How to implement is_enum_class type trait? [duplicate]

Answer 1

You check whether the enumeration is convertible to int.

template 
using is_scoped_enum = std::integral_constant{}
                                                  && std::is_enum{}>;

These static assertions will succeed:

enum e {};
enum class e2 {};

static_assert( is_scoped_enum::value, "" );
static_assert( !is_scoped_enum::value, "" );
static_assert( !is_scoped_enum::value, "" );

Demo.