The bridge module reference

The Core concepts in chapter 2 covered the high level model that CXX uses to represent a language boundary. This chapter builds on that one to document an exhaustive reference on the syntax and functionality of #[cxx::bridge].

• extern "Rust" — exposing opaque Rust types, Rust functions, Rust methods to C++; functions with lifetimes.

• extern "C++" — binding opaque C++ types, C++ functions, C++ member functions; sharing an opaque type definition across multiple bridge modules or different crates; using bindgen-generated data structures across a CXX bridge; Rust orphan-rule-compatible way to request that particular glue code be emitted in a specific bridge module.

• Shared types — shared structs; shared enums; using Rust as source of truth vs C++ as source of truth.

• Attributes — working with namespaces; giving functions a different name in their non-native language.

• Async functions — integrating async C++ with async Rust.

• Error handling — representing fallibility on the language boundary; accessing a Rust error message from C++; customizing the set of caught exceptions and their conversion to a Rust error message.