#include <future>
#include <ios>
#include <string>
#include <system_error>

struct my_error_category : public std::error_category {
	const char* name() const noexcept override {
		return "potato";
	}

	std::string message(int) const override {
		return "message goes here";
	}
};

int main() {
	auto& generic_cat = std::generic_category();
	auto& system_cat = std::system_category();
	auto& iostream_cat = std::iostream_category();
	auto& future_cat = std::future_category();
	const auto& my_cat = my_error_category();

	std::error_code generic(42, generic_cat);
	std::error_code system(42, system_cat);
	std::error_code iostream(42, iostream_cat);
	std::error_code future(42, future_cat);
	std::error_code my(42, my_cat);
}