rust-lang / rust-lang/rust-clippy
New lint: prefer union field access to transmuting into an union
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A-lint
E-medium
L-guidelines
L-unnecessary
T-middle
- Dominant language
- Rust
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Description
This code
pub unsafe fn bad(a: [u32; 4], idx: usize) -> u64 {
union A { _a: [u32; 4], b: [u64; 2] };
::std::mem::transmute::<[u32; 4], A>(a).b[idx]
}
should be more idiomatically be written as this:
pub unsafe fn better(a: [u32; 4], idx: usize) -> u64 {
union A { a: [u32; 4], b: [u64; 2] };
A { a: a }.b[idx] // the a: a has been added for clarity, a suffices
}
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the Rust playground examples linked in the issue and compare the transmute form with direct union field access. Trace how an equivalent Clippy lint identifies this pattern and reports a replacement; done means the lint recognizes the shown case and provides the idiomatic suggestion, with coverage for the example behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- tooling
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100