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Trait std::iter::ExactSizeIterator

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

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

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 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());

fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty #35428)

Returns true if the iterator is empty.

This method has a default implementation using self.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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Implementors

impl ExactSizeIterator for std::ascii::EscapeDefault[src]

impl ExactSizeIterator for EscapeDebug[src]

impl ExactSizeIterator for std::char::EscapeDefault[src]

impl ExactSizeIterator for EscapeUnicode[src]

impl ExactSizeIterator for ToLowercase[src]

impl ExactSizeIterator for ToUppercase[src]

impl ExactSizeIterator for Args[src]

impl ExactSizeIterator for ArgsOs[src]

impl ExactSizeIterator for Range<i8>[src]

impl ExactSizeIterator for Range<i16>[src]

impl ExactSizeIterator for Range<i32>[src]

impl ExactSizeIterator for Range<isize>[src]

impl ExactSizeIterator for Range<u8>[src]

impl ExactSizeIterator for Range<u16>[src]

impl ExactSizeIterator for Range<u32>[src]

impl ExactSizeIterator for Range<usize>[src]

impl ExactSizeIterator for RangeInclusive<i8>[src]

impl ExactSizeIterator for RangeInclusive<i16>[src]

impl ExactSizeIterator for RangeInclusive<u8>[src]

impl ExactSizeIterator for RangeInclusive<u16>[src]

impl<'_> ExactSizeIterator for Bytes<'_>[src]

impl<'_, A> ExactSizeIterator for std::option::Iter<'_, A>[src]

impl<'_, A> ExactSizeIterator for std::option::IterMut<'_, A>[src]

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

impl<'_, I> ExactSizeIterator for Splice<'_, I> where
    I: Iterator, [src]

impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::Iter<'_, K, V>[src]

impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::IterMut<'_, K, V>[src]

impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::Keys<'_, K, V>[src]

impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::Values<'_, K, V>[src]

impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::ValuesMut<'_, K, V>[src]

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

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

impl<'_, T> ExactSizeIterator for std::collections::binary_heap::Iter<'_, T>[src]

impl<'_, T> ExactSizeIterator for std::collections::btree_set::Iter<'_, T>[src]

impl<'_, T> ExactSizeIterator for std::collections::linked_list::Iter<'_, T>[src]

impl<'_, T> ExactSizeIterator for std::collections::linked_list::IterMut<'_, T>[src]

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

impl<'_, T> ExactSizeIterator for std::collections::vec_deque::Iter<'_, T>[src]

impl<'_, T> ExactSizeIterator for std::collections::vec_deque::IterMut<'_, T>[src]

impl<'_, T> ExactSizeIterator for std::result::Iter<'_, T>[src]

impl<'_, T> ExactSizeIterator for std::result::IterMut<'_, T>[src]

impl<'_, T> ExactSizeIterator for Chunks<'_, T>[src]

impl<'_, T> ExactSizeIterator for ChunksExact<'_, T>[src]

impl<'_, T> ExactSizeIterator for ChunksExactMut<'_, T>[src]

impl<'_, T> ExactSizeIterator for ChunksMut<'_, T>[src]

impl<'_, T> ExactSizeIterator for std::slice::Iter<'_, T>[src]

impl<'_, T> ExactSizeIterator for std::slice::IterMut<'_, T>[src]

impl<'_, T> ExactSizeIterator for RChunks<'_, T>[src]

impl<'_, T> ExactSizeIterator for RChunksExactMut<'_, T>[src]

impl<'_, T> ExactSizeIterator for RChunksMut<'_, T>[src]

impl<'_, T> ExactSizeIterator for Windows<'_, T>[src]

impl<'_, T> ExactSizeIterator for std::vec::Drain<'_, T>[src]

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

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

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

impl<'a, T> ExactSizeIterator for RChunksExact<'a, T>[src]

impl<A> ExactSizeIterator for std::option::IntoIter<A>[src]

impl<A, B> ExactSizeIterator for Zip<A, B> where
    A: ExactSizeIterator,
    B: ExactSizeIterator, [src]

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

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

impl<I> ExactSizeIterator for Box<I> where
    I: ExactSizeIterator + ?Sized, [src]

impl<I> ExactSizeIterator for Enumerate<I> where
    I: ExactSizeIterator, [src]

impl<I> ExactSizeIterator for Fuse<I> where
    I: ExactSizeIterator, [src]

impl<I> ExactSizeIterator for Peekable<I> where
    I: ExactSizeIterator, [src]

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

impl<I> ExactSizeIterator for Skip<I> where
    I: ExactSizeIterator, [src]

impl<I> ExactSizeIterator for StepBy<I> where
    I: ExactSizeIterator, [src]

impl<I> ExactSizeIterator for Take<I> where
    I: ExactSizeIterator, [src]

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

impl<K> ExactSizeIterator for std::collections::hash_set::IntoIter<K>[src]

impl<K, '_> ExactSizeIterator for std::collections::hash_set::Drain<'_, K>[src]

impl<K, '_> ExactSizeIterator for std::collections::hash_set::Iter<'_, K>[src]

impl<K, V> ExactSizeIterator for std::collections::btree_map::IntoIter<K, V>[src]

impl<K, V> ExactSizeIterator for std::collections::btree_map::IntoKeys<K, V>[src]

impl<K, V> ExactSizeIterator for std::collections::btree_map::IntoValues<K, V>[src]

impl<K, V> ExactSizeIterator for std::collections::hash_map::IntoIter<K, V>[src]

impl<K, V> ExactSizeIterator for std::collections::hash_map::IntoKeys<K, V>[src]

impl<K, V> ExactSizeIterator for std::collections::hash_map::IntoValues<K, V>[src]

impl<K, V, '_> ExactSizeIterator for std::collections::hash_map::Drain<'_, K, V>[src]

impl<K, V, '_> ExactSizeIterator for std::collections::hash_map::Iter<'_, K, V>[src]

impl<K, V, '_> ExactSizeIterator for std::collections::hash_map::IterMut<'_, K, V>[src]

impl<K, V, '_> ExactSizeIterator for std::collections::hash_map::Keys<'_, K, V>[src]

impl<K, V, '_> ExactSizeIterator for std::collections::hash_map::Values<'_, K, V>[src]

impl<K, V, '_> ExactSizeIterator for std::collections::hash_map::ValuesMut<'_, K, V>[src]

impl<T> ExactSizeIterator for std::collections::binary_heap::IntoIter<T>[src]

impl<T> ExactSizeIterator for IntoIterSorted<T> where
    T: Ord, [src]

impl<T> ExactSizeIterator for std::collections::btree_set::IntoIter<T>[src]

impl<T> ExactSizeIterator for std::collections::linked_list::IntoIter<T>[src]

impl<T> ExactSizeIterator for std::collections::vec_deque::IntoIter<T>[src]

impl<T> ExactSizeIterator for Empty<T>[src]

impl<T> ExactSizeIterator for Once<T>[src]

impl<T> ExactSizeIterator for std::result::IntoIter<T>[src]

impl<T> ExactSizeIterator for std::vec::IntoIter<T>[src]

impl<T, const N: usize> ExactSizeIterator for std::array::IntoIter<T, N>[src]

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© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/iter/trait.ExactSizeIterator.html