https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65312
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- I believe this is a GCC extension, G++ implements the proposed resolution of http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#253 and since all sub-objects of List are correctly initialized, no initializer is required for the member of that type.
