[Bug c++/89481] constexpr function allows writing one active union member and reading another

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89481

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2019-02-25
                 CC|                            |jakub at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC trunk starting with r269052 aka PR89336 fix will reject this too for
-std=c++14 and -std=c++17 too:
pr89481.C:20:29:   in ‘constexpr’ expansion of ‘all_zeros()’
pr89481.C:10:32: error: change of the active member of a union from
‘all_zeros()::mix::numeric’ to ‘all_zeros()::mix::bytes’
   10 |     zero.bytes[sizeof(double)] = '\0';
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
It is accepted with -std=c++2a where changing of active member is allowed.