Example Bindings
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
Point out:
- 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 amod
calledffi
in your code. - Native support for C++'s
std::unique_ptr
in Rust - Native support for Rust slices in C++
- Calls from C++ to Rust, and Rust types (in the top part)
- Calls from Rust to C++, and C++ types (in the bottom part)
Common misconception: It looks like a C++ header is being parsed by Rust,
but this is misleading. This header is never interpreted by Rust, but simply
#include
d in the generated C++ code for the benefit of C++ compilers.