Re: [PATCH experiment 00/16] C++20 coroutine backend

[Hanna Reitz]

On 17.03.22 16:11, Paolo Bonzini wrote:
> On 3/16/22 13:32, Stefan Hajnoczi wrote:
> > You can define rules and a way to enforce a subset of C++, but I think
> > over time the code will be C++. A policy that is complicated discourages
> > contributors.
> >
> > For these reasons I think that if code runs through a C++ compiler we
> > should just allow C++. Either way, it will take time but that way no one
> > will feel betrayed when C++ creeps in.
>
> Fair enough.  We even already have some conventions that will make any 
> C++ that creeps in less weird (for example, mandatory typedef of 
> structs).
>
> I don't think it would be a big deal overall.  I actually agree that 
> we should "just allow C++", what matters more to have style rules that 
> make QEMU's flavors of C and C++ consistent.

I just want to throw in that I personally am absolutely not confident in 
reviewing C++ code.  As for Rust, you keep mentioning that we don’t have 
anyone who would “shepherd us through the learning experience”, but I 
find the very same argument applies to C++.

C++ may start out looking like C, but if used ideally, then it is a very 
different language, too.  I understand the difference is that we can 
incrementally convert our C code to C++, but I’m not comfortable 
overseeing that process, which I would have to do as a maintainer.  
Assuming our overall stance does change to “just allowing C++”, I’d feel 
unjust if I were to reject C++isms just based on the fact that I don’t 
know C++, so I’d be forced to learn C++.  I’m not strictly opposed to 
that (though from experience I’m more than hesitant), but forcing 
maintainers to learn C++ is something that has a cost associated with it.

My biggest gripe about C++ is that as far as I understand there are many 
antipatterns, many of which I think stem from the exact fact that it is 
kind of compatible with C, and so you can easily accidentally write 
really bad C++ code; but without years of experience, I’m absolutely not 
confident that I could recognize them.  Now, I might say I’d just 
disallow complicated stuff, and keep everything C-like, but from what 
I’ve heard, C-like C++ seems to be exactly one case that is considered 
bad C++.  I’m really under the impression that I’d need years of 
experience to discern good from bad C++, and I don’t have that experience.

Hanna