请教问题

using hrc = std::chrono::high_resolution_clock;
decltype(hrc::now()) invincible_before;
if (take_damage())
{
auto now = hrc::now();
if (now > invincible_before)
{
hp -= damage;
invincible_before = now + std::chrono::seconds(3); // invincible in next 3s, for example
}
else
{
// player is invincible now!
}

问一下gpt