Rust: Provide array impls for arrays up to length 44
Currently various traits are provided for arrays up to length 32: https://github.com/rust-lang/rust/blob/master/src/libcore/array.rs#L259-L264
I'm requesting this be extended up to length 44.
Why? Because bindgen relies on AsMut<[T]> for fixed-size arrays, and the linux kernel has some structs with 44-element arrays. Providing impls up to length 44 would permit bindgening the full kernel headers without needing to whitelist/blacklist elements. I realize this is vaguely whack-a-mole, but it's a valuable use-case in my, 100% biased, opinion.
If this idea is acceptable, I'm happy to prepare a patch.
alex
All 9 comments
Once const generics are implemented, we'll be able to implement traits on arrays for any length. It's probably better to wait till then, rather than special-casing for a particular codebase now.
varkor
on 30 May 2018
Yes, that's clearly the right long term solution. The nice thing about the short term solution is that I could have a patch in in an hour and be able to use it in tomorrow's nightly :-)
alex
on 30 May 2018
I've gone ahead and submitted #51318. If the core team has interest in this, the PR is available for consideration.
alex
on 3 Jun 2018
@alex How are you bindgen-ing linux kernel headers? TMK linux relies on a handful of gcc optimizations, attributes, and non-standard extensions, so you can't use clang to compile it. Is that outdated knowledge?
mark-i-m
on 3 Jun 2018
@varkor Is there an idea of how long it will be before basic const generics are ready? (btw, thanks for all your work on that!)
mark-i-m
on 3 Jun 2018
@mark-i-m: before the focus switched to the refactorings (which are now almost done), I felt we were relatively close to an initial implementation. It's hard to give a good estimate, because quite a lot has changed since then, but personally I'd really like to aim for something working by July or so (as soon as https://github.com/rust-lang/rust/pull/48149 is merged, I think we'll be in a position to make swift headway).
varkor
on 3 Jun 2018
@mark-i-m you can look at https://github.com/alex/linux-kernel-module-rust to see how it works. It seems to be working at any rate 🤷♂️
alex
on 3 Jun 2018
@alex It looks like it is close, but not quite there yet. https://lwn.net/Articles/734071/... It will probably work until you need touch a weirder data structure like struct page...
Anyway I don't want to derail the thread...
Given that const generics on nightly might be only a month away, my vote would be to wait...
mark-i-m
on 3 Jun 2018
There's a proper tracking issue for this here now: https://github.com/rust-lang/rust/issues/61415.
varkor
on 3 Jun 2019
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Most helpful comment
@mark-i-m: before the focus switched to the refactorings (which are now almost done), I felt we were relatively close to an initial implementation. It's hard to give a good estimate, because quite a lot has changed since then, but personally I'd really like to aim for something working by July or so (as soon as https://github.com/rust-lang/rust/pull/48149 is merged, I think we'll be in a position to make swift headway).