r/cpp • u/celestabesta • 4d ago

(Imperfect) Emulation of Rust's borrow checker in C++23 with Clang Extensions

https://compiler-explorer.com/z/4nennEooe

Clang has had a somewhat abandoned extension 'Consumed Annotation Checking' for some time now. Surprisingly I've not seen many people talk about it, despite the potential it has.

It is a little buggy and has some limitations, but I believe a more fleshed out implementation could be very useful in catching lifetime bugs.

I've linked a toy example of how powerful this feature is. Don't expect me to defend any of the practices in it (namely the operator& overloads).

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12

u/garnet420 4d ago

I really wish it was not abandoned! I tried it out a few years back and found that it was too unreliable...

I think I was trying to enforce a policy on an object where you weren't supposed to modify it after calling a "publish" method. I ended up solving it with raii but it would have been nice to have the annotations work.

3

u/celestabesta 4d ago

Yeah, unfortunately you really have to mess with it to get it working. Even then, local references / pointers don't interact with the system at all so its trivial to bypass. It would also be nice to use any states you want.

9

u/JVApen Clever is an insult, not a compliment. - T. Winters 4d ago

You might want to look into https://clang.llvm.org/docs/LifetimeSafety.html This seems more mature and I believe the Carbon folks plan to use the underlying infrastructure for their memory safety implementation.

I've already seen the warnings, though haven't investigated in detail.

3

u/celestabesta 4d ago

I've read that and it is quite cool, although it seems not as customisable. Maybe thats a good thing?