dtolnay/cxx

Box clone() member function to call Clone on opaque Rust types

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#105 opened on Apr 11, 2020

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help wanted

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Description

We should provide a way to constrain that some opaque Rust type implements Clone and then expose the Clone impl to C++ via a clone() member function on rust::Box.

Something like:

mod ffi {
    extern "Rust" {
        type ClonableR: Clone;
    }

    extern "C++" {
        fn f(b: Box<ClonableR>); // C++ will be able to clone b
    }
}

  template <typename T>
  class Box {
+   Box clone() const noexcept;
  };

Contributor guide

Research direction
Study how cxx currently handles the Clone trait for opaque types. Look at the code generation for Box to understand how to add a clone() method. Implement the constraint that T: Clone in Rust and expose the corresponding C++ method. Test with a sample.
Tech stack
rustcpp
Domain
backendapideveloper experience
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
RustC++
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30