On Fri, 29 May 2020, Jason Merrill wrote:
> On 5/22/20 10:56 AM, Patrick Palka wrote:
> > On Fri, 22 May 2020, Patrick Palka wrote:
> >
> > > When comparing two special member function templates to see if one hides
> > > the other (as per P0848R3), we need to check satisfaction which we can't
> > > do on templates. So this patch makes add_method skip the eligibility
> > > test on member function templates and just lets them coexist.
> >
> > It just occurred to me that this problem isn't limited to member function
> > templates. Consider this valid testcase which we currently reject:
> >
> > template<bool B> struct g {
> > g() requires B && false;
> > g() requires B;
> > };
> >
> > g<true> b; // error
> >
> > During add_method, we check satisfaction of both default constructors,
> > and since their constraints are dependent, constraints_satisfied_p
> > returns true for both sets of constraints. We then see that
> > 'B && false' is more constrained than 'B' and therefore discard the second
> > constructor. Since we discarded the second default constructor at
> > definition time, the instantiation g<true> has no eligible default
> > constructor.
> >
> > I am not sure what to do from here...
>
> I looked at this and it seems enough to let the functions coexist without
> trying to compare their constraints if processing_template_decl; we'll handle
> the hiding properly when the class template is instantiated.
>
> So this is what I'm committing:
Aha, that makes sense now, thanks! Somehow I convinced myself that
during class template instantiation we don't call add_method, so I
instead tried to remove that block of code from add_method altogether.
Needless to say that didn't work very well..
