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| -rw-r--r-- | src/tools/clippy/src/docs/mut_from_ref.txt | 26 |
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diff --git a/src/tools/clippy/src/docs/mut_from_ref.txt b/src/tools/clippy/src/docs/mut_from_ref.txt new file mode 100644 index 000000000..cc1da1254 --- /dev/null +++ b/src/tools/clippy/src/docs/mut_from_ref.txt @@ -0,0 +1,26 @@ +### What it does +This lint checks for functions that take immutable references and return +mutable ones. This will not trigger if no unsafe code exists as there +are multiple safe functions which will do this transformation + +To be on the conservative side, if there's at least one mutable +reference with the output lifetime, this lint will not trigger. + +### Why is this bad? +Creating a mutable reference which can be repeatably derived from an +immutable reference is unsound as it allows creating multiple live +mutable references to the same object. + +This [error](https://github.com/rust-lang/rust/issues/39465) actually +lead to an interim Rust release 1.15.1. + +### Known problems +This pattern is used by memory allocators to allow allocating multiple +objects while returning mutable references to each one. So long as +different mutable references are returned each time such a function may +be safe. + +### Example +``` +fn foo(&Foo) -> &mut Bar { .. } +```
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