pub fn closure_to_ffi<F: Fn(i32, i32) -> i32>(f: F) -> (*mut F, unsafe extern "C" fn(*mut F, i32, i32) -> i32) {
    unsafe extern "C" fn call_closure_from_ffi<F: Fn(i32, i32) -> i32>(f: *mut F, a: i32, b: i32) -> i32 {
        (*f)(a, b)
    }
    (Box::into_raw(Box::new(f)), call_closure_from_ffi::<F>)
}

pub fn main() {
    closure_to_ffi(|x, y| x + y);
}