On 05/03/2025 7:10 am, Tiago Freire via Std-Proposals wrote:
> I think that to a certain extent the user who is doing the markings
> should be responsible for doing it right.
>
> What we want is for a way to cache values instead of wasting time with
> expensive but deterministic computations. And we already know that the
> compiler can't always validate if a function is or isn't "pure".
>
> The compiler is just going to have to trust that the developer did the
> right thing, and if they didn't the compiler is still going to be able
> to generate some code and it is going to be their problem that the
> program does the wrong thing.
>
> It would be nice if the compiler could warn if they know for sure that
> the user did the wrong thing, but it doesn't need to cover every corner
> case and be a perfect 100% detection. (if it could do that, the
> classification probably wouldn't be needed).
>
The classification would still be useful, because at that point it is a
contract (no as in the c++ contracts), like noexcept.

You tell your user that a function is pure; that they can cache the
result and reuse it, instead of calling the function every time, that it
has no side-effects, and so on.
And with 100% detection the compiler helps you to find where the
contract is broken.