[Bug c++/105351] [concepts] Constraint checking does correctly match static member attributes

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105351

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Gawain Bolton from comment #4)
> Finally, this also begs the question as to how one could write a requirement
> to ensure a class has a static attribute.

One way is to replace the requirement 'T::attr2' with 'typename
dummy<&T::attr2>' where 'dummy' is the class template

  template<auto*> struct dummy;

This works because template arguments are constant expressions, and constant
expressions are evaluated even in unevaluated contexts, so the bullet point
that ensadc pointed out in comment #3 no longer applies.

This makes both Clang and GCC happy: https://godbolt.org/z/c8q355hfh