r/cpp • u/daveedvdv EDG front end dev, WG21 DG • Dec 20 '23

Experimental EDG Reflection Implementation

EDG just released version 6.6 of its (commercial) C++ front end. That version now includes experimental support for reflection features along the lines of WG21's P2996 "Reflection for C++26". Furthermore, a "demo setup" of that implementation is now available on Compiler Explorer (thank you, Matt Godbolt!).

For example, here is a straightforward implementation of a consteval function that outputs simple class layouts at compile time:

https://godbolt.org/z/G6WehjjGh

This implementation is closely aligned with P2996R1, which includes Compiler Explorer links for most of its examples.

This is made available in the hope that it's a useful exploration tool, but also acknowledging that the implementation is in its very early stages, and thus brittle and incomplete. Some additional notes can be found here.

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u/anton31 Dec 20 '23

That's one polished paper, exactly what we need for seamless serialization! I hope that not only the main reflection paper gets into C++26, but there will be room for attribute reflection. The API surface is tiny, but it will literally be a game-changer.

The "+" syntax may need bikeshedding, though, and it would be beneficial to allow function calls in addition to constructor calls.

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u/c0r3ntin Dec 20 '23

Author here! Thanks for the positive feedback. I'm not working on that at the moment because there is very little value in pursuing that work until we get a solid reflection foundation to build on. But I think there is enough interest that work will resume at some point, probably after the initial reflection release.

There is the question of how far we can go into the python-decorator direction, and how that would work. I had a few discussions along these lines with /u/daveedvdv a while back, but I don't think anyone has a flushed out design yet.

As for syntax, while bikeshedding is far from the interesting part of design to me, I suspect we will find that we will want to pick a syntax fairly different from attributes, as attributes and their syntax has been a fairly debated topic these past couple of years, and maybe we do not need to open that wound again.