std::chrono:: is_clock

From cppreference.com
C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
Date and time utilities
Time point
(C++11)
(C++20)
Duration
(C++11)
Clocks
(C++11)
(C++11)
is_clock
(C++20)
(C++20)
(C++20)
(C++20)
Time of day
(C++20) (C++20)
(C++20) (C++20)
(C++20)

Calendar
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
Time zone
(C++20)
(C++20)
(C++20) (C++20) (C++20) (C++20)
(C++20)
chrono I/O
(C++20)
C-style date and time
Defined in header <chrono>
template < class T >
struct is_clock ;
(since C++20)

If T satisfies the Clock requirements, provides the member constant value equal true . For any other type, value is false .

For the purpose of this trait, the extent to which an implementation determines that a type cannot meet the Clock requirements is unspecified, except that a minimum T shall not qualify as a Clock unless it meets all following conditions:

  • T::rep
  • T::period
  • T::duration
  • T::time_point
  • T::is_steady
  • T::now()

If the program adds specializations for std::is_clock or std::is_clock_v , the behavior is undefined.

Template parameters

T - a type to check

Helper variable template

template < class T >
constexpr bool is_clock_v = is_clock < T > :: value ;
(since C++20)

Inherited from std:: integral_constant

Member constants

value
[static]
true if T satisfies the Clock requirements, false otherwise
(public static member constant)

Member functions

operator bool
converts the object to bool , returns value
(public member function)
operator()
(C++14)
returns value
(public member function)

Member types

Type Definition
value_type bool
type std:: integral_constant < bool , value >

Possible implementation 

template<class>
struct is_clock : std::false_type {};
 
template<class T>
    requires
        requires
        {
            typename T::rep;
            typename T::period;
            typename T::duration;
            typename T::time_point;
            T::is_steady; // type is not checked
            T::now();     // return type is not checked
        }
struct is_clock<T> : std::true_type {};

Notes

If T otherwise meets the Clock requirements, but T::is_steady is not of type const bool , or T::now() is not of type T :: time_point , the result of is_clock_v<T> is unspecified.

Example

Run this code 
#include <chrono>
#include <ratio>
 
static_assert
(
    std::chrono::is_clock_v<std::chrono::utc_clock> and
    not std::chrono::is_clock_v<std::chrono::duration<int, std::exa>>
);
 
int main() {}
Retrieved from " https://en.cppreference.com/mwiki/index.php?title=cpp/chrono/is_clock&oldid=176446 "