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

[Markus Armbruster <armbru@redhat.com>]

Hanna Reitz <hreitz@redhat.com> writes:

> 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.

Me neither.

>                         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++,

Bad C++ in need of rework, presumably.

>                                              but I’m not comfortable 
> overseeing that process, which I would have to do as a maintainer. 

That makes two of us.

The plain language version of "I'm not comfortable serving" is of course
"I do not intend to serve".

> 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.

I'm a lot more interested in learning Rust than in (re-)learning C++.

> 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.

Right.