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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)

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 >
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 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 scoped
void 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);
 
enum struct C { final, import, module };
static_assert(std::is_scoped_enum_v<C> == true);
 
enum class D : int { pre, post, override };
static_assert(std::is_scoped_enum_v<D> == true);
 
enum class 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) [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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