RuntimeCompiledCPlusPlus VS PyDev.Debugger

hscpp (Hotswap C++) is an experimental library I created which allows you to hot-reload C++. It was heavily inspired by Runtime Compiled C++, and works by linking DLLs into your project at runtime.

The only recent attempt to make something like this practical, as far as I know, was RCCpp. Going by the GH activity, it looks like it kind of went nowhere.

FYI I maintain a list of runtime compiled C++ approaches on this wiki: https://github.com/RuntimeCompiledCPlusPlus/RuntimeCompiledCPlusPlus/wiki/Alternatives

There is https://github.com/RuntimeCompiledCPlusPlus/RuntimeCompiledC...

The idea is to use virtual functions, and recompile new classes into a shared library. The shared lib is linked into the running program, and old instances of the classes are deleted and replaced by new instances constructed from the share library.

I am working on a library using the same (stolen) idea here:

https://github.com/jheruty/hscpp

Proof of concept demo:

https://m.youtube.com/watch?v=pjGngeKgni8

hscpp is still very alpha, and I’m sure I’ll find lots of bugs as I work on a “real” demo. In contrast, Runtime Compiled C++ is quite mature and is used in real game projects.

Note that this approach very much limits your architecture. For example, you won’t be able to use statics, as the newly compiled shared libraries won’t see them.

It’s a finicky thing, worth it to me, but not something you can just plop in to an established project.

Well of course it's possible to generate executable code at runtime in C++ since clang itself is written in C++, but it's definitely a much larger undertaking, but there's two such efforts I know of, Cling and RuntimeCompiledCPlusPlus.

[1] https://github.com/fabioz/PyDev.Debugger/

Ha, I'm just working on integrating the `pydev.debugger` code reloading into `debugpy` (so that the code reloading from the PyDev debugger will be available for Python-VSCode debugger users too).

The in-memory reloading (which may be seen at: https://github.com/fabioz/PyDev.Debugger/blob/main/_pydevd_b...) unfortunately doesn't work all the time (fixing the references at runtime in Python is difficult), but it works well enough for the cases where you have a simple function and change it (that file does explain some of the issues that the reloading faces).

One major issue is that after doing the reload, you need to get out of the function and then back into it to see the difference -- so, if you're stopped in the function in a breakpoint, it's not possible to simply drop the function and restart it as Python itself doesn't support that... maybe that's a good idea for a PEP ;)

Anyways, when it works, it's pretty nice in that you don't have to restart your whole debug session to see changes (the other approach, which webservers use in general is just restart the whole process, so, for instance, Django has an initial process just monitoring for changes and a 2nd process which is actually serving requests which is restarted when something changes -- not as good if you have a heavy startup or are working with something where you have to click through multiple things to get to the state which you want).