> I don't know how common it actually is but I have seen some cases where
> `std::forward` has been used multiple times on the same forwarding
> reference by mistake and I think this feature would catch at least some
> those mistakes.

This can be checked by clang-tidy already. It does not require a
language change.

https://godbolt.org/z/ec58376rz

On Thu, 27 Aug 2026 at 06:03, Ted Lyngmo via Std-Proposals
<std-proposals_at_[hidden]> wrote:
>
> 2026-08-25 22:30, Tiago Freire:
> > Or maybe a std::destroy(), that burns a physical hole in your memory so that it can never be re-used again....
>
> :-)
>
> > In all seriousness, we can discuss hypothetical features, but the important part is it must have a point.
> > What problem you are trying to solve? Why would I want it solved? Does this do that?
> >
> > Is there an answer to those questions?
> My impression is that it's to get a compilation error on redacted
> variables if one tries to use them and that this is to avoid common(?)
> errors occuring when using moved-from variables in an unsafe manner.
>
> I don't know how common it actually is but I have seen some cases where
> `std::forward` has been used multiple times on the same forwarding
> reference by mistake and I think this feature would catch at least some
> those mistakes. If it's enough of a problem to add the feature I don't
> know. Static analyzers also gets better and better so perhaps it'll be a
> none issue in a few years.
>
> If we go ahead with the idea then perhaps an alternative to a
> `std::redact`/`std::unredact` pair of functions with magic properties
> would be to take inspiration from clang's "consumable" attributes?
>
> [[clang::consumable(unconsumed)]] on the class
> [[clang::set_typestate(consumed)]] on the move constructor/destructive
> operations
> [[clang::callable_when(unconsumed)]] on member functions that require an
> unconsumed object
> [[clang::return_typestate(...)]]/[[clang::param_typestate(...)]] for
> propagating state through function boundaries.
>
> Vibe coded example: https://godbolt.org/z/nhjfsbKxv
>
> I noticed that it doesn't mark an object as consumed if one uses `Stream
> a = static_cast<Stream&&>(obj);` instead of `Stream a = std::move(obj);`
> so there are obvious gaps in the current implementation.
>
> Perhaps someone here's been involved in adding these attributes and
> could describe them in more detail (if they are "close enough" to what's
> been discussed for redact/unredact)?
>
> Br,
> Ted
>
> Ps. Sorry if this has already been up for discussion. I think I've
> missed a few messages in this thread.
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-- 
Yongwei Wu
URL: http://wyw.dcweb.cn/