[Development] C++20 structural types (was: C++20 @ Qt)
marc.mutz at qt.io
Sat Nov 5 08:24:29 CET 2022
On 04.11.22 16:49, Thiago Macieira wrote:
> I've just hit this: should we make some of our very simple types even simpler
> so they're structural types and thus can be passed as template parameters?
> For example, QFlags. I've just tried it and I get:
> error: ‘QFlags<Qt::AlignmentFlag>’ is not a valid type for a template non-type
> parameter because it is not structural
> note: ‘QFlags<Qt::AlignmentFlag>::i’ is not public
>  https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0732r2.pdf
I wrote about this in the comparison sub-thread:
On 03.11.22 10:40, Marc Mutz via Development wrote:
> One can even now = default the equality operator. Then the compiler
> creates one based on for member-wise equality. If all such members have
> an = default'ed equality operator, and with a few other other
> requirements, the type in question has Strong Structural Equality, and
> thus can be used as arguments to non-type template parameters (NTTP).
> QFlags and QFixed are examples where this might come in handy. There are
> probably others, too.
There's also https://bugreports.qt.io/browse/QTBUG-94266
I'll clone that for QFixed.
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