std::is_scoped_enum
From cppreference.com
Defined in header <type_traits> | ||
template<class T > struct is_scoped_enum; | (since C++23) | |
std::is_scoped_enum is a UnaryTypeTrait.
Checks whether T is a scoped enumeration type. Provides the member constant value which is equal to true, if T is a scoped enumeration type. Otherwise, value is equal to false.
If the program adds specializations for std::is_scoped_enum or std::is_scoped_enum_v, the behavior is undefined.
Contents |
[edit]Template parameters
| T | - | a type to check |
[edit]Helper variable template
template<class T > constexprbool is_scoped_enum_v = is_scoped_enum<T>::value; | (since C++23) | |
Inherited from std::integral_constant
Member constants
value [static] | true if T is a scoped enumeration type, 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> |
[edit]Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_is_scoped_enum | 202011L | (C++23) | std::is_scoped_enum |
[edit]Possible implementation
namespace detail {void test_conversion(...);// selected when E is complete and scopedvoid test_conversion(int)= delete;// selected when E is complete and unscoped template<class E> concept is_scoped_enum_impl =std::is_enum_v<E>&&// checked first requires { detail::test_conversion(E{});};// ill-formed before overload resolution// when E is incomplete}// namespace detail template<class T>struct is_scoped_enum :std::bool_constant<detail::is_scoped_enum_impl<T>>{}; |
[edit]Example
Run this code
#include <type_traits> static_assert(std::is_scoped_enum_v<int>==false); class A {}; static_assert(std::is_scoped_enum_v<A>==false); enum B { self_test = std::is_scoped_enum_v<B>}; static_assert(std::is_scoped_enum_v<B>==false); static_assert(!self_test); enumstruct C { final, import, module }; static_assert(std::is_scoped_enum_v<C>==true); enumclass D :int{ pre, post, override }; static_assert(std::is_scoped_enum_v<D>==true); enumclass E; static_assert(std::is_scoped_enum_v<E>==true); int main(){}
[edit]See also
(C++11) | checks if a type is an integral type (class template) |
(C++11) | checks if a type is an arithmetic type (class template) |
(C++11) | checks if a type is a scalar type (class template) |
(C++11) | checks if a type is an enumeration type (class template) |
