Rust Bridge Declarations

#[cxx::bridge]
mod ffi {
    extern "Rust" {
        type MyType; // Opaque type
        fn foo(&self); // Method on `MyType`
        fn bar() -> Box<MyType>; // Free function
    }
}
struct MyType(i32);
impl MyType {
    fn foo(&self) {
        println!("{}", self.0);
    }
}
fn bar() -> Box<MyType> {
    Box::new(MyType(123))
}

• Items declared in the extern "Rust" reference items that are in scope in the parent module.
• The CXX code generator uses your extern "Rust" section(s) to produce a C++ header file containing the corresponding C++ declarations. The generated header has the same path as the Rust source file containing the bridge, except with a .rs.h file extension.