[Bug c++/63876] static data members of template classes w/ default ctors gives "undefined reference" error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63876

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID
           Severity|major                       |normal

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
You've only declared a specialization, this is not a definition:

template<> std::mutex CRTP_class< Foo >::mutex_;


You can make it a definition with an initializer:

template<> std::mutex CRTP_class< Foo >::mutex_{};