[Bug libstdc++/52114] SFINAE out the rvalue iostream operators to give better error messages

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52114

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-02-04 22:53:11 UTC ---
(In reply to comment #5)
> (In reply to comment #2)
> > Yesterday I was wondering: is there something in C++11 saying explicitly that
> > these tricks are allowed,
> In N3242, 14.8.2/{7,8}

The question is not about the language rules, we know it works. The question is
whether modifying the signature of the function is allowed. It would change the
return type if called for a type that overloads operator<< with a return type
that is not ostream&