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Auto merge of #85975 - the8472:revert-take-tra, r=scottmcm

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Revert "implement TrustedRandomAccess for Take iterator adapter"

This reverts commit 37a5b515e9 (#83990).

The original change unintentionally caused side-effects from certain iterator chains combining `take`, `zip` and `next_back()` to be omitted which is observable by user code and thus likely a breaking change

Technically one could declare it not a breaking change since `Zip`'s API contract is silent about about its backwards iteration behavior but on the other hand there is nothing in the stable Iterator API that could justify the currently observable behavior. And either way, this impact wasn't noticed or discussed in the original PR.

Fixes #85969
This commit is contained in:
bors 2021-06-09 11:24:54 +00:00
commit 38bc9b9933
1 changed files with 1 additions and 22 deletions
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23
library/core/src/iter/adapters/take.rs
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@ -1,8 +1,5 @@
use crate::cmp;
use crate::iter::{
adapters::zip::try_get_unchecked, adapters::SourceIter, FusedIterator, InPlaceIterable,
TrustedLen, TrustedRandomAccess,
};
use crate::iter::{adapters::SourceIter, FusedIterator, InPlaceIterable, TrustedLen};
use crate::ops::{ControlFlow, Try};
/// An iterator that only iterates over the first `n` iterations of `iter`.
@ -114,15 +111,6 @@ fn ok<B, T>(mut f: impl FnMut(B, T) -> B) -> impl FnMut(B, T) -> Result<B, !> {
self.try_fold(init, ok(fold)).unwrap()
}
unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> <I as Iterator>::Item
where
Self: TrustedRandomAccess,
{
// SAFETY: the caller must uphold the contract for
// `Iterator::__iterator_get_unchecked`.
unsafe { try_get_unchecked(&mut self.iter, idx) }
}
}
#[unstable(issue = "none", feature = "inplace_iteration")]
@ -219,12 +207,3 @@ impl<I> FusedIterator for Take<I> where I: FusedIterator {}
#[unstable(feature = "trusted_len", issue = "37572")]
unsafe impl<I: TrustedLen> TrustedLen for Take<I> {}
#[doc(hidden)]
#[unstable(feature = "trusted_random_access", issue = "none")]
unsafe impl<I> TrustedRandomAccess for Take<I>
where
I: TrustedRandomAccess,
{
const MAY_HAVE_SIDE_EFFECT: bool = I::MAY_HAVE_SIDE_EFFECT;
}