Trait enso_prelude::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 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

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());

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);

Implementations on Foreign Types

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

pub fn len(&self) -> usize

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

pub fn len(&self) -> usize

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

pub fn len(&self) -> usize

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

pub fn len(&self) -> usize

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

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 IntoValues<K, V>

pub fn len(&self) -> usize

impl<K> ExactSizeIterator for IntoIter<K>

pub fn len(&self) -> usize

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

pub fn len(&self) -> usize

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

pub fn len(&self) -> usize

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

pub fn len(&self) -> usize

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

impl<A> ExactSizeIterator for IntoIter<A>

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<T> ExactSizeIterator for IntoIter<T>

impl ExactSizeIterator for EscapeUnicode

pub fn len(&self) -> usize

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

impl ExactSizeIterator for ToLowercase

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

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

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

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> ExactSizeIterator for Iter<'_, T>

pub fn len(&self) -> usize

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

impl<T> ExactSizeIterator for IntoIter<T>

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

pub fn len(&self) -> usize

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 IntoIter<K, V>

pub fn len(&self) -> usize

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 IterMut<'_, K, V>

pub fn len(&self) -> usize

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 IterMut<'_, T>

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 IntoIter<T>

pub fn len(&self) -> usize

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

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

pub fn len(&self) -> usize

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

pub fn len(&self) -> usize

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<T> ExactSizeIterator for IntoIter<T>

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<'_, 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<T> ExactSizeIterator for IntoIterSorted<T> where
    T: Ord, 

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

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

impl<T> ExactSizeIterator for IntoIter<T>

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

impl<'_> ExactSizeIterator for U32Digits<'_>

pub fn len(&self) -> usize

impl<'_> ExactSizeIterator for U64Digits<'_>

pub fn len(&self) -> usize

impl<'a> ExactSizeIterator for ArrayIter<'a>

impl<'a, T, R, C, S> ExactSizeIterator for MatrixIterMut<'a, T, R, C, S> where
    C: Dim,
    T: Scalar,
    R: Dim,
    S: 'a + StorageMut<T, R, C>, 

pub fn len(&self) -> usize

impl<'a, T, R, C, S> ExactSizeIterator for RowIter<'a, T, R, C, S> where
    C: Dim,
    T: Scalar,
    R: Dim,
    S: 'a + Storage<T, R, C>, 

pub fn len(&self) -> usize

impl<'a, T, R, C, S> ExactSizeIterator for RowIterMut<'a, T, R, C, S> where
    C: Dim,
    T: Scalar,
    R: Dim,
    S: 'a + StorageMut<T, R, C>, 

pub fn len(&self) -> usize

impl<'a, T, R, C, S> ExactSizeIterator for MatrixIter<'a, T, R, C, S> where
    C: Dim,
    T: Scalar,
    R: Dim,
    S: 'a + Storage<T, R, C>, 

pub fn len(&self) -> usize

impl<'a, T, R, C, S> ExactSizeIterator for ColumnIterMut<'a, T, R, C, S> where
    C: Dim,
    T: Scalar,
    R: Dim,
    S: 'a + StorageMut<T, R, C>, 

pub fn len(&self) -> usize

impl<'a, T, R, C, S> ExactSizeIterator for ColumnIter<'a, T, R, C, S> where
    C: Dim,
    T: Scalar,
    R: Dim,
    S: 'a + Storage<T, R, C>, 

pub fn len(&self) -> usize

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<'_, 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 enso_prelude::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 enso_prelude::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, 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
    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, 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, B> ExactSizeIterator for enso_prelude::iter::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, 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<T> ExactSizeIterator for Empty<T>

pub fn len(&self) -> usize

impl<T> ExactSizeIterator for Once<T>

pub fn len(&self) -> usize