array<T, 0>

40124.cpp

template<class T>
struct Container
{
	union wrapper {
		constexpr wrapper(): b() {}
		~wrapper() = default;
		
		bool b;
		T t;
	} w;
	
	Container(int) { }
};

template<class T>
class Foo
{
public:
	const Container<T> c { 0 };
	
	constexpr const T* data() const {
		return &c.w.t;
	}
};

inline constexpr bool member_is_consexpr(Foo<int> const& foo)
{
	return foo.data() && true;
}

int main()
{
	const Foo<int> foo {};
	const Foo<int> bar {{}}; // error
	static_assert(member_is_consexpr(foo)); // works
	static_assert(std::is_aggregate<Foo<int>>::value); // works
}