rust-ffi | generate bindings to a rust foreign function interface | Wrapper library

I was following Michael-F-Bryan's Dynamic Loading & Plugins chapter from his Rust FFI guide, but I am storing the plugins in a HashMap (HashMap<&'static str, Box) instead of a Vec so that I can call the functions of a Plugin individually.

I would like the plugins to define a asynchronous function with it's own loop that communicates with the main part of the application using channels (std or tokio).

Working around the fact that you can't have async functions in traits was easy thanks to the async_trait crate, but the issue that I am now facing is, that I cannot spawn a new thread with the module because the new thread might outlive the PluginManager.

I tried to recreate this in a rust playground without the dynamic modules and I'm facing the same error here (note: this does not include any kind of channel communication)

Unlike the first error, I was unable to recreate a rust playground for the second one (as it happens at runtime). Instead of spawning a new thread, I was using tokio's event loop to handle the async functions. This works in the sandbox, but not when using a shared library as plugin. At runtime it throws:

I have followed the instructions from here and here

And although the .a library and the functions work as expected on Debug (simulator and real device), when I Archive and test through TestFlight the Flutter App begins with a grey background (which I read that it means some kind of error).

If I go ahead and remove all calls of the Rust lib then the Testflight opens normally.

Note: I have also added the .a library as a Linked framework from the XCode and I have included the .h file to the bridging-header.h of the project.

I have also

• run flutter build --release
• cleared the derived data
• pods cache
• even re-made the iOS folder from scratch.

Is there something else that I'm missing here?

I found this question, but it is 3 years old and since then, crates like cxx have come into existence. Is it possible now to construct a C++ object from Rust, or do I still have to create a shim?

As part of mapping a C interface to Rust, I want to handle a union that stored a few native types directly and have a pointer to an allocated type for all others.

How can I implement a parameterized wrapper type around the union that can select and use the appropriate field based on the wrapper type parameter?

In this case, I want to add a Rust wrapper that reads the data structure directly and not a solution that converts it to a Rust-native type first. Adding other support types to "trick" the compiler is fine though. The end goal is to be able to write code similar to this: