Trait nom::lib::std::prelude::v1::rust_2021::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 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<'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<'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 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 ExactSizeIterator for ToUppercase

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 EscapeDebug

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 ExactSizeIterator for EscapeDefault

impl ExactSizeIterator for EscapeDefault

pub fn len(&self) -> usize

impl ExactSizeIterator for EscapeUnicode

pub fn len(&self) -> usize

impl<'a> ExactSizeIterator for EscapeAscii<'a>

impl ExactSizeIterator for ToLowercase

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Implementors

impl ExactSizeIterator for Range<i8>

impl ExactSizeIterator for Range<i16>

impl ExactSizeIterator for Range<i32>

impl ExactSizeIterator for Range<isize>

impl ExactSizeIterator for Range<u8>

impl ExactSizeIterator for Range<u16>

impl ExactSizeIterator for Range<u32>

impl ExactSizeIterator for Range<usize>

impl ExactSizeIterator for RangeInclusive<i8>

impl ExactSizeIterator for RangeInclusive<i16>

impl ExactSizeIterator for RangeInclusive<u8>

impl ExactSizeIterator for RangeInclusive<u16>

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<'_, A> ExactSizeIterator for nom::lib::std::option::Iter<'_, A>

impl<'_, A> ExactSizeIterator for nom::lib::std::option::IterMut<'_, A>

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

impl<'_, K> ExactSizeIterator for nom::lib::std::collections::hash_set::Drain<'_, K>

pub fn len(&self) -> usize

impl<'_, K> ExactSizeIterator for nom::lib::std::collections::hash_set::Iter<'_, K>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::Iter<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::IterMut<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::Keys<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::Values<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::ValuesMut<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Drain<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Iter<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::IterMut<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Keys<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Values<'_, K, V>

pub fn len(&self) -> usize

impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::ValuesMut<'_, K, V>

pub fn len(&self) -> usize

impl<'_, T> ExactSizeIterator for nom::lib::std::collections::binary_heap::Drain<'_, T>

pub fn is_empty(&self) -> bool

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

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

impl<'_, T> ExactSizeIterator for nom::lib::std::collections::binary_heap::Iter<'_, T>

pub fn is_empty(&self) -> bool

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

impl<'_, T> ExactSizeIterator for nom::lib::std::collections::btree_set::Iter<'_, T>

pub fn len(&self) -> usize

impl<'_, T> ExactSizeIterator for nom::lib::std::collections::linked_list::Iter<'_, T>

impl<'_, T> ExactSizeIterator for nom::lib::std::collections::linked_list::IterMut<'_, T>

impl<'_, T> ExactSizeIterator for nom::lib::std::collections::vec_deque::Drain<'_, T>

impl<'_, T> ExactSizeIterator for nom::lib::std::collections::vec_deque::Iter<'_, T>

pub fn is_empty(&self) -> bool

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

impl<'_, T> ExactSizeIterator for nom::lib::std::collections::vec_deque::IterMut<'_, T>

pub fn is_empty(&self) -> bool

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

impl<'_, T> ExactSizeIterator for nom::lib::std::result::Iter<'_, T>

impl<'_, T> ExactSizeIterator for nom::lib::std::result::IterMut<'_, T>

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

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> ExactSizeIterator for ChunksExactMut<'_, T>

pub fn is_empty(&self) -> bool

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

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

impl<'_, T> ExactSizeIterator for nom::lib::std::slice::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 nom::lib::std::slice::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<'_, 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 RChunksMut<'_, T>

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

impl<'_, T, A> ExactSizeIterator for nom::lib::std::vec::Drain<'_, T, A> where
    A: Allocator, 

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

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
    I: ExactSizeIterator<Item = &'a T>,
    T: 'a + Copy, 

pub fn len(&self) -> usize

pub fn is_empty(&self) -> bool

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

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<A> ExactSizeIterator for nom::lib::std::option::IntoIter<A>

impl<A, B> ExactSizeIterator for Zip<A, B> where
    A: ExactSizeIterator,
    B: 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, 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<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<K> ExactSizeIterator for nom::lib::std::collections::hash_set::IntoIter<K>

pub fn len(&self) -> usize

impl<K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::IntoIter<K, V>

pub fn len(&self) -> usize

impl<K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::IntoKeys<K, V>

pub fn len(&self) -> usize

impl<K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::IntoValues<K, V>

pub fn len(&self) -> usize

impl<K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::IntoIter<K, V>

pub fn len(&self) -> usize

impl<K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::IntoKeys<K, V>

pub fn len(&self) -> usize

impl<K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::IntoValues<K, V>

pub fn len(&self) -> usize

impl<T> ExactSizeIterator for nom::lib::std::collections::binary_heap::IntoIter<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 nom::lib::std::collections::btree_set::IntoIter<T>

pub fn len(&self) -> usize

impl<T> ExactSizeIterator for nom::lib::std::collections::linked_list::IntoIter<T>

impl<T> ExactSizeIterator for nom::lib::std::collections::vec_deque::IntoIter<T>

pub fn is_empty(&self) -> bool

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

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 nom::lib::std::result::IntoIter<T>

impl<T, A> ExactSizeIterator for nom::lib::std::vec::IntoIter<T, A> where
    A: Allocator, 

pub fn is_empty(&self) -> bool

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

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