https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120682
--- Comment #2 from Benjamin Schulz <schulz.benjamin at googlemail dot com> --- Hi there, if that testcase is "invalid", then that means that the mapper statement does not work with template classes at all It would mean that for a struct with a template datatype template <typename T> struct myvec { size_t len; T *data; }; and must first write something like typedef std::myvec<double> doublevec; before one can use the mapper then on doublevec. But that makes the mapper rather useless for usage with templates as one has to define a specific mapper for each template usage...