http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50711
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-10-13 08:18:07 UTC --- See http://lwg.github.com/issues/lwg-defects.html#1225 and also 1270 result_of cannot be used for SFINAE, it requires that its arguments be a valid expression
