator for std::collections::vec_deque::IterMut<'a, T>

Source§

#### type Item = &'a mut T

1.0.0 · Source§

### impl<'a, T> Iterator for std::result::Iter<'a, T>

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T> Iterator for std::result::IterMut<'a, T>

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#### type Item = &'a mut T

1.0.0 · Source§

### impl<'a, T> Iterator for Chunks<'a, T>

Source§

#### type Item = &'a [T]

1.31.0 · Source§

### impl<'a, T> Iterator for ChunksExact<'a, T>

Source§

#### type Item = &'a [T]

1.31.0 · Source§

### impl<'a, T> Iterator for ChunksExactMut<'a, T>

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#### type Item = &'a mut [T]

1.0.0 · Source§

### impl<'a, T> Iterator for ChunksMut<'a, T>

Source§

#### type Item = &'a mut [T]

1.0.0 · Source§

### impl<'a, T> Iterator for std::slice::Iter<'a, T>

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T> Iterator for std::slice::IterMut<'a, T>

Source§

#### type Item = &'a mut T

1.31.0 · Source§

### impl<'a, T> Iterator for RChunks<'a, T>

Source§

#### type Item = &'a [T]

1.31.0 · Source§

### impl<'a, T> Iterator for RChunksExact<'a, T>

Source§

#### type Item = &'a [T]

1.31.0 · Source§

### impl<'a, T> Iterator for RChunksExactMut<'a, T>

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#### type Item = &'a mut [T]

1.31.0 · Source§

### impl<'a, T> Iterator for RChunksMut<'a, T>

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#### type Item = &'a mut [T]

1.0.0 · Source§

### impl<'a, T> Iterator for Windows<'a, T>

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#### type Item = &'a [T]

Source§

### impl<'a, T> Iterator for std::sync::mpmc::Iter<'a, T>

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#### type Item = T

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### impl<'a, T> Iterator for std::sync::mpmc::TryIter<'a, T>

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#### type Item = T

1.0.0 · Source§

### impl<'a, T> Iterator for std::sync::mpsc::Iter<'a, T>

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#### type Item = T

1.15.0 · Source§

### impl<'a, T> Iterator for std::sync::mpsc::TryIter<'a, T>

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#### type Item = T

1.0.0 · Source§

### impl<'a, T, A> Iterator for std::collections::btree_set::Difference<'a, T, A>
where T: Ord, A: Allocator + Clone,

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#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T, A> Iterator for std::collections::btree_set::Intersection<'a, T, A>
where T: Ord, A: Allocator + Clone,

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#### type Item = &'a T

1.77.0 · Source§

### impl<'a, T, P> Iterator for ChunkBy<'a, T, P>
where T: 'a, P: FnMut(&T, &T) -> bool,

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#### type Item = &'a [T]

1.77.0 · Source§

### impl<'a, T, P> Iterator for ChunkByMut<'a, T, P>
where T: 'a, P: FnMut(&T, &T) -> bool,

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#### type Item = &'a mut [T]

1.27.0 · Source§

### impl<'a, T, P> Iterator for std::slice::RSplit<'a, T, P>
where P: FnMut(&T) -> bool,

Source§

#### type Item = &'a [T]

1.27.0 · Source§

### impl<'a, T, P> Iterator for RSplitMut<'a, T, P>
where P: FnMut(&T) -> bool,

Source§

#### type Item = &'a mut [T]

1.0.0 · Source§

### impl<'a, T, P> Iterator for std::slice::RSplitN<'a, T, P>
where P: FnMut(&T) -> bool,

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#### type Item = &'a [T]

1.0.0 · Source§

### impl<'a, T, P> Iterator for RSplitNMut<'a, T, P>
where P: FnMut(&T) -> bool,

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#### type Item = &'a mut [T]

1.0.0 · Source§

### impl<'a, T, P> Iterator for std::slice::Split<'a, T, P>
where P: FnMut(&T) -> bool,

Source§

#### type Item = &'a [T]

1.51.0 · Source§

### impl<'a, T, P> Iterator for std::slice::SplitInclusive<'a, T, P>
where P: FnMut(&T) -> bool,

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#### type Item = &'a [T]

1.51.0 · Source§

### impl<'a, T, P> Iterator for SplitInclusiveMut<'a, T, P>
where P: FnMut(&T) -> bool,

Source§

#### type Item = &'a mut [T]

1.0.0 · Source§

### impl<'a, T, P> Iterator for SplitMut<'a, T, P>
where P: FnMut(&T) -> bool,

Source§

#### type Item = &'a mut [T]

1.0.0 · Source§

### impl<'a, T, P> Iterator for std::slice::SplitN<'a, T, P>
where P: FnMut(&T) -> bool,

Source§

#### type Item = &'a [T]

1.0.0 · Source§

### impl<'a, T, P> Iterator for SplitNMut<'a, T, P>
where P: FnMut(&T) -> bool,

Source§

#### type Item = &'a mut [T]

1.0.0 · Source§

### impl<'a, T, S, A> Iterator for std::collections::hash_set::Difference<'a, T, S, A>
where T: Eq + Hash, S: BuildHasher, A: Allocator,

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T, S, A> Iterator for std::collections::hash_set::Intersection<'a, T, S, A>
where T: Eq + Hash, S: BuildHasher, A: Allocator,

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T, S, A> Iterator for std::collections::hash_set::SymmetricDifference<'a, T, S, A>
where T: Eq + Hash, S: BuildHasher, A: Allocator,

Source§

#### type Item = &'a T

1.0.0 · Source§

### impl<'a, T, S, A> Iterator for std::collections::hash_set::Union<'a, T, S, A>
where T: Eq + Hash, S: BuildHasher, A: Allocator,

Source§

#### type Item = &'a T

1.94.0 · Source§

### impl<'a, T, const N: usize> Iterator for ArrayWindows<'a, T, N>

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#### type Item = &'a [T; N]

1.0.0 · Source§

### impl<A> Iterator for std::ops::Range<A>
where A: Step,

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#### type Item = A

1.0.0 · Source§

### impl<A> Iterator for RangeFrom<A>
where A: Step,

Source§

#### type Item = A

1.26.0 · Source§

### impl<A> Iterator for RangeInclusive<A>
where A: Step,

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#### type Item = A

1.0.0 · Source§

### impl<A> Iterator for std::option::IntoIter<A>

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#### type Item = A

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### impl<A> Iterator for OptionFlatten<A>
where A: Iterator,

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#### type Item = <A as Iterator>::Item

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### impl<A> Iterator for RangeFromIter<A>
where A: Step,

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#### type Item = A

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### impl<A> Iterator for RangeInclusiveIter<A>
where A: Step,

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#### type Item = A

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### impl<A> Iterator for RangeIter<A>
where A: Step,

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#### type Item = A

1.0.0 · Source§

### impl<A> Iterator for Repeat<A>
where A: Clone,

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#### type Item = A

1.82.0 · Source§

### impl<A> Iterator for RepeatN<A>
where A: Clone,

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#### type Item = A

1.0.0 · Source§

### impl<A, B> Iterator for Chain<A, B>
where A: Iterator, B: Iterator<Item = <A as Iterator>::Item>,

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#### type Item = <A as Iterator>::Item

1.0.0 · Source§

### impl<A, B> Iterator for Zip<A, B>
where A: Iterator, B: Iterator,

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#### type Item = (<A as Iterator>::Item, <B as Iterator>::Item)

1.43.0 · Source§

### impl<A, F> Iterator for OnceWith<F>
where F: FnOnce() -> A,

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#### type Item = A

1.28.0 · Source§

### impl<A, F> Iterator for RepeatWith<F>
where F: FnMut() -> A,

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#### type Item = A

1.0.0 · Source§

### impl<B, I, F> Iterator for FilterMap<I, F>
where I: Iterator, F: FnMut(<I as Iterator>::Item) -> Option<B>,

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#### type Item = B

1.0.0 · Source§

### impl<B, I, F> Iterator for Map<I, F>
where I: Iterator, F: FnMut(<I as Iterator>::Item) -> B,

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#### type Item = B

1.57.0 · Source§

### impl<B, I, P> Iterator for MapWhile<I, P>
where I: Iterator, P: FnMut(<I as Iterator>::Item) -> Option<B>,

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#### type Item = B

1.0.0 · Source§

### impl<B, I, St, F> Iterator for Scan<I, St, F>
where I: Iterator, F: FnMut(&mut St, <I as Iterator>::Item) -> Option<B>,

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#### type Item = B

1.0.0 · Source§

### impl<B: BufRead> Iterator for std::io::Lines<B>

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#### type Item = Result<String, Error>

1.0.0 · Source§

### impl<B: BufRead> Iterator for std::io::Split<B>

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#### type Item = Result<Vec<u8>, Error>

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### impl<G> Iterator for FromCoroutine<G>
where G: Coroutine<Return = ()> + Unpin,

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#### type Item = <G as Coroutine>::Yield

1.0.0 · Source§

### impl<I> Iterator for &mut I
where I: Iterator + ?Sized,

Implements `Iterator` for mutable references to iterators, such as those produced by `Iterator::by_ref`.

This implementation passes all method calls on to the original iterator.

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#### type Item = <I as Iterator>::Item

1.9.0 · Source§

### impl<I> Iterator for DecodeUtf16<I>
where I: Iterator<Item = u16>,

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#### type Item = Result<char, DecodeUtf16Error>

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### impl<I> Iterator for ByRefSized<'_, I>
where I: Iterator,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I> Iterator for Cycle<I>
where I: Clone + Iterator,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I> Iterator for Enumerate<I>
where I: Iterator,

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#### type Item = (usize, <I as Iterator>::Item)

1.0.0 · Source§

### impl<I> Iterator for Fuse<I>
where I: Iterator,

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#### type Item = <I as Iterator>::Item

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### impl<I> Iterator for Intersperse<I>
where I: Iterator, <I as Iterator>::Item: Clone,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I> Iterator for Peekable<I>
where I: Iterator,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I> Iterator for Rev<I>
where I: DoubleEndedIterator,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I> Iterator for Skip<I>
where I: Iterator,

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#### type Item = <I as Iterator>::Item

1.28.0 · Source§

### impl<I> Iterator for StepBy<I>
where I: Iterator,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I> Iterator for Take<I>
where I: Iterator,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I, A> Iterator for Box<I, A>
where I: Iterator + ?Sized, A: Allocator,

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#### type Item = <I as Iterator>::Item

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### impl<I, A> Iterator for std::collections::vec_deque::Splice<'_, I, A>
where I: Iterator, A: Allocator,

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#### type Item = <I as Iterator>::Item

1.21.0 · Source§

### impl<I, A> Iterator for std::vec::Splice<'_, I, A>
where I: Iterator, A: Allocator,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I, F> Iterator for Inspect<I, F>
where I: Iterator, F: FnMut(&<I as Iterator>::Item),

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#### type Item = <I as Iterator>::Item

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### impl<I, F, R, const N: usize> Iterator for MapWindows<I, F, N>
where I: Iterator, F: FnMut(&[<I as Iterator>::Item; N]) -> R,

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#### type Item = R

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### impl<I, G> Iterator for IntersperseWith<I, G>
where I: Iterator, G: FnMut() -> <I as Iterator>::Item,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I, P> Iterator for Filter<I, P>
where I: Iterator, P: FnMut(&<I as Iterator>::Item) -> bool,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I, P> Iterator for SkipWhile<I, P>
where I: Iterator, P: FnMut(&<I as Iterator>::Item) -> bool,

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#### type Item = <I as Iterator>::Item

1.0.0 · Source§

### impl<I, P> Iterator for TakeWhile<I, P>
where I: Iterator, P: FnMut(&<I as Iterator>::Item) -> bool,

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#### type Item = <I as Iterator>::Item

1.29.0 · Source§

### impl<I, U> Iterator for Flatten<I>
where I: Iterator, <I as Iterator>::Item: IntoIterator<IntoIter = U, Item = <U as Iterator>::Item>, U: Iterator,

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#### type Item = <U as Iterator>::Item

1.0.0 · Source§

### impl<I, U, F> Iterator for FlatMap<I, U, F>
where I: Iterator, U: IntoIterator, F: FnMut(<I as Iterator>::Item) -> U,

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#### type Item = <U as IntoIterator>::Item

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### impl<I, const N: usize> Iterator for ArrayChunks<I, N>
where I: Iterator,

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#### type Item = [<I as Iterator>::Item; N]

1.0.0 · Source§

### impl<K, A: Allocator> Iterator for std::collections::hash_set::IntoIter<K, A>

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#### type Item = K

1.88.0 · Source§

### impl<K, F, A: Allocator> Iterator for std::collections::hash_set::ExtractIf<'_, K, F, A>
where F: FnMut(&K) -> bool,

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#### type Item = K

1.0.0 · Source§

### impl<K, V, A> Iterator for std::collections::btree_map::IntoIter<K, V, A>
where A: Allocator + Clone,

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#### type Item = (K, V)

1.54.0 · Source§

### impl<K, V, A> Iterator for std::collections::btree_map::IntoKeys<K, V, A>
where A: Allocator + Clone,

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#### type Item = K

1.54.0 · Source§

### impl<K, V, A> Iterator for std::collections::btree_map::IntoValues<K, V, A>
where A: Allocator + Clone,

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#### type Item = V

1.0.0 · Source§

### impl<K, V, A: Allocator> Iterator for std::collections::hash_map::IntoIter<K, V, A>

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#### type Item = (K, V)

1.54.0 · Source§

### impl<K, V, A: Allocator> Iterator for std::collections::hash_map::IntoKeys<K, V, A>

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#### type Item = K

1.54.0 · Source§

### impl<K, V, A: Allocator> Iterator for std::collections::hash_map::IntoValues<K, V, A>

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#### type Item = V

1.88.0 · Source§

### impl<K, V, F, A: Allocator> Iterator for std::collections::hash_map::ExtractIf<'_, K, V, F, A>
where F: FnMut(&K, &mut V) -> bool,

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#### type Item = (K, V)

1.91.0 · Source§

### impl<K, V, R, F, A> Iterator for std::collections::btree_map::ExtractIf<'_, K, V, R, F, A>
where A: Allocator + Clone, K: PartialOrd, R: RangeBounds<K>, F: FnMut(&K, &mut V) -> bool,

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#### type Item = (K, V)

1.0.0 · Source§

### impl<R: Read> Iterator for std::io::Bytes<R>

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#### type Item = Result<u8, Error>

1.0.0 · Source§

### impl<T> Iterator for std::result::IntoIter<T>

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#### type Item = T

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### impl<T> Iterator for std::sync::mpmc::IntoIter<T>

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#### type Item = T

1.1.0 · Source§

### impl<T> Iterator for std::sync::mpsc::IntoIter<T>

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#### type Item = T

1.2.0 · Source§

### impl<T> Iterator for Empty<T>

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#### type Item = T

1.2.0 · Source§

### impl<T> Iterator for Once<T>

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#### type Item = T

1.6.0 · Source§

### impl<T, A> Iterator for std::collections::binary_heap::Drain<'_, T, A>
where A: Allocator,

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#### type Item = T

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### impl<T, A> Iterator for DrainSorted<'_, T, A>
where T: Ord, A: Allocator,

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#### type Item = T

1.0.0 · Source§

### impl<T, A> Iterator for std::collections::binary_heap::IntoIter<T, A>
where A: Allocator,

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#### type Item = T

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### impl<T, A> Iterator for IntoIterSorted<T, A>
where T: Ord, A: Allocator,

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#### type Item = T

1.0.0 · Source§

### impl<T, A> Iterator for std::collections::btree_set::IntoIter<T, A>
where A: Allocator + Clone,

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#### type Item = T

1.0.0 · Source§

### impl<T, A> Iterator for std::collections::linked_list::IntoIter<T, A>
where A: Allocator,

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#### type Item = T

1.6.0 · Source§

### impl<T, A> Iterator for std::collections::vec_deque::Drain<'_, T, A>
where A: Allocator,

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#### type Item = T

1.0.0 · Source§

### impl<T, A> Iterator for std::collections::vec_deque::IntoIter<T, A>
where A: Allocator,

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#### type Item = T

1.6.0 · Source§

### impl<T, A> Iterator for std::vec::Drain<'_, T, A>
where A: Allocator,

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#### type Item = T

1.0.0 · Source§

### impl<T, A> Iterator for std::vec::IntoIter<T, A>
where A: Allocator,

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#### type Item = T

1.34.0 · Source§

### impl<T, F> Iterator for FromFn<F>
where F: FnMut() -> Option<T>,

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#### type Item = T

1.34.0 · Source§

### impl<T, F> Iterator for Successors<T, F>
where F: FnMut(&T) -> Option<T>,

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#### type Item = T

1.87.0 · Source§

### impl<T, F, A> Iterator for std::collections::linked_list::ExtractIf<'_, T, F, A>
where A: Allocator, F: FnMut(&mut T) -> bool,

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#### type Item = T

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### impl<T, F, A> Iterator for std::collections::vec_deque::ExtractIf<'_, T, F, A>
where A: Allocator, F: FnMut(&mut T) -> bool,

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#### type Item = T

1.87.0 · Source§

### impl<T, F, A> Iterator for std::vec::ExtractIf<'_, T, F, A>
where A: Allocator, F: FnMut(&mut T) -> bool,

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#### type Item = T

1.91.0 · Source§

### impl<T, R, F, A> Iterator for std::collections::btree_set::ExtractIf<'_, T, R, F, A>
where A: Allocator + Clone, T: PartialOrd, R: RangeBounds<T>, F: FnMut(&T) -> bool,

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#### type Item = T

1.40.0 · Source§

### impl<T, const N: usize> Iterator for std::array::IntoIter<T, N>

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#### type Item = T