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Using Rust in Scylla is not intuitive, the doc explains the entire process of adding new Rust source files to Scylla. What happens during compilation is also explained. Signed-off-by: Wojciech Mitros <wojciech.mitros@scylladb.com>
39 lines
1.6 KiB
Markdown
39 lines
1.6 KiB
Markdown
# Rust and C++
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Rust introduces many useful features that are missing in C++. This document
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shows how to use them in Scylla.
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## Using Rust in Scylla
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To create a Rust package `new_pkg` and use it in a C++ source file:
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1. Create a new package in the `rust` directory using `cargo new new_pkg --lib`
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2. Modify crate type to a static library by adding
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```
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[lib]
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crate-type = ["staticlib"]
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```
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to `new_pkg/Cargo.toml`
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3. Add `"new_pkg",` to the workspace members list in `Cargo.toml`
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4. Write your Rust code in `new_pkg/src/lib.rs`
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5. To export a function `fn foo(x: i32) -> i32`, add its declaration as follows to the same file
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```
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#[cxx::bridge(namespace = "rust")]
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mod ffi {
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extern "Rust" {
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fn inc(x: i32) -> i32;
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}
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}
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```
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6. Add `"rust/new_pkg/src/lib.rs"` to the `rusts` list in `configure.py`
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7. Include the `rust/new_pkg.hh` header and use `rust::foo()` in the selected c++ file.
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## Rust interoperability implementation
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Using Rust alongside C++ in scylla is made possible by the Rust crate CXX. The `cxx::bridge` macro,
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together with `mod ffi` and `extern "Rust"` mark items to be exported to C++. During compilation,
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a compatible version is generated with temporary names. It can be later linked with a header file, generated from the source code using `cxxbridge` command. The header exposed all items with original names and can be included like any other c++ header.
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Compilation is managed by `cargo`. Like in any Rust project, modules added to Scylla can be fully
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customized using corresponding `Cargo.toml` files. Currently, all modules are compiled to static
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libraries (TODO: dynamic or flexible)
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