| /// An iterator that always continues to yield `None` when exhausted. |
| /// |
| /// Calling next on a fused iterator that has returned `None` once is guaranteed |
| /// to return [`None`] again. This trait should be implemented by all iterators |
| /// that behave this way because it allows optimizing [`Iterator::fuse`]. |
| /// |
| /// Note: In general, you should not use `FusedIterator` in generic bounds if |
| /// you need a fused iterator. Instead, you should just call [`Iterator::fuse`] |
| /// on the iterator. If the iterator is already fused, the additional [`Fuse`] |
| /// wrapper will be a no-op with no performance penalty. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// [`Iterator::fuse`]: ../../std/iter/trait.Iterator.html#method.fuse |
| /// [`Fuse`]: ../../std/iter/struct.Fuse.html |
| #[stable(feature = "fused", since = "1.26.0")] |
| pub trait FusedIterator: Iterator {} |
| |
| #[stable(feature = "fused", since = "1.26.0")] |
| impl<I: FusedIterator + ?Sized> FusedIterator for &mut I {} |
| |
| /// 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 a [`.size_hint`] of `(usize::MAX, None)`. |
| /// |
| /// The iterator must produce exactly the number of elements it reported |
| /// or diverge before reaching the end. |
| /// |
| /// # Safety |
| /// |
| /// This trait must only be implemented when the contract is upheld. |
| /// Consumers of this trait must inspect [`.size_hint`]’s upper bound. |
| /// |
| /// [`None`]: ../../std/option/enum.Option.html#variant.None |
| /// [`usize::MAX`]: ../../std/usize/constant.MAX.html |
| /// [`.size_hint`]: ../../std/iter/trait.Iterator.html#method.size_hint |
| #[unstable(feature = "trusted_len", issue = "37572")] |
| pub unsafe trait TrustedLen: Iterator {} |
| |
| #[unstable(feature = "trusted_len", issue = "37572")] |
| unsafe impl<I: TrustedLen + ?Sized> TrustedLen for &mut I {} |