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Implement TrustedLen for Fuse<I: TrustedLen> #81599

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Merged
merged 2 commits into from
Feb 2, 2021
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Implement TrustedLen for Fuse<I: TrustedLen> #81599

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9989334
Add SAFETY comment for the `TrustedRandomAccess` impl of `iter::Fuse`
sdroege Feb 1, 2021
12b605a
Implement `TrustedLen` for `iter::Fuse<I: TrustedLen>`
sdroege Jan 31, 2021
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15 changes: 14 additions & 1 deletion library/core/src/iter/adapters/fuse.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
use crate::intrinsics;
use crate::iter::adapters::{zip::try_get_unchecked, InPlaceIterable, SourceIter};
use crate::iter::{DoubleEndedIterator, ExactSizeIterator, FusedIterator, TrustedRandomAccess};
use crate::iter::{
DoubleEndedIterator, ExactSizeIterator, FusedIterator, TrustedLen, TrustedRandomAccess,
};
use crate::ops::Try;

/// An iterator that yields `None` forever after the underlying iterator
Expand Down Expand Up @@ -182,8 +184,19 @@ where
}
}

#[unstable(feature = "trusted_len", issue = "37572")]
// SAFETY: `TrustedLen` requires that an accurate length is reported via `size_hint()`. As `Fuse`
// is just forwarding this to the wrapped iterator `I` this property is preserved and it is safe to
// implement `TrustedLen` here.
unsafe impl<I> TrustedLen for Fuse<I> where I: TrustedLen {}

#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
// SAFETY: `TrustedRandomAccess` requires that `size_hint()` must be exact and cheap to call, and
// `Iterator::__iterator_get_unchecked()` must be implemented accordingly.
//
// This is safe to implement as `Fuse` is just forwarding these to the wrapped iterator `I`, which
// preserves these properties.
unsafe impl<I> TrustedRandomAccess for Fuse<I>
where
I: TrustedRandomAccess,
Expand Down