5 ms·

Zngur: A C++/Rust interop tool

154 points by hkalbasi 2y ago

jdright 2y ago
This is insane. Is this being used in some codebase? How stable is it? What are the plans for it? I have so many questions, but will stick with these for now.
boguscoder 2y ago
Interesting. Any clue how this compares to https://cxx.rs/ https://cxx.rs/
- boguscoder 2y ago
  Maybe I should learn to read! https://hkalbasi.github.io/zngur/how_it_compares.html https://hkalbasi.github.io/zngur/how_it_compares.html
uneekname 2y ago
I've been learning Rust and really enjoying it, but the primary downside (compared to C++) is the lack of access to the large, well-tested libraries that exist in C++. For example, my work would benefit from using the CGAL library [0], something that be nontrivial to rewrite in Rust. As much as I like Rust, at some point it's a better idea to use C++ to tap into libraries like that. Does anyone have thoughts about how mature Zngur/CXX/etc. are for a project like mine? Would it be reasonable to invest effort in creating those bindings? Thanks. [0] https://www.cgal.org/ https://www.cgal.org/
- npalli 2y ago
  So, Zngur allows you to use arbitrary Rust types in C++, store them by value in the C++ stack, and call arbitrary Rust methods and functions on them. But it doesn't bridge any C++ type into Rust, since it is not possible with the same ergonomic You want to use C++ libraries from Rust. This only does interop the other way.
  - dkersten 2y ago
    It seems to do both: https://hkalbasi.github.io/zngur/tutorial.html#calling-c-from-rust https://hkalbasi.github.io/zngur/tutorial.html#calling-c-fro... It sound like your quoted text is just saying that it’s not as ergonomic, you cannot use arbitrary C++ types directly in Rust, but you can use arbitrary Rust types in C++.
  - ogoffart 2y ago
    For calling C++ libraries from Rust, there is also https://crates.io/crates/cpp https://crates.io/crates/cpp
  - tialaramex 2y ago
    Zngur does allow you to execute arbitrary C++ from Rust. Unfortunately it chooses to just assume your C++ is sound, it does explicitly warn you that you're signing up for this, but realistically this just doubles down on the known bad assumption in C++ that programmers are infallible. Rather than (like Rust's native C FFI) marking the arbitrary C++ as unsafe, Zngur chooses to have you explicitly opt in if you want your code marked unsafe. We know from years of practical experience that C++ programmers rely heavily on unstated assumptions for the correctness of code, a practice which does not scale. A very large proportion of the C++ stdlib itself has a narrow contract, yet few practitioners memorise these contracts and they're unchecked - disaster looms.
- throwup238 2y ago
  I’m using cxx/cxx-qt in a Rust QT app with substantial interop with Qt/QML and lots of C++ code (because Gpt/Claude make implementing some stuff easier in C++). It’s definitely mature enough because Qt’s libs are no joke. At this point I have a Claude project set up with Cxx documentation and it autogenerates most of my bindings.
  - slimsag 2y ago
    Do you have some specific usage of Claude to help? Or how do you use Claude/Gpt for this more precisely?
    - oneshtein 2y ago
      IMHO, he created RAG from documentation to provide more context for Claude, so he then can call Claude with a task like "Generate bindings in Rust language for C++ class Foo from the Bar library.".
    - nestorD 2y ago
      Not the OP but I have done similar things. Claude has a workspace option that let's you preset a set of documents (here the documentation of the library used) and a system prompt to be included when starting a new chat in the given workspace. Those will be in its, fairly large, context window (overall, independently of its intelligence, I have found Claude current UI to have an edge when dealing with files).
  - heavyset_go 2y ago
    How was your experience using Qt with Rust? Is it awkward writing models and QObjects in Rust? I'm a fan of QML and would love to use Rust with it if pleasant Qt bindings are finally there.
    - _flux 2y ago
      Do you know Slint? I haven't really used it, but it seems to use the same idea, except it's native to Rust but comes with its own C++ and JavaScript bindings. I believe the project was started by some folks that left Qt (or some company that held the IPR at some point..).
- bschwindHN 2y ago
  I've used cxx.rs to bind to the OpenCascade CAD kernel. It was a lot of work but the bindings seem to work well.
- hkalbasi 2y ago
  Zngur allows you to write functions operating over Rust types, adding methods to Rust types and implementing Rust traits for C++ and Rust types inside C++. So you can write a rusty wrapper for the C++ library inside C++. If you want to immediately use a C++ library in Rust with minimal manual effort, check out autocxx [0]. Its generated api isn't very idiomatic Rust, and it uses Pin, moveit, ... but it covers a good percent of C++ apis and you can also make an idiomatic wrapper for it in Rust. [0] https://docs.rs/autocxx/latest/autocxx/ https://docs.rs/autocxx/latest/autocxx/
mastax 2y ago
Wow! Amazing how reframing the problem to exclude C++ types in rust makes it all so much more elegant.
pjmlp 2y ago
This kind of tools are great, as C++ isn't going away any time soon, and Rust is decades away to be relevant in some domains, specially those where C++ only recently took over C.
benreesman 2y ago
Having only glanced at the code I can’t offer much insight beyond “looks plausible”. A far more important point is to address is that any FFI story with C++ that’s well executed is going to be great for the Rust ecosystem, and historically the community’s commitment to C++ interop has seemed tepid at best. Even if one admits that Rust is strictly better than C++ for problems in the relevant domains, which seems an extraordinary claim that exceeds extraordinary evidence, there is still an ocean of C++ that we just can’t rewrite in even a decade, maybe not in a century. There are use cases where Rust is just strictly a better choice: anything with an attack surface like a shell or an SSH daemon, or probably even a browser is an obvious candidate for a language with better reasoning about common attack vectors. I trust my Rust user land a lot more than my C userland. But the “rewrite everything in Rust and push that via bad interop” is limiting the adoption of a cool language. I’m a big fan of efforts to be more incremental.
- tialaramex 2y ago
  > we just can’t rewrite in even a decade, maybe not in a century. The former claim seems unlikely as stated ("cannot") but is at least plausible in practice ("will not"). The latter makes no sense. C++ didn't exist fifty years ago, so you're asking that we believe somehow C++ was so well suited to some unspecified problems that rewriting software in a better language will take more than twice as long.
  - codetrotter 2y ago
    I mean, there’s a lot of systems out there now that are so relied upon by other systems and people that you literally have to probably be bug for bug compatible with the existing system if you’re gonna have any chance of doing a rewrite of it in another language. That kind of thing takes time. And all of that time spent is also time that you continuously will have to justify to the executives why exactly we are doing this rewrite again and why there have been 0 new features added to the system because everyone has been busy with the rewrite. Or you assign just part of the people to the rewrite and the rest of the teams continue adding features to the existing system, and now you have to constantly play catch-up. Or everyone is responsible for both rewriting and for adding features, and new features are added into the legacy code and then also written in the new language. It’s possible. I’ve been on teams that successfully rewrote legacy software in Rust. But until it literally becomes something that directly impacts revenue in an indisputable way – say through fines imposed for security incidents and those incidents being due to memory safety – there’s still a lot of organizations that will completely refuse these kinds of rewrites no matter how good the evidence is that they should be doing so for many reasons.
hi-v-rocknroll 2y ago
Isn't Google offering funding for this exact topic?

154 points by hkalbasi 2y ago

This is insane. Is this being used in some codebase? How stable is it? What are the plans for it? I have so many questions, but will stick with these for now.

boguscoder 2y ago

Interesting. Any clue how this compares to https://cxx.rs/ https://cxx.rs/

boguscoder 2y ago
Maybe I should learn to read! https://hkalbasi.github.io/zngur/how_it_compares.html https://hkalbasi.github.io/zngur/how_it_compares.html

uneekname 2y ago

I've been learning Rust and really enjoying it, but the primary downside (compared to C++) is the lack of access to the large, well-tested libraries that exist in C++. For example, my work would benefit from using the CGAL library [0], something that be nontrivial to rewrite in Rust. As much as I like Rust, at some point it's a better idea to use C++ to tap into libraries like that. Does anyone have thoughts about how mature Zngur/CXX/etc. are for a project like mine? Would it be reasonable to invest effort in creating those bindings? Thanks. [0] https://www.cgal.org/ https://www.cgal.org/

npalli 2y ago
So, Zngur allows you to use arbitrary Rust types in C++, store them by value in the C++ stack, and call arbitrary Rust methods and functions on them. But it doesn't bridge any C++ type into Rust, since it is not possible with the same ergonomic You want to use C++ libraries from Rust. This only does interop the other way.
- dkersten 2y ago
  It seems to do both: https://hkalbasi.github.io/zngur/tutorial.html#calling-c-from-rust https://hkalbasi.github.io/zngur/tutorial.html#calling-c-fro... It sound like your quoted text is just saying that it’s not as ergonomic, you cannot use arbitrary C++ types directly in Rust, but you can use arbitrary Rust types in C++.
- ogoffart 2y ago
  For calling C++ libraries from Rust, there is also https://crates.io/crates/cpp https://crates.io/crates/cpp
- tialaramex 2y ago
  Zngur does allow you to execute arbitrary C++ from Rust. Unfortunately it chooses to just assume your C++ is sound, it does explicitly warn you that you're signing up for this, but realistically this just doubles down on the known bad assumption in C++ that programmers are infallible. Rather than (like Rust's native C FFI) marking the arbitrary C++ as unsafe, Zngur chooses to have you explicitly opt in if you want your code marked unsafe. We know from years of practical experience that C++ programmers rely heavily on unstated assumptions for the correctness of code, a practice which does not scale. A very large proportion of the C++ stdlib itself has a narrow contract, yet few practitioners memorise these contracts and they're unchecked - disaster looms.
throwup238 2y ago
I’m using cxx/cxx-qt in a Rust QT app with substantial interop with Qt/QML and lots of C++ code (because Gpt/Claude make implementing some stuff easier in C++). It’s definitely mature enough because Qt’s libs are no joke. At this point I have a Claude project set up with Cxx documentation and it autogenerates most of my bindings.
- slimsag 2y ago
  Do you have some specific usage of Claude to help? Or how do you use Claude/Gpt for this more precisely?
  - oneshtein 2y ago
    IMHO, he created RAG from documentation to provide more context for Claude, so he then can call Claude with a task like "Generate bindings in Rust language for C++ class Foo from the Bar library.".
  - nestorD 2y ago
    Not the OP but I have done similar things. Claude has a workspace option that let's you preset a set of documents (here the documentation of the library used) and a system prompt to be included when starting a new chat in the given workspace. Those will be in its, fairly large, context window (overall, independently of its intelligence, I have found Claude current UI to have an edge when dealing with files).
- heavyset_go 2y ago
  How was your experience using Qt with Rust? Is it awkward writing models and QObjects in Rust? I'm a fan of QML and would love to use Rust with it if pleasant Qt bindings are finally there.
  - _flux 2y ago
    Do you know Slint? I haven't really used it, but it seems to use the same idea, except it's native to Rust but comes with its own C++ and JavaScript bindings. I believe the project was started by some folks that left Qt (or some company that held the IPR at some point..).
bschwindHN 2y ago
I've used cxx.rs to bind to the OpenCascade CAD kernel. It was a lot of work but the bindings seem to work well.
hkalbasi 2y ago
Zngur allows you to write functions operating over Rust types, adding methods to Rust types and implementing Rust traits for C++ and Rust types inside C++. So you can write a rusty wrapper for the C++ library inside C++. If you want to immediately use a C++ library in Rust with minimal manual effort, check out autocxx [0]. Its generated api isn't very idiomatic Rust, and it uses Pin, moveit, ... but it covers a good percent of C++ apis and you can also make an idiomatic wrapper for it in Rust. [0] https://docs.rs/autocxx/latest/autocxx/ https://docs.rs/autocxx/latest/autocxx/

mastax 2y ago

Wow! Amazing how reframing the problem to exclude C++ types in rust makes it all so much more elegant.

pjmlp 2y ago

This kind of tools are great, as C++ isn't going away any time soon, and Rust is decades away to be relevant in some domains, specially those where C++ only recently took over C.

benreesman 2y ago

Having only glanced at the code I can’t offer much insight beyond “looks plausible”. A far more important point is to address is that any FFI story with C++ that’s well executed is going to be great for the Rust ecosystem, and historically the community’s commitment to C++ interop has seemed tepid at best. Even if one admits that Rust is strictly better than C++ for problems in the relevant domains, which seems an extraordinary claim that exceeds extraordinary evidence, there is still an ocean of C++ that we just can’t rewrite in even a decade, maybe not in a century. There are use cases where Rust is just strictly a better choice: anything with an attack surface like a shell or an SSH daemon, or probably even a browser is an obvious candidate for a language with better reasoning about common attack vectors. I trust my Rust user land a lot more than my C userland. But the “rewrite everything in Rust and push that via bad interop” is limiting the adoption of a cool language. I’m a big fan of efforts to be more incremental.

tialaramex 2y ago
> we just can’t rewrite in even a decade, maybe not in a century. The former claim seems unlikely as stated ("cannot") but is at least plausible in practice ("will not"). The latter makes no sense. C++ didn't exist fifty years ago, so you're asking that we believe somehow C++ was so well suited to some unspecified problems that rewriting software in a better language will take more than twice as long.
- codetrotter 2y ago
  I mean, there’s a lot of systems out there now that are so relied upon by other systems and people that you literally have to probably be bug for bug compatible with the existing system if you’re gonna have any chance of doing a rewrite of it in another language. That kind of thing takes time. And all of that time spent is also time that you continuously will have to justify to the executives why exactly we are doing this rewrite again and why there have been 0 new features added to the system because everyone has been busy with the rewrite. Or you assign just part of the people to the rewrite and the rest of the teams continue adding features to the existing system, and now you have to constantly play catch-up. Or everyone is responsible for both rewriting and for adding features, and new features are added into the legacy code and then also written in the new language. It’s possible. I’ve been on teams that successfully rewrote legacy software in Rust. But until it literally becomes something that directly impacts revenue in an indisputable way – say through fines imposed for security incidents and those incidents being due to memory safety – there’s still a lot of organizations that will completely refuse these kinds of rewrites no matter how good the evidence is that they should be doing so for many reasons.

hi-v-rocknroll 2y ago

Isn't Google offering funding for this exact topic?