Trait TrustedLen 

pub unsafe trait TrustedLen: Iterator { }

🔬This is a nightly-only experimental API. (trusted_len #37572)

An iterator that reports an accurate length using size_hint.

The iterator reports a size hint where it is either exact (lower bound is equal to upper bound), or the upper bound is None. The upper bound must only be None if the actual iterator length is larger than usize::MAX. In that case, the lower bound must be usize::MAX, resulting in an Iterator::size_hint() of (usize::MAX, None).

The iterator must produce exactly the number of elements it reported or diverge before reaching the end.

When shouldn’t an adapter be TrustedLen?

If an adapter makes an iterator shorter by a given amount, then it’s usually incorrect for that adapter to implement TrustedLen. The inner iterator might return more than usize::MAX items, but there’s no way to know what k elements less than that will be, since the size_hint from the inner iterator has already saturated and lost that information.

This is why Skip<I> isn’t TrustedLen, even when I implements TrustedLen.

Safety

This trait must only be implemented when the contract is upheld. Consumers of this trait must inspect Iterator::size_hint()’s upper bound.

Implementors

impl TrustedLen for ToLowercase

impl TrustedLen for ToUppercase

impl TrustedLen for Bytes<'_>

Available on non-crate feature ferrocene_subset only.

impl<'a, I, T> TrustedLen for Cloned<I>

where T: 'a + Clone, I: TrustedLen<Item = &'a T>,

impl<'a, I, T> TrustedLen for Copied<I>

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

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for Range<A>

where A: TrustedStep,

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for RangeFrom<A>

where A: TrustedStep,

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for RangeInclusive<A>

where A: TrustedStep,

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for std::option::IntoIter<A>

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for std::option::Iter<'_, A>

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for std::option::IterMut<'_, A>

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for OptionFlatten<A>

where A: TrustedLen,

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for RangeFromIter<A>

where A: TrustedStep,

impl<A> TrustedLen for RangeInclusiveIter<A>

where A: TrustedStep,

impl<A> TrustedLen for RangeIter<A>

where A: TrustedStep,

impl<A> TrustedLen for std::result::IntoIter<A>

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for std::result::Iter<'_, A>

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for std::result::IterMut<'_, A>

Available on non-crate feature ferrocene_subset only.

impl<A> TrustedLen for Repeat<A>

where A: Clone,

impl<A> TrustedLen for RepeatN<A>

where A: Clone,

impl<A, B> TrustedLen for Chain<A, B>

where A: TrustedLen, B: TrustedLen<Item = <A as Iterator>::Item>,

Available on non-crate feature ferrocene_subset only.

impl<A, B> TrustedLen for Zip<A, B>

where A: TrustedLen, B: TrustedLen,

Available on non-crate feature ferrocene_subset only.

impl<A, F> TrustedLen for OnceWith<F>

where F: FnOnce() -> A,

impl<A, F> TrustedLen for RepeatWith<F>

where F: FnMut() -> A,

impl<B, I, F> TrustedLen for Map<I, F>

where I: TrustedLen, F: FnMut(<I as Iterator>::Item) -> B,

impl<I> TrustedLen for &mut I

where I: TrustedLen + ?Sized,

impl<I> TrustedLen for Enumerate<I>

where I: TrustedLen,

Available on non-crate feature ferrocene_subset only.

impl<I> TrustedLen for Flatten<I>

where I: Iterator, <I as Iterator>::Item: IntoIterator, FlattenCompat<I, <<I as Iterator>::Item as IntoIterator>::IntoIter>: TrustedLen,

impl<I> TrustedLen for Fuse<I>

where I: TrustedLen,

impl<I> TrustedLen for Peekable<I>

where I: TrustedLen,

impl<I> TrustedLen for Rev<I>

where I: TrustedLen + DoubleEndedIterator,

Available on non-crate feature ferrocene_subset only.

impl<I> TrustedLen for Skip<I>

where I: Iterator + TrustedRandomAccess,

Available on non-crate feature ferrocene_subset only.

impl<I> TrustedLen for StepBy<I>

where I: Iterator + TrustedRandomAccess,

Available on non-crate feature ferrocene_subset only.

impl<I> TrustedLen for Take<I>

where I: TrustedLen,

Available on non-crate feature ferrocene_subset only.

impl<I, U, F> TrustedLen for FlatMap<I, U, F>

where I: Iterator, U: IntoIterator, F: FnMut(<I as Iterator>::Item) -> U, FlattenCompat<Map<I, F>, <U as IntoIterator>::IntoIter>: TrustedLen,

impl<K, V> TrustedLen for std::collections::btree_map::Iter<'_, K, V>

impl<K, V> TrustedLen for std::collections::btree_map::IterMut<'_, K, V>

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

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

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

impl<K, V, A> TrustedLen for std::collections::btree_map::IntoIter<K, V, A>

where A: Allocator + Clone,

impl<K, V, A> TrustedLen for IntoKeys<K, V, A>

where A: Allocator + Clone,

impl<K, V, A> TrustedLen for IntoValues<K, V, A>

where A: Allocator + Clone,

impl<T> TrustedLen for std::collections::btree_set::Iter<'_, T>

impl<T> TrustedLen for std::collections::vec_deque::Iter<'_, T>

impl<T> TrustedLen for std::collections::vec_deque::IterMut<'_, T>

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

Available on non-crate feature ferrocene_subset only.

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

Available on non-crate feature ferrocene_subset only.

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

Available on non-crate feature ferrocene_subset only.

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

Available on non-crate feature ferrocene_subset only.

impl<T> TrustedLen for std::slice::Iter<'_, T>

impl<T> TrustedLen for std::slice::IterMut<'_, T>

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

Available on non-crate feature ferrocene_subset only.

impl<T> TrustedLen for RChunksExact<'_, T>

Available on non-crate feature ferrocene_subset only.

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

Available on non-crate feature ferrocene_subset only.

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

Available on non-crate feature ferrocene_subset only.

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

Available on non-crate feature ferrocene_subset only.

impl<T> TrustedLen for Empty<T>

impl<T> TrustedLen for Once<T>

impl<T, A> TrustedLen for DrainSorted<'_, T, A>

where T: Ord, A: Allocator,

impl<T, A> TrustedLen for IntoIterSorted<T, A>

where T: Ord, A: Allocator,

impl<T, A> TrustedLen for std::collections::btree_set::IntoIter<T, A>

where A: Allocator + Clone,

impl<T, A> TrustedLen for std::collections::vec_deque::IntoIter<T, A>

where A: Allocator,

impl<T, A> TrustedLen for Drain<'_, T, A>

where A: Allocator,

impl<T, A> TrustedLen for std::vec::IntoIter<T, A>

where A: Allocator,

impl<T, const N: usize> TrustedLen for std::array::IntoIter<T, N>

Available on non-crate feature ferrocene_subset only.