static_assert can allow constant expressions to report errors. However, the
message that can be passed to it must be a string literal. It can't even be
a string evaluated at compile time - which results in the error messages
not being as helpful as they could be.



On Thu, 26 Mar 2020, 8:14 am Michał Policht via Std-Proposals, <
std-proposals_at_[hidden]> wrote:

> From your paper:
> > However, a general issue is that constant expressions cannot report
> errors when failure would occur
>
> Isn't `static_assert` a mechanism, which allows constant expressions to
> report errors?
>
> Regards,
> Michał
>
>
> > I've done some work on this, and wrote a draft paper
> > <
> https://github.com/chorman0773/CXX-Papers/blob/master/std_error_function.md
> >.
> > I am interested in any feedback.
> > I decided on a similar function, std::compiler_error, which has the same
> > compile time behavior, but its UB at runtime. This would allow users to
> > write std::error, with whatever runtime behavior they wish.
> > I would be interested in any feedback people have, both on the
> > semantics, and in the structure of the paper itself.
> > Thank you to the great people on the std-proposals mailing list.
> >
> > On Fri, 6 Mar 2020 at 11:07, connor horman <chorman64_at_[hidden]
> > <mailto:chorman64_at_[hidden]>> wrote:
> >
> > constinit won't downgrade (as the standard requires a constant
> > expression initializer). I did forget about that.
> >
> > On Fri, 6 Mar 2020 at 10:13, Thiago Macieira via Std-Proposals
> > <std-proposals_at_[hidden]
> > <mailto:std-proposals_at_[hidden]>> wrote:
> >
> > On Friday, 6 March 2020 06:46:56 PST connor horman via
> > Std-Proposals wrote:
> > > Currently it is not possible to implement std::error in a way
> > that it will
> > > work with initializing non-constexpr variables. Throwing an
> > exception
> > > simply downgrades to runtime, only erroring if the result is
> > needed at
> > > compile time.
> >
> > Does that also apply to constinit variables?
> >
> > --
> > Thiago Macieira - thiago (AT) macieira.info
> > <http://macieira.info> - thiago (AT) kde.org <http://kde.org>
> > Software Architect - Intel System Software Products
> >
> >
> >
> > --
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> >
> >
>
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