Well, I can't say anything about being implementation defined or not. What
I can say is it's currently impossible, so for this to work either standard
needs to expand or make it implementation defined.
std::bit_cast creates copies which is not the same thing.
My main issue with the current state of the language is, you can do these
things at runtime. I have various constructs that make use of type punning,
but I can't use any of them at compile time. I need to have an alternative
that solves the same problem to be able to do it in compile time. Even then
behaviour isn't exactly the same.

Regarding UB, compilers have all the information about literally anything
when it's executed at compile time. Compilers are smart, they can handle it.

On Sat, Nov 30, 2024 at 1:45 PM Sebastian Wittmeier via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> The current typeless memory is either
>
> - std::byte, char, unsigned char
>
>
>
> As compile-time evaluation tries to avoid UB nearly completely and also
> tries to not use any implementation-defined features, there is less room
> for low-level inspection or modification.
>
>
>
> There is also constexpr std::bit_cast
>
>
>
> What usage examples do you have for the typeless_memory, which are not
> implementation-defined, allow the compiler to check and avoid UB (which
> e.g. entails an understanding of object lifetimes, types and memory
> locations) and which cannot be solved with the current tools in the
> standard library?
>
>
>
>
> -----Ursprüngliche Nachricht-----
> *Von:* James via Std-Proposals <std-proposals_at_[hidden]>
> *Gesendet:* Sa 30.11.2024 10:56
> *Betreff:* [std-proposals] std::typeless_memory (type punning)
> *An:* std-proposals_at_[hidden];
> *CC:* James <james.business.84_at_[hidden]>;
> Currently you can do whatever you want at runtime when it comes to type
> punning. Sure, all of them might not be safe, but you have some ways to do
> it safely. However in compile time (as far as I know) there is no way to
> achieve type punning.
>
> So I'd like to see this type, in standard library
> https://godbolt.org/z/1dEjYW1hW
>
> It's only purpose is to allow treating some underlying memory as whatever
> type you want in compile time without using extra memory. It would also
> provide a shortcut for runtime usage
> Currently you can't achieve that due to placement new and reinterpret_cast
> not being usable in compile time context
>
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