leocelente / meta-something

Generating C++ from C++

Meta something

Started as a dive into C++ Reflection, ended up as a little bit of fun in code generation.

I got curious by the HubrisOS, it uses a configuration file that describes the system's processes. The role of the OS is to give its best effort to keep the system on that state. Then a I thought: what if configuration and behavior could be represented in a single place. That means that the compile-time configuration and data need to affect the system's function. So maybe with the use of reflection in C++ (that I had briefly heard of) I could construct a class that contains all that I need, from that the rest of the program can be generated in compile-time. Inspired by crect, I dived into reflection libraries (metacpp, reflang, refl-cpp) and clang's experimental branch. But nothing seemed to work easily and while researching how they worked I saw that they generate code containing metadata with the help of libclang. So eventually, after a few days without much success I started to build my own library that generates code from code.

Basically the goal is, given:

#include "main.gen.cpp"

struct MySystem {
  int resource;
  float resource2;
  void task() {}

  void task2() {}
};

int main() {
  auto system = Generate<MySystem>();
  return system();
}

The special library will populate the file main.gen.cpp with a scheduler that runs all methods as tasks. After that is basically done I'll look into adding special parameters as custom attributes that adapt the generated code. Imagine:

#include "main.gen.cpp"

struct MySystem {
  void task0() [[isr, address(0x80)]] {}
  void task1() [[run_once, timeout(100ms)]] {}
  void task2() [[restart_on_failure]] {}
};

One of the goals is to be as transparent as possible so that the framework can be easily ported to different systems, with special attention to embedded devices.