namespace std::chrono {
class file_clock {
public:
using rep = a signed arithmetic type;
using period = ratio<unspecified, unspecified>;
using duration = chrono::duration<rep, period>;
using time_point = chrono::time_point<file_clock>;
static constexpr bool is_steady = unspecified;
static time_point now() noexcept;
// Conversion functions, see below
};
}