Recently I was writing a class that had overloaded read methods for various data types. One of the sets of types I wanted to handle were integral std::chrono::time_points. For this I wrote the following code:

  // Return a timestamp from a chunk at a given offset as if from an
  // integer in network byte order
  template <IsTimePoint T>
  requires std::integral<typename T::rep>
  [[nodiscard]] T read(length_t offset = 0) const {
    return T{typename T::duration{read<typename T::rep>(offset)}};

Elsewhere I included a concept for matching time_point types:

template <typename T>
concept IsTimePoint =
  requires {
    typename T::clock;
    typename T::duration;
    typename T::rep;
    typename T::period;
    requires std::chrono::is_clock_v<typename T::clock>;
    requires std::same_as<T,
                          std::chrono::time_point<typename T::clock,
                            std::chrono::duration<typename T::rep,
                              typename T::period>>>;

The code works. My question is whether this was a good way to solve this problem or whether there is a simpler solution that I have overlooked. Part of the reason for this project is for me to learn C++20, but I often worry that I might be using new techniques because they are new rather than because they are the right tool for the job.


1 Answer 1


It seems there is a simpler solution. Shamelessly stolen from this post:

template<class, template<class...> class>
static constexpr bool is_specialization = false;

template<template<class...> class T, class... Args>
static constexpr bool is_specialization<T<Args...>, T> = true;

template<class T>
concept IsTimePoint = is_specialization<T, std::chrono::time_point>;

On the other hand, consider whether you really want to have the low-level function read() construct values of these high-level types. The calling code has to know what the type is of the integer that it reads, then it can construct an appropriate std::chrono::time_point from it itself.


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