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Comment by miohtama | Hacker News Reader

It’s clear that the value promise of Carbon is to make it attractive to port existing C++ applications to it.

But how this is accomplished, article does not go into detail in this. Is there going to be ABI compatibility with C++? What are the features that make Carbon a better porting target than Rust?

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The official webisite (https://github.com/carbon-language/carbon-lang) goes into better detail, but the gist is that you can basically #include C++ libraries and use their APIs as-is, without needing to resort to unsafe blocks or having to write more idiomatic wrappers.

Does this mean that Carbon needs to include a whole C++ compiler as a part of Carbon compiler?

Carbon uses LLVM as a backend, so I imagine they just call into Clang for such things.

There is ABI compatibility insofar that Carbon will be able to integrate C++ at the AST level within the compiler.

This is quite smart as you are basically getting ABI compatibility for free. Assuming you have the source code to the C++.

I'm not sure how it will work with dynamic or proprietary libraries, but as I understand it that is already a technically unsolved ABI problem with C++.

Rust will require a complete re-write or extensive work implementing a C-like interface for your C++ API. Carbon will be able to use C++ classes natively, including calling methods etc.

I think Carbon will be a much better choice for extending a C++ project.

Rust might be a good choice if you are able to start from scratch or the project has C bindings.

How did the firefox team handle it? They have moved parts to Rust while the rest is still C++.

Firefox is porting or replacing entire libraries.

(The idea with Carbon is you could replace specific C++ classes or headers.)

Wasn’t https://cxx.rs/ supposed to make writing C-bindings unnecessary?

Rust is closer to the the type of languages we need to move to but Carbon makes it easier to port away from existing C++ software. If it's a new project, use Rust if you can. Use Carbon if you need to deal with C++. Rust can interoperate with C++ but with more difficulty.

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