#include <iostream>

struct Matrix {
	static const int ColsAtCompileTime = 1;
	enum {RowsAtCompileTime = 42};
};

void foo(const int& x) {
	std::cout << x << std::endl;
}

int main() {
	foo(Matrix::RowsAtCompileTime);  // works
	foo(Matrix::ColsAtCompileTime);  // error!
	return 0;
}