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std::is_scoped_enum

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Defined in header <type_traits>
template< class T >
struct is_scoped_enum;
 (since C++23)

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.

The behavior of a program that adds specializations for is_scoped_enum or is_scoped_enum_v is undefined.

Contents

[edit] Template parameters

T - a type to check

[edit] Helper variable template

template< class T >
inline constexpr bool is_scoped_enum_v = is_scoped_enum<T>::value;
 (since C++23)
[edit]

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
__cpp_lib_is_scoped_enum

[edit] Possible implementation

namespace detail {
namespace { // avoid ODR-violation
template<class T>
auto test_sizable(int) -> decltype(sizeof(T), std::true_type{});
template<class>
auto test_sizable(...) -> std::false_type;
 
template<class T>
auto test_nonconvertible_to_int(int)
    -> decltype(static_cast<std::false_type (*)(int)>(nullptr)(std::declval<T>()));
template<class>
auto test_nonconvertible_to_int(...) -> std::true_type;
 
template<class T>
constexpr bool is_scoped_enum_impl = std::conjunction_v<
    decltype(test_sizable<T>(0)),
    decltype(test_nonconvertible_to_int<T>(0))
>;
}
} // namespace detail
 
template<class>
struct is_scoped_enum : std::false_type {};
 
template<class E>
    requires std::is_enum_v<E>
struct is_scoped_enum<E> : std::bool_constant<detail::is_scoped_enum_impl<E>> {};

[edit] Example

Run this code
#include <iostream>
#include <type_traits>
 
class A {};
 
enum E {};
 
enum struct Es { oz };
 
enum class Ec : int {};
 
int main() 
{
    std::cout << std::boolalpha;
    std::cout << std::is_scoped_enum_v<A> << '\n';
    std::cout << std::is_scoped_enum_v<E> << '\n';
    std::cout << std::is_scoped_enum_v<Es> << '\n';
    std::cout << std::is_scoped_enum_v<Ec> << '\n';
    std::cout << std::is_scoped_enum_v<int> << '\n';
}

Output: 

false
false
true
true
false

[edit] See also

(C++11)
 checks if a type is an integral type
(class template) [edit]
(C++11)
 checks if a type is an arithmetic type
(class template) [edit]
(C++11)
 checks if a type is a scalar type
(class template) [edit]
(C++11)
 checks if a type is an enumeration type
(class template) [edit]
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