绑定示例

CXX requires that the whole C++/Rust boundary is declared in cxx::bridge modules inside .rs source code.

#[cxx::bridge]
mod ffi {
    extern "Rust" {
        type MultiBuf;

        fn next_chunk(buf: &mut MultiBuf) -> &[u8];
    }

    unsafe extern "C++" {
        include!("example/include/blobstore.h");

        type BlobstoreClient;

        fn new_blobstore_client() -> UniquePtr<BlobstoreClient>;
        fn put(self: &BlobstoreClient, buf: &mut MultiBuf) -> Result<u64>;
    }
}

// Definitions of Rust types and functions go here

Speaker Notes

指出：

  • Although this looks like a regular Rust mod, the #[cxx::bridge] procedural macro does complex things to it. The generated code is quite a bit more sophisticated - though this does still result in a mod called ffi in your code.
  • Native support for C++’s std::unique_ptr in Rust
  • Native support for Rust slices in C++
  • 从 C++ 调用 Rust，并使用 Rust 类型（顶部位置）
  • 从 Rust 调用 C++，并使用 C++ 类型（底部位置）

常见误解：这 看似 Rust 在解析 C++ 头文件，其实具有误导性。Rust 不会对此头文件进行解释，只是在生成的 C++ 代码中添加 #include，以便于 C++ 编译器 使用。