[英]C++ user-defined literals for any type
現在,用戶定義的文字接受一組有限的類型作為輸入參數(請參見此處 )。 有沒有計划接受任何類型作為輸入參數,如果不是,那是為什么呢?
例如,我可能希望能夠以不同的格式(秒,毫秒等)獲得std :: chrono :: duration,並且會執行類似的操作
constexpr double operator"" _s(std::chrono::nanosecond time)
{
return std::chrono::duration_cast<std::chrono::duration<double, std::chrono::seconds::period>>(time).count();
}
constexpr long operator"" _us(std::chrono::nanoseconds time)
{
return std::chrono::duration_cast<std::chrono::microseconds>(time).count();
}
// And so on ...
int main()
{
auto t0 = std::chrono::high_resolution_clock::now();
// do some stuff
auto t1 = std::chrono::high_resolution_clock::now();
std::cout << "Time in seconds : " << (t1 - t0)_s << "s\n";
std::cout << "Time in microseconds : " << (t1 - t0)_us << "µs\n";
return 0;
}
也許您可以改用輔助結構:
#include <chrono>
#include <iostream>
using namespace std::literals::chrono_literals;
template <class Duration>
struct dc {
using rep = typename Duration::rep;
const std::chrono::nanoseconds time;
constexpr dc(std::chrono::nanoseconds time):time(time) { }
constexpr operator rep() {
return std::chrono::duration_cast<Duration>(time).count();
}
};
using s_ = dc<std::chrono::seconds>;
using us_ = dc<std::chrono::microseconds>;
// And so on ...
template <us_::rep N>
struct S {
};
int main()
{
auto t0 = std::chrono::high_resolution_clock::now();
// do some stuff
auto t1 = std::chrono::high_resolution_clock::now();
std::cout << "Time in seconds : " << s_(t1 - t0) << "s\n";
std::cout << "Time in microseconds : " << us_(t1 - t0) << "µs\n";
S<us_(10us)> us;
(void)us;
return 0;
}
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