Tuples

(Supported by cpp, and nanobind, queried with #[diplomat::cfg(supports=tuples)])

In languages with tuples, Diplomat can treat structures as being tuples on the boundary between Rust and the backend when marked as such:

#[diplomat::attr(auto, tuple)]
pub struct SomeStruct {
    x: f32,
    y: f32
}

impl SomeStruct {
    pub fn some_fn() -> SomeStruct;
}

In C++, SomeStruct will be returned as

std::tuple<float, float>

Tuples do not support non-static methods, since past the boundary a tuple is not the struct it was generated from.

See https://github.com/rust-diplomat/diplomat/issues/1145 for the tracking issue for Tuples.