The Bridge Module

CXX relies on a description of the function signatures that will be exposed from each language to the other. You provide this description using extern blocks in a Rust module annotated with the #[cxx::bridge] attribute macro.

# // Copyright 2023 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
{{#include ../../../../third_party/cxx/blobstore/src/main.rs:bridge}}

• The bridge is generally declared in an ffi module within your crate.
• From the declarations made in the bridge module, CXX will generate matching Rust and C++ type/function definitions in order to expose those items to both languages.
• To view the generated Rust code, use cargo-expand to view the expanded proc macro. For most of the examples you would use cargo expand ::ffi to expand just the ffi module (though this doesn't apply for Android projects).
• To view the generated C++ code, look in target/cxxbridge.