[Bug c++/66834] [concepts] concept parameter kind mismatch causes hard error

["andrew.n.sutton at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66834

--- Comment #2 from Andrew Sutton <andrew.n.sutton at gmail dot com> ---
I think that this is invalid too. There's an expansion from an
uninstantiated template argument pack into a pair of template
parameters.

I think the program must be ill-formed in this case. It's not possible
to substitute a single pack through the two parameters declared for
ExplicitlyConvertible in order to normalize the constraint.

The TS is silent on this, but the resolution should be the same as that of
1430.

Andrew Sutton


On Fri, Jul 10, 2015 at 10:48 PM, jason at gcc dot gnu.org
<gcc-bugzilla@gcc.gnu.org> wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66834
>
> --- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> ---
> This was introduced by my patch for bug 66092, applying the tentative
> resolution of core issue 1430 to concepts as well as alias templates.  This
> makes sense to me since they have the same issue of needing to substitute
> dependent arguments into the template, in this case during normalization.
>
> So I think your example is invalid, but it could use some discussion in core.
>
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