Messages in this thread | | | Date | Wed, 28 Jun 2023 11:41:59 +0000 | From | Benno Lossin <> | Subject | Re: [PATCH 3/7] rust: init: make guards in the init macros hygienic |
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On 25.06.23 22:54, Gary Guo wrote: > On Sat, 24 Jun 2023 09:25:10 +0000 > Benno Lossin <benno.lossin@proton.me> wrote: > >> Use hygienic identifiers for the guards instead of the field names. This >> makes the init macros feel more like normal struct initializers, since >> assigning identifiers with the name of a field does not create >> conflicts. >> Also change the internals of the guards, no need to make the `forget` >> function `unsafe`, since users cannot access the guards anyways. Now the >> guards are carried directly on the stack and have no extra `Cell<bool>` >> field that marks if they have been forgotten or not, instead they are >> just forgotten via `mem::forget`. > > The code LGTM, so: > > Reviewed-by: Gary Guo <gary@garyguo.net> > > Although this will cause the new expansion we have to be no longer > compatible with a totally-proc-macro impl, if we want to do everything > in proc macro in the future. > > If we have the paste macro upstream ( > https://github.com/nbdd0121/linux/commit/fff00461b0be7fd3ec218dcc428f25886b5ec04a > ) then we can replace the `guard` with `paste!([<$field>])` and keep > the expansion identical. >
I tried it and it seems to work, but I am not sure why the hygiene is set correctly. Could you maybe explain why this works? ``` $crate::__internal::paste!{ let [<$field>] = unsafe { $crate::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field)) }; $crate::__init_internal!(init_slot($use_data): @data($data), @slot($slot), @guards([<$field>], $($guards,)*), @munch_fields($($rest)*), ); } ```
i.e. why can't a user access the guard? I think it is because the hygiene of the `[<>]` is used, but not sure why that works.
-- Cheers, Benno
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