Get size of std::array without an instance

Question

Given this struct:

struct Foo {   std::array<int, 8> bar; }; 

How can I get the number of elements of the bar array if I don't have an instance of Foo?

Answer 1

You may use std::tuple_size:

std::tuple_size<decltype(Foo::bar)>::value 

Answer 2

Despite the good answer of @Jarod42, here is another possible solution based on decltype that doesn't use tuple_size.
It follows a minimal, working example that works in C++11:

#include<array>  struct Foo {     std::array<int, 8> bar; };  int main() {     constexpr std::size_t N = decltype(Foo::bar){}.size();     static_assert(N == 8, "!"); } 

std::array already has a constexpr member function named size that returns the value you are looking for.