rust-cpp

by mystor

mystor / rust-cpp

Embed C++ directly inside your rust code!

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rust-cpp - Embed C++ code directly in Rust

Build Status Build status Documentation

rust-cpp
is a build tool & macro which enables you to write C++ code inline in your rust code.

This crate's interface is still very unstable, however, thanks to custom derive, it now has one of the first potentially stable interfaces. The current macro interface should either remain fairly stable, meaning that programs built with it will likely build with minimal, or no, changes when updating to new versions.

Usage

For usage information and in-depth documentation, see the

cpp
crate module level documentation.

Warning about Macros

The build phase cannot identify and parse the information found in

cpp!
blocks which are generated with rust's macro system. These blocks will attempt to generate rust code, but will not generate the corresponding C++ code. The procedural macro tries to avoid allowing the build to succeed if the
cpp!
block is generated, but this is not guaranteed. Do not create
cpp!
blocks with macros to avoid this.

History

rust-cpp
has had multiple different implementations. The code for these old implementations is still present in the tree today.

rustc_plugin

rust-cpp
started 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
syntex
plugin.
syntex
is an extraction of the rust compiler's internal
syntax
library, 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-cpp
used a stable
macro_rules!
macro to perform the rust code generation, and a build step based on
syntex
to 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
or
master
)

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-cpp
uses a fork of
syn
for its rust code parsing.

rust-cpp
now 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
syntex
which could take a long time to build.

The fork of

syn
(
cpp_syn
) which
rust-cpp
uses differs from
syn
in that it keeps track of source location information for each AST node. This feature has not been landed into
syn
yet as it is a breaking change, and none of
syn
's other consumers would make use of it yet.

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