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std::is_scoped_enum - cppreference.com

template< class T >
struct is_scoped_enum;

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.

template< class T >
constexpr bool is_scoped_enum_v = is_scoped_enum<T>::value;

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>> {};

#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() {}

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