clarify safety documentation of ptr::swap and ptr::copy #114794
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r? @m-ou-se (rustbot has picked a reviewer for you, use r? to override) |
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library/core/src/intrinsics.rs
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| /// * `src` must remain valid for reads even after `dst` is written, and vice versa. | ||
| /// (In other words, there cannot be aliasing restrictions on the use of these pointers.) | ||
| /// |
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I didn't quite understand what this meant in practice until I checked out #81005.
Maybe there's a different way of wording this?
Would it work to not add this bullet point, but instead add "during the entire call to swap()" to the first two bullet points? (Maybe with a clarifying note saying that this means that the src and dst regions may not overlap.)
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They may overlap though, the pointers just must allow overlapping access. So for instance passing ptr and ptr.add(N) is fine even if things overlap. However passing &mut *ptr twice generates two fresh mutable references and now if things overlap, that lead to UB due to aliasing violations.
It's hard to precisely say this while the aliasing model is still being determined.
add "during the entire call to swap()" to the first two bullet points?
If we do that I think we have to say what happens during the call. So we could say something like
srcmust be [valid] for reads ofcount * size_of::<T>()bytes, and must remain valid even ifdstis written to forcount * size_of::<T>()bytes.
But that seems very similar to the current wording, so I am not sure if it is clear enough.
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Not sure if this wording is any better, but it's the best I could come up with so far. |
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@m-ou-se I think I replied to all your comments -- what's the next step for this PR? |
My mother tongue uses the same word for "if" and "when" so this is probably just me missing a connotation that will be obvious to native speakers. I changed the wording. @bors r=m-ou-se |
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@bors rollup |
clarify safety documentation of ptr::swap and ptr::copy Closes rust-lang#81005
…iaskrgr Rollup of 3 pull requests Successful merges: - rust-lang#114794 (clarify safety documentation of ptr::swap and ptr::copy) - rust-lang#115397 (Add support to return value in StableMIR interface and not crash due to compilation error) - rust-lang#115559 (implied bounds: do not ICE on unconstrained region vars) Failed merges: - rust-lang#115532 (Implement SMIR generic parameter instantiation) r? `@ghost` `@rustbot` modify labels: rollup
Closes #81005