c++ - SFINAE 将实例化类型限制为 std::chrono::duration 类型

Question

我想做类似的事情

template <typename T>
class TemporalAlarmDelay<T, std::enable_if<std::is_base_of<std::chrono::duration< , >, T>::value, T>::type>
{
public:
    explicit TemporalAlarmDelay(T delay)
        : mDelay(delay)
    {

    }

private:
    T mDelay;
    std::chrono::steady_clock::time_point mTriggerTime;
};


int main(int argc, char** args)
{
    TemporalAlarmDelay<std::chrono::nanoseconds> nanosecondDelay;   // this should work
    TemporalAlarmDelay<std::chrono::milliseconds> millisecondDelay; // this should work 
    TemporalAlarmDelay<std::chrono::seconds> secondDelay;           // this should work
    TemporalAlarmDelay<int> failDelay;                              // fail to instantiate
}

目的是限制 std::chrono::duration 的类型(例如 std::chrono::milliseconds、std::chrono: :seconds).最好的方法是什么？根据我的示例，我认为我可以使用 std::is_base_of，但我现在意识到辅助类型(例如 std::chrono::milliseconds、std::chrono::seconds 等)不要使用继承——糟糕，多么愚蠢的想法。

Answer 1

对于您的问题最简单的解决方案...

#include <chrono>

class TemporalAlarmDelay
{
public:
    explicit TemporalAlarmDelay(std::chrono::steady_clock::duration delay)
        : mDelay(delay)
    {

    }

private:
    std::chrono::steady_clock::duration   mDelay;
    std::chrono::steady_clock::time_point mTriggerTime;
};


int main()
{
    using namespace std::chrono_literals;
    TemporalAlarmDelay nanosecondDelay{1ns};   // this works
    TemporalAlarmDelay millisecondDelay{1ms};  // this works
    TemporalAlarmDelay secondDelay{1s};        // this works
    TemporalAlarmDelay failDelay{1};           // compile-time error
}