Union discussions #369
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| # Unions | ||
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| ## Outstanding questions | ||
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| * Is `#[repr(Rust)]` the bag-o-bytes union repr, or do we want to propose a new repr? | ||
| * *Discussion:* [#73: Validity of unions][#73] | ||
| * The following questions are all implicitly answered if `#[repr(Rust)]` is the bag-o-bytes repr, but remain open if not: | ||
| * Do `#[repr(Rust)]` unions guarantee all fields at offset 0? | ||
| * *Discussion*: [#353: Offsets of union fields][#353] | ||
| * Do `#[repr(Rust)]` unions have internal padding? | ||
| * *Discussion*: [#354: Do #[repr(Rust)] unions have internal padding?][#354] | ||
| * Do `#[repr(transparent)]` unions ever have niches? | ||
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There was a problem hiding this comment. This one, OTOH, is answered by bag-of-bytes -- right? |
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| * *Discussion*: [#364: What is the value model/validity invariant for transparent unions?][#364] | ||
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| ## Closed discussion issues: | ||
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| * [#13: Representation of unions][#13] | ||
| * [#156: Layout of repr(C) unions has padding][#156] | ||
| * [#298: Is `repr(transparent)` completely transparent within `repr(Rust)` types?][#298] | ||
| * [#352: What is the safety invariant, if any, for unions?][#352] | ||
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| [#13]: https://github.com/rust-lang/unsafe-code-guidelines/issues/13 | ||
| [#156]: https://github.com/rust-lang/unsafe-code-guidelines/issues/156 | ||
| [#298]: https://github.com/rust-lang/unsafe-code-guidelines/issues/298 | ||
| [#352]: https://github.com/rust-lang/unsafe-code-guidelines/issues/352 | ||
| [#353]: https://github.com/rust-lang/unsafe-code-guidelines/issues/353 | ||
| [#354]: https://github.com/rust-lang/unsafe-code-guidelines/issues/354 | ||
| [#364]: https://github.com/rust-lang/unsafe-code-guidelines/issues/364 | ||
| [#73]: https://github.com/rust-lang/unsafe-code-guidelines/issues/73 | ||
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Even bag-of-bytes unions could have fields at non-0 offsets. Not sure if there is any reason to do that, but this makes it sound like there is a necessary logical implication from bag-of-bytes to 0-offset, which I don't think is the case.