True, and so can C call back into go code with cgo. The problem is that it still requires that the main function be in a Rust/Go binary. A program written in C can't currently call into a library written in one of these two languages since the runtimes don't work unless they control the main entry point.
From the Rust doc linked: "The primary motivation of extern functions is to create callbacks for foreign functions that expect to receive function pointers."
Then is it even possible to make a program that can use libraries written in Rust and Go and C++? If everyone wants to control main(), is there an escape hatch provided by any of these languages, like a C function that can be explicitly invoked near program start?
You can do this with C++ already. Rust's plan seems to be to eliminate or reduce its runtime and give up the entry point. Go doesn't appear to have a plan.
If you read what you linked to it says the main purpose is to provide C functions with callback arguments when called from Rust. It isn't clear from what you have written that this mechanism is available to generally access from C programs and scripting languages.
