NAME¶

std::chrono::is_clock - std::chrono::is_clock

Synopsis¶

Defined in header <chrono>
template< class T > (since C++20)
struct is_clock;

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:

* Each of the following qualified identifiers is valid and denotes a type:

* T::rep
* T::period
* T::duration
* T::time_point
* Each of the following expressions is well-formed when treated as an unevaluated
operand:

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

Inherited from std::integral_constant

Member constants¶

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

Member functions¶

operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (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; // not required to be bool
T::now(); // not required to be T::time_point
}
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>>
);
}