You can do it via the C ABI, and use opaque pointers to represent higher-level Rust/C++ concepts if you want to.
Firefox is a mixed C++ / Rust codebase with a relatively close coupling between Rust and C++ components in places (layout/dom/script are in C++ while style is in Rust, and a mix of WebRender (Rust) and Skia (C++) are used for rendering with C++ glue code)
> You can do it via the C ABI, and use opaque pointers to represent higher-level Rust/C++ concepts
Yeah but, you can do the same in Swift
My understanding from a brief read of the Swift issue is that they kept running into bugs in the Swift compiler which, in practice, prevented them from doing the things that they ought to be do in theory. This went on for long enough, that they got fed up and abandoned Swift.
The Rust compiler is incredibly solid (across all target platforms), and while it's C/C++ interop is relatively simplistic, what does exist is extensively battle tested in production codebases.