c++ - Incomplete types and initializer_list -

i trying model meta data serializing/de-serializing c++ objects. here captures nuts & bolts of need; compiles gcc 5.2 (g++ sample.cpp -std=c++14) , clang 3.6 (clang++ sample.cpp -std=c++14).

my question struct typeinfo in example. contains std::initializer_list of itself. standards-conforming?

#include <cstdint> #include <initializer_list>  enum class typecode : std::uint8_t { boolean, int, object, string, sentinel };  struct typeinfo {     typecode typecode_;      char fieldname_[64];      union     {         std::uint16_t textminlength_;         std::uint16_t objectversionmajor_;     };      union     {         std::uint16_t textmaxlength_;         std::uint16_t objectversionminor_;     };      //  set if typecode_ = object     std::initializer_list < typeinfo > objecttypeinfos_; };  int main() {     typeinfo const sti { typecode::string, "updatedby", { .textminlength_ = 0 }, { .textmaxlength_ = 16 } };      typeinfo const iti { typecode::int, "amount", { 0 }, { 0 } };      typeinfo const oti { typecode::object, "starttime", { .objectversionmajor_ = 1 }, { .objectversionminor_ = 0 }, {       typeinfo { typecode::int, "weekdays", { 0 }, { 0 } },       typeinfo { typecode::int, "timeofday", { 0 }, { 0 } },       typeinfo { typecode::string, "timezone", { .textminlength_ = 0 }, { .textmaxlength_ = 5 } }     } };      typeinfo const noti { typecode::object, "schedule", { .objectversionmajor_ = 1 }, { .objectversionminor_ = 0 }, {       typeinfo { typecode::int, "id", { 0 }, { 0 } },       typeinfo { typecode::string, "description", { .textminlength_ = 0 }, { .textmaxlength_ = 16 } },       typeinfo { typecode::object, "starttime", { .objectversionmajor_ = 1 }, { .objectversionminor_ = 0 }, {         typeinfo { typecode::int, "weekdays", { 0 }, { 0 } },         typeinfo { typecode::int, "timeofday", { 0 }, { 0 } },         typeinfo { typecode::string, "timezone", { .textminlength_ = 0 }, { .textmaxlength_ = 5 } }       } }     } }; } 

that induces undefined behavior current wording. @ point of instantiation of std::initializer_list<typeinfo>, typeinfo incomplete, hence [res.on.functions]/(2.5) applies:

in particular, effects undefined in following cases:
(2.5) — if incomplete type (3.9) used template argument when instantiating template component, unless allowed component.

… , incomplete types not allowed initializer_list yet - however, that's defective. lwg issue 2493 opts fix this:

the typical use-case of std::initializer_list<t> pass-by-value parameter of t's constructor. however, contravenes [res.on.functions]/2.5 because initializer_list doesn't allow incomplete types (as example std::unique_ptr ([unique.ptr]/5) , std::enable_shared_from_this ([util.smartptr.enab]/2)).

a resolution copy-paste relevant text such paragraph.

i.e. code fine (and officially fine after resolution of aforementioned dr).