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Merge pull request #242 from camelid/improve-transmutes

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Improve formatting of "Transmutes" chapter
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Yuki Okushi 4 years ago committed by GitHub
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@ -15,14 +15,18 @@ boggling.
is going to cause arbitrary chaos that can't really be predicted. Do not is going to cause arbitrary chaos that can't really be predicted. Do not
transmute `3` to `bool`. Even if you never *do* anything with the `bool`. Just transmute `3` to `bool`. Even if you never *do* anything with the `bool`. Just
don't. don't.
* Transmute has an overloaded return type. If you do not specify the return type * Transmute has an overloaded return type. If you do not specify the return type
it may produce a surprising type to satisfy inference. it may produce a surprising type to satisfy inference.
* Transmuting an & to &mut is UB.
* Transmuting an & to &mut is *always* UB. * Transmuting an `&` to `&mut` is UB.
* Transmuting an `&` to `&mut` is *always* UB.
* No you can't do it. * No you can't do it.
* No you're not special. * No you're not special.
* Transmuting to a reference without an explicitly provided lifetime * Transmuting to a reference without an explicitly provided lifetime
produces an [unbounded lifetime] produces an [unbounded lifetime].
* When transmuting between different compound types, you have to make sure they * When transmuting between different compound types, you have to make sure they
are laid out the same way! If layouts differ, the wrong fields are going to are laid out the same way! If layouts differ, the wrong fields are going to
get filled with the wrong data, which will make you unhappy and can also be UB get filled with the wrong data, which will make you unhappy and can also be UB
@ -47,7 +51,7 @@ pointer casts or `union`s, but without any of the lints or other basic sanity
checks. Raw pointer casts and `union`s do not magically avoid the above rules. checks. Raw pointer casts and `union`s do not magically avoid the above rules.
[unbounded lifetime]: unbounded-lifetimes.html [unbounded lifetime]: ./unbounded-lifetimes.md
[transmute]: ../std/mem/fn.transmute.html [transmute]: ../std/mem/fn.transmute.html
[transmute_copy]: ../std/mem/fn.transmute_copy.html [transmute_copy]: ../std/mem/fn.transmute_copy.html
[ucg-layout]: https://rust-lang.github.io/unsafe-code-guidelines/layout.html [ucg-layout]: https://rust-lang.github.io/unsafe-code-guidelines/layout.html

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