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