c++ - Simple constexpr function failed to compile with GCC (clang is OK) -

the following code does not compile gcc 5.2 (c++14). does compile clang 3.6 (c++14). (original code can found here)

#include <cstddef> #include <algorithm> #include <type_traits> #include <utility>  template <typename t> class aggregate_wrapper;  template <typename t, std::size_t n> class aggregate_wrapper<t[n]> { public:   using array = t[n];    template <typename... ts, typename = decltype(array{std::declval<ts>()...})>   aggregate_wrapper(ts&&... xs)       : arr_{std::forward<ts>(xs)...} {     // nop   }    aggregate_wrapper(const array& arr) {     std::copy(arr, arr + n, arr_);   }   aggregate_wrapper(array&& arr) {     std::move(arr, arr + n, arr_);   }    operator t* () {     return arr_;   }   operator const t* () const {     return arr_;   }    constexpr std::size_t size() const {     return n;   }  private:   array arr_; };  int main() {   aggregate_wrapper<int[3]> arr;   static_assert(arr.size() == 3, ""); } 

the error message produced is

main.cpp: in function 'int main()': main.cpp:44:3: error: non-constant condition static assertion    static_assert(arr.size() == 3, "");    ^ main.cpp:44:25: error: call non-constexpr function 'constexpr std::size_t aggregate_wrapper<t [n]>::size() const [with t = int; long unsigned int n = 3ul; std::size_t = long unsigned int]'    static_assert(arr.size() == 3, "");                          ^ main.cpp:34:25: note: 'constexpr std::size_t aggregate_wrapper<t [n]>::size() const [with t = int; long unsigned int n = 3ul; std::size_t = long unsigned int]' not usable constexpr function because:    constexpr std::size_t size() const {                          ^ main.cpp:34:25: error: enclosing class of constexpr non-static member function 'constexpr std::size_t aggregate_wrapper<t [n]>::size() const [with t = int; long unsigned int n = 3ul; std::size_t = long unsigned int]' not literal type main.cpp:10:7: note: 'aggregate_wrapper<int [3]>' not literal because:  class aggregate_wrapper<t[n]> {        ^ main.cpp:10:7: note:   'aggregate_wrapper<int [3]>' not aggregate, not have trivial default constructor, , has no constexpr constructor not copy or move constructor 

any ideas? should code compile according standard?

or make existing variadic constructor serve constexpr constructor perform default construction:

template <typename... ts, typename = decltype(array{std::declval<ts>()...})> constexpr                      // <---- add aggregate_wrapper(ts&&... xs)    : arr_{std::forward<ts>(xs)...} {    // nop }