std::chrono::is_clock
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is_clock
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Defined in header
<chrono>
template< class T >
struct is_clock;
(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.
Contents
[edit] Template parameters
T
-
a type to check
[edit] Helper variable template
template< class T >
constexpr bool is_clock_v = is_clock<T>::value;
(since C++20)
constexpr bool is_clock_v = is_clock<T>::value;
Inherited from std::integral_constant
Member constants
value
[static]
T satisfies the Clock requirements, false otherwise (public static member constant)
Member functions
operator bool
(public member function)
operator()
(C++14)
(public member function)
Member types
Type
Definition
value_type
bool
type
std::integral_constant <bool, value>
[edit] 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 {};
[edit] 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.
[edit] 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() {}