mystor/ rust-cpp
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Description
Embed C++ directly inside your rust code!
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rust-cpp - Embed C++ code directly in Rust
Overview
rust-cppis a build tool & macro which enables you to write C++ code inline in your rust code.
let name = std::ffi::CString::new("World").unwrap();
let name_ptr = name.as_ptr();
let r = unsafe {
cpp!([name_ptr as "const char *"] -> u32 as "int32_t" {
std::cout << "Hello, " << name_ptr << std::endl;
return 42;
})
};
assert_eq!(r, 42)
The crate also help to expose some C++ class to Rust by automatically implementing trait such as Drop, Clone (if the C++ type can be copied), and others
cpp_class!{
#[derive(PartialEq)]
unsafe struct MyClass as "std::unique_ptr"
}
Usage
For usage information and in-depth documentation, see the
cppcrate module level documentation.
Differences with the cxx
crate
This crate allows to write C++ code "inline" within yout Rust functions, while with the
cxxcrate, you have to write a bit of boiler plate to have calls to functions declared in a different
.cppfile. Having C++ code inline might be helpful when trying to call to a C++ library and that one may whish to make plenty of call to small snipets. It can otherwise be fastidious to write and maintain the boiler plate for many small functions in different places.
These crate can also be used in together. The
cxxcrate offer some usefull types such as
CxxStringthat can also be used wth this crate.
The
cxxbridge does more type checking which can avoid some classes of errors. While this crate can only check for equal size and alignement.
History
rust-cpphas had multiple different implementations. The code for these old implementations is still present in the tree today.
rustc_plugin
rust-cppstarted life as a unstable compiler plugin. This code no longer builds on modern nightly rusts, but it had some features which are still unavailable on more recent versions of
rust-cpp, as it was able to take advantage of the rust compiler's type inference by abusing a lint pass to collect type information.
Development on the original version ceased for 2 major reasons:
1) The rustc internal libraries changed very often, meaning that constant maintenance work was required to keep it working on the latest nightly versions.
2) The plugin had no support for stable rust, which is undesirable because the majority of crates are not built with the latest nightly compiler, and requiring unstable features is a deal breaker for them.
These limitations led to the development of the next phase of
rust-cpp's lifetime.
stable (a.k.a v0.1
)
The next phase in
rust-cpp's lifetime was when it was rewritten as a
syntexplugin.
syntexis an extraction of the rust compiler's internal
syntaxlibrary, and has support for performing procedural macro expansions by rewriting rust source files.
Performing a full rewrite of the source tree was very unfortunate, as it would mean that all compiler errors in crates which use the plugin would be reported in a generated file instead of at the original source location. Instead, this version of
rust-cppused a stable
macro_rules!macro to perform the rust code generation, and a build step based on
syntexto perform the c++ code generation and compilation.
Unfortunately this architecture meant that one of the neatest features, closures, was not available in this version of
rust-cpp. Implementing that feature required some form of procedural code generation on the rust side, which was not possible in rust at that time without performing full text rewrites of the source code.
Macros 1.1 and syn (a.k.a. v0.2
)
This is the current implementation of
rust-cpp. In
rustc 1.15, the first form of procedural macros, custom derive, was stabilized. Alongside this, @dtolnay implemented
syn, which was a small, fast to compile, crate for parsing rust code.
rust-cppuses a fork of
synfor its rust code parsing.
rust-cppnow internally uses a custom derive to implement the procedural components of the rust code generation, which means that closures are available again! It also builds much more quickly than the previous version as it no longer depends on
syntexwhich could take a long time to build.
The fork of
syn(
cpp_syn) which
rust-cppuses differs from
synin that it keeps track of source location information for each AST node. This feature has not been landed into
synyet as it is a breaking change, and none of
syn's other consumers would make use of it yet.
v0.5
The syn version was upgraded to
syn 1.0Since
syndid not allow to access the actual source location or text, the
cpp_builduses its own rust lexer, forked from the
proc_macro2crate.