[Bug c++/80662] libstdc++ basic_string casting oddity

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80662

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|libstdc++                   |c++

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And further:

namespace std
{
  struct ostream
  {
    ostream& operator<<(const char*)
    {
      return *this;
    }
  };

#ifndef UNCONSTRAINED
  // GCC 7 code

  template<typename _Ostream, typename _Tp>
    inline ostream&
    operator<<(_Ostream&& __os, const _Tp&__x)
    {
      return __os;
    }
#else
  // GCC 6 code

  template<typename _Tp>
    inline ostream&
    operator<<(ostream&& __os, const _Tp&)
    {
      return __os;
    }
#endif
}

struct my_stream : public std::ostream {
    template<typename T>
    my_stream& operator<<(T&& value)
    {
        std::ostream::operator<<(value);
        return *this;
    }
};

int main()
{
    my_stream& s = (my_stream{} << "hello world");
}

G++ chooses std::operator<<

Clang chooses my_stream::operator<<

EDG and VC++ say they're ambiguous.

Changing to component=c++, but I'm not convinced G++ is actually wrong here.