std::chrono::is_clock

 

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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

Run this code

#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>>
    );
}