Trait af_core::iter::__std_iter::ExactSizeIterator

pub trait ExactSizeIterator: Iterator {
    pub fn len(&self) -> usize { ... }
    pub fn is_empty(&self) -> bool { ... }
}

An iterator that knows its exact length.

Many Iterators don't know how many times they will iterate, but some do. If an iterator knows how many times it can iterate, providing access to that information can be useful. For example, if you want to iterate backwards, a good start is to know where the end is.

When implementing an ExactSizeIterator, you must also implement Iterator. When doing so, the implementation of Iterator::size_hint must return the exact size of the iterator.

The len method has a default implementation, so you usually shouldn't implement it. However, you may be able to provide a more performant implementation than the default, so overriding it in this case makes sense.

Note that this trait is a safe trait and as such does not and cannot guarantee that the returned length is correct. This means that unsafe code must not rely on the correctness of Iterator::size_hint. The unstable and unsafe TrustedLen trait gives this additional guarantee.

Examples

Basic usage:

// a finite range knows exactly how many times it will iterate
let five = 0..5;

assert_eq!(5, five.len());

In the module-level docs, we implemented an Iterator, Counter. Let's implement ExactSizeIterator for it as well:

impl ExactSizeIterator for Counter {
    // We can easily calculate the remaining number of iterations.
    fn len(&self) -> usize {
        5 - self.count
    }
}

// And now we can use it!

let counter = Counter::new();

assert_eq!(5, counter.len());

Provided methods

pub fn len(&self) -> usize

Returns the exact length of the iterator.

The implementation ensures that the iterator will return exactly len() more times a Some(T) value, before returning None. This method has a default implementation, so you usually should not implement it directly. However, if you can provide a more efficient implementation, you can do so. See the trait-level docs for an example.

This function has the same safety guarantees as the Iterator::size_hint function.

Examples

Basic usage:

// a finite range knows exactly how many times it will iterate
let five = 0..5;

assert_eq!(5, five.len());

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

Returns true if the iterator is empty.

This method has a default implementation using ExactSizeIterator::len(), so you don't need to implement it yourself.

Examples

Basic usage:

#![feature(exact_size_is_empty)]

let mut one_element = std::iter::once(0);
assert!(!one_element.is_empty());

assert_eq!(one_element.next(), Some(0));
assert!(one_element.is_empty());

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

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Implementations on Foreign Types

impl<K, V> ExactSizeIterator for IntoKeys<K, V>

pub fn len(&self) -> usize

impl<'a> ExactSizeIterator for CommandEnvs<'a>

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, K, V> ExactSizeIterator for Values<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for Drain<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K> ExactSizeIterator for Iter<'_, K>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for IterMut<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for ValuesMut<'_, K, V>

pub fn len(&self) -> usize

impl<K> ExactSizeIterator for IntoIter<K>

pub fn len(&self) -> usize

impl<K, V> ExactSizeIterator for IntoIter<K, V>

pub fn len(&self) -> usize

impl ExactSizeIterator for ArgsOs

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'a> ExactSizeIterator for CommandArgs<'a>

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, K, V> ExactSizeIterator for Keys<'_, K, V>

pub fn len(&self) -> usize

impl<K, V> ExactSizeIterator for IntoValues<K, V>

pub fn len(&self) -> usize

impl<'_, K> ExactSizeIterator for Drain<'_, K>

pub fn len(&self) -> usize

impl ExactSizeIterator for Args

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, K, V> ExactSizeIterator for Iter<'_, K, V>

pub fn len(&self) -> usize

impl<'_, T> ExactSizeIterator for ChunksExact<'_, T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, T, const N: usize> ExactSizeIterator for ArrayWindows<'_, T, N>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, T, const N: usize> ExactSizeIterator for ArrayChunks<'_, T, N>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl ExactSizeIterator for Range<usize>

impl ExactSizeIterator for ToUppercase

impl<'_, T> ExactSizeIterator for RChunks<'_, T>

impl<'_, T> ExactSizeIterator for RChunksExactMut<'_, T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, T> ExactSizeIterator for Chunks<'_, T>

impl ExactSizeIterator for Range<i16>

impl<'_, A> ExactSizeIterator for IterMut<'_, A>

impl ExactSizeIterator for Range<i8>

impl ExactSizeIterator for Range<i32>

impl<'_, T> ExactSizeIterator for ChunksMut<'_, T>

impl<'_> ExactSizeIterator for Bytes<'_>

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<T> ExactSizeIterator for IntoIter<T>

impl ExactSizeIterator for RangeInclusive<u16>

impl ExactSizeIterator for Range<u16>

impl ExactSizeIterator for EscapeDefault

impl ExactSizeIterator for RangeInclusive<u8>

impl ExactSizeIterator for EscapeDebug

impl ExactSizeIterator for Range<u8>

impl<'_, T> ExactSizeIterator for Iter<'_, T>

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, T> ExactSizeIterator for IterMut<'_, T>

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl ExactSizeIterator for EscapeUnicode

pub fn len(&self) -> usize

impl<'_, T> ExactSizeIterator for Iter<'_, T>

impl ExactSizeIterator for RangeInclusive<i16>

impl ExactSizeIterator for Range<u32>

impl ExactSizeIterator for RangeInclusive<i8>

impl<A> ExactSizeIterator for IntoIter<A>

impl<'_, T> ExactSizeIterator for RChunksMut<'_, T>

impl<'_, A> ExactSizeIterator for Iter<'_, A>

impl<'_, T, const N: usize> ExactSizeIterator for ArrayChunksMut<'_, T, N>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, I> ExactSizeIterator for &'_ mut I where
    I: ExactSizeIterator + ?Sized, 

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, T> ExactSizeIterator for ChunksExactMut<'_, T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<T, const N: usize> ExactSizeIterator for IntoIter<T, N>

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl ExactSizeIterator for ToLowercase

impl<'_, T> ExactSizeIterator for IterMut<'_, T>

impl ExactSizeIterator for Range<isize>

impl ExactSizeIterator for EscapeDefault

pub fn len(&self) -> usize

impl<'_, T> ExactSizeIterator for Windows<'_, T>

impl<'a, T> ExactSizeIterator for RChunksExact<'a, T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<T> ExactSizeIterator for IntoIter<T>

impl<'_, T> ExactSizeIterator for IterMut<'_, T>

impl<'_, T> ExactSizeIterator for IterMut<'_, T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<T> ExactSizeIterator for IntoIterSorted<T> where
    T: Ord, 

impl<'_, T> ExactSizeIterator for Drain<'_, T>

impl<K, V> ExactSizeIterator for IntoValues<K, V>

pub fn len(&self) -> usize

impl<'_, I, A> ExactSizeIterator for Splice<'_, I, A> where
    I: Iterator,
    A: Allocator, 

impl<K, V> ExactSizeIterator for IntoKeys<K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for IterMut<'_, K, V>

pub fn len(&self) -> usize

impl<T> ExactSizeIterator for IntoIter<T>

pub fn len(&self) -> usize

impl<T> ExactSizeIterator for IntoIter<T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<T> ExactSizeIterator for IntoIter<T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, T> ExactSizeIterator for Iter<'_, T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, T> ExactSizeIterator for Iter<'_, T>

impl<I, A> ExactSizeIterator for Box<I, A> where
    I: ExactSizeIterator + ?Sized,
    A: Allocator, 

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, K, V> ExactSizeIterator for Values<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for ValuesMut<'_, K, V>

pub fn len(&self) -> usize

impl<K, V> ExactSizeIterator for IntoIter<K, V>

pub fn len(&self) -> usize

impl<'_, T> ExactSizeIterator for DrainSorted<'_, T> where
    T: Ord, 

impl<T, A> ExactSizeIterator for IntoIter<T, A> where
    A: Allocator, 

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, K, V> ExactSizeIterator for Keys<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for Iter<'_, K, V>

pub fn len(&self) -> usize

impl<'_, T> ExactSizeIterator for Iter<'_, T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, T> ExactSizeIterator for Iter<'_, T>

pub fn len(&self) -> usize

impl<'_, T> ExactSizeIterator for Drain<'_, T>

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<'_, T, A> ExactSizeIterator for Drain<'_, T, A> where
    A: Allocator, 

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<A> ExactSizeIterator for IntoIter<A> where
    A: Array, 

impl<'a, T> ExactSizeIterator for Drain<'a, T> where
    T: Array, 

pub fn len(&self) -> usize

impl<'a> ExactSizeIterator for IndexVecIter<'a>

impl ExactSizeIterator for IndexVecIntoIter

impl<'a, S, T> ExactSizeIterator for SliceChooseIter<'a, S, T> where
    T: 'a,
    S: Index<usize, Output = T> + 'a + ?Sized, 

pub fn len(&self) -> usize

impl<'r> ExactSizeIterator for CaptureNames<'r>

impl<'r> ExactSizeIterator for CaptureNames<'r>

impl<T> ExactSizeIterator for IntoIter<T> where
    T: Send, 

impl<'_, T> ExactSizeIterator for IterMut<'_, T> where
    T: Send, 

impl<T> ExactSizeIterator for CachedIntoIter<T> where
    T: Send, 

impl<'a, T> ExactSizeIterator for CachedIterMut<'a, T> where
    T: 'a + Send, 

impl<'a> ExactSizeIterator for Keys<'a>

pub fn len(&self) -> usize

impl<'a> ExactSizeIterator for IterMut<'a>

pub fn len(&self) -> usize

impl<'a> ExactSizeIterator for ValuesMut<'a>

pub fn len(&self) -> usize

impl<'a> ExactSizeIterator for Values<'a>

pub fn len(&self) -> usize

impl ExactSizeIterator for IntoIter

pub fn len(&self) -> usize

impl<'a> ExactSizeIterator for Iter<'a>

pub fn len(&self) -> usize

impl<T> ExactSizeIterator for IntoIter<T> where
    T: Buf, 

impl<T, N> ExactSizeIterator for GenericArrayIter<T, N> where
    N: ArrayLength<T>, 

pub fn len(&self) -> usize

impl<'p, A, I> ExactSizeIterator for ArrayVecSplice<'p, A, I> where
    I: Iterator<Item = <A as Array>::Item>,
    A: Array, 

pub fn len(&self) -> usize

impl<'p, A, I> ExactSizeIterator for TinyVecSplice<'p, A, I> where
    I: Iterator<Item = <A as Array>::Item>,
    A: Array, 

pub fn len(&self) -> usize

impl<'a, T> ExactSizeIterator for ArrayVecDrain<'a, T> where
    T: 'a + Default, 

impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> where
    (K, V): 'a,
    (K, V): BTreeValue, 

impl<A> ExactSizeIterator for ConsumingIter<A> where
    A: HashValue + Clone, 

impl<'a, A> ExactSizeIterator for Iter<'a, A> where
    A: 'a + Ord, 

impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V>

impl<'a, K, V> ExactSizeIterator for Values<'a, K, V>

impl<'a, A> ExactSizeIterator for Iter<'a, A>

impl<A> ExactSizeIterator for ConsumingIter<A> where
    A: BTreeValue + Clone, 

impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> where
    K: 'a + Ord,
    V: 'a, 

impl<'a, A> ExactSizeIterator for IterMut<'a, A> where
    A: Clone, 

impl<'a, A> ExactSizeIterator for Iter<'a, A> where
    A: Clone, 

impl<A> ExactSizeIterator for ConsumingIter<A> where
    A: Clone, 

impl<A> ExactSizeIterator for ConsumingIter<A> where
    A: Hash + Eq + Clone, 

impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> where
    K: Clone,
    V: Clone, 

impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> where
    K: 'a + Ord,
    V: 'a, 

impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V>

impl<A, T> ExactSizeIterator for Iter<A, T>

impl<'a, A, N> ExactSizeIterator for Drain<'a, A, N> where
    A: 'a,
    N: ChunkLength<A> + 'a, 

impl<A, N> ExactSizeIterator for Iter<A, N> where
    N: ChunkLength<A>, 

impl<'a, A, T> ExactSizeIterator for Drain<'a, A, T>

impl<'a, A> ExactSizeIterator for Drain<'a, A> where
    A: Array,
    <A as Array>::Item: 'a, 

impl<A> ExactSizeIterator for IntoIter<A> where
    A: Array, 

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Implementors

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

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

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

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<A> ExactSizeIterator for RepeatN<A> where
    A: Clone, 

impl<A> ExactSizeIterator for af_core::iter::Zip<(A,)> where
    A: ExactSizeIterator, 

impl<A, B> ExactSizeIterator for af_core::iter::__std_iter::Zip<A, B> where
    A: ExactSizeIterator,
    B: ExactSizeIterator, 

impl<A, B> ExactSizeIterator for af_core::iter::Zip<(A, B)> where
    A: ExactSizeIterator,
    B: ExactSizeIterator, 

impl<A, B, C> ExactSizeIterator for af_core::iter::Zip<(A, B, C)> where
    C: ExactSizeIterator,
    A: ExactSizeIterator,
    B: ExactSizeIterator, 

impl<A, B, C, D> ExactSizeIterator for af_core::iter::Zip<(A, B, C, D)> where
    C: ExactSizeIterator,
    D: ExactSizeIterator,
    A: ExactSizeIterator,
    B: ExactSizeIterator, 

impl<A, B, C, D, E> ExactSizeIterator for af_core::iter::Zip<(A, B, C, D, E)> where
    C: ExactSizeIterator,
    E: ExactSizeIterator,
    D: ExactSizeIterator,
    A: ExactSizeIterator,
    B: ExactSizeIterator, 

impl<A, B, C, D, E, F> ExactSizeIterator for af_core::iter::Zip<(A, B, C, D, E, F)> where
    C: ExactSizeIterator,
    E: ExactSizeIterator,
    F: ExactSizeIterator,
    D: ExactSizeIterator,
    A: ExactSizeIterator,
    B: ExactSizeIterator, 

impl<A, B, C, D, E, F, G> ExactSizeIterator for af_core::iter::Zip<(A, B, C, D, E, F, G)> where
    C: ExactSizeIterator,
    E: ExactSizeIterator,
    F: ExactSizeIterator,
    D: ExactSizeIterator,
    A: ExactSizeIterator,
    B: ExactSizeIterator,
    G: ExactSizeIterator, 

impl<A, B, C, D, E, F, G, H> ExactSizeIterator for af_core::iter::Zip<(A, B, C, D, E, F, G, H)> where
    C: ExactSizeIterator,
    E: ExactSizeIterator,
    F: ExactSizeIterator,
    D: ExactSizeIterator,
    H: ExactSizeIterator,
    A: ExactSizeIterator,
    B: ExactSizeIterator,
    G: ExactSizeIterator, 

impl<A, B, C, D, E, F, G, H, I> ExactSizeIterator for af_core::iter::Zip<(A, B, C, D, E, F, G, H, I)> where
    C: ExactSizeIterator,
    E: ExactSizeIterator,
    F: ExactSizeIterator,
    I: ExactSizeIterator,
    D: ExactSizeIterator,
    H: ExactSizeIterator,
    A: ExactSizeIterator,
    B: ExactSizeIterator,
    G: ExactSizeIterator, 

impl<A, B, C, D, E, F, G, H, I, J> ExactSizeIterator for af_core::iter::Zip<(A, B, C, D, E, F, G, H, I, J)> where
    C: ExactSizeIterator,
    E: ExactSizeIterator,
    F: ExactSizeIterator,
    I: ExactSizeIterator,
    D: ExactSizeIterator,
    H: ExactSizeIterator,
    A: ExactSizeIterator,
    B: ExactSizeIterator,
    G: ExactSizeIterator,
    J: ExactSizeIterator, 

impl<A, B, C, D, E, F, G, H, I, J, K> ExactSizeIterator for af_core::iter::Zip<(A, B, C, D, E, F, G, H, I, J, K)> where
    C: ExactSizeIterator,
    E: ExactSizeIterator,
    F: ExactSizeIterator,
    I: ExactSizeIterator,
    D: ExactSizeIterator,
    H: ExactSizeIterator,
    A: ExactSizeIterator,
    K: ExactSizeIterator,
    B: ExactSizeIterator,
    G: ExactSizeIterator,
    J: ExactSizeIterator, 

impl<A, B, C, D, E, F, G, H, I, J, K, L> ExactSizeIterator for af_core::iter::Zip<(A, B, C, D, E, F, G, H, I, J, K, L)> where
    C: ExactSizeIterator,
    E: ExactSizeIterator,
    F: ExactSizeIterator,
    I: ExactSizeIterator,
    D: ExactSizeIterator,
    H: ExactSizeIterator,
    A: ExactSizeIterator,
    K: ExactSizeIterator,
    B: ExactSizeIterator,
    G: ExactSizeIterator,
    L: ExactSizeIterator,
    J: ExactSizeIterator, 

impl<A, F> ExactSizeIterator for OnceWith<F> where
    F: FnOnce() -> A, 

pub fn len(&self) -> usize

impl<B, I, F> ExactSizeIterator for Map<I, F> where
    F: FnMut(<I as Iterator>::Item) -> B,
    I: ExactSizeIterator, 

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<I> ExactSizeIterator for Enumerate<I> where
    I: ExactSizeIterator, 

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<I> ExactSizeIterator for Fuse<I> where
    I: ExactSizeIterator, 

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<I> ExactSizeIterator for Peekable<I> where
    I: ExactSizeIterator, 

impl<I> ExactSizeIterator for Rev<I> where
    I: ExactSizeIterator + DoubleEndedIterator, 

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<I> ExactSizeIterator for Skip<I> where
    I: ExactSizeIterator, 

impl<I> ExactSizeIterator for StepBy<I> where
    I: ExactSizeIterator, 

impl<I> ExactSizeIterator for Take<I> where
    I: ExactSizeIterator, 

impl<I> ExactSizeIterator for ExactlyOneError<I> where
    I: ExactSizeIterator, 

impl<I> ExactSizeIterator for MultiPeek<I> where
    I: ExactSizeIterator, 

impl<I> ExactSizeIterator for PeekNth<I> where
    I: ExactSizeIterator, 

impl<I> ExactSizeIterator for Step<I> where
    I: ExactSizeIterator, 

impl<I> ExactSizeIterator for Tee<I> where
    I: ExactSizeIterator,
    <I as Iterator>::Item: Clone, 

impl<I> ExactSizeIterator for WithPosition<I> where
    I: ExactSizeIterator, 

impl<I, F> ExactSizeIterator for Inspect<I, F> where
    F: FnMut(&<I as Iterator>::Item),
    I: ExactSizeIterator, 

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

impl<I, F> ExactSizeIterator for PadUsing<I, F> where
    F: FnMut(usize) -> <I as Iterator>::Item,
    I: ExactSizeIterator, 

impl<I, F> ExactSizeIterator for Update<I, F> where
    F: FnMut(&mut <I as Iterator>::Item),
    I: ExactSizeIterator, 

impl<I, J> ExactSizeIterator for ZipEq<I, J> where
    I: ExactSizeIterator,
    J: ExactSizeIterator, 

impl<L, R> ExactSizeIterator for Either<L, R> where
    R: ExactSizeIterator<Item = <L as Iterator>::Item>,
    L: ExactSizeIterator, 

impl<T> ExactSizeIterator for Empty<T>

pub fn len(&self) -> usize

impl<T> ExactSizeIterator for Once<T>

pub fn len(&self) -> usize

impl<T> ExactSizeIterator for TupleBuffer<T> where
    T: HomogeneousTuple, 

impl<T, U> ExactSizeIterator for ZipLongest<T, U> where
    T: ExactSizeIterator,
    U: ExactSizeIterator, 

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