#include <iostream>
#include <array>
using namespace std;

struct Foo
{
   static constexpr double bar = 1.23;
   static constexpr std::array<double, 4> acgt_default_background_frequencies = {0.281774, 0.222020, 0.228876, 0.267330};
};

int main() {
	cout << Foo::bar << endl; // this works
	cout << Foo::acgt_default_background_frequencies[0] << endl; // this doesn't work
	return 0;
}