Attribute Macro extern_rust_type

#[extern_rust_type]

Declare that this is a Rust type which is to be exported to C++. You can use this in two ways:

• as an attribute macro on a Rust type, for instance:

  #[extern_rust_type]
  struct Bar;

• as a directive within the include_cpp macro, in which case provide the type path in brackets:

  include_cpp!(
      #include "input.h"
      extern_rust_type!(Bar)
      safety!(unsafe)
  );
  struct Bar;

These may be used within references in the signatures of C++ functions, for instance. This will contribute to an extern "Rust" section of the generated cxx bindings, and this type will appear in the C++ header generated for use in C++.

Finding these bindings from C++

You will likely need to forward-declare this type within your C++ headers before you can use it in such function signatures. autocxx can’t generate headers (with this type definition) until it’s parsed your header files; logically therefore if your header files mention one of these types it’s impossible for them to see the definition of the type.

If you’re using multiple sets of include_cpp! directives, or a mixture of include_cpp! and #[cxx::bridge] bindings, then you may be able to #include "cxxgen.h" to refer to the generated C++ function prototypes. In this particular circumstance, you’ll want to know how exactly the cxxgen.h header is named, because one will be generated for each of the sets of bindings encountered. The pattern can be set manually using autocxxgen’s command-line options. If you’re using autocxx’s build.rs support, those headers will be named cxxgen.h, cxxgen1.h, cxxgen2.h according to the order in which the include_cpp or cxx::bridge bindings are encountered. Attribute to state that a Rust type is to be exported to C++ in the extern "Rust" section of the generated cxx bindings.