impl UniquePtrTarget for T;

[adetaylor]

Builds on top of #325. Fixes #236.

[sbrocket]

Can we do this without exposing - and requiring users to know - the internal trait names like UniquePtrTarget? In #308 dtolnay@ suggested something like impl Vec<T> {} and impl UniquePtr<T> {}.

[adetaylor]

Yes, probably, I will amend that way after I eventually rebase on top of your stuff.

[sbrocket]

One other thing to consider here. For Vec and Box after my PR #308, the following only fails at C++ compile time because we don't have traits similar to UniquePtrTarget and VectorElement for those that can be checked with a trait bound.

#[cxx::bridge]
mod here {
    struct Shared {
        z: usize,
    }
}

#[cxx::bridge]
mod there {
    type Shared = crate::here::Shared;

    extern "C" {
        fn c_take_rust_vec_shared(v: Vec<Shared>);
    }
}

fn main() {}

We might want to add those in a separate PR to improve the diagnostics, plus then we can point people at this option.

[dtolnay]

Thanks for the PR. :) I ended up merging #336 instead, which follows the approach from #312 (comment) of using impl UniquePtr<T> {} for a requested instantiation. As @sbrocket points out, this is more closely connected to the public API of the cxx crate and we avoid making the user learn a second set of names for the internal names of the traits.

[adetaylor]

Sounds good. Thank you!