Arithmetic operator overloads

(Supported by and cpp and nanobind, queried with supports = arithmetic)

+-*/ and their in-place variants can be overloaded in languages that support it by applying an attribute to single-argument functions taking self. The Names are

#![allow(unused)]
fn main() {
#[diplomat::bridge]
mod ffi {
    #[diplomat::opaque]
    struct OpaqueInt(i32);

    impl OpaqueInt {
        #[diplomat::attr(auto, add)]
        pub fn add(&self, v: i32) -> Box<OpaqueInt> {
            Box::new(Self(self.0 + v))
        }

        #[diplomat::attr(auto, add_assign)]
        pub fn inplace_add(&mut self, v: i32) {
            self.0 += v;
        }
    }
}
}