Vec<Vec<T>>

[Timmmm]

Sorry for the deluge of questions! Is it possible to return Vec<Vec<SomeStruct>> from a bridge function? It says the inner Vec is not a supported type. We've tried various things (currently resorting to a single-field struct which kind of sucks).

[dtolnay]

You can wrap either the outer or inner vec in a struct. Inner vec (probably what you found):

#[cxx::bridge]
mod ffi {
    struct VecT {
        vec: Vec<T>,
    }
    extern "Rust" {
        type T;
        fn f() -> Vec<VecT>;
    }
}

Outer vec, which may be more convenient depending on what this is interacting with on the Rust side:

struct VecVecT {
    vec: Vec<Vec<T>>,
}

#[cxx::bridge]
mod ffi {
    extern "Rust" {
        type T;
        type VecVecT;
        fn get(&self, i: usize) -> &Vec<T>;

        fn f() -> Box<VecVecT>;
    }
}

[Timmmm]

Ah wrapping the outer Vec is nicer but we need to be able to access the contents from C++ unfortunately. I presume supporting Vec<Vec<>> and other nested types isn't really hard, it just hasn't been done yet?

Thanks for all the help!