cxx VS crubit

There are cxx and autocxx, what else do you propose to do?

I would like to see a comparison of how this compares to Rust. In terms of interoperability it has Cxx (https://cxx.rs) to offer safe bindings to C++ but also has great support for Android, Linux and many other systems. You don't even need to hack together Windows bindings (as explained in the blog post) because Microsoft offers official bindings (https://crates.io/crates/windows). I'm not sure if I'd call it a superpower if any potential interoperability has to be written to be used (compared to it already being available). Or rather, in comparison to what is interoperability a Swift superpower? Certainly not C++ or C which can be used in a far wider set of targets.

We selected Qt as a cross-platform solution. The C++/Rust interface is the clunkiest and ugliest part of the application, and rather complex because some state is shared between several windows in the GUI and several threads in the backend, and any component might modify that state at any time, and updates have to be transmitted to the other components without introducing inconsistencies. Using cxx [1] helped a little, though.

The project began in 2020, and I'm not sure what I'd choose as a GUI framework today – definitely not Qt Widgets, though.

[1] https://cxx.rs/

If the build process for the C library isn't too involved I recommend using cxx bridge (https://cxx.rs/) and letting cargo handle the build and linking. cxx basically allows you to describe the bidirectional interface (although it sounds like you only need 1 direction, which is fine too) in Rust code and it provides a "good enough" API for compiling C code inside the build.rs file.

The tooling for the first kind -- calling Rust from another language -- is a bit less developed, and tends to rely on code generation that doesn't necessarily produce a natural C API. cbindgen, uniffi, cxx, and Diplomat all take this course.

I would like to utilize OMPL's functionality in Rust code, so I want to call into OMPL C++ code somehow in Rust. I've seen two (non-mutually-exclusive) options so far: - rust-cpp, which allows you to write C++ code in Rust within the cpp!() macro. - cxx, which allows you to define both sides of the FFI boundary manually (as opposed to bindgen's automatic generation).

I'm not sure how to do this in cxx; issues like https://github.com/dtolnay/cxx/issues/447 suggest that this isn't settled yet?

I use non-vendored dependencies for the Buck build in https://github.com/dtolnay/cxx.

There's also the cpp and cxx crates for doing C++/Rust interop, but they probably aren't appropriate to use in all cases. The C ABI is definitely the safest way to go unless you're really trying to marry Rust and C++ code bases, not just writing library bindings.

There's also cxx (can't vouch for it personally but it claims to make things a lot easier) https://github.com/dtolnay/cxx

See also:

Thomas Neumann's current proposal for memory safe C++ using dependency tracking:

- https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p27...

Google's proposal for memory safety using Rust-like lifetime analysis:

- https://discourse.llvm.org/t/rfc-lifetime-annotations-for-c/...

- https://github.com/google/crubit/tree/main/lifetime_analysis

For the people who are curious: crubit is an attempt to develop the way to seamlessly integrate C++ and Rust.

Please see the experimentation and proposals at https://github.com/google/crubit/blob/main/docs/lifetime_annotations_cpp.md and https://github.com/google/crubit/blob/main/docs/lifetimes_static_analysis.md

autocxx is good, though crubit is aiming for direct bidirectional interop

The areas you mentioned (CLI, web services, low level systems programming) are not mutually exclusive. Doing a good job on one doesn't mean something else is affected.

The folks who worked on the most popular command line argument parser (https://docs.rs/clap/latest/clap/#example) made a positive contribution that didn't detract from any other use case.

Similarly, the folks working on improving Rust for web services will also make it better for systems programming. In a blog post published today (https://blog.rust-lang.org/inside-rust/2022/07/27/keyword-ge...), they discuss keyword generics, a feature that will be equally helpful for `async` code and `const` functions evaluated at compile time.

There is already some interoperability with C++ (http://cxx.rs) and ongoing research into automating this interoperability (https://github.com/google/autocxx, https://github.com/google/crubit). Feels like there's enough effort

This language was started by folks at Google. (Although it's interesting that they're publishing it under a separate github org, which suggests ambitions beyond Google's needs.) Google has a huge, performance-sensitive C++ codebase. At Google, major product teams' backends are typically written in C++, as well as common infrastructure like D (disk server), Colossus (distributed filesystem), Spanner (distributed SQL database), and Borg (cluster management). More than a few people would love for it all to be be written in Rust instead, but migration would be challenging, to say the least. I'm told people are looking into it—see Crubit for example. But AFAIK, no one's decided yet whether Google will stay with C++ for all these things, migrate some to Rust, migrate some to Carbon, and/or do something else entirely.

It's currently unclear if Rust can interop with C++ with high fidelity. For example https://docs.rs/moveit/latest/moveit/ and https://github.com/google/crubit/blob/main/rs_bindings_from_... provide functionality to use non-trivially relocatable C++ types from Rust.