[Development] About the timeline and phases to support C++20 with and in Qt

[Marc Mutz]

On 03.02.24 18:13, Thiago Macieira wrote:
> On Wednesday, 21 December 2022 09:51:52 PST Vladimir Minenko via Development
> wrote:
>> We got four user stories on Qt Bug Reports:
>>
>> 1. Use C++20 code with Qt - https://bugreports.qt.io/browse/QTBUG-109360
>> 2. C++20 is required for the development of Qt itself -
>> https://bugreports.qt.io/browse/QTBUG-109361
>> 3. C++20 is mandatory for users of Qt -
>> https://bugreports.qt.io/browse/QTBUG-109362
> 
> Those tasks haven't got any updates recently. What's the status?
> 
> I'd like to ask that we go to #3 for 6.8 or 6.9.

We don't drop supported compilers except in LTS+1 releases. That means 
6.9 at the earliest. In the last round, these were the objections:

a. QNX and Integrity don't support it, yet
b. We'd like to avoid forcing users to switch their projects to C++20,
    which is the rationale for separating (2) and (3) above.

I think (a) is a blocker, unless we allow different platforms to have 
different minimum C++ version requirements. That won't help with 
whatever you're thinking about when you ask to require C++20, because it 
means we'll need to maintain C++17-compatibility in the vast majority of 
the code-base.

I have some sympathy for (b), and I could live with the required 
#ifsef'ery for the time being, because it would be something that's 
required for (public) headers only.

Jani, Vladimir: do we have line-of-sight for C++20 support in QNX, 
Integrity, VxWorks and WebAssembly?

Thanks,
Marc

-- 
Marc Mutz <marc.mutz at qt.io>
Principal Software Engineer

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