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Result/Option layout guarantee clarifications #146509

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@RalfJung RalfJung commented Sep 13, 2025 •
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  • It seems worth spelling out that this guarantee allows particular transmutes.
  • After the Result section was written, the Option section it referenced gained more guarantees, saying that None is represented as [0u8; N]. Those guarantees were not meant to apply to Result. Make the Result section more self-contained to make this more clear.
  • "Type has no fields" is unclear since there is no general definition of what the fields of some arbitrary type are. Replace that by a more accurate description of the actual check implemented here.

r? @traviscross

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Sep 13, 2025
@RalfJung RalfJung force-pushed the res-opt-layout-guarantees branch from fe2ac5c to 0b3d10d Compare September 13, 2025 15:29
RalfJung
RalfJung commented Sep 13, 2025
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@RalfJung RalfJung force-pushed the res-opt-layout-guarantees branch from 0b3d10d to 57a8745 Compare September 13, 2025 15:45
@RalfJung RalfJung added the I-lang-nominated Nominated for discussion during a lang team meeting. label Sep 13, 2025
@traviscross traviscross added T-lang Relevant to the language team P-lang-drag-2 Lang team prioritization drag level 2.https://rust-lang.zulipchat.com/#narrow/channel/410516-t-lang. I-lang-radar Items that are on lang's radar and will need eventual work or consideration. labels Sep 13, 2025
@traviscross traviscross removed I-lang-nominated Nominated for discussion during a lang team meeting. P-lang-drag-2 Lang team prioritization drag level 2.https://rust-lang.zulipchat.com/#narrow/channel/410516-t-lang. labels Sep 17, 2025
@RalfJung RalfJung mentioned this pull request Sep 20, 2025
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