整数文字必须接受为 unsigned long long code>。负号不是文字的一部分，而是在返回值之后应用。

Integer literals need to be accepted as unsigned long long. The negative sign is not part of the literal, it is applied after the fact, to the returned value.

constexpr int64_t operator "" _jpy(unsigned long long l)
{
  return static_cast<int64_t>(l);
}