devela::_dep::_std::prelude::rust_2015

Trait ExactSizeIterator

1.55.0 · Source

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

Available on crate feature std only.

Expand description

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.

§When shouldn’t an adapter be `ExactSizeIterator`?

If an adapter makes an iterator longer, then it’s usually incorrect for that adapter to implement ExactSizeIterator. The inner exact-sized iterator might already be usize::MAX-long, and thus the length of the longer adapted iterator would no longer be exactly representable in usize.

This is why Chain<A, B> isn’t ExactSizeIterator, even when A and B are both ExactSizeIterator.

§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 mut counter = Counter::new();

assert_eq!(5, counter.len());
let _ = counter.next();
assert_eq!(4, counter.len());

Provided Methods§

1.0.0 · Source

fn len(&self) -> usize ⓘ

Returns the exact remaining 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 mut range = 0..5;

assert_eq!(5, range.len());
let _ = range.next();
assert_eq!(4, range.len());

Source

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);

Implementors§

1.0.0 · Source§

impl ExactSizeIterator for devela::_core::ascii::EscapeDefault

1.20.0 · Source§

impl ExactSizeIterator for EscapeDebug

1.11.0 · Source§

impl ExactSizeIterator for devela::_core::char::EscapeDefault

1.11.0 · Source§

impl ExactSizeIterator for EscapeUnicode

1.35.0 · Source§

impl ExactSizeIterator for ToLowercase

1.35.0 · Source§

Trait ExactSizeIteratorCopy item path

§When shouldn’t an adapter be ExactSizeIterator?

§Examples

Provided Methods§

fn len(&self) -> usize ⓘ

§Examples

fn is_empty(&self) -> bool

§Examples

Implementors§

impl ExactSizeIterator for devela::_core::ascii::EscapeDefault

impl ExactSizeIterator for EscapeDebug

impl ExactSizeIterator for devela::_core::char::EscapeDefault

impl ExactSizeIterator for EscapeUnicode

impl ExactSizeIterator for ToLowercase

impl ExactSizeIterator for ToUppercase

impl ExactSizeIterator for IterRange<i8>

impl ExactSizeIterator for IterRange<i16>

impl ExactSizeIterator for IterRange<isize>

impl ExactSizeIterator for IterRange<u8>

impl ExactSizeIterator for IterRange<u16>

impl ExactSizeIterator for IterRange<usize>

impl ExactSizeIterator for IterRangeInclusive<i8>

impl ExactSizeIterator for IterRangeInclusive<u8>

impl ExactSizeIterator for Bytes<'_>

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 ArrayIntoIter

impl ExactSizeIterator for ArrayIter<'_>

impl ExactSizeIterator for BorrowedTupleIterator<'_, '_>

impl ExactSizeIterator for BoundDictIterator<'_>

impl ExactSizeIterator for BoundFrozenSetIterator<'_>

impl ExactSizeIterator for BoundListIterator<'_>

impl ExactSizeIterator for BoundSetIterator<'_>

impl ExactSizeIterator for BoundTupleIterator<'_>

impl ExactSizeIterator for Args

impl ExactSizeIterator for ArgsOs

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

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

impl<'a, 'bump, I> ExactSizeIterator for devela::_dep::bumpalo::collections::vec::Splice<'a, 'bump, I>where I: Iterator,

impl<'a, 'bump, T> ExactSizeIterator for devela::_dep::bumpalo::collections::vec::Drain<'a, 'bump, T>

impl<'a, I> ExactSizeIterator for devela::_dep::bumpalo::boxed::Box<'a, I>where I: ExactSizeIterator + ?Sized,

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

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

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

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

impl<'a, T, const CAP: usize> ExactSizeIterator for arrayvec::arrayvec::Drain<'a, T, CAP>where T: 'a,

impl<'bump, T> ExactSizeIterator for devela::_dep::bumpalo::collections::vec::IntoIter<'bump, T>where T: 'bump,

impl<'c, 'h> ExactSizeIterator for SubCaptureMatches<'c, 'h>

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

impl<'s, T, const CAP: usize, S: Storage> ExactSizeIterator for DestaqueIter<'s, T, CAP, u8, S>

impl<'s, T, const CAP: usize, S: Storage> ExactSizeIterator for DestaqueIter<'s, T, CAP, u16, S>

impl<'s, T, const CAP: usize, S: Storage> ExactSizeIterator for DestaqueIter<'s, T, CAP, u32, S>

impl<'s, T, const CAP: usize, S: Storage> ExactSizeIterator for DestaqueIter<'s, T, CAP, usize, S>

impl<'s, T, const CAP: usize, S: Storage> ExactSizeIterator for StackIter<'s, T, CAP, u8, S>

impl<'s, T, const CAP: usize, S: Storage> ExactSizeIterator for StackIter<'s, T, CAP, u16, S>

impl<'s, T, const CAP: usize, S: Storage> ExactSizeIterator for StackIter<'s, T, CAP, u32, S>

impl<'s, T, const CAP: usize, S: Storage> ExactSizeIterator for StackIter<'s, T, CAP, usize, S>

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

impl<A> ExactSizeIterator for devela::_core::option::IntoIter<A>

impl<A> ExactSizeIterator for devela::_core::option::Iter<'_, A>

impl<A> ExactSizeIterator for devela::_core::option::IterMut<'_, A>

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

impl<A, B> ExactSizeIterator for Zip<A, B>where A: ExactSizeIterator, B: ExactSizeIterator,

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

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

impl<BUF: DstBuf, DST> ExactSizeIterator for DstValue<DST, BUF>where DST: ExactSizeIterator + ?Sized,

impl<F, A> ExactSizeIterator for Take<RepeatWith<F>>where F: FnMut() -> A,

impl<I1, I2> ExactSizeIterator for Mix<I1, I2>where I1: Source + ExactSizeIterator, <I1 as Iterator>::Item: FromSample<<I2 as Iterator>::Item> + Sample, I2: Source + ExactSizeIterator, <I2 as Iterator>::Item: Sample,

impl<I> ExactSizeIterator for &mut Iwhere I: ExactSizeIterator + ?Sized,

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

Trait ExactSizeIterator

§When shouldn’t an adapter be `ExactSizeIterator`?

impl<'a, 'bump, I> ExactSizeIterator for devela::_dep::bumpalo::collections::vec::Splice<'a, 'bump, I>
where I: Iterator,

impl<'a, I> ExactSizeIterator for devela::_dep::bumpalo::boxed::Box<'a, I>
where I: ExactSizeIterator + ?Sized,

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

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

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

impl<'a, T, const CAP: usize> ExactSizeIterator for arrayvec::arrayvec::Drain<'a, T, CAP>
where T: 'a,

impl<'bump, T> ExactSizeIterator for devela::_dep::bumpalo::collections::vec::IntoIter<'bump, T>
where T: 'bump,

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

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

impl<A, B> ExactSizeIterator for Zip<A, B>
where A: ExactSizeIterator, B: ExactSizeIterator,

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

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

impl<BUF: DstBuf, DST> ExactSizeIterator for DstValue<DST, BUF>
where DST: ExactSizeIterator + ?Sized,

impl<F, A> ExactSizeIterator for Take<RepeatWith<F>>
where F: FnMut() -> A,

impl<I1, I2> ExactSizeIterator for Mix<I1, I2>
where I1: Source + ExactSizeIterator, <I1 as Iterator>::Item: FromSample<<I2 as Iterator>::Item> + Sample, I2: Source + ExactSizeIterator, <I2 as Iterator>::Item: Sample,

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

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

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

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

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

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 Amplify<I>
where I: Source + ExactSizeIterator, <I as Iterator>::Item: Sample,

impl<I> ExactSizeIterator for AutomaticGainControl<I>
where I: Source + ExactSizeIterator, <I as Iterator>::Item: Sample,

impl<I> ExactSizeIterator for BltFilter<I>
where I: Source<Item = f32> + ExactSizeIterator,

impl<I> ExactSizeIterator for ChannelVolume<I>
where I: Source + ExactSizeIterator, <I as Iterator>::Item: Sample,

impl<I> ExactSizeIterator for FadeIn<I>
where I: Source + ExactSizeIterator, <I as Iterator>::Item: Sample,

impl<I> ExactSizeIterator for FadeOut<I>
where I: Source + ExactSizeIterator, <I as Iterator>::Item: Sample,

impl<I> ExactSizeIterator for LinearGainRamp<I>
where I: Source + ExactSizeIterator, <I as Iterator>::Item: Sample,

impl<I> ExactSizeIterator for Spatial<I>
where I: Source + ExactSizeIterator, <I as Iterator>::Item: Sample,

impl<I> ExactSizeIterator for Speed<I>
where I: Source + ExactSizeIterator, <I as Iterator>::Item: Sample,

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

impl<I, A> ExactSizeIterator for devela::_dep::_alloc::vec::Splice<'_, I, A>
where I: Iterator, A: Allocator,

impl<I, D> ExactSizeIterator for SamplesConverter<I, D>
where I: Source + ExactSizeIterator, <I as Iterator>::Item: Sample, D: FromSample<<I as Iterator>::Item> + Sample,

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

impl<I, F, R, const N: usize> ExactSizeIterator for MapWindows<I, F, N>
where I: ExactSizeIterator, F: FnMut(&[<I as Iterator>::Item; N]) -> R,

impl<I, const N: usize> ExactSizeIterator for devela::_core::iter::ArrayChunks<I, N>
where I: ExactSizeIterator,

impl<K, A> ExactSizeIterator for devela::_dep::hashbrown::hash_set::Drain<'_, K, A>
where A: Allocator,

impl<K, A> ExactSizeIterator for devela::_dep::hashbrown::hash_set::IntoIter<K, A>
where A: Allocator,

impl<K, V, A> ExactSizeIterator for devela::_dep::_alloc::collections::btree_map::IntoIter<K, V, A>
where A: Allocator + Clone,

impl<K, V, A> ExactSizeIterator for devela::_dep::_alloc::collections::btree_map::IntoKeys<K, V, A>
where A: Allocator + Clone,

impl<K, V, A> ExactSizeIterator for devela::_dep::_alloc::collections::btree_map::IntoValues<K, V, A>
where A: Allocator + Clone,

impl<K, V, A> ExactSizeIterator for devela::_dep::hashbrown::hash_map::Drain<'_, K, V, A>
where A: Allocator,

impl<K, V, A> ExactSizeIterator for devela::_dep::hashbrown::hash_map::IntoIter<K, V, A>
where A: Allocator,

impl<K, V, A> ExactSizeIterator for devela::_dep::hashbrown::hash_map::IntoKeys<K, V, A>
where A: Allocator,

impl<K, V, A> ExactSizeIterator for devela::_dep::hashbrown::hash_map::IntoValues<K, V, A>
where A: Allocator,

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

impl<L, R> ExactSizeIterator for IterEither<L, R>
where L: ExactSizeIterator, R: ExactSizeIterator,