[Development] C++20 comparisons @ Qt (was: Re: C++20 @ Qt)

[Volker Hilsheimer]

> On 14 Nov 2023, at 09:40, Marc Mutz via Development <development at qt-project.org> wrote:
> 
> On 14.11.23 09:31, Marc Mutz via Development wrote:
> [...]
>> And then naming them Qt::partial_ordering is just consequent, because
>> users can reach ultimate SC by doing something like
>> 
>>      #ifdef __cpp_lib_three_way_comparison
>>      using std::partial_ordering;
>>      ~~~~
>>      #else
>>      using Qt::partial_ordering;
>>      #endif
>> 
>>      ~~~ use unqualified partial_ordering ~~~
> 
> This will also mean that in Qt 7 we can maintain 100% SC with Qt 6 by 
> simply saying
> 
>    namespace Qt {
>        using partial_ordering = std::partial_ordering;
>        using weak_ordering = std::weak_ordering;
>        using strong_ordering = std::strong_ordering;
>    }
> 
> Done.


I agree with Marc here.

It’s tempting to add some Qt::Ordering::Partial, but it only makes things harder in the not-so-long run. From C++ 23 on, we can expect std::partial/weak/strong_ordering to become as ubiquitous as “true” and “false”. We should not invent our own.

Adding Qt::snake_case interims that are BC with std, with conversion from/to QPartialOrdering, is the right thing to do.

Volker