std::iter::DoubleEndedIterator - Rust
Description: API documentation for the Rust `DoubleEndedIterator` trait in crate `std`.
Keywords: rust, rustlang, rust-lang, DoubleEndedIterator

# 1.0.0[−][src]Trait std::iter::DoubleEndedIterator

    pub trait DoubleEndedIterator: Iterator {
        fn next_back(&mut self) -> Option<Self::Item>;

        fn nth_back(&mut self, n: usize) -> Option<Self::Item> { ... }
        fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
        where
            F: FnMut(B, Self::Item) -> R,
            R: Try<Ok = B>,
        { ... }
        fn rfold<B, F>(self, init: B, f: F) -> B
        where
            F: FnMut(B, Self::Item) -> B,
        { ... }
        fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
        where
            P: FnMut(&Self::Item) -> bool,
        { ... }
    }

An iterator able to yield elements from both ends.

Something that implements `DoubleEndedIterator` has one extra capability over something that implements `Iterator`: the ability to also take `Item`s from the back, as well as the front.

It is important to note that both back and forth work on the same range, and do not cross: iteration is over when they meet in the middle.

In a similar fashion to the `Iterator` protocol, once a `DoubleEndedIterator` returns `None` from a `next_back()`, calling it again may or may not ever return `Some` again. `next()` and `next_back()` are interchangeable for this purpose.

# Examples

Basic usage:

    let numbers = vec![1, 2, 3, 4, 5, 6];

    let mut iter = numbers.iter();

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

Run

## Required methods

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

Removes and returns an element from the end of the iterator.

Returns `None` when there are no more elements.

The trait-level docs contain more details.

# Examples

Basic usage:

    let numbers = vec![1, 2, 3, 4, 5, 6];

    let mut iter = numbers.iter();

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

Run

# Remarks

The elements yielded by `DoubleEndedIterator`'s methods may differ from the ones yielded by `Iterator`'s methods:

    let vec = vec![(1, 'a'), (1, 'b'), (1, 'c'), (2, 'a'), (2, 'b')];
    let uniq_by_fst_comp = || {
        let mut seen = std::collections::HashSet::new();
        vec.iter().copied().filter(move |x| seen.insert(x.0))
    };

    assert_eq!(uniq_by_fst_comp().last(), Some((2, 'a')));
    assert_eq!(uniq_by_fst_comp().next_back(), Some((2, 'b')));

    assert_eq!(
        uniq_by_fst_comp().fold(vec![], |mut v, x| {v.push(x); v}),
        vec![(1, 'a'), (2, 'a')]
    );
    assert_eq!(
        uniq_by_fst_comp().rfold(vec![], |mut v, x| {v.push(x); v}),
        vec![(2, 'b'), (1, 'c')]
    );

Run
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## Provided methods

### `fn nth_back(&mut self, n: usize) -> Option<Self::Item>`1.37.0

Returns the `n`th element from the end of the iterator.

This is essentially the reversed version of `nth`. Although like most indexing operations, the count starts from zero, so `nth_back(0)` returns the first value from the end, `nth_back(1)` the second, and so on.

Note that all elements between the end and the returned element will be consumed, including the returned element. This also means that calling `nth_back(0)` multiple times on the same iterator will return different elements.

`nth_back()` 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.iter().nth_back(2), Some(&1));

Run

Calling `nth_back()` multiple times doesn't rewind the iterator:

    let a = [1, 2, 3];

    let mut iter = a.iter();

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

Run

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

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

Run

### `fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Ok = B>,` 1.27.0

This is the reverse version of `try_fold()`: it takes elements starting from the back of the iterator.

# Examples

Basic usage:

    let a = ["1", "2", "3"];
    let sum = a.iter()
        .map(|&s| s.parse::<i32>())
        .try_rfold(0, |acc, x| x.and_then(|y| Ok(acc + y)));
    assert_eq!(sum, Ok(6));

Run

Short-circuiting:

    let a = ["1", "rust", "3"];
    let mut it = a.iter();
    let sum = it
        .by_ref()
        .map(|&s| s.parse::<i32>())
        .try_rfold(0, |acc, x| x.and_then(|y| Ok(acc + y)));
    assert!(sum.is_err());

    // Because it short-circuited, the remaining elements are still
    // available through the iterator.
    assert_eq!(it.next_back(), Some(&"1"));

Run

### `fn rfold<B, F>(self, init: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,` 1.27.0

An iterator method that reduces the iterator's elements to a single, final value, starting from the back.

This is the reverse version of `fold()`: it takes elements starting from the back of the iterator.

`rfold()` 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, `rfold()` 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.

# Examples

Basic usage:

    let a = [1, 2, 3];

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

    assert_eq!(sum, 6);

Run

This example builds a string, starting with an initial value and continuing with each element from the back until the front:

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

    let zero = "0".to_string();

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

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

Run

### `fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,` 1.27.0

Searches for an element of an iterator from the back that satisfies a predicate.

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

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

Because `rfind()` 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`.

# Examples

Basic usage:

    let a = [1, 2, 3];

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

    assert_eq!(a.iter().rfind(|&&x| x == 5), None);

Run

Stopping at the first `true`:

    let a = [1, 2, 3];

    let mut iter = a.iter();

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

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

Run
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## Implementations on Foreign Types

### `impl<'a, T, P> DoubleEndedIterator for SplitInclusiveMut<'a, T, P> where
P: FnMut(&T) -> bool,` [src]

#### `fn next_back(&mut self) -> Option<&'a mut [T]>`[src]

### `impl<'a, P> DoubleEndedIterator for SplitInclusive<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: ReverseSearcher<'a>,` [src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a, T, P> DoubleEndedIterator for SplitInclusive<'a, T, P> where
P: FnMut(&T) -> bool,` [src]

#### `fn next_back(&mut self) -> Option<&'a [T]>`[src]

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## Implementors

### `impl DoubleEndedIterator for EscapeDefault`[src]

#### `fn next_back(&mut self) -> Option<u8>`[src]

### `impl DoubleEndedIterator for Args`[src]

#### `fn next_back(&mut self) -> Option<String>`[src]

### `impl DoubleEndedIterator for ArgsOs`[src]

#### `fn next_back(&mut self) -> Option<OsString>`[src]

### `impl<'_> DoubleEndedIterator for Bytes<'_>`[src]

#### `fn next_back(&mut self) -> Option<u8>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<Bytes<'_> as Iterator>::Item>`[src]

#### `fn rfind<P>(&mut self, predicate: P) -> Option<<Bytes<'_> as Iterator>::Item> where
P: FnMut(&<Bytes<'_> as Iterator>::Item) -> bool,` [src]

### `impl<'_> DoubleEndedIterator for std::string::Drain<'_>`[src]

#### `fn next_back(&mut self) -> Option<char>`[src]

### `impl<'_, I> DoubleEndedIterator for Splice<'_, I> where
I: Iterator,` [src]

#### `fn next_back(&mut self) -> Option<<Splice<'_, I> as Iterator>::Item>`[src]

### `impl<'_, T> DoubleEndedIterator for std::collections::binary_heap::Drain<'_, T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<'_, T> DoubleEndedIterator for std::collections::vec_deque::Drain<'_, T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<'_, T> DoubleEndedIterator for std::vec::Drain<'_, T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<'a> DoubleEndedIterator for Components<'a>`[src]

#### `fn next_back(&mut self) -> Option<Component<'a>>`[src]

### `impl<'a> DoubleEndedIterator for std::path::Iter<'a>`[src]

#### `fn next_back(&mut self) -> Option<&'a OsStr>`[src]

### `impl<'a> DoubleEndedIterator for CharIndices<'a>`[src]

#### `fn next_back(&mut self) -> Option<(usize, char)>`[src]

### `impl<'a> DoubleEndedIterator for Chars<'a>`[src]

#### `fn next_back(&mut self) -> Option<char>`[src]

### `impl<'a> DoubleEndedIterator for Lines<'a>`[src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a> DoubleEndedIterator for LinesAny<'a>`[src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a> DoubleEndedIterator for SplitAsciiWhitespace<'a>`[src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a> DoubleEndedIterator for SplitWhitespace<'a>`[src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a, A> DoubleEndedIterator for std::option::Iter<'a, A>`[src]

#### `fn next_back(&mut self) -> Option<&'a A>`[src]

### `impl<'a, A> DoubleEndedIterator for std::option::IterMut<'a, A>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut A>`[src]

### `impl<'a, I> DoubleEndedIterator for &'a mut I where
I: DoubleEndedIterator + ?Sized,` [src]

#### `fn next_back(&mut self) -> Option<<I as Iterator>::Item>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item>`[src]

### `impl<'a, I, T> DoubleEndedIterator for Cloned<I> where
I: DoubleEndedIterator<Item = &'a T>,
T: 'a + Clone,` [src]

#### `fn next_back(&mut self) -> Option<T>`[src]

#### `fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, <Cloned<I> as Iterator>::Item) -> R,
R: Try<Ok = B>,
Cloned<I>: Sized,` [src]

#### `fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc where
F: FnMut(Acc, <Cloned<I> as Iterator>::Item) -> Acc,` [src]

### `impl<'a, I, T> DoubleEndedIterator for Copied<I> where
I: DoubleEndedIterator<Item = &'a T>,
T: 'a + Copy,` [src]

#### `fn next_back(&mut self) -> Option<T>`[src]

#### `fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, <Copied<I> as Iterator>::Item) -> R,
R: Try<Ok = B>,
Copied<I>: Sized,` [src]

#### `fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc where
F: FnMut(Acc, <Copied<I> as Iterator>::Item) -> Acc,` [src]

### `impl<'a, K, V> DoubleEndedIterator for std::collections::btree_map::Iter<'a, K, V> where
K: 'a,
V: 'a,` [src]

#### `fn next_back(&mut self) -> Option<(&'a K, &'a V)>`[src]

### `impl<'a, K, V> DoubleEndedIterator for std::collections::btree_map::IterMut<'a, K, V> where
K: 'a,
V: 'a,` [src]

#### `fn next_back(&mut self) -> Option<(&'a K, &'a mut V)>`[src]

### `impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V>`[src]

#### `fn next_back(&mut self) -> Option<&'a K>`[src]

### `impl<'a, K, V> DoubleEndedIterator for std::collections::btree_map::Range<'a, K, V>`[src]

#### `fn next_back(&mut self) -> Option<(&'a K, &'a V)>`[src]

### `impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V>`[src]

#### `fn next_back(&mut self) -> Option<(&'a K, &'a mut V)>`[src]

### `impl<'a, K, V> DoubleEndedIterator for Values<'a, K, V>`[src]

#### `fn next_back(&mut self) -> Option<&'a V>`[src]

### `impl<'a, K, V> DoubleEndedIterator for ValuesMut<'a, K, V>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut V>`[src]

### `impl<'a, P> DoubleEndedIterator for MatchIndices<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,` [src]

#### `fn next_back(&mut self) -> Option<(usize, &'a str)>`[src]

### `impl<'a, P> DoubleEndedIterator for Matches<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,` [src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a, P> DoubleEndedIterator for RMatchIndices<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,` [src]

#### `fn next_back(&mut self) -> Option<(usize, &'a str)>`[src]

### `impl<'a, P> DoubleEndedIterator for RMatches<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,` [src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a, P> DoubleEndedIterator for std::str::RSplit<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,` [src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a, P> DoubleEndedIterator for RSplitTerminator<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,` [src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a, P> DoubleEndedIterator for std::str::Split<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,` [src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a, P> DoubleEndedIterator for SplitTerminator<'a, P> where
P: Pattern<'a>,
<P as Pattern<'a>>::Searcher: DoubleEndedSearcher<'a>,` [src]

#### `fn next_back(&mut self) -> Option<&'a str>`[src]

### `impl<'a, T> DoubleEndedIterator for std::collections::binary_heap::Iter<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a T>`[src]

### `impl<'a, T> DoubleEndedIterator for std::collections::btree_set::Iter<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a T>`[src]

### `impl<'a, T> DoubleEndedIterator for std::collections::btree_set::Range<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a T>`[src]

### `impl<'a, T> DoubleEndedIterator for std::collections::linked_list::Iter<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a T>`[src]

### `impl<'a, T> DoubleEndedIterator for std::collections::linked_list::IterMut<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut T>`[src]

### `impl<'a, T> DoubleEndedIterator for std::collections::vec_deque::Iter<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a T>`[src]

#### `fn rfold<Acc, F>(self, accum: Acc, f: F) -> Acc where
F: FnMut(Acc, <Iter<'a, T> as Iterator>::Item) -> Acc,` [src]

#### `fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, <Iter<'a, T> as Iterator>::Item) -> R,
R: Try<Ok = B>,
Iter<'a, T>: Sized,` [src]

### `impl<'a, T> DoubleEndedIterator for std::collections::vec_deque::IterMut<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut T>`[src]

#### `fn rfold<Acc, F>(self, accum: Acc, f: F) -> Acc where
F: FnMut(Acc, <IterMut<'a, T> as Iterator>::Item) -> Acc,` [src]

### `impl<'a, T> DoubleEndedIterator for std::result::Iter<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a T>`[src]

### `impl<'a, T> DoubleEndedIterator for std::result::IterMut<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut T>`[src]

### `impl<'a, T> DoubleEndedIterator for Chunks<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a [T]>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<Chunks<'a, T> as Iterator>::Item>`[src]

### `impl<'a, T> DoubleEndedIterator for ChunksExact<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a [T]>`[src]

#### `fn nth_back(
&mut self,
n: usize
) -> Option<<ChunksExact<'a, T> as Iterator>::Item>`[src]

### `impl<'a, T> DoubleEndedIterator for ChunksExactMut<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut [T]>`[src]

#### `fn nth_back(
&mut self,
n: usize
) -> Option<<ChunksExactMut<'a, T> as Iterator>::Item>`[src]

### `impl<'a, T> DoubleEndedIterator for ChunksMut<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut [T]>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<ChunksMut<'a, T> as Iterator>::Item>`[src]

### `impl<'a, T> DoubleEndedIterator for std::slice::Iter<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a T>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<&'a T>`[src]

### `impl<'a, T> DoubleEndedIterator for std::slice::IterMut<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut T>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<&'a mut T>`[src]

### `impl<'a, T> DoubleEndedIterator for RChunks<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a [T]>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<RChunks<'a, T> as Iterator>::Item>`[src]

### `impl<'a, T> DoubleEndedIterator for RChunksExact<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a [T]>`[src]

#### `fn nth_back(
&mut self,
n: usize
) -> Option<<RChunksExact<'a, T> as Iterator>::Item>`[src]

### `impl<'a, T> DoubleEndedIterator for RChunksExactMut<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut [T]>`[src]

#### `fn nth_back(
&mut self,
n: usize
) -> Option<<RChunksExactMut<'a, T> as Iterator>::Item>`[src]

### `impl<'a, T> DoubleEndedIterator for RChunksMut<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a mut [T]>`[src]

#### `fn nth_back(
&mut self,
n: usize
) -> Option<<RChunksMut<'a, T> as Iterator>::Item>`[src]

### `impl<'a, T> DoubleEndedIterator for Windows<'a, T>`[src]

#### `fn next_back(&mut self) -> Option<&'a [T]>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<Windows<'a, T> as Iterator>::Item>`[src]

### `impl<'a, T, P> DoubleEndedIterator for std::slice::RSplit<'a, T, P> where
P: FnMut(&T) -> bool,` [src]

#### `fn next_back(&mut self) -> Option<&'a [T]>`[src]

### `impl<'a, T, P> DoubleEndedIterator for RSplitMut<'a, T, P> where
P: FnMut(&T) -> bool,` [src]

#### `fn next_back(&mut self) -> Option<&'a mut [T]>`[src]

### `impl<'a, T, P> DoubleEndedIterator for std::slice::Split<'a, T, P> where
P: FnMut(&T) -> bool,` [src]

#### `fn next_back(&mut self) -> Option<&'a [T]>`[src]

### `impl<'a, T, P> DoubleEndedIterator for SplitMut<'a, T, P> where
P: FnMut(&T) -> bool,` [src]

#### `fn next_back(&mut self) -> Option<&'a mut [T]>`[src]

### `impl<A> DoubleEndedIterator for Repeat<A> where
A: Clone,` [src]

#### `fn next_back(&mut self) -> Option<A>`[src]

### `impl<A> DoubleEndedIterator for std::ops::Range<A> where
A: Step,` [src]

#### `fn next_back(&mut self) -> Option<A>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<A>`[src]

### `impl<A> DoubleEndedIterator for RangeInclusive<A> where
A: Step,` [src]

#### `fn next_back(&mut self) -> Option<A>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<A>`[src]

#### `fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, <RangeInclusive<A> as Iterator>::Item) -> R,
R: Try<Ok = B>,
RangeInclusive<A>: Sized,` [src]

#### `fn rfold<B, F>(self, init: B, f: F) -> B where
F: FnMut(B, <RangeInclusive<A> as Iterator>::Item) -> B,
RangeInclusive<A>: Sized,` [src]

### `impl<A> DoubleEndedIterator for std::option::IntoIter<A>`[src]

#### `fn next_back(&mut self) -> Option<A>`[src]

### `impl<A, B> DoubleEndedIterator for Chain<A, B> where
A: DoubleEndedIterator,
B: DoubleEndedIterator<Item = <A as Iterator>::Item>,` [src]

#### `fn next_back(&mut self) -> Option<<A as Iterator>::Item>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<A as Iterator>::Item>`[src]

#### `fn rfind<P>(&mut self, predicate: P) -> Option<<Chain<A, B> as Iterator>::Item> where
P: FnMut(&<Chain<A, B> as Iterator>::Item) -> bool,` [src]

#### `fn try_rfold<Acc, F, R>(&mut self, acc: Acc, f: F) -> R where
F: FnMut(Acc, <Chain<A, B> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
Chain<A, B>: Sized,` [src]

#### `fn rfold<Acc, F>(self, acc: Acc, f: F) -> Acc where
F: FnMut(Acc, <Chain<A, B> as Iterator>::Item) -> Acc,` [src]

### `impl<A, B> DoubleEndedIterator for Zip<A, B> where
A: DoubleEndedIterator + ExactSizeIterator,
B: DoubleEndedIterator + ExactSizeIterator,` [src]

#### `fn next_back(
&mut self
) -> Option<(<A as Iterator>::Item, <B as Iterator>::Item)>`[src]

### `impl<A, F> DoubleEndedIterator for OnceWith<F> where
F: FnOnce() -> A,` [src]

#### `fn next_back(&mut self) -> Option<A>`[src]

### `impl<B, I, F> DoubleEndedIterator for FilterMap<I, F> where
F: FnMut(<I as Iterator>::Item) -> Option<B>,
I: DoubleEndedIterator,` [src]

#### `fn next_back(&mut self) -> Option<B>`[src]

#### `fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
Fold: FnMut(Acc, <FilterMap<I, F> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
FilterMap<I, F>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <FilterMap<I, F> as Iterator>::Item) -> Acc,` [src]

### `impl<B, I, F> DoubleEndedIterator for Map<I, F> where
F: FnMut(<I as Iterator>::Item) -> B,
I: DoubleEndedIterator,` [src]

#### `fn next_back(&mut self) -> Option<B>`[src]

#### `fn try_rfold<Acc, G, R>(&mut self, init: Acc, g: G) -> R where
G: FnMut(Acc, <Map<I, F> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
Map<I, F>: Sized,` [src]

#### `fn rfold<Acc, G>(self, init: Acc, g: G) -> Acc where
G: FnMut(Acc, <Map<I, F> as Iterator>::Item) -> Acc,` [src]

### `impl<I> DoubleEndedIterator for Box<I> where
I: DoubleEndedIterator + ?Sized,` [src]

#### `fn next_back(&mut self) -> Option<<I as Iterator>::Item>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item>`[src]

### `impl<I> DoubleEndedIterator for Enumerate<I> where
I: ExactSizeIterator + DoubleEndedIterator,` [src]

#### `fn next_back(&mut self) -> Option<(usize, <I as Iterator>::Item)>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<(usize, <I as Iterator>::Item)>`[src]

#### `fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
Fold: FnMut(Acc, <Enumerate<I> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
Enumerate<I>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <Enumerate<I> as Iterator>::Item) -> Acc,` [src]

### `impl<I> DoubleEndedIterator for Fuse<I> where
I: DoubleEndedIterator,` [src]

#### `fn next_back(&mut self) -> Option<<I as Iterator>::Item>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item>`[src]

#### `fn try_rfold<Acc, Fold, R>(&mut self, acc: Acc, fold: Fold) -> R where
Fold: FnMut(Acc, <Fuse<I> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
Fuse<I>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, acc: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <Fuse<I> as Iterator>::Item) -> Acc,` [src]

#### `fn rfind<P>(&mut self, predicate: P) -> Option<<Fuse<I> as Iterator>::Item> where
P: FnMut(&<Fuse<I> as Iterator>::Item) -> bool,` [src]

### `impl<I> DoubleEndedIterator for Peekable<I> where
I: DoubleEndedIterator,` [src]

#### `fn next_back(&mut self) -> Option<<Peekable<I> as Iterator>::Item>`[src]

#### `fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, <Peekable<I> as Iterator>::Item) -> R,
R: Try<Ok = B>,
Peekable<I>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <Peekable<I> as Iterator>::Item) -> Acc,` [src]

### `impl<I> DoubleEndedIterator for Rev<I> where
I: DoubleEndedIterator,` [src]

#### `fn next_back(&mut self) -> Option<<I as Iterator>::Item>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item>`[src]

#### `fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, <Rev<I> as Iterator>::Item) -> R,
R: Try<Ok = B>,
Rev<I>: Sized,` [src]

#### `fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc where
F: FnMut(Acc, <Rev<I> as Iterator>::Item) -> Acc,` [src]

#### `fn rfind<P>(&mut self, predicate: P) -> Option<<Rev<I> as Iterator>::Item> where
P: FnMut(&<Rev<I> as Iterator>::Item) -> bool,` [src]

### `impl<I> DoubleEndedIterator for Skip<I> where
I: DoubleEndedIterator + ExactSizeIterator,` [src]

#### `fn next_back(&mut self) -> Option<<Skip<I> as Iterator>::Item>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<I as Iterator>::Item>`[src]

#### `fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
Fold: FnMut(Acc, <Skip<I> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
Skip<I>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <Skip<I> as Iterator>::Item) -> Acc,` [src]

### `impl<I> DoubleEndedIterator for StepBy<I> where
I: DoubleEndedIterator + ExactSizeIterator,` [src]

#### `fn next_back(&mut self) -> Option<<StepBy<I> as Iterator>::Item>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<StepBy<I> as Iterator>::Item>`[src]

#### `fn try_rfold<Acc, F, R>(&mut self, init: Acc, f: F) -> R where
F: FnMut(Acc, <StepBy<I> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,` [src]

#### `fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc where
F: FnMut(Acc, <StepBy<I> as Iterator>::Item) -> Acc,
StepBy<I>: Sized,` [src]

### `impl<I> DoubleEndedIterator for Take<I> where
I: DoubleEndedIterator + ExactSizeIterator,` [src]

#### `fn next_back(&mut self) -> Option<<Take<I> as Iterator>::Item>`[src]

#### `fn nth_back(&mut self, n: usize) -> Option<<Take<I> as Iterator>::Item>`[src]

#### `fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
Fold: FnMut(Acc, <Take<I> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
Take<I>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <Take<I> as Iterator>::Item) -> Acc,
Take<I>: Sized,` [src]

### `impl<I, F> DoubleEndedIterator for Inspect<I, F> where
F: FnMut(&<I as Iterator>::Item),
I: DoubleEndedIterator,` [src]

#### `fn next_back(&mut self) -> Option<<I as Iterator>::Item>`[src]

#### `fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
Fold: FnMut(Acc, <Inspect<I, F> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
Inspect<I, F>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <Inspect<I, F> as Iterator>::Item) -> Acc,` [src]

### `impl<I, P> DoubleEndedIterator for Filter<I, P> where
I: DoubleEndedIterator,
P: FnMut(&<I as Iterator>::Item) -> bool,` [src]

#### `fn next_back(&mut self) -> Option<<I as Iterator>::Item>`[src]

#### `fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
Fold: FnMut(Acc, <Filter<I, P> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
Filter<I, P>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <Filter<I, P> as Iterator>::Item) -> Acc,` [src]

### `impl<I, U> DoubleEndedIterator for Flatten<I> where
I: DoubleEndedIterator,
U: DoubleEndedIterator,
<I as Iterator>::Item: IntoIterator,
<<I as Iterator>::Item as IntoIterator>::IntoIter == U,
<<I as Iterator>::Item as IntoIterator>::Item == <U as Iterator>::Item,` [src]

#### `fn next_back(&mut self) -> Option<<U as Iterator>::Item>`[src]

#### `fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
Fold: FnMut(Acc, <Flatten<I> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
Flatten<I>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <Flatten<I> as Iterator>::Item) -> Acc,` [src]

### `impl<I, U, F> DoubleEndedIterator for FlatMap<I, U, F> where
F: FnMut(<I as Iterator>::Item) -> U,
I: DoubleEndedIterator,
U: IntoIterator,
<U as IntoIterator>::IntoIter: DoubleEndedIterator,` [src]

#### `fn next_back(&mut self) -> Option<<U as IntoIterator>::Item>`[src]

#### `fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
Fold: FnMut(Acc, <FlatMap<I, U, F> as Iterator>::Item) -> R,
R: Try<Ok = Acc>,
FlatMap<I, U, F>: Sized,` [src]

#### `fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc where
Fold: FnMut(Acc, <FlatMap<I, U, F> as Iterator>::Item) -> Acc,` [src]

### `impl<K, V> DoubleEndedIterator for std::collections::btree_map::IntoIter<K, V>`[src]

#### `fn next_back(&mut self) -> Option<(K, V)>`[src]

### `impl<T> DoubleEndedIterator for std::collections::binary_heap::IntoIter<T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<T> DoubleEndedIterator for std::collections::btree_set::IntoIter<T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<T> DoubleEndedIterator for std::collections::linked_list::IntoIter<T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<T> DoubleEndedIterator for std::collections::vec_deque::IntoIter<T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<T> DoubleEndedIterator for Empty<T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<T> DoubleEndedIterator for Once<T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<T> DoubleEndedIterator for std::result::IntoIter<T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<T> DoubleEndedIterator for std::vec::IntoIter<T>`[src]

#### `fn next_back(&mut self) -> Option<T>`[src]

### `impl<const N: usize, T> DoubleEndedIterator for std::array::IntoIter<T, N> where
[T; N]: LengthAtMost32,` [src]

#### `fn next_back(&mut self) -> Option<<IntoIter<T, N> as Iterator>::Item>`[src]

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