Class underlying_type

test/doctest.h:968–968

        // Compiler intrinsics
        template <typename T> struct is_enum { static DOCTEST_CONSTEXPR bool value = __is_enum(T); };
        template <typename T> struct underlying_type { using type = __underlying_type(T); };

        template <typename T> struct is_pointer : false_type { };
        template <typename T> struct is_pointer<T*> : true_type { };