Hello I want to know how do I port from C to Rust?

See like this old thread I really don't understand how do I port function pointer like Example: int wl_proxy_add_listener(struct wl_proxy *proxy, void (**implementation)(void), void *data); But how do I translate to Rust like this? void (**implementation)(void) Warning it has double pointers inside function pointer. To implementation: *mut unsafe extern "C" fn() or implementation: Option<*mut unsafe extern "C" fn()> Is it correct or wrongly??