Rust dynamically link .so library

Question

I have the following scenario and goals:

• Implement a library in Rust that has to be shared by many binaries
• Keep the size of the binary as small as possible

As far as I know, a way to get it is:

• Compile the library with crate-type = "dylib". This generates the desired .so library
• Use the crate libloading to dynamically access the library objects from within a binary.

I successfully implemented a very basic example and the size of the compiled files are small enough. Here's the code:

lib.rs

#[no_mangle]
pub fn minicall() -> u8 {
    3u8
}

main.rs

fn main() {
    unsafe {
        let lib = libloading::Library::new("liblibtest.so").unwrap();
        let func: libloading::Symbol<unsafe extern fn() -> u32> = lib.get(b"minicall").unwrap();
        let r = func();
        println!("r = {r}");
    }
}

Now, I need to expand my example by adding types and method to the lib, for example:

lib.rs

pub struct User {
    username: String,
    email: String,
}

impl User {
    fn new(username: String, email: String) -> User {
        User {
            username,
            email
        }
    }
}

#[no_mangle]
pub fn minicall() -> u8 {
    3u8
}

and then, use them in my binary:

main.rs

fn main() {
    unsafe {
        let lib = libloading::Library::new("liblibtest.so").unwrap();
        
        let func: libloading::Symbol<unsafe extern fn() -> u32> = lib.get(b"minicall").unwrap();
        let r = func();
        println!("r = {r}");

        let user = ????  <----------------------
    }
}

How can I get access to types and methods in the library? Please note that evereything is in Rust, no C is involved.