# Is reborrowing documented anywhere?

**URL:** <https://internals.rust-lang.org/t/is-reborrowing-documented-anywhere/8245>\
**Category:** Uncategorized\
**Created:** [August 20, 2018, 4:47pm UTC](https://internals.rust-lang.org/t/is-reborrowing-documented-anywhere/8245 "2018-08-20T16:47:44Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![matklad](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/matklad/32/12266_2.png) [@matklad](https://internals.rust-lang.org/u/matklad)\
**Post date:** [August 20, 2018, 4:47pm UTC](https://internals.rust-lang.org/t/is-reborrowing-documented-anywhere/8245/1 "2018-08-20T16:47:44Z")

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An important bit to understand when writing Rust code is that passing `&'a mut` around often inserts automatic reborrows, like `&mut *x`, which allows to “shorten” a unique lifetime and can _easy_ be confused with variance.

Is this behavior documented anywhere?

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**Author:** ![steveklabnik](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/steveklabnik/32/4524_2.png) [@steveklabnik](https://internals.rust-lang.org/u/steveklabnik)\
**Post date:** [August 20, 2018, 4:59pm UTC](https://internals.rust-lang.org/t/is-reborrowing-documented-anywhere/8245/2 "2018-08-20T16:59:56Z")

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Basically not. It’s mentioned offhand in the reference but not really documented well.

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**Author:** ![mbrubeck](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/mbrubeck/32/174_2.png) [@mbrubeck](https://internals.rust-lang.org/u/mbrubeck)\
**Post date:** [August 20, 2018, 5:02pm UTC](https://internals.rust-lang.org/t/is-reborrowing-documented-anywhere/8245/3 "2018-08-20T17:02:18Z")

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There was a bit of an attempt as part of [RFC 2364](https://github.com/rust-lang/rfcs/pull/2364), which was postponed because the language team feels it would be better to do it after MIR borrowck, NLL, and Chalk are complete.

Old versions of the Rustonomicon had a brief description of reborrowing in the [References](https://doc.rust-lang.org/1.19.0/nomicon/references.html#liveness) chapter.

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**Author:** ![system](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/system/32/14092_2.png) [@system](https://internals.rust-lang.org/u/system)\
**Post date:** [March 25, 2019, 8:30am UTC](https://internals.rust-lang.org/t/is-reborrowing-documented-anywhere/8245/4 "2019-03-25T08:30:44Z")

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