Represent enums with nullable pointers where possible #6001
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Closes #1271. |
bors
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Apr 22, 2013
Specifically: all enums with two variants, where one has zero size (and thus at most one inhabitant) and the other has a field where the null value would not be allowed (such as a safe pointer), are now represented by storing a null pointer in the field in question. This is a generalization of representing `Option<~T>`, `Option<@t>`, and `Option<&T>` with nullable pointers, thus fixing Tony Hoare's “billion dollar mistake”.
flip1995
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Sep 10, 2020
…ishearth Restrict unnecessary_sort_by to non-reference, Copy types `Vec::sort_by_key` closure parameter is `F: FnMut(&T) -> K`. The lint's suggestion destructures the `T` parameter; this was probably done to avoid different unnamed lifetimes when `K = Reverse<&T>`. This change fixes two issues: * Destructuring T when T is non-reference requires the type to be Copy, otherwise we would try to move from a shared reference. We make sure `T: Copy` holds. * Make sure `T` is actually non-reference. I didn't go for destructuring multiple levels of references, as we would have to compensate in the closure body by removing derefs and maybe adding parens, which would add more complexity. changelog: Restrict [`unnecessary_sort_by`] to non-reference, Copy types Fixes rust-lang#6001
flip1995
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Oct 9, 2020
…hansch unnecessary sort by: avoid dereferencing the suggested closure parameter This change tries to simplify the solution for problematic cases but is less restrictive than rust-lang#6006. * We can't dereference shared references to non-Copy types, so the new suggestion does not do that. Note that this implies that the suggested closure parameter will be a reference. * We can't take a reference to the closure parameter in the returned key, so we don't lint in those cases. This can happen either because the key borrows from the parameter (e.g. `|a| a.borrows()`), or because we suggest `|a| Reverse(a)`. If we did we would hit this error: ``` error: lifetime may not live long enough --> /home/ebroto/src/ebroto-clippy/tests/ui/unnecessary_sort_by.fixed:19:25 | 19 | vec.sort_by_key(|b| Reverse(b)); | -- ^^^^^^^^^^ returning this value requires that `'1` must outlive `'2` | || | |return type of closure is Reverse<&'2 isize> | has type `&'1 isize` error: aborting due to previous error ``` Note that Clippy does not currently have the (MIR-based) machinery necessary to check that what is borrowed is actually the closure parameter. changelog: [`unnecessary_sort_by`]: avoid dereferencing the suggested closure parameter Fixes rust-lang#6001
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Specifically: all enums with two variants, where one has zero size (and thus at most one inhabitant) and the other has a field where the null value would not be allowed (such as a safe pointer), are now represented by storing a null pointer in the field in question.
This is a generalization of representing
Option<~T>,Option<@T>, andOption<&T>with nullable pointers, thus fixing Tony Hoare's “billion dollar mistake”.