std::chrono::is_clock

From cppreference.com
< cpp‎ | chrono
 
 
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
(C++11)
Relational operators (deprecated in C++20)
Integer comparison functions
(C++20)(C++20)(C++20)   
(C++20)
Swap and type operations
(C++14)
(C++11)
(C++11)
(C++11)
(C++17)
Common vocabulary types
(C++11)
(C++17)
(C++17)
(C++17)
(C++11)
(C++17)
(C++23)
Elementary string conversions
(C++17)
(C++17)
 
Date and time utilities
Time point
(C++11)
(C++20)
Duration
(C++11)
Clocks
(C++11)      
is_clock
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
Time of day
(C++20)(C++20)
(C++20)(C++20)
(C++20)

Calendars
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)(C++20)
Time zones
(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 of the following conditions:

  • The qualified-ids T::rep, T::period, T::duration, and T::time_point are all valid and each denotes a type;
  • The expressions T::is_steady and T::now() are each well-formed when treated as an unevaluated operand.

The behavior of a program that adds specializations for std::is_clock or std::is_clock_v is undefined.

Template parameters

T - a type to check

Helper variable template

template< class T >
inline 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;
            T::now();
        }
struct is_clock<T> : std::true_type {};

Example

#include <chrono>
#include <ratio>
 
int main()
{
    static_assert
    (
        std::chrono::is_clock_v<std::chrono::utc_clock>
        and
        not std::chrono::is_clock_v<std::chrono::duration<int, std::exa>>
    );
}