On Thu, Jul 11, 2024 at 4:34 PM Tiago Freire via Std-Proposals
<std-proposals_at_[hidden]> wrote:
>
> > The only reason to have mandatory RVO is if the user can be sure that it's going to happen and be told when it can't happen. It's very easy to accidentally make NVRO impossible according to your rules when refactoring the code. So we need a syntax to tell the compiler we want it to tell us when it could not do it.
>
> I agree with having a gadget to be able to tell you "when it cannot do it". But that's a different thing from having a gadget that tells it that "it must do it" or "to what to do it too".
> Warning that it didn't do it when you expect it too. Is a different thing from adding a rule as to when it must do it.
> The doing it part should require no annotation. You can have an annotation to tell you if it did.

Think about it like this: who is it that actually *care* about NRVO?

If I'm writing code and I don't care about whether NRVO is happening
in that code, then... I don't need a change to the standard. My code
does not rely on NRVO, so while I might *prefer* it, I don't need the
standard to *enforce* it.

If I'm writing code which by its nature *requires* NRVO, then I need
to enforce it. I *need* to use that "annotation to tell you if it
did", because I actually care about it happening.

So why not tie that "annotation to tell you if it did" to the actual
enforcement rules of the compiler? Why not leave it as an optimization
unless the person uses the annotation?