Trait TrustedLen

Source

pub unsafe trait TrustedLen: Iterator { }

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

Expand description

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 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.

TrustedLen

Trait TrustedLen Copy item path

§When shouldn’t an adapter be TrustedLen?

§Safety

Implementors§

impl TrustedLen for ToLowercase

impl TrustedLen for ToUppercase

impl TrustedLen for Bytes<'_>

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

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

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

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

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

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

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

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

impl<A, B> TrustedLen for Chain<A, B>where A: TrustedLen, B: TrustedLen<Item = A::Item>,

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

impl<A, F: FnMut() -> A> TrustedLen for RepeatWith<F>

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

impl<A: Clone> TrustedLen for Repeat<A>

impl<A: Clone> TrustedLen for RepeatN<A>

impl<A: TrustedStep> TrustedLen for Range<A>

impl<A: TrustedStep> TrustedLen for RangeFrom<A>

impl<A: TrustedStep> TrustedLen for RangeInclusive<A>

impl<A: TrustedStep> TrustedLen for IterRange<A>

impl<A: TrustedStep> TrustedLen for IterRangeFrom<A>

impl<A: TrustedStep> TrustedLen for IterRangeInclusive<A>

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

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

impl<I> TrustedLen for Flatten<I>where I: Iterator<Item: IntoIterator>, FlattenCompat<I, <I::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,

impl<I> TrustedLen for Skip<I>where I: Iterator + TrustedRandomAccess,

impl<I> TrustedLen for StepBy<I>where I: Iterator + TrustedRandomAccess,

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

impl<I: TrustedLen + ?Sized> TrustedLen for &mut I

impl<I: TrustedLen> TrustedLen for Take<I>

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

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

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

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

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

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

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

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

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

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

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

impl<T> TrustedLen for Empty<T>

impl<T> TrustedLen for Once<T>

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

Trait TrustedLen

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

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

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

impl<A, B> TrustedLen for Chain<A, B>
where A: TrustedLen, B: TrustedLen<Item = A::Item>,

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

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

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

impl<I> TrustedLen for Flatten<I>
where I: Iterator<Item: IntoIterator>, FlattenCompat<I, <I::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,

impl<I> TrustedLen for Skip<I>
where I: Iterator + TrustedRandomAccess,

impl<I> TrustedLen for StepBy<I>
where I: Iterator + TrustedRandomAccess,

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