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Add a note about the correctness and the effect on unsafe code to the ExactSizeIterator docs

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As it is a safe trait it does not provide any guarantee that the
returned length is correct and as such unsafe code must not rely on it.

That's why `TrustedLen` exists.

Fixes https://github.com/rust-lang/rust/issues/81739
This commit is contained in:
Sebastian Dröge 2021-02-04 10:40:20 +02:00
parent e708cbd91c
commit f436630ac8
1 changed files with 6 additions and 0 deletions
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6
library/core/src/iter/traits/exact_size.rs
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@ -13,6 +13,12 @@
/// implement it. However, you may be able to provide a more performant
/// implementation than the default, so overriding it in this case makes sense.
///
/// Note that this trait is a safe trait and as such does *not* and *cannot*
/// guarantee that the returned length is correct. This means that `unsafe`
/// code **must not** rely on the correctness of [`Iterator::size_hint`]. The
/// unstable and unsafe [`TrustedLen`](super::marker::TrustedLen) trait gives
/// this additional guarantee.
///
/// [`len`]: ExactSizeIterator::len
///
/// # Examples