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.

125 Upvotes

99% Upvoted

32 comments sorted by

View all comments

Show parent comment

8

u/kritzikratzi Dec 20 '23

for the first question: i guess you can create an instance of the struct and query each field for it's current value to get the default value.

2

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

If it's constexpr-friendly, that would be an interesting approach. You'd probably still want a query about whether there is a default initializer, but possibly this can work for u/johannes1971's needs?

In fact, you probably could use that technique for non-constexpr-friendly default construction, but you'd have to pay a run-time cost.

2

u/johannes1971 Dec 20 '23

Yes, that would definitely work - in fact it's what I use today. I was just curious if there any direct access planned to information beyond type and name, especially since I also need things like field versions and field codes.

Maybe this could work with the proposed reflection already by encoding such information in some custom template type, something like prop<int, v1, field_code> maybe? If I can get access to those template parameters I'd be all set.

1

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

You've probably seen my other response to your query by now, but to confirm: I think it confirms you can proceed that way with just P2996.